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GEOL7330 Potential Field Methods - Day2 01-21-2023 AM
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00:00 Recording. Do you do what you do man? Got it. Okay
00:10 8 30 on the dot. So any any questions from yesterday Stephanie.
00:21 I think I'm good. Okay um well I was thinking that I was
00:29 through the lecture notes this morning for and I was making little corrections and
00:38 like that and they're in here and highlighting them and I'm probably going to
00:42 through while it's still fresh in my . I'm gonna go through yesterday's lecture
00:48 you know there were little things that know that I was commenting on and
00:52 gonna go back through and kind of of smooth that over a little bit
00:57 I'll highlight those changes and I'll send I'll upload those and then um uh
01:06 type if you don't mind moving them and that way you'll have sort of
01:12 whatever an attitude version that's a little better. Um Anyways and I hope
01:20 don't mind that I hope that works for you so okay so no questions
01:26 let's just go move forward. Um the other class going right now you
01:33 ? Yes so it's not good to talking that. Okay all right very
01:42 then you don't have to um okay get started with number two cat lecture
01:49 two and this morning going to talk instruments acquisition and processing so still I
01:59 not as boring as theory but um you know still not really the the
02:09 good stuff that we're building up to acquisition and instrumentation so uh we'll start
02:19 gravity and then we'll do Magnetics just that. Well that sort of,
02:24 sort of theme will be what we all through this stuff even through this
02:30 and processing and anomaly enhancements. So right, so gravity surveys are carried
02:38 using a gravity meter or some people groove immature doesn't matter. Um Grove
02:46 is kind of, people say that in south America and europe and africa
02:55 you know Southeast Asia, maybe even , a lot of people in this
03:00 just say gravity meter. Um There two basic types, those that measure
03:08 measurements and and those are the most and they use springs or vibrating vibrating
03:17 mechanisms. And then there's uh I know of one type. I mean
03:24 instrument that's an absolute measurement and it's free fall. So it just measures
03:30 the timing of the, when it drops, drops a weight and it
03:36 past some sensors and it measures that accurately. And then it figures
03:41 you know uh what the gravitational attraction from that. So we'll start with
03:50 relative measurement instruments. The zero the very first one was Lacosta,
03:57 and Ellen are meters were invented in early 19 hundreds, 1930 ish.
04:05 think. So not even 100 years . And before that people did measure
04:12 gravity instruments, we, as we in our historical observations, but they
04:18 a Tarzan balance which is a It's a gradient measurement. So it's
04:25 the derivative of the field which is as the derivative of the potential.
04:33 that idea goes back to cavendish like 7/17 century, I think. So
04:42 torsion balance and now it's funny because grade geometry is now there are modern
04:52 and we're not gonna talk about them you want to have that. But
04:55 have material for that in the in extra lecture, we could do an
05:00 lecture if you wanted to learn about geometry and heat flow at the
05:05 you think about it and we'll decide of doing the exam on that on
05:11 10th. We could do that lecture the 10th and then do the exam
05:15 the 14th. If you just like find that you're just in love with
05:19 material that I present. So Um So the zero length string instrument
05:27 characterized by an infinite period. That's it's called zero length. That kind
05:33 a weird name. And the infinite of suspension entails infinite displacement theoretically.
05:43 so this is why Lucien lacoste. never met him. I did see
05:47 one time. Um This is why called it the zero length string and
05:52 said it should be called the zero length length spring. But it's kind
06:00 , you know too wordy. So equilibrium the gravitational torque on the
06:07 A little figure here on the side is the spring and then uh
06:15 Is this dimension um B. Is dimension along this lever that's connected to
06:22 spring. D. Is the length From the point the fulcrum to um
06:31 weight. Well I mean some some well to a distance that's perpendicular from
06:39 mass that's attached to this lever. so of course remember your physics 102
06:48 one or whatever in Houston. Um called 13 30 I think physics or
06:53 3. It's a four hour credit least. It was when I took
06:56 . So Mass MG is the gravitational . Mass times gravity. Okay so
07:09 at equilibrium it's this weight times this times the co sign of of this
07:18 here. So basically um Right. if you remember your physics D.
07:27 this angle is the moment of right? And then the torque on
07:33 string I guess torque K. I is equal to B times A.
07:42 this angle. So that's the the moment of the torque I
07:48 And then if you set the zero other, the cosine angles fall
07:53 You just have this little formula So that's how it works. It's
07:58 it's um Yeah, alright there's probably are used to be the most common
08:09 instrument around and um but Eleanor through sales and restructuring etcetera etcetera. They
08:24 were bought out, downsize et cetera cetera. They are now owned by
08:28 company in Denver called Ed Con. they're mostly just, I don't know
08:35 they're building new machines I think they be but I know that they're doing
08:39 lot of service. They do a of rentals of their machines but but
08:44 tracks who are based up in Toronto instruments, They make the c.
08:52 think they make some more advanced ones they are far and away the most
08:58 instruments they have basically taken over and their design is simpler they're easier to
09:06 their, you know easy to operate carry around. They might even be
09:10 . Um and and uh like that this is the most popular kind here
09:20 it has these support strings as a string spring and uh yeah that's how
09:29 works a little bit different. And the absolute gravity meter also there might
09:40 some other instruments besides Eleanor's and syntax I don't know what they are.
09:47 wouldn't surprise me if like there's a grab immature or something like that or
09:51 a chinese group amateur. Okay. the absolute, this is the one
09:57 know but this is it's made by company that first meeting was called Micro
10:02 . Micro G. Is also owned Ed Con these days so you
10:06 you know and that is not a company, you know it's a small
10:11 but the whole phenomena of you know buying little companies sort of thing in
10:21 case this is how it works. have a flea of free falling um
10:26 chamber, it's a vacuum chamber and drops through here and it gets lifted
10:31 up. Um and there's a interference and some mirrors in here and it
10:38 measures the time and here is a of the uh instrument south and then
10:49 guess the data, I mean the and and all the whatever this the
10:57 know pC cards and things like And of course you just plug it
11:00 your laptop and just do it. it's very easy. The the
11:05 And R. Meter. I don't a picture one. Yeah. Here
11:09 have to actually like look in this you look inside here I think and
11:14 eyeball it to level it up and to see what it's doing I
11:22 And then here's one um this is Prudhoe Bay and I have a little
11:28 history. I'm gonna show you about these instruments in Prudhoe Bay. Of
11:33 I guess that looks like a looks a fox out there to me.
11:38 you know, so they're environmentally friendly guess. Okay so now there's
11:44 this is a this is another relative , a borehole gravity. So there's
11:50 borehole tool. And Schlumberger has these they're really big and fat so they
11:57 go in a lot of holes that drilled these days. But this is
12:00 a little little zero length spring mechanism there. And they can measure density
12:09 because you measure some response here and response there and there's a formula that
12:14 can just solve it will calculate density and they measure far into the
12:21 In fact, the spacing that you your measurements over is kind of dictates
12:26 far into the formation it can but but it's unaffected by mud and
12:35 casing, things like that. So really useful tools um they are limited
12:42 they're big and fat and plus you go too far off an angle,
12:48 , like so little horizontal drilling for guys. So they are limited,
12:53 are used still today, but not lot. Um people in the past
12:59 been trying to develop gravity instruments that be smaller that can go into smaller
13:08 and you know, survive higher temperatures . Also a limitation, I should
13:15 that. So I need to add that to the, The discussion
13:21 , uh make a note four hole limitation but they're trying to but there
13:31 folks, there have been attempts, have spent lots of money trying to
13:34 this because if you can build a instrument that could survive high temperatures and
13:42 and be able to put in all sized well holes, There would be
13:47 lot of money because it would because I said, they measured density deep
13:51 the formation much farther than any wire tool. You know, any robi
13:58 they use now because those things, know, they barely see past the
14:02 . So it would be a big . So there's a lot of money
14:06 be made. Um the the reason they can't be, I mean the
14:19 magnetometers uh work on on a molecular . They're not mechanical at all.
14:29 uh that's the reason. If you figure out how to measure gravity at
14:35 molecular level, then that would be cool. But you know, the
14:41 is called, you know, the main forces of nature, right
14:45 electro Magnetics and the too weak and forces. Atomic forces, you
14:51 that hold matter together and then the atomic forces of course radioactive decay.
14:57 gravity is gravity at small scales is weak. But of course, as
15:02 talked yesterday, galactic scales can actually time. So so the small scale
15:07 very weak and so molecularly looks like not possible but it doesn't stop people
15:12 trying. They could should still keep . So, um what is
15:18 This is a one more comment on . If the stations of a borehole
15:22 survey were separated by less than 70 the time between read so they could
15:28 it every 18 minutes and the gravity with a borehole would measure you know
15:35 micro gals. 10 micro gals is 1/100 of a millimeter. So basically
15:44 they're saying for intervals greater than 20 this is a measuring density. It
15:49 be point oh two grand for C. C. Her less.
15:56 they're very they can measure very small differences in gravity and hence small differences
16:07 density. Um I'm gonna make a also to come up with some nominal
16:17 formation penetrations. I'll look at uh it later. Maybe I'll tell you
16:23 I look it up anyways I'll try best to remember. Okay so now
16:28 are actually instruments they have also taken and R. Meters and stuck them
16:33 a stuck them in a little you know water type bell that they
16:42 off boats and then um measure the at the at the water about
16:48 And there's there's a whole big database you can still get. That's called
16:53 Schaefer. I think it's owned by now or maybe still buy food
17:00 But one or the other and it's the whole of the gulf coast and
17:04 an old old database but it doesn't that data is Very good quality and
17:10 a water bottom database for the many on the shelf going all the way
17:17 to the 60 s government. So uh so for purposes measuring. Right
17:24 it's 1/100 of a millimeter google or would be 10 micro gals.
17:30 Plus or minus 10. And it's But for time land better precision.
17:38 . Yeah it's very accurate. But saying it's still limited for environmental
17:44 time lapse etcetera. Fair enough. They do use measure gravity, that
17:53 bottom. But this is this this is kind of like an aside
17:58 we're going to look at the time study on Prudhoe Bay, like I
18:02 earlier. Uh Now this is so is an interesting point because all these
18:11 are gonna claim just just amazing accuracy you know, Eleanor and sent
18:19 They claim their accuracy is 1-5 micrograms it might be sitting on the lab
18:25 the bench in the laboratory. But me, the way I view these
18:32 is what is the what is the , you know, one of the
18:38 wavelength and not only amplitudes that I measure um with confidence, you
18:49 Um So you know, oh what I just do? Okay.
19:01 Never mind. Um Yeah, in case. Right. So what that's
19:08 I make, that's how I like think about it. I don't really
19:11 because first of all these values are . You know, so it's like
19:16 root mean square or something. And uh I don't know what that
19:23 So in any case yeah, I you know, whatever they're wonderful but
19:29 not I'm not sure what they mean in terms of what what I can
19:33 with confidence. So that's just something think about. Okay, so here's
19:41 comparison of Eleanor and Centrex meters and so you can see the scale is
19:52 Micro gowns maximum and this is um see, this is a you from
20:00 to 2008. Um So I get is that right? Is that that
20:08 160 days? Um So these are guess bench measurements And um 2.1 micro
20:20 . 8.9 micro gals. Okay, see that's what this level is.
20:24 numbers, they coincide. So the I guess of the LNR was 8.9
20:32 goals and the means the scent tracks for the most part around 2.1.
20:36 guess there was some big spikes in . But This is so this this
20:44 , this is 3/100 of a I mean, you know, who
20:53 right. But I guess this, was published uh and uh I guess
20:59 guess this was a big deal back the day for those guys.
21:04 fine, fine and dandy. Uh look at magnetic instrumentation there. My
21:10 ones remember victor vacuum, who worked golf and worked with with the whatever
21:18 Defense Department during World War Two to this instrument, this is the flux
21:24 and it has a resolution of about gamma one nano Tesla. And um
21:31 here's where I added added something with highlight. I'll do the same thing
21:34 the other notes. Excuse me. Okay, so they measure relative field
21:49 again. So it's a three access and this is this is the
21:56 So you see the coils, you that coil, you have two sets
21:59 coils this way, a set of this way and a set of coils
22:03 way. And and basically they're each each access consists of a pair of
22:12 but opposite lee woven inductive coils. here's a little sort of sketch of
22:19 . So there these are they are opposite and then they are coiled around
22:28 a magnetized, saturated, you highly permeable material and there which is
22:38 right? When you when you pump current through it, you're gonna saturate
22:44 because remember electricity currents produce a magnetic , that kind of right hand
22:50 So from your physics Physics one and one is going one way that is
22:56 the other way, they're gonna cancel . And and I and this is
23:03 they become sensitive to fluctuations. very bad. Um Yeah, so
23:11 at this closer, here's our little figure again um we're gonna have a
23:18 B one secondary B two and then an equilibrium be in equilibrium the current
23:28 going to produce fields that can you know oppose each other, this
23:34 in time. So they're gonna just each other in time, they're going
23:37 cancel out to zero. Now if if the ambient field is not
23:48 Then these two coils because their wound Lee, one is gonna work in
23:55 negative way against the inducing build other going to be going to be positive
24:02 . So they're not gonna be the . So when you sum them,
24:06 going to have some output signal and that output signal is gonna be proportional
24:14 the magnetic field. That's the And and if you want me to
24:23 or back up, just jump in tell me to do that because,
24:27 know, I don't want to wait go back 100 slides or something like
24:31 . Okay. Alright. So that the that's the first magnetometers that were
24:42 . And then when I first started the business, they were still using
24:46 . In fact, they do still these but they used them for
24:50 I'll explain that when we talk about . Okay, So then there's two
24:58 of um uh what we call them resident uh uh magnetometers. There's
25:10 it's called a pro one is called first one that was called a proton
25:15 . It's a residence type magnetometer and resolution is about an order of magnitude
25:22 than the flux gate. And it . And it's called a proton procession
25:28 it if you look at. So right half side of the figure is
25:34 of like a gravitational sort of analog the, to the magnetic side.
25:42 ? And this is again at the level. Uh there's, you
25:48 and so you have if you haven't take a spinning top for and you've
25:52 this before, I'm sure it will process or gyrate about some axes.
26:02 ? Well, that's how, that's a proton procession worse it will gyrate
26:09 the Larmore frequency of protons in the rich fluid. So there's a
26:16 here's the coil right here. These lines that's represented coil and then the
26:22 of the coil is has to be at a high angle to the ambient
26:27 direction, right to the inclination. then they they pulse, it pulse
26:37 coil with some electricity and then it relax it. And as it
26:43 then the the the uh the protons the in the hydrogen, which fluid
26:54 will begin to process. And you and that precession can be detected with
27:02 to frequency. And that frequency then turn, is related to the field
27:08 , if that makes sense. here's here's a picture of one down
27:17 , I've actually operated one of Um So you have a little
27:21 I mean, we'll read out And you key in like your location
27:27 some details. And then you just this on a stick away, you
27:32 have any, you know any metal in your pockets and things like
27:37 And then you make sure make sure coil is oriented at a high angle
27:43 the field. Then you and you it, you take measurements and it
27:51 four or 5 every second. There be interference like power lines. They
27:56 a magnetic field and you know, have to be careful not to rotate
28:02 sensor, but they do require a of power to operate. So,
28:08 that's the thing. But proton I mean the department has one of
28:14 , so, you know, um right now there's another residence type magnetometer
28:25 an alkaline vapor or they're also called pumped. And they have a
28:30 That's another order of magnitude better than . So two orders of magnitude better
28:36 a flux gate. One order of better than a proton procession. They
28:44 sample 20 hertz. So they sample times faster than the proton precession.
28:50 don't need as much power. So are great, they're great instruments.
28:58 and how they work is they have lamp that pulses and there's an absorption
29:05 and then it goes into a photo and then that is measured. And
29:10 that that response is of course proportional the earth's field strength. Um and
29:19 here's like a little picture of how , how it works. So the
29:23 pumped refers to the lamp, the that's pumped. Okay, so how
29:29 that work? And and and how that actually work? So on this
29:34 we start with some initial energy A. One, A. Two
29:37 B. So this B. Is . A. One A two are
29:43 here. So you have some uh have some charges which reside down
29:50 And This is this is uh a . Okay. And then at two
29:59 some irradiation during the radiation charges in one will jump to be But
30:08 But when he returned he returned to . two As they fall, they
30:13 be re excited. So the idea , you want to overpopulate one level
30:19 this case a. two at the of a one. That's the
30:24 Um And then once it's completed, everything has been moved from A.
30:29 to A. Two. And I know all the details. I just
30:34 this conceptual idea. Um And then radio frequency signal, I used to
30:43 say R. F. I just out radio frequency that it takes to
30:51 Back to a one always. I to go from a one to
30:56 two that's proportional to the fuel So that's how it works. But
31:01 the idea is that there's a there's lamp that pumps it, it excites
31:08 that change in their level of uh levels. And that energy level is
31:18 to the field strength, if that sense? That's how those work.
31:25 , so now let's go to survey of gravity or a magnetic survey.
31:32 you might want to survey an entire or an exploration play or a specific
31:39 or in the case of an engineering , you know something, you
31:43 some ah piece of land or something that. So there are things to
31:54 . We want to consider the the of the target. Uh what sort
32:00 density and magnetic susceptibility contrast you would to see what kind of rock properties
32:06 expect to, what kind of resolution need to um you know, to
32:12 detect the target and then um something I do a lot that's often
32:17 make a feasibility model. Stick these these variables, you know, use
32:23 basin size or the or the study size, target depths, rock properties
32:32 then forward calculate what the what those look like and see if, if
32:43 data can resolve that. So that's way to do it. So,
32:47 survey method um that depends on the as well. So there may be
32:51 issues, is it marine or mountainous, desert, jungle etcetera and
32:57 stuff. Like is there a war on? You know, you're not
33:02 be doing a gravity survey in, know, in Kiev these days.
33:05 probably not gonna be, you advisable. Um And then is it
33:12 to be like individual stations, are gonna dynamic? You know, you're
33:16 to have a moving platform, like aircraft or or a boat or something
33:21 that. And then of course the , is it gonna be you know
33:27 how how are you know, what the intervals between lines or stations that
33:33 you going to need to effectively you , resolve your target then? Of
33:39 . How much money do you So these are ideas. These are
33:43 to think about when you're going to a survey. So let's go through
33:48 one on one survey resolution. It of course the size of the target
33:52 its signal strength based on rock Special resolution depends on the sampling of
33:58 field and of course the amplitude will on the sensitivity of the instrument,
34:04 the field, the size and depth the source controls the labeling. This
34:08 kind of a kind of a rule thumb thing to step the bottom in
34:12 box which is important. And they be close enough together to detect the
34:20 but they also you have to have of them outboard to capture the entire
34:24 that the source is going to Um I should make a note on
34:31 sampling sampling wide enough. Um No lost a regular sample provided that the
34:50 frequency is greater than twice the highest component. I that's Nyquist right.
34:57 means that the spacing of measurements must less than half the minimum wavelength.
35:05 , so this is the bottom. is the rule of phone sources typically
35:09 anomalies with wavelengths that are on the of four times their depth. That's
35:16 four times the distance from the instrument the source. So that's important.
35:23 when you're have an airborne platform because have to count the not just the
35:29 below the surface, but the distance the surface to the nominal elevation that
35:36 flying at. So the wavelength, lambda equals four dot Z.
35:44 So dot the extra line station is times that. Alright, so that's
35:49 important rule of thumb to remember. spatial sampling in land based surveys,
35:57 grid approach is commonly used and it's know like in two orthogonal directions in
36:09 surveys and airborne surveys, you'll have sort of survey line versus tile line
36:17 . So surveying is always all about loops. You want to reoccupy stations
36:23 you want to tie lines that you've or or marked out or sailed.
36:33 you can minimize those missed ties between line intersections. Or you can or
36:39 minimize when you re occupy a station in loops for like a land gravity
36:45 , you want to re occupy one your stations so that you can tie
36:49 miss ties or tie the drift of instrument. Okay, uh Special sampling
37:00 um between discrete measurements sets uh sets limit on minimum wavelength. And talking
37:06 that shorter wavelengths can only originate from long wavelengths can be so long wavelengths
37:13 be produced by shallow or deep But that's that's really not true in
37:18 real world. I mean it can your sources are, you know homogeneous
37:23 you know, that's just not Right? So I will show you
37:28 I mean by this later. But this long wait list can be produced
37:33 shallow sources is technically correct. But what happens is you have a long
37:39 anomaly. Sure. But if it's shallow source there will be short wavelengths
37:45 on that long on that broad And those short wavelengths will tell you
37:50 deep the sources. So this is is really an old school idea.
37:56 don't believe, I mean I need express that butter. So the choice
38:00 profiles and the orientation of these They place limits. Right. So
38:06 spaced lines. Mean that as I talking yesterday, even though you're sampling
38:11 line for like a moving platform and or airborne, it's the spacing of
38:17 lines that actually limit your resolution in of making a grid. Right?
38:25 then of course the orientation of your lines that that puts in a spatial
38:32 mutual bias into your data. So often folks like to fly for
38:39 surveys in the dip direction because I want to enhance those features. Those
38:45 that they know about. But when think about it, if you know
38:49 them in enhancing them is only going tell you more about what you already
38:54 . So quite often it's good to oblique to these main structures or even
39:00 if they're there, they're dominant, gonna come, they're gonna show up
39:05 but you're gonna you're gonna especially, know, you're gonna especially bias against
39:11 features that might be dipping in an to that and those might be
39:16 So those are ideas to think about terms of just survey design.
39:23 so there are whatever 46 different types gravity surveys and that's sort of been
39:30 about that indirectly. But land So so there you're out there walking
39:36 or you're jumping around from using a or a helicopter or something from different
39:43 and you make measurements at individual You surveyed those in, then you
39:49 that data somehow. And then we borehole gravity gravity. So we can
39:56 we can do borehole surveys. So are of course an individual holes.
40:03 could, if you have a field might do these in a field and
40:07 a really I mean I don't know I've ever seen that done. I
40:11 I've seen a lot of literature and but I don't know if I've ever
40:15 one where they did a bunch of measurements in the field. But I'll
40:21 that's been done. I mean Amoco to own a borehole tool I think
40:26 they used to do a lot of surveys back in the day. Um
40:33 was bought by BP F. I maybe 20 years ago or so.
40:40 Amoco was one of the original companies Standard, which was one of the
40:45 companies. Okay, so as I this water bottom instrument. So there's
40:50 bottom surveys and I don't know very , you know, Yeah, I
40:56 know that there's this big survey. these stations that were measured on the
41:03 coast uh platform out there. I'm shelf but I don't know any others
41:12 honestly. It's not, I haven't , I could probably find some if
41:16 look but I just don't know. then of course marine surveys um they
41:23 they are all over the place. mean every passive margin, you know
41:30 around, you know in the gulf Mexico, the east, in both
41:35 both flanks of the central and south oceans, the north atlantic oceans around
41:42 um in the, you know in southeast Asia, all around Australia.
41:51 And in fact, you know, open file marine gravity data that you
41:56 you can download for the world and free. So and then there's airborne
42:05 . Airborne gravity wasn't a thing until the 90s. I mean people were
42:12 it in the 80s but it really wasn't viable. Wasn't just wasn't good
42:21 . They didn't have ways because the is that you're bouncing around on the
42:26 and you're producing accelerations that are just , you know, instrument just can't
42:33 . So you actually have to have which are a kind of gravity meter
42:39 that are accurate enough to correct for turbulence to be able to correct because
42:50 the turbulence the from from the it's just like, you know,
42:57 and orders of magnitude greater. The acceleration of those is just far and
43:04 greater than the acceleration of this earth . So but since the late
43:10 the mid to late nineties, these the instruments and the survey basically the
43:16 , the accelerometers that they use to for the for the turbulence have are
43:24 enough now to do that. In they're good enough now to the flight
43:29 after surveys. So they're taking off then there's satellite gravity. Now there's
43:39 there's two kinds there's where the meter actually installed on the satellite and I
43:44 like to grace mission that we talked yesterday but there's also granted this determined
43:51 I mentioned this but it's determined by the height of the ocean surface,
43:57 isn't, as I said, there's exponential surface or the Joyed. And
44:02 again, I see I keep saying , you can't forget that now.
44:06 and it calculates free air from that surface. Okay, the best
44:17 the best data in terms of you know, in terms of amplitude
44:22 resolution, land gravity is the best is the second best. Um I
44:30 well okay borehole and borehole and and about the marine? But they're there
44:37 you know, they're rare. You'll see those marine is pretty good.
44:41 then airborne. So I think I some resolution tables. I'll show you
44:47 . But just here's a couple gratuitous of gravity instruments in action. These
44:55 all relative instruments. Uh No not one. This is I guess this
45:01 a L. R. Meter. what my figure says here. So
45:05 you know your your environment. This maybe maybe a pasture, maybe wooded
45:12 , desert area, mountainous in the I think this might be from Prudhoe
45:19 . So this might but they did Eleanor and Prudhoe Bay. And then
45:22 just somebody down there reading it, know, writing down his notes,
45:28 making a terrain correction. So and yeah, these are all land surveys
45:37 then so marine surveys, the issues because it's a moving platform. Um
45:45 have accelerations from the moving platform and can degrade. So um and often
45:53 I said that there's a ton of but at least in the industry whenever
45:59 oil and gas companies whenever they contract is like some seismic data, some
46:05 data to be acquired. As I , like over a passive margin.
46:13 uh, they often will add on and magnetic instruments. And so basically
46:22 course in there and the cost added is like, you know, pennies
46:28 the dollar. It's just nothing, know, it's just a few
46:32 So obviously, you know, with to survey design, you're just at
46:36 mercy of whatever they're gonna, they're go out there and shoot and that's
46:40 the way life is. So, know, I mean you don't have
46:45 control over line spacing or tie lines anything like that. Um, and
46:53 of course to deal with the ship . You know, the instruments are
46:59 on a gyro stabilized platform and then damped a little bit, they're out
47:05 filter a little bit. So so gravity is basically time averaged over several
47:12 . So it's not, it can't nearly as good as land, you
47:17 , letting the instruments settle down and it, measuring it as over
47:23 And then those moving platform uh issues greater with airborne platforms and they fly
47:32 from either from helicopters or from fixed . So they can do it both
47:38 . Now this, this is a and it's a big, it's a
47:43 , it's a single engine aircraft but big and in that they have the
47:49 instrument, but you can see at back end of that there's a little
47:53 that has a magnetometer. So that there is flying gravity and Magnetics.
48:03 And your notes probably say 10-15 That just shows you how long I've
48:09 teaching this class. It should not , I'm gonna change I changed it
48:14 years. So mm So airborne. they have to be in addition to
48:26 the asthma and the the flightline space they have to worry about the variable
48:33 flown. And they can fly either which is constant altitude or what we
48:39 drape surveys or it's a constant terrain . Um If if you're a relatively
48:47 area then you know you can you fly just constant parametric which is very
48:53 to work with. But these days drapes they want to get as close
48:57 the source as possible. So everyone a drape survey. And yeah,
49:04 I said, accelerations can be problematic grabbing. That's absolutely true. Um
49:17 , so here's just an example of flight lines basically. This again,
49:20 is a caravan, there's a gravity and then of course there's the stinger
49:25 has the magnetometer. Um for The flight path should include a similar
49:32 of flight line. I mean in perfect world, you would fly the
49:36 lines basically I've organized and I planned that way. But what people typically
49:42 is because you know it costs money fly these things. They fly a
49:47 of survey lines in their preferred orientation then they just tie those and the
49:53 and the ratio is typically 3215 to , even as much as 10 to
49:59 depending on what kind of survey, know what they think they're doing.
50:03 um yeah and again this puts in spatial bias a spatial tuning as I'm
50:11 it. Okay, so airborne gravity is filtered because of these, the
50:21 . And so here's a little this is from, I don't even
50:26 the source of this, but this an old example basically Milligan's. So
50:32 scale here goes, you know, to 200 mg, not just
50:36 Y. I the biggest anomalies in world after processing are like on the
50:42 of 80 mg, sell them over . So having it having 100 million
50:52 only, that's pretty darn big. So this is this is a huge
50:58 and it's over. Let's see these these are in kilometers. Yeah,
51:03 is a 48 100. So this 40 that's 200. So this is
51:09 , this is 400 kilometers across. this is this is stretched over a
51:14 area, but then you just see the how the time average, the
51:20 to smooth out the turbulence Flying at . That's that's pretty fast. I
51:28 that's actually incredibly, I think like day like I think a caravan flight
51:35 fly, they can fly on your 100 kilometers an hour, Maybe even
51:42 little less. Maybe 100 knots. don't want transit translates. Okay,
51:48 how are satellite data? Said it an L. Timber. So you
51:52 have one of the missions was Jason question real quick on the previous side
52:01 like the anomaly. So what what of feature could we be looking at
52:06 could be that anomaly like a ridge something or No, I normally is
52:12 big will learn this. But basically amplitude anomalies. Remember I showed you
52:19 pitfall yesterday with regard to Magnetics in Gulf of Mexico that that the big
52:25 amplitude anomaly. It couldn't be a because it would require like 25 km
52:31 throw on a fault which is not . Um same thing with gravity 200
52:41 anomaly could not be a fault because would the throw on. It would
52:46 be not physical. So that means probably compositional. So you're going from
52:51 sort of basement rocks that maybe, know, lower density than other basement
53:00 next to them. And yeah, you're going from maybe whatever granted to
53:07 granule, like maybe there's some you know what I mean? So
53:12 , mostly big giant anomalies high empty are typically produced by composition not,
53:20 structured and it's kind of a rule thumb, but it's it's pretty
53:24 Yeah. Good question though. Okay. Okay. So getting back
53:29 the how the satellite data are So All right so here's our ellipse
53:36 R. W. G. Reference spheroid. And here's our
53:40 Oid. And so the ge I don't know why they have a
53:46 surface. It's the mean it is mean surface height. So I don't
53:50 what's going on. Ocean surface Oh so I guess they're saying that
53:58 the ocean goes up I guess it's tide or something like that. But
54:04 so the altimeter like shoots a laser down and it measures the height of
54:10 of the sea surface. That's a weird. I don't know if I
54:15 I'm going to go on that Figure this out because So what happens
54:22 the laser does penetrate. But I it's only like about 15cm or maybe
54:29 a little bit more. That's why that's why when you get into shallow
54:34 shallow waters, satellite data is less because the laser its interference with the
54:44 bottle because it's penetrating. So I they make a little correction for the
54:50 of the laser. So that's something should know I guess shouldn't um I'm
54:57 check check um sad grab G. all timber but everything I told you
55:10 correct. And my confusion ists with to this figure. It's not really
55:16 exactly. Okay. Alright so here's bunch of words about satellite gravity.
55:23 There's been there's been over the six missions Geo SAT which is a
55:29 . S. Navy E. S. One E. R.
55:31 . To cross at two. That's E. S. A. And
55:35 Topex Poseidon and Jason one. That's Nasa. Uh C N.
55:43 S. Is that that's the I don't know what the initial staff
55:52 but it can be used. They out to average out C state C
55:57 and sea level uh produce after removal surface disturbing factors. So I guess
56:04 what that figure is showing. It's tides and currents and stuff and you
56:09 those out to provide a measurement of geode. There's a horizontal gradient is
56:17 by definition and the satellites are There are the satellites are about 800
56:24 above the surface and they're moving at ground speed of about 7m/s,
56:31 And They're they're making an altitude measurement instantaneous C service every 10th of a
56:41 . And then the distance between so sampling along line is yeah right 700
56:47 . So mhm. Um Then they have many other just keep orbiting the
56:54 and they just stack that data out same way. You would you know
56:58 reflection data. Um We're not the way but the idea is the same
57:05 measurements are averaged over 10 the footprint the laser beam. It says here
57:12 about one or two kilometers but for for eight m wavelength it's raises about
57:18 kilometers um resolution They claim is 3-5 gals over 4-8 km. I think
57:30 like again like an rms thing. think if you compare the satellite data
57:36 you compare it to uh um if can if you compare it to like
57:49 data I think the numbers you get more like five Milligan's maybe plus or
57:56 a couple. So that they have it's pretty close. But I think
57:59 in terms of wavelengths I think it's like about 12 10 plus or minus
58:06 maybe 12 plus it's not it's not kilometers it's just now. So anyways
58:13 sounds like graph is beautiful because it's over the world's ocean basis. It's
58:18 beautiful data. Um Okay and then of course the kind like I said
58:26 the instruments actually in in the satellite you know as we said Grace launched
58:34 2002. So it's been up there over 20 years now. And uh
58:41 been using this lots of papers there's a session or two on Grace data
58:46 the A. G. U. you can see here they're actually like
58:50 um Inferring changes in currents and water from measuring the surface of the ocean
58:58 here in these in these trade these over the north atlantic. So And
59:04 here are these neat figures they Remember these are like tiny, they're
59:09 , you know, variations. These are probably on the order of,
59:13 know, less than a meter, on a meter level. So these
59:18 enormously perturbed models. But, you , very interesting. And the same
59:26 goes is the same. But this a this is a satellite gradient
59:30 So you have uh here's the instrument that sits in the in the
59:36 I guess. And yeah, this , let's see, this is weaker
59:44 pull and stronger. Very nice, , very quantitative um launched in 2009
59:54 state of the art for 2009, guess. And they're trying to infer
59:59 deuttel fluctuations, you know, So what's going on here. If you
60:04 the picture I showed you the These are where the big highs and
60:07 are of the G. OID. . So what is the what is
60:15 relative accuracy of all these all these and and and uh um data
60:26 So this is instrumentation. Well, it says surveys here. So I
60:32 we're talking about time. Yeah, . It was very, very
60:38 Um I'll just take it as words . So the first one was done
60:43 long time ago now. And I Dave chappelle used to work at
60:47 he published a paper and he so this is going this is a
60:52 log and wavelength versus log in amplitude . So this is really a big
61:01 difference going up and across and published bars. So he doesn't have a
61:08 of confidence in Waveland resolution. Land or marine. I guess everyone
61:15 But you can see absolute measurements are absolute best of course and boreholes are
61:24 better than land. So um I guess I had land and borehole
61:30 but I did have water bottom, . And then chip born on the
61:34 wavelength resolution but less in terms of because because you have that vertical motion
61:42 the turbulence, the boat going up down that just creates a greater
61:47 And then airborne Up here and then here now satellite in 98 wasn't nearly
61:54 good as it is now. I showing you 2014, 2014 there's a
62:02 paper by sand. Well here it , right here, the landmark paper
62:07 science by land Sandwell and others. yeah, So even after fair heads
62:15 here in 2012 but it's the same of thing. He has great geometry
62:20 here, but it's again it's a log plot. Chef born and he's
62:27 showing arrows, showing that uh I that they are getting better. So
62:33 a handle that gives you a handle what the relative resolution of these things
62:39 but but I wouldn't take, I take any of this stuff as being
62:45 today. I mean I would say general trend, the placement of these
62:49 but I don't think this is accurate . Um slide 30 comment accuracy.
63:02 making a point here to comment on . Um Okay now I'm gonna show
63:08 this little um this little case history which basically in Prudhoe Bay remember this
63:17 the north slope of Alaska. So only people that have enough money to
63:21 for that are the biggies Exxon Um Arco from back in the day
63:29 was up there but you know no oil companies can they just don't have
63:35 cash to do that. So Okay the first survey was 1994 and then
63:48 reoccupied those stations, these are gravity and they reoccupied those stations three years
63:55 . And the idea is that there injecting gas and water into you know
64:06 into wells around the production wells to to you know enhance the recovery.
64:13 the idea. And then uh this and her last name is I can't
64:19 her first name but she she um think I have her name here.
64:30 can't find her day but she she at Exxon at that time and she
64:39 of this paper uh discussing this four . You know this time lapse method
64:48 monitor the water flood and this this a huge deal. I mean everyone
64:52 like whoa. I'm always talking about and her co authors were Ferguson.
65:01 was Ferguson is that was a professor U T. D. The other
65:06 authors were um uh yeah, hair there was that Exxon Ferguson and Carl
65:16 were at UtD University texas Dallas and guy named brady was with our co
65:24 that's with the cola of that original . Um and then, and then
65:34 reoccupied that station in those same stages 6000 to 2003, 56 and
65:42 And around about 2003, they started integrating this with not just Eleanor
65:50 So they use Eleanor meters up to , I think 2002 or three,
65:56 they introduced the absolute meter around this . And then I think they dropped
66:03 towards the end when they're just using end. There's some overlap with the
66:08 meter. And then they and then published papers in 2011 and 2008 2
66:15 2008. And reporting on this this whole experiment, which was,
66:20 know, just a huge deal was of talks and a lot of,
66:24 know, a lot of excitement around stuff. Okay, so if you
66:29 know much about the north slope, this, this is basically, there's
66:33 basically this enormous sin klein and anna . So this is the kovel trough
66:40 the barrel art. So this is is with the you know this these
66:45 are you know situated just um Outboard the Brooks range here. Right?
66:51 it's kind of like a four land of over print because this is technically
66:59 margin out here. But you have four land structure, this broad sort
67:05 asymmetric basin in board and a flexible out board which is the barrel arch
67:13 this is the cross section through So and this paper was published in
67:21 tonight. I mean it's not related this survey but it's just a really
67:24 figure to show you the the regional of the of the North Social NPR
67:32 and Anwar. Our NPR is the Petroleum Research Reserve area or something like
67:39 . And that's where like biden's been to kind of keep gas prices down
67:46 Anwar was protected but I think they're up in there now. So but
67:50 was a wilderness protected area for a time. Um So the first Alaska
67:58 sale was in 1960 for companies which doesn't exist anymore. I think
68:04 still some gas station that's the gas with the green dinosaur, the green
68:10 brachiosaurus or brontosaurus or whatever is Sinclair bp leased most of the koval trough
68:17 is which is down here. But and Exxon least prudhoe bay which is
68:23 here which is just on the out the you know the flank of the
68:28 arch In 65. And then they the largest discovery in 68 in the
68:35 arch. Um The 5000 ft Yeah the folds are five. Yeah
68:44 relief is 5000 ft on these Um Of the what the hell's Mirian
68:53 which is a previous recipient through lower cretaceous rocks. Okay so So then
69:07 is hairs paper. So then in Hair reports on the first feasibility
69:12 part one of this four part study they demonstrate the viability of the water
69:19 surveillance. And they added this surveys out 94 97. So the reservoir
69:25 about 8500 ft down and it dips the south right into the Colville
69:32 Um In the preliminary test they had of 5 to 10 micro gals which
69:40 you know five which is a well to 5, 10 5 micrograms which
69:51 5000 to 1, 1/100 of a . Now they did some feasibility
69:58 Some modeling suggests that after five years water injection Um the graphic difference would
70:04 about 100 micrograms. After 15 it would be about 180, Based
70:10 this and the worst case inversion scenarios 10 to 15 micro gallons of
70:18 So they need to, they need have they need to estimate the mass
70:24 by 10-20% to make make it Right? So this paper, Heron
70:35 Exxon? Yeah, same players. possible zones were modeled um to invert
70:44 gravity between gravity stations. The gravity are from 762 m to 1200
70:54 So on the order of a So that's 3000 ft. Okay,
71:03 . Um Okay, so then now looking at after all these surveys are
71:12 , uh then they start rolling out three next papers. So after after
71:19 , so they were collecting data all years, almost every year. They
71:25 a year in '04. But then in 05 and six occupying the same
71:33 . So in the second paper they about how they improved their their acquisition
71:39 and instrumentation to achieve. Because they I mean this is they always did
71:45 in january when Prudhoe Bay was iced and like they would drive around on
71:51 equipment out there of course it's pretty cold and they would, you
71:56 drill, drill through the ice using these augers that, you know,
72:02 use for ice fishing and stuff. I remember the guys who talked these
72:07 all the time what was going And they would, they were like
72:11 the best way they could figure out to account for the density of the
72:15 later, which is important. It like the correction because that mass
72:21 you know, calculable frozen sea And they would take like a a
72:30 pole like you know uh you know sticks you use when you ski for
72:37 country skiing because they would have a edge, a little thing you could
72:42 on that would that could when you it in the hole, it would
72:46 on the bottom of the ice. could use that that length to
72:50 Think so yeah, it was pretty cause they were out there. These
72:58 giant track driven machine machines to go the occupy the different stations every
73:05 but on the tables at the bottom left is that they have time and
73:10 dependent factors. So the fact is of course latitude elevation, you
73:15 and so these are the these are accuracy of the measurements, you
73:21 pressure. They're worried about pressure. mean as many things as tides,
73:25 course, tides are a big deal gravity corrections and uh seismic noise.
73:35 then on the on the table on right single survey gravity and elevation
73:40 So here's their error budget. So the tide and ocean load, one
73:45 gal, they had to be within barometric pressure, one micro gal.
73:50 on and so forth. Total less than 11 micro gal. So
73:55 , so they said that they quoting paper, they adopted a highly redundant
74:00 procedure. Kabul was statistically robust. just I'm chocolate because just like this
74:07 verb age estimation of of a drift necessary to produce relative movement through.
74:14 Yeah so um okay so Now with three, I haven't started any data
74:25 . I'm gonna show you some Uh now this is surveys 2003-2007 And
74:32 they this is using the a. , this is the absolute gravity.
74:38 so they have 300 stations out That's all the little plus signs down
74:43 . We have 100 and 50 square I guess. Uh surveys +3356
74:53 Um And precision they're saying is better five micro gowns. So now this
75:03 Ferguson and akin that's you t d you grow and john see john
75:11 I know john very well. He's consultant and then named brady again.
75:17 brady was through all these papers. Well at least up to here with
75:23 so he wasn't Arconada Bp because bp Arco and then um Yeah um Let
75:33 see uh Polar motion. Yeah okay case of polar motion that was under
75:40 sorry I'm jumping on behind. Oh okay. I'm sorry these these path
75:48 a tree contours are are two ft two ft animals at 88 ft Yeah
76:04 ft 2 ft. And so the the water bottom is really flat out
76:08 in Prudhoe Bay. That's the point Okay let me just go on
76:14 So here are results from those and you're looking at are the averages over
76:20 years in the upper right? From , 2 years and B is three
76:27 average and C is a four year . So 303, 206 and
76:39 And then the color scale is the for all of them. And it's
76:43 from looks like minus 30 to 70 plans 20 sold almost 100 Micro
76:52 So a 10th of a mil igel range or just under 1/100 of a
77:00 ago, I'm sorry. Yeah, are micro gowns, right? So
77:04 hundreds of a miller go. So yeah, this is a tiny,
77:08 range. But if you look at anomalies, they're really hang together pretty
77:13 . I mean, it doesn't look just random noise, Right? I
77:16 this is, I mean you do the sense that it's, there is
77:23 bit of randomness in there, but definitely got signal in here. If
77:27 ask me, especially with the four average. So what does this
77:32 What it's higher judges that means. where I guess the water. So
77:38 trying to force, that's where they're to force the, so this is
77:42 arts through here and the code and trough is down here. So where
77:47 the injection wells? Yeah, they're the south injection wells are down
77:53 So they're right here. Oh I . So yeah, so that's that's
77:59 response to the injection. So the is heavier and it's pushing things
78:04 The water is accumulating down there. , that's what that means.
78:08 Yeah. So that's just adding the which is higher density than than,
78:12 know, oil. So and then is um uh one year and two
78:23 averages. So here's just 05206. let's see the two year 032.
78:31 I don't have, I have 03206 here. That's three years.
78:37 so 0506 And then 0572 years and 06207. So these to add to
78:47 this, I guess that makes And again it's the same color
78:56 So these are pretty subtle changes. I think, I mean it doesn't
79:01 that bad. I mean there's no where there's, there are some single
79:07 . There are some single station which kind of like a dead giveaway
79:13 you know, something's funny going on a single station anomaly is not something
79:18 you want. Okay, so then the final paper Which was published later
79:28 O. H. in '07 rally no age. Uh in this
79:35 the authors were Ferguson again clopping from G Chen roof. You grow Siebert
79:41 hair. She was a song by and brady. So brady was the
79:48 the only braider and Ferguson were the authors that were in all four
79:56 In any case the station is again the right the water injection. Now
80:01 see now we have a really nice . So it said gas injection of
80:06 blue, the Mondeo monitoring wells. bigger black ones, they had victor
80:13 injection. I'm not sure what that , but that's down here. So
80:16 injecting in regional areas as well. they're re injecting with gas up in
80:23 . So it's pretty. And then these little gray ones, those are
80:27 production wells. So this is a needed to say that is really well
80:35 . Yes, it's six ft, ft contour. And yeah, they
80:40 a GPS base stations to triangulate their positions. Then there's a cross section
80:47 goes through here. So the water is expanding into the gas cat and
80:54 the expected rate, but it's exhibiting symmetric behavior that is consistent with a
80:59 degree of structural control. So that think there's some faults that are
81:06 affecting the flow down there of of the injection and the flow of
81:11 , you know, being able to the hydrocarbons. So again here again
81:21 . Uh, some of the cumulative this time, they're talking in terms
81:25 cumulative mass distributions. So they're, decided to, they've taken their
81:31 their version models and now they're you know, mass and I guess
81:35 is killer tons. And so the year average, I mean I mean
81:43 for the two year average 03205 is A 03206 isn't being in the four
81:50 03207. So you can see the steadily increasing in a systematic way.
81:58 this is very nice. I think very impressive work. Um And then
82:06 here is uh uh huh. More of mass 2, 2 and one
82:15 . So kind of very specific and on their integration of reflection data with
82:22 Well and this gravity, this is course these structures are they're not interpreted
82:27 this, this gravity inversion there you know from reflection data but I
82:36 know you'd you'd be hard pressed to me that there's some there's you
82:43 um strong correlations but I mean with structures these structures, but maybe maybe
82:51 some Yeah, I don't know, mean is so the over is overall
82:58 and a trough to the south but going to be, you know,
83:03 on that. There can certainly be superimposed on that broad feature.
83:10 I don't know, I don't know how you can relate this mass distribution
83:18 these map structures but yeah, I know, I mean this is this
83:28 a high where there's not a low these are highs that are outboard that
83:34 there before and this is a high it's a low and this is so
83:44 two years before. Yeah. Yeah got me. I don't get anyways
83:55 this this is this is claimed to pretty pretty successful so I don't know
84:04 any other times. I'm sure there . It's not something it's not uh
84:09 not like in my on my radar I don't really have a dog in
84:15 fight so I don't wanna be too here but in any case it is
84:21 is something that's a very famous study yeah there you have it. Okay
84:30 switching to Magnetics. Let's see, to Magnetics. I've been blabbing here
84:40 an hour and a half. Do want to take a break or do
84:43 want me to drive on? Let's like a quick break if that's
84:50 Sure you wanna meet here at Channel . That'll work. Okay. Alright
84:57 me just that my connecting work. about that my connection went down so
85:06 I don't know what happened. Well know what happened when I connected with
85:10 . Sorry about that. Um Yeah know of course it's gonna happen today
85:21 while I'm teaching, luckily luckily it back and we can we can resume
85:32 can room resume the festivities. Okay all of the previous sections on gravity
85:42 and you know I had a little of the Kobe study. But the
85:51 was, you know, kind of method is and how good they
85:54 how you know what you can measure them and the resolution of them etcetera
86:00 . And then. Okay, so questions about this material so far?
86:08 good so far so good. I'm gonna take that as a positive
86:15 . Um Okay let's let's talk about texas magnetic survey and they're quite similar
86:26 there's a couple of differences. So we, you know, we can
86:32 land surveys and we can do marine as well. And in marines they
86:38 have the magnetometer on the boat. put it, they drag it behind
86:42 boat in a and whatever. Uh know a vessel that they call a
86:51 because the boat is made of metal often and there's just a lot of
86:56 related to that. They also have toll marine magnetometers. There's a fair
87:05 of literature out there on the results using this instrument. It's pretty
87:12 especially if you're mapping. Um Sea spreading announcement. Remember I talked about
87:18 Jurassic magnetic quiet zone yesterday where there , there were fluctuations between the pole
87:25 versus was really fast and the field very weak. So if you measure
87:32 the sea surface like out in the pacific where there are some of the
87:37 , somebody's Jurassic aged magnetic crimes. know the sea floor reversal bits of
87:47 atmosphere that's been reversed. Um, the surface, some of these anomalies
87:55 the reversals. They just sort of and form big broad regions of highs
88:00 lows. But they've done some deep experiments where they're right on top of
88:06 sea floor and they can really define reversals very well. So yeah,
88:14 toes is a thing. It's pretty . And of course airborne Magnetics is
88:19 a big deal. Um, you do it with a fixed wing aircraft
88:23 helicopters. Um, with helicopters quite they're, they're a secondary,
88:32 you know, there's a lot of E. M. Surveys, especially
88:38 mining purposes and to stick a magnetometer , on, on the aircraft is
88:46 very simple, very easy to So they do that. And then
88:52 , satellite, uh, they use flux gate and cesium vapor And of
88:57 , MAg sat, I showed you , I showed you black and white
89:01 of it before. But here's a image of Mag said again. You
89:05 , it's just like there's a single wavelength that's percolating through this. Now
89:11 map is plus or -20°20 gammas Nano where I think the one I showed
89:19 last night was customized 11. So has a little bit more of a
89:23 on it. I don't know what deal with that is, but the
89:28 quality of magnetic anomaly data is actually , Um Next would be marine and
89:42 data is more noisy than marine or . And I think that's just because
89:49 so close to the source. It's . It's not intuitive but the best
89:56 best magnetic data the highest quality is data. So marine service there's the
90:05 he's holding uh the fish that has magnetometer inside of it. It's towed
90:12 . Of course deep Tojust be the thing. Except this is down here
90:18 and like a lot of marine gravity their collective with reflection data. And
90:23 they're just an add on. And it's like pennies on the dollar and
90:27 very much and the same caveat supply spacing, sampling um tying ties with
90:40 stations as well. Um Yeah I know what the nominal distance is that
90:49 drag these behind the boats is look yeah you have to make a you
91:00 to make a heading correction. Yeah also with regard to, well I
91:08 we'll talk about this stuff. We about processing. Okay so airborne surveys
91:16 measurements clicked by aircraft since the 19 . Remember that first U.
91:22 G. S. Survey was was 49 47 something like that anyways.
91:28 remember the USgs made the first survey But they can they can be collected
91:36 variable heights. Sometimes they fly into surveys at two elevations and done a
91:42 with those calculated the gradient. Again drape and drape survey, we just
91:50 of follow the train and a constant called barometric again same as before.
92:01 for shallow sources, you want to close to the source. So here
92:05 two planes with stingers attached. I know what kind of aircraft it looks
92:10 a titan. This here, this here, this is a titan,
92:14 Cessna titan. And this picture used hang on the big version that used
92:23 hang on. It says Arrow Service the top there it was It was
92:30 the lobby of Aero Service. I at Arrow Service in from 81 to
92:36 . This is the first job I in Houston when I moved down here
92:41 michigan and before michigan I was in army, they hired me over the
92:48 because of my experience in the I was I was a photo
92:53 I was. So the jets would missions for us. I was in
92:59 intelligence and the jets would fly missions us and they would, you know
93:03 pictures of equipment, tanks, and personnel carriers and stuff like that and
93:11 would identify those those equipment. We we would mobilize the air bases,
93:17 Force bases and then The you know F4s would fly our missions for us
93:22 we would debrief the pilots and then the imagery and make a report.
93:30 I had I had a good you know, a good experience of
93:33 at airborne imagery. So they just and in those days that was before
93:40 . Right. GPS didn't really take until the nineties, late eighties and
93:45 um mental eating. So when they surveys over land they would take
93:53 They would have a little 35 millimeter that would take pictures, you
93:58 continuous, very, you know, shots. And then we would take
94:05 that big long strips of film and at a light table with with a
94:11 event. And and you know pick points to track the flight path on
94:20 map and then read those coordinates and that would be input into the
94:26 That's how they would position the data the for the for the survey in
94:34 case going now going from there to before I started working for myself In
94:42 and 97 I was working for my survey company. They're based out of
94:48 and they this airplane, this very airplane in the lower right had
94:54 you know, they ended up owning through a bunch of different company acquisitions
94:58 sales and stuff. And I organized survey in Marignane base in Peru for
95:08 . And they flew there. We four guys in the crew down
95:11 They flew the survey and then the was finished. They mobilized that aircraft
95:16 of there and they were gonna fly marignane from the Amoco base station to
95:22 little jungle town called Pucallpa. That's in the in the jungle uh east
95:31 the east of the Andes and the just went missing. The they don't
95:38 what happened to the crew complained, just went missing. So you know
95:44 those days there was a lot well little planes go missing all the
95:47 down there because people that you know the drug trade down there, they
95:54 little planes for that stuff. So just steel planes kill people, stuff
95:59 that. So anyways that plane um known for a long time. I
96:04 for a long time um that incident lost another plane down there and two
96:11 were killed and then we found that that ran into the side of a
96:17 . And then um the last incident that we had a pilot that was
96:25 by the pool in you know after flight and he had a heart attack
96:33 fell into the pool and drowned. we lost like seven guys in like
96:40 months. These are all surveys that organized. It's not my fault that
96:46 this bad stuff happened. That was I decided I was gonna go back
96:52 school, get a PhD. So started my company And started working on
96:58 at the same time in 97. anyways every time I see that photo
97:05 remember that. Um So why am showing it here? I don't know
97:09 there you have. Okay so um surveys just like marines, gravity
97:20 you know that you're concerned with the same things in terms of the flight
97:25 spacing, how much you tie And uh you know the biases was
97:33 to the orientation and the spacing of lines and the altitude in terms of
97:39 from the source. These are all for flying surveys. So here's some
97:48 of instruments. So these are birds they also call them. So they're
97:55 fish in the bird's airborne survey. here's the helicopter, they also do
98:02 with fixed wing, I don't have picture of a fixed wing aircraft with
98:05 of these things. And here is here is a helicopter with a Stinger
98:14 they fly surveys with ultralights. In . In fact, let me show
98:19 something. Let me see here. is it at uh where is it
98:25 here? It is this I just this this morning. So this is
98:32 they're doing surveys now with with drones uh I think pretty successful. But
98:42 now the F. A. So can only do them. No I
98:52 only see the zoom meeting like login or something. Can you see
99:00 Stephanie? No sir, not Hold it. I'll stop it.
99:05 I can only see your uh I only see the zoom meeting. There
99:10 go. Okay, now I can it. No, but now I
99:19 now it's on the screen now. , Alright then. So this is
99:29 , I found this on the internet , which is a big instrumentation company
99:35 this is one of their promotional bits . You still see it?
99:43 Okay, so this is there's the , it's in that little So I
99:54 they're flying a mag survey over this . Yeah, now that's got to
100:22 very cost effective. Okay, all right, sorry about that,
100:36 sorry about it, but I just that that was kind of fun.
100:43 we back out of the program Back under the slides. Not
100:47 I'm still looking at Youtube. Do need to do something? Okay,
100:59 I'm at the slide. Okay, . Alright, I used to have
101:07 little video of this one. So a here's another drone that that they
101:13 to launched with like a slingshot and it's got little hooks on the
101:22 And I have this tool, this crane thing and the plane would just
101:29 into it and it would, you , catch that wire and it would
101:35 , you know, flip around and and land that way. But I
101:42 the helicopter type drones are probably make sense to me. So yeah.
101:50 , so, okay, I have little cash history of a deep toe
102:00 survey uh in the in the the uh Iberia uh when they call it
102:13 abyssal depths abyssal deep the I. . B. The Iberia. So
102:18 is off the continent of West Iberia is Portugal and Spain. That's
102:24 And they flew this they I'm sorry this is marine data. They acquired
102:32 data in and around some ODP So um it's a fluctuating magnetometer and
102:46 they towed it over some some magnetic and also as well as some some
102:55 type, some mantle rocks which were as the basin opened. So which
103:02 a which is uh which is something has a lot has had a lot
103:08 attention ever since then. I mean it's been you know it's been It's
103:15 over 20 years and it's still like just are in love with this
103:23 Okay, so this is a reconstruction of the study area. So here's
103:29 right? So there's Spain and Portugal there there's France 19 and then it's
103:36 reconstruction. So it's a reconstruction of the age of the reconstruction. Um
103:48 closing this Atlantic, the North Atlantic gotta be like a 60 m.
103:53 reconstruction that's in 60 to 100 million , something like that. So when
104:01 closed the central atlantic and the mediterranean actually have overlap in the in the
104:11 sea. And I'm sorry the leprosy in the north atlantic. So um
104:24 the area where they're interested in is here, it's called the uh the
104:33 abyssal plain. And that area right is where they did the deep
104:37 This just gives you some context for . So on the right here is
104:44 map of modern present day with some contours. It looks like it looks
104:52 it's 500 m, something like that . But so these are the ODP
104:59 8 97 99 we're gonna talk about and here they are in cross section
105:06 97 8 99 8 98. And are called these are prototype ridges.
105:16 how those forms basically when this basin over. When you know when the
105:24 central atlantic north atlantic broke apart and these passive margins. The continental crust
105:32 , you know, stretched and But it's um but because this area
105:38 a, is a magma star, what they call it a magmatic margin
105:42 non volcanic margin. There wasn't enough to produce the ocean floor. And
105:50 in many cases you have like that's lower crust but prototype that meditates
105:58 upper mantle rocks. So the idea is that you stretch it so much
106:05 continent breaks apart until you finally just the upper mantle, it's just,
106:11 know, it's just exposed and once exposed, it hydrates because the seawater
106:18 to it and prototypes can be serpent . Ized. And when there's a
106:23 , they swell and that's that's the for producing these things. Okay.
106:31 the altar made these Ghabra, those thing is that they think they're altered
106:37 being hydrated. Um Yeah. Water depths on the order of five
106:56 . So the magnetic data, here's magnetic data or that. So,
107:03 here's the lines. There's well 8 99 8 99 909 01. Which
107:11 the same ones is in here. , so the mag survey this is
107:15 this is called the this this indenture . This is the uh Iberia abyssal
107:25 . And this is what they're They're just calling the tsunami the JN
107:32 an M. Zero M zero. means Mesozoic zero is I believe Right
107:42 here. And that would be 100 million years ago. Right?
107:53 And then just these triangles to represent they're calling a pretty tight ridge based
108:02 the samples from these from these wells they that they drove through. So
108:11 profile, I'm gonna show you Okay. First of all. First
108:17 is this bottom one, the straight here. It goes from this
108:21 Anomaly, which is a big positive the way to 901. The second
108:29 , I'll show you is just this one that just goes from just inboard
108:33 the J. To uh 8 So here's, What do you measure
108:42 the surface? You have a the fish you're driving. And this
108:47 what you measure the amplitude is plus -200 gammas. 200 nano teslas.
108:53 the deep toe anomaly is much Plus or -400 nano teslas. And
108:59 can see but you can see that same thing, right? This
109:03 Is that one? This one is one? This one is that one
109:06 on and so forth. It's just you're closer to the source. So
109:11 a bigger anomalies. Now they have little model and they calculate what contribution
109:19 , you know, topography on the floor would produce. So that's what
109:24 is. So you subtract this one the measure deep toe. And that's
109:31 that's the dotted line down here. then they made a model here uh
109:37 on, based on, you these the well penetration as well as
109:49 , the anomalies. So their this their calling us M. three.
109:55 mrs Mesozoic crowns go from M. to M. M. 40 to
110:12 . m. 42. Which coincides ages 1 20 M. A 1
110:21 M. A. Now, a . When I say Cron, Cron
110:28 the actual piece of ocean crust. what it is. Okay,
110:34 quite often you'll see you might read the literature. People identify an anomaly
110:40 say this is crown. Right? is Crown M3. They'll say
110:45 And that's just a total art. just really the anomaly over the crime
110:52 I'm not trying to be nitpicky but just want to explain. And so
110:57 crimes, those are bits of ocean that are created by sea floor
111:06 Okay, so that means if someone identified an M. That means they
111:12 that sea floor spreading process is That's that's the what I'm getting to
111:18 this. M three M zero would outboard of that Because M0 is a
111:26 kick. That's remember I talked about long normal. So the law Norrell
111:32 between Cron C% 34 which Which ended which the beginning of the long normal start
111:43 80 M. A. & 34 was the last um reversal map
111:52 the center zone. Then you You know, 40 million years of
111:59 polarization. No, no magnetic field , then you had M zero M
112:08 is a negative because it's right next the long normal, which is all
112:13 . So M zero is out here and it's going to be a
112:17 That's why I was looking at this for a minimum that I can
112:23 see I can track this. So thinking this is probably M zero.
112:28 this is M. Three Then that this is probably M2M2 is a positive
112:36 . So what they're calling the I would call em to now.
112:40 only reason I know all of this so well is because I Actually written
112:44 couple of papers on this stuff with Hall, you can get them from
112:47 website if you want. 2018 and . Okay so that's what's going on
112:55 . So here's just an example of toast data which is obviously much better
113:04 surface and then you can use it kind of sort out what's going on
113:09 the In the in the in the in the basin below or in this
113:14 in the exposed uh process. So the shorter one and this is uh
113:21 the need to surface analogy. It's flat um the deep toe lots more
113:27 in it. Basic relief. And here's the results and then here's their
113:31 model of that as well. Does that make sense with your, would
113:38 explain that adequately do you think? I think so. Okay. Good
113:45 good. No questions and I'll move . So here is the our summary
113:51 the data acquisition with regard to There are two types of gravity
113:57 The relative ones those zero length springs some sort of spring then this
114:05 Which is the weight drop and you collect that the platforms for grabs your
114:11 wells, marine water bottom. I I think I misspelled in your copy
114:17 something. That's why it's highlighted here and satellite and the precision is reported
114:29 be on the order of 1 to micro gals. Um although that's not
114:37 serve a resolution if you ask me . The types of instruments are flux
114:43 which are vector components. And then two the two resident instruments which are
114:48 scale Urz. So they don't actually the vector direction which is a
114:56 And those are of course the proton in the alkaline also called the optically
115:02 one. And the platforms are land , marine deep toe. See I
115:07 that there are magnetic susceptibility tools that susceptibility. I don't know if they
115:13 magnetic. So this is a little a little unclear. Um deep toe
115:18 and satellite and precision flux A 10th a now Tesla. This should be
115:29 . I started um data acquisition acquisition like 73 ah session Resolution 0
115:48 I'll make that correct. Yeah because go on orders of magnitude .01 report
115:56 and .001 for optically pump. And for survey planning it depends on the
116:01 of the of the survey, depends the target area. The sort the
116:06 kind of contrast you expect should make feasibility study. Um under consider the
116:15 spacing what kind of instruments and you the platform and then of course the
116:22 , jungles, deserts, there's a going on or something like that.
116:28 we were I'm gonna drive on. data processing they're for gravity corrections.
116:37 are two main categories of temporal corrections then there are spatial corrections. So
116:44 temporal corrections are the title corrections and drift and special. We have to
116:49 with the latitude of the survey Um make two corrections with regard to
116:58 , the free air and then bouquet train corrections at both correction. We
117:06 talk about that, but that's for platforms, ships and airplanes. And
117:12 there's mist hikers, which is basically you're processing your for leveling the
117:23 So this is a really busy but let's just go through it by
117:28 numbers here. So here's our little of the earth and then here's our
117:34 mountains and valleys and different data. don't I don't care about this stuff
117:41 much down here, I don't think important. Okay, so the latitude
117:48 actually is correct for three things. attracts a correct for attraction of the
117:57 as a whole. So what accounts that? It accounts for centrifugal force
118:06 to the rotation of the earth. it Uh common accounts for the radius
118:13 the earth because Paul is 20 the diameter is 20 km less for
118:20 radius rather is 20 km less at pole, that is at the
118:25 So the earth is like an old spiraling. So that's that's the main
118:35 . The terrain correction, correct for near the near the instrument that are
118:44 the instrument and it corrects for avoids the instrument that are below the
118:50 And so there are there are charts used that we used to do these
118:55 in the old days. Nowadays, can do this with D E.
118:58 . S very effectively. And then free air correction just corrects for how
119:04 you are above sea level, just distance from the center of the earth
119:09 account for any mass around it. the elevation and the bug a correction
119:16 , it corrects for that mass difference there. So that's how that
119:22 Now folks still like to do static . I don't think it's a
119:29 I mean, I don't like to it. I think there's a lot
119:33 assumptions and there's a question of whether , you know, quite often they
119:40 ice, aesthetic questions where the earth not static, it's dynamic. It's
119:44 over a subduction zone or something. mean, it just defies the reason
119:49 do it. But I have a have a few slides in lecture number
119:56 and I'll repeat this. I'll do slide is duplicated in there. So
120:01 go back to this when I start I talk about this, I talk
120:05 this in interpretation because it's really an . It's not a processing thing.
120:11 don't think so. Here's the processing for gravitating. I'm sorry, take
120:19 gravity measurement. And the first thing need is correct for tides and the
120:25 draft and then you do the spatial . This would be for land,
120:30 latitude, free air bouquet and That's the flow. Now for marine
120:39 airborne, it's the same except you to add this, that was
120:47 So the initial bouquet, it's called simple bouquet. And then when you
120:53 the train collection, that's called the bouquet. Okay, so the title
121:14 . So the gravitational attraction mentioned at service includes attraction from all other celestial
121:22 . So with the exception of the because it's so big and the moon
121:27 it's so close, everything else are not really, you know, we
121:33 we don't sense mars or venus or or anything like that. So I
121:39 just need to worry about the sun the moon. Um The title correction
121:44 complicated because the gravity attraction, the and the moon vary over different time
121:49 daily and monthly and the vertical component tide is so you have D.
121:55 . Z for the tide, it's some function of the moon.
122:00 m moon as our sons. It this complex function of co sign and
122:09 distances and the mass of each of . So and r. Is the
122:21 of the rigid earth. So where's at there? It is right right
122:34 . And alpha is the geometric angle M. S. M.
122:39 Okay. Alright, so that is formula. Well what the heck does
122:42 mean? So I'm sorry wow, just got Mhm. So regarding the
122:55 earth, the real earth acts So the odder layers are deformed.
123:04 actually it's not just the water that up and down, the actual earth
123:08 up and down The earth goes up the order of 10 cm. With
123:15 with the variation in the with the and moon during the attraction the sun
123:19 moon. Of course that's tiny compared the size of the earth. But
123:23 does amount for about I guess what the maximum time 0.3 mg girls,
123:29 a six hour period. So here's it works. Here's here's our earth
123:34 around and there's this angle alpha. it's a survey area, let's say
123:40 survey areas right there. So that is from the center of the earth
123:45 the moon and the sun. So way to really get a handle on
123:50 the tide correction is. We just at maximum attractions, maximum possible attractions
123:58 sticking all these values in that formula get, the maximum tide from the
124:03 is 0.5 mg. So 50 So it is it is arguably
124:12 The moon is even more. It's twice as much. So the maximum
124:16 , the moon is .11 mil So the maximum possible attraction From the
124:23 is .16 million uh approximately. So micro gap. So, um,
124:33 important. But uh, you I mean if I'm saying that the
124:39 the, you know, the rule thumb resolution of gravity surveys is on
124:45 order one mg. It's still kind in the noise, but it needs
124:50 be done. I mean we're geophysicists crying out loud. We want to
124:55 solve the queen. So um, , so drift correction. Now,
125:00 meters are mechanical devices. So they from temperature and, you know,
125:09 fatigue, et cetera, pressure. they that instrument and even though like
125:16 are very careful when they build them people are very careful when they,
125:19 they take care of them. The still drift. Just just this measurement
125:24 change sitting on the bench in your . So, as I said
125:31 we had to repeat with the tie at the reoccupy stations. And of
125:36 we always assume that it's a linear because we are some kind of physicists
125:42 physicists think everything can be reduced to sort of linear linear relationship is an
125:50 and we don't really know what the . But from these tests.
125:56 yeah. So tests have been to been done and They think that they
126:04 they can make this argument all So here's here's examples of instrument
126:08 So note the scale. These are is our .05 increment of Miller
126:17 So these are not great. You , they don't change a lot.
126:24 are over. Yes. Was seven in the morning at two o'clock in
126:28 afternoon. So 8:00 - 3:00. So here's how it works basically.
126:37 you have stations, you have a occupied for the first time and then
126:42 go out and you measure B. . D. E. F.
126:45 you re occupy A. So there's one to a. Two and here's
126:49 your other measurements. So basically you much linear. You rotate everything back
126:53 the A. One and a two the same level. And that's how
126:57 , that's schematically how you do Very simple. Um tide and drift
127:06 tide summary. Okay, so the often the base station reoccupied but is
127:12 but it means it's gonna cost more you got to keep going back very
127:17 . Uh Yeah, you can only drift rates can only be computed at
127:24 . This is important. You can do the tide correction after you correct
127:30 the instrument makes sense. Make sure values that you measure are corrected internally
127:38 you start to make tied crates. for marine data navigation C state variations
127:45 it impossible to reoccupy the site. it is calculated from repeat measurements made
127:51 support of embarkation, which really is drag because like you could be weeks
127:57 a month. You're gonna assume a , you know, a linear
128:01 And that's probably just not true. so you have to just you
128:06 but quite often in the marine survey get chances to to sail some ties
128:13 your survey lines and you can do misty analysis which will help reduce that
128:19 error. So yeah, cross line are important for the mistake correction.
128:31 , latitude correction. Um The predicted of G. Not at any particular
128:40 for a sphere spherical symmetric urge is by the latitude formula. So it's
128:48 so it's a function of Insigne and it has to do with the difference
128:55 at the grab G. At the and A. And B. Are
129:01 . I guess there are constants that the shape of the ellipse oid.
129:07 , so Here is the latest 1967 for this was published in blakely
129:15 It's probably a new one out by , don't. So you approach so
129:25 basically attract, you subtract this equation you plug in whatever your latitude is
129:32 this in this uh this lambda. you solve that. So the
129:37 G. R. F. The . G. F. I'm
129:41 indicates that the north south upgrading of earth's field is given by this.
129:45 this is .81-2 times a sign of latitude will tell you the gradient of
129:54 the uh the field changes. Yeah it's very important. It's very key
130:02 know what your latitude position is. . so what does that look
130:08 So here's a little uh longitude latitude all the little survey stations in there
130:16 um this is that data grid it so these are the contours and the
130:22 and again it's going so this is yeah blue 185 so 135-185. And
130:29 is good at five million gal Here's a latitude correction. So it's
130:34 a function of latitude and it's increasing it looks like it increases from whatever
130:41 be almost Well it looks like 0 Whatever 32 or 33. So you
130:51 that from that and down here you this. So I mean the latitude
130:56 does really swamp the signal. If gotta look at gravity data and you
131:02 it's just got this enormous ramp going it. You can bet that it's
131:07 been corrected for electric correction has not applied and if that's the case then
131:14 can bet it's probably not been processed all because correction is the first thing
131:20 do then you do elevation corrections and corrections and things. Okay so the
131:29 formula gives G at mean sea level means but if you're at a different
131:38 , free air and boogie to do is just for the elevation, the
131:43 is for the mass between that elevation the mean sea level. Just kind
131:50 begs the question and this is a that I asked my colleagues a long
131:55 ago. And and the answers I are very interesting. Remember the
132:02 it measures the height of the sea surface. It measures the G.
132:06 . If you're out there on the sailing around, you're not at mean
132:11 level, you're sitting on the OID, Which maybe five or 10
132:16 above sea level or below sea level even more maybe 50 m. So
132:24 wouldn't you do a free air correction that? And I asked, I've
132:30 my colleagues, it turns out that people like me who interpret data say
132:37 , you should do it. But people who acquire these companies that acquire
132:42 data and process it and say it doesn't matter. That's funny.
132:49 anyways, yeah, so the gravitational decreases as elevation increases. This is
132:59 rate at third. Almost a third a milligram per meter is just because
133:03 getting further away from the source. just, you know, it's just
133:07 just Newton's law right further away from source. So for extreme elevations,
133:15 need to add a term to correct h um to so this this is
133:25 this is the term you're adding for elevations. I'm not sure what that
133:31 . I mean, I'm not sure the what would be extreme mount Everest
133:37 the the Mariana trench or something like in any case. Uh yeah,
133:45 point. Oh, so that is . It's about 1/4 of this signature
133:50 . This this value here. So effect of the free of gravity and
133:55 signals is related to two factors the of elevations in the area and severity
134:02 horizontal elevation. So I guess if is a clip, if you're
134:08 you know, in the in the the Utah surveying around all those enormous
134:19 , then maybe we need to think this sort of thing. So if
134:26 are smooth, of course little impact . So three aircraft. So here's
134:34 little survey again and then here's the contoured at 10 m. So it's
134:40 got enough, it's got a bit relief. It looks like it's
134:42 you know, going from it's about 10 to 24. Just got about
134:49 and 100 and 20 m of It looks like something like that.
134:55 then there's the stations on top of . If we zoom into this corner
135:00 here in the southeast but we have ranged from 23-102. No, that's
135:06 same. It's the same color Right, okay. And these are
135:09 stations down here. Um So the meant site. So we have
135:17 Okay, yeah, applying that equation the value at 23:50 should be right
135:24 . The free expression is 725.21 mil . Note that the fear anomaly Contains
135:36 over print of topography. This is important. three here is dominated by
135:42 . So quite often bouquet corrections are by contractors in the ocean basis.
135:55 when you model data in marine you don't model Blue Gate should model
136:02 air because the stations are at the surface. They're not alone. The
136:11 . Whereas we're in in land the stations are, you know,
136:16 draped on the topography. So you to account, you need to do
136:20 boo gay because you have that I mean you do bouquets and marine
136:24 but you don't need to model. don't need to make a model of
136:28 . You can just use free air the stations are at the sea
136:35 If that makes sense to you. that make sense to you don't do
136:37 need to explain a little bit Um No. Okay. Alright.
136:50 . I will explain it better. when we get to doing the exercise
136:55 the way. Um I talked to guys last night and she quint and
137:03 trying, I told him I really to make a decision. I want
137:07 do like Wednesday because um I want , I want to do the exercise
137:15 . So I want to be, want you to be able to grab
137:18 software and install it on you, on your machine so that we can
137:25 together on the model saturday for the . So that's the plan. And
137:35 I mean it's it's just a nightmare I'm working on it. I am
137:41 persevering. Okay, no problem. , so for land based gravity measurements
137:49 sea level, the decrease in the gravity field above sea level accompanied by
137:54 traction. The material between right, is for the bug a correction and
137:58 amount subtracted is due to an infinite slab. Right? This is the
138:03 PG road to PG Ro H It's gamma here but it's G.
138:10 the the international gravity gravitational constant or 04193 rho times H where H.
138:20 a meter. So that's the big crash. But the way to think
138:24 bouquet crash is not as a slab , way to think about it is
138:30 you're minimizing the effect of topography. , free air data is dominated by
138:39 and so what the bouquet correction does it accommodates for that surface contrast such
138:46 it tries to you know, you it to be, you wanted to
138:51 make it invisible so that you are at anomalies produced by the subsurface.
138:59 , so there are lots of ways decide on what road to use.
139:04 you know, well as core samples the last thing as we talked about
139:14 it must be a representative of the that exists between the highest and
139:18 So you gotta. So now some like to try to do what they
139:22 a variable density bouquet, I think just nutty because you you have more
139:29 a chance of producing anomalies that don't exist than you do of actually
139:36 you know the effect of topography. and as usual the bouquet approximation,
139:43 have low relief, just like for relief. You know these corrections don't
139:48 much of an impact on the In fact for like offshore free air
139:54 over like continental shelves is de facto because the shelves are pretty flat.
140:02 when you do a bouquet correction over a continental shelf doesn't change the data
140:07 much because the things flat. So a picture showing you what all that
140:13 . So here's a here's our Here's our observed gravity. Alright?
140:19 subtracted um the latitude correction, We the free air correction and now we're
140:27 the bouquet all corrections and gravity subtract the measured signal. So that's just
140:34 truism. Subtract. Subtract. Subtract . Remember. So here we have
140:43 here's here's the sea level, say that B. And we're making a
140:48 here at p at some elevation. . Right? So we got this
140:53 between A and b. Well we to account for the material to complete
141:01 the material that's missing here and the that's added here. And if so
141:13 you have a station, if you a station here, you can see
141:15 this material would add to the blue correction. I would add to the
141:20 data because you have this attraction over . But what about the valley?
141:31 How does that work? You need you still need to subtract it because
141:36 subtracting what's already been subtracted, So you're subtracting what's already been
141:43 So it's adding that right? You to you need to add in the
141:50 area, you need to add this fill in it. But it still
141:57 a subtraction. Yeah, I gotta about that. Huh? But the
142:03 remember civil boogie is just a That complete includes the train tracks.
142:09 all Deficiencies from one and 2 and from three and 4. I wasn't
142:16 on purpose to be confusing but I that the book is always subtracted but
142:21 is a negative so it would be less of a value anyways, Don't
142:30 about it. I'm not going to you on it. So, so
142:34 here. This this is a figure Nettleton 1976. It's an old figure
142:40 Middleton. There's a very famous book petroleum prospecting with magnetic data and
142:51 L. Nettle to louis L. was a very famous uh practitioner of
142:58 magnetic p. I think he was gulf oil guy. And this and
143:03 is called the Nettleton method for determining books you should use whenever you look
143:10 legacy data, gravity data. This economics you can bet They're gonna use
143:17 for the bouquet correction density. The formula right here the big agency right
143:24 they're gonna use 2.67. It is is a universal value and actually there's
143:30 no good reason for it. David I mentioned earlier I used to work
143:35 Arco. He gave a talk once he really dug into this thing.
143:41 was the origin of using 2.67 2.67 as I said is the density
143:47 courts. But it turns out that um why it's used for bouquet is
143:55 just no good reason. It's just people do. And in fact you
143:59 assume that's what it is and in it's what I do. It's what
144:03 do because that's what everybody else in world has always done. It's really
144:06 of ridiculous. But now what? so what you can do so if
144:12 get legacy data you take that and you have an area where you you
144:17 think, you know you look at bouquet anomaly man and it either correlates
144:22 anti correlates very well with topography. in this case the top curve here
144:29 correlates and the bottom one anti correlates ? If you see that, what
144:36 can do is you can strip out can you can take the topography take
144:42 bouquet corrections. Formula with 1.67 and out that correction and then you can
144:48 an analysis like this. You can it in three D. As
144:51 You just test a bunch of bug corrections For different values until you minimize
144:59 effect of topography. Remember that that's the reason we do it in
145:02 first place and once you minimize it that's your boo gay density correction in
145:08 case. 2.2. So this is that all of us do. We
145:14 know. It's gonna be 1 We all know that to check the
145:21 versus the data with gravity data. want to always check topography versus free
145:28 versus books versus your residuals. You want to be checking in because because
145:36 biggest density contrast that's that's measured by is the topographic surface and that is
145:44 even if it's underwater, that's the density contract. The second biggest density
145:52 that affects the data is the contrast the bases across the mojo. You're
145:58 from 2.9 - 3.0 So that's a grams per cubic centimeter contrast. So
146:10 biggest Destiny contrast. This is That's what I'm saying it over and
146:13 . The biggest Destiny contrast is at surface or the water bottom. But
146:21 rocks and soil meet water or air the second biggest is at the base
146:28 the crust at the mojo but this the way that you can do
146:33 you can apply to sort of minimize you don't want you don't need to
146:37 trying to interpret anomalies that pretty much can just go out there and walk
146:41 . There's no reason to try to it right. You want to get
146:45 of that. You don't like look stuff that's beneath it. Okay enough
146:49 me uh preaching there. So train . So the topography surrounding each site
146:58 you know, doesn't conform to the . So we need to do a
147:01 train corrections. And for for land . I mean even marine now everyone
147:08 D. E. M. But back in the day there was
147:12 was called the hammer method. And broke up circles around your station in
147:18 of zones and compartments. And the was just just tedious and time consuming
147:26 really just, you know, what that look like? So here are
147:31 the different zones you have zones A L. And then so and then
147:37 zone is broken in the compartment or . So this in this case,
147:43 J. Has 16 different compartments or and zone zone B in here as
147:50 radius of six 0.56 ft to 54 . Zone J 8500 and 78 to
148:01 Zone M 48,000. Right? So is this is, you know,
148:07 just under two miles, just under miles. So it's big. So
148:13 you get out here the contribution is . You can start using contour
148:20 And then so here's here's the idea that it's uh you have to pocket
148:27 topography in. Each compartment is then with a flat top prison. And
148:35 the mean elevation of each present is . And then you have all these
148:39 and compartments. So you can you're to get a sense for what kind
148:43 a nightmare this stuff is. But important because you need to really reduce
148:49 the you know the external mass excesses deficiencies that affect the measurement. So
148:58 again, nobody does this anymore, all done with D. M.
149:01 . Now. Um But here for reference are the original hammer charts.
149:07 for zones B C E F. . And it shows with with regard
149:14 uh radius and I guess radius and . Right? That it uh table
149:25 going to use the compartment or injured use. Okay. See for each
149:31 do two undulations. Right. This okay. This correction applied to.
149:37 . Yeah. Customize oh, closer eyes. This is right. This
149:43 the height. Yeah. In any these are the table. These are
149:47 historical value going all the way out em. So F. Y.
149:51 if you ever someone ever asks you hammer, you know it um As
149:59 said D. M. Another approaches mathematical functions. You can try,
150:04 can try to approximate the topographic with sort of you know, Aunt or
150:11 . Now, marine, what we do is we just we fill the
150:15 layer with the density. So wie wir dancing is one point oh three
150:22 1.0 to 6. Just a little more dense than one. And you
150:30 to. And the water bottom densities range from like 1.9 to 2.2 on
150:40 order. So far less than land course. Um So what you would
150:45 is you would just what I I build a three D. Model
150:49 just a water layer. I like . The attraction of that layer at
150:55 density of point uh 97. So assuming the water bottom density of
151:04 The shallow density density is too. then so when I calculated the attraction
151:10 .97 I add that to the free gravity. And I've got it.
151:16 I've created a bouquet a correction of of two rather. So that would
151:26 dense if I make the water layer too. And the sediment density directly
151:31 it is to you see basically I that horizon. I've erased that density
151:38 . So there are no anomalies. mean theoretically are being produced by that
151:42 contrast. That's the idea, it's same sort of idea as I was
151:48 showing you back here as sort of thing is adding density to sort of
151:56 the effect of topography. That's the of bouquet. I know it's a
152:02 correction, yada, yada yada. the point of it, the point
152:06 the reason we do it is to topography. I hope you'll never forget
152:13 now. Mm Okay, so that correction those votes harvey you want to
152:23 it that is a correction that that corrects for a moving platform.
152:31 so the Earth is rotating but if have a moving platform, like a
152:37 a boat or an aircraft or an or helicopter, then there's gonna be
152:44 scent refusal, you know, accelerations related to that. So here we're
152:52 down on the Earth is rotating this um and from the north, looking
152:59 from the north pole. And so have the acquisition plan. The elbows
153:05 subtracts from the angular velocity. I , well the measurement, if you're
153:11 on where you're flying, if you're this way, it's gonna subtract from
153:15 angular velocities. Earth rotation. If flying this way or some component in
153:20 direction, it's going to be act it's going to be added to the
153:25 velocity of the Earth's rotation. So got to correct for that. And
153:33 here's our little survey and surface up . You have this this angle lambda
153:40 the center of the earth, through survey area. And you have another
153:46 measurement that extends from the axis perpendicular our area. Right? So uh
153:54 latter the line of longitude with with is this? This is a
154:01 Let me just see if I can this out. Uh alpha alpha is
154:07 heading. Okay, that's the right? That's the direction we're
154:10 Okay, so you have these So this is the at most formula
154:16 oh three times the velocity that you're in. That times the cosine sine
154:23 of latitude sign of the heading plus velocity squared. That's the formula.
154:34 I'm gonna test you on that. , I'm not kidding. But yeah
154:38 how you correct for the the relative of the aircraft or or the
154:51 Okay, september um let me I don't I think I'm almost
154:57 We got yeah, I mean 11 . Okay, so with magnetic corrections
155:04 really there's really just one. I let's just think about but first this
155:12 how the magnetic field varies. It lots of variation in the field because
155:17 know, it's a there's a daily and there's secular time variations and then
155:24 the big correction is has to do the core field. The field that's
155:30 in the earth in the Earth. and outer cores. And that correction
155:38 called the I. G. F. The international geomagnetic reference
155:44 Um And that is thought to be by a geodynamic dynamo. So we
155:51 our measured data total intensity field and do a Daryl correction. I think
155:58 is optional line leveling. If you a good job of your survey line
156:04 this should go away anyways. And gotten into many animated discussions with magnetic
156:14 processes about this process is you anyway, so you they would correct
156:22 barrel and then correct for the main the the core field using the
156:27 G. R. F. And you're just left with total intensity magnetic
156:31 data D. T. Here. , so um external temporal crests.
156:41 the external contributions in Earth field are small, less than 100 now tests
156:47 some magnetic storms can be over 500 , especially at the polar areas.
156:54 external contributions ignore originally from the Solar winds interact with the Earth's field
157:02 . Can be they actually, there's there's a sunspot cycle 11 years.
157:07 might have heard of this. Um they can also have very short micro
157:12 stations which can dominate which kind you know, cause problems. But
157:19 Mag surveys, the most important variation the daily or the diurnal variation.
157:26 they can range from 5 to 50 they can even be bigger over the
157:32 area over the course of the And they are caused primarily by ionic
157:39 but they can also be from two currents in the earth beneath the surface
157:46 . And the correction is called the because the dominant variability is linked to
157:52 cycles. Even to lurks are are to daily cycles. Okay so here's
158:02 comparison uh the horizontal variation mentioned Four observatories. So there are different
158:09 there are different magnetic observatories around the . I don't know how many,
158:13 are maybe 50 maybe 100. But are just, they measure the Earth's
158:19 permanently. So quite often you'll you'll some survey David and maybe your base
158:26 goes down because you have to have base station while you serve it.
158:30 have to plane up capturing data and back wherever your hotel is. You
158:34 a base station. They're just sits one spot and collects maG data.
158:39 that's how they figure out what the variation is. Because you don't really
158:44 what the declaration that you're flying along data on the dynamic platform. So
158:48 can So they read out the dire base station data and that tells them
158:53 if there are any storms or micro . Alright so getting back to
158:58 So here is four different observatories, in Hawaii, one in Arizona,
159:04 in the UK and one in And at different geomagnetic latitudes. So
159:13 is 21 degrees 40 degrees 50 degrees 60 degrees all in the northern
159:22 So 20° is pretty low. And and of course this range is 20
159:26 tests. See they're using the term that means nanna test. I knew
159:32 was gonna happen. Um Yeah. I have notes on this slide
159:46 Okay. Yeah. In any case can see that and as you go
159:51 in latitude that the effect is bigger bigger and bigger over 24 hour
160:02 Yeah 0 24 hours. So you see midday it goes up a lot
160:06 then down a lot. Uh This at a very this is at a
160:11 of 20° and then it's interesting in . It goes it goes down a
160:18 lot. All right because the sun hitting these low latitudes more directly.
160:27 is really interesting. It does go but it goes down first six.
160:31 that's quite interesting. All right. they've actually done studies and this is
160:38 study I'd like to show my friends don't like that want to process
160:43 So in Australia, in this area down here in western eastern Australia.
160:51 took um I got five measurements, stations and they I guess they put
161:00 in the ground, They dug holes put these things on the ground and
161:03 measured events from october 26 November So they measured almost a full
161:13 Um All at about the same latitude or take and the same latitude give
161:19 take. So this is called the area in new south Wales in
161:31 I'm sorry. Uh, so, , So here's their correlations. I
161:44 they correlate reasonably well. So this 10 nano tesla and um, this
161:52 at one end. This is the in october variation november 23rd over looks
162:02 15 minutes. They're just comparing some minutes from all five of these.
162:09 one is flat, this machine must broken but there is some similarity but
162:14 not exactly the same. 10. you have a very eight seat.
162:20 is a high, this is a . So they're not correlating exactly the
162:26 . So, but the argument that make is that what's happening at the
162:31 station is not necessarily happening where the is flying. That's the point I'm
162:37 . And you can see they are . I mean they are significantly different
162:41 some cases. I mean this to , this, you know, and
162:46 , these guys are all pretty close . I mean they're all right
162:50 What 25 km. I mean sometimes base, sometimes the nearest airport is
162:57 km away from the survey area, 600 km away. So you know
163:05 is this is pretty small. So always been my argument is that what's
163:10 at the base station is not necessarily at the airplane anyways. So there's
163:19 making a big deal about nothing. . But then all when you,
163:23 you level the data properly those variations come out will be leveled out.
163:29 saw the difference on the order of a few nano Tesla. Anyway so
163:36 pulsations are another temporal uh fluctuation, small amplitude on the order of Frequency
163:46 at .0123 Hz and able to is than 10. Now again these things
163:52 be depending on the while they're short spans so they can contaminate the data
163:59 they can have amplitudes up to tens . So this this is a good
164:07 to have a base station though because may pick up these you may pick
164:13 these features um at the base station still you may not but you have
164:19 you still have to compare. So not arguing against the base station.
164:23 still have to compare that data. you survey data, magnetic storms are
164:28 different animal. Those are just bad . They can exceed 1000. They
164:33 be thousands of nano Tesla and they be very localized and they're really common
164:40 the northern latitudes. When I was World Geoscience that was the in between
164:46 company between between between arrow service and debt that I worked at. We
164:53 the north slope and we flew the thing and and of course it was
165:00 was just all kinds of noise but just what we did was our strategy
165:05 just put two planes up there and flew nonstop all day and all night
165:10 we flew in the summer time. so there's 24 hour daylight and we
165:15 and then, we basically. you , we had two processors up their
165:22 the data on a daily basis and re flights nonstop. So every flight
165:29 go up do some re flights then survey lines and basically and then like
165:35 it to the processes to fix and did it, we did it I
165:38 and ended up being ended up making . Um But that strategy because otherwise
165:47 you sit around you otherwise just gonna sitting around waiting for the storm to
165:51 . And then by the time you out and mold and fly and then
165:53 back. So just we just decided to fly straight through so that they
165:58 be pretty bad, especially at high . So here's the the the temporal
166:10 processing slow. Okay so you measure data, you check the base station
166:18 the diagonal. Is there any bad ? Yes. Re fly. You
166:23 you say this line between this tie this tie re fly. If not
166:29 you then you can if you want can apply this daily correction. But
166:34 like I demonstrated with that Australia it's really not not an issue shouldn't
166:42 might actually produce an at least by this thing. But in all honestly
166:47 a very very it's it's over each . It's a tiny variation because we
166:52 back that study results, This is minutes. So in 10 minutes I
167:00 you're flying you're flying 130 knots. you know, that's that's not that
167:06 of variation. It's kind of a wavelength correction in the, in the
167:11 . Okay. Now the basically the required correction is the core field and
167:19 removing the I G R F. the I G R F is,
167:23 know, it's determined with the sort like DeAndre harmonic harmonic uh polynomial solution
167:33 it's um, so it varies with to position and yeah, so the
167:43 of the components of the field that geometric observatory. So we use these
167:47 again and just a taylor series in and co sign. And the internationally
167:57 values of the coefficients are used to a model field or the Earth coastal
168:04 . Historical sets of coefficients are labeled . So every time the I G
168:08 F is is updated the retired version year. The retired version.
168:17 it's not thrown away. It's just D G R F with the year
168:22 it was retired. So we have whole history. So, so that
168:27 if you come across some legacy some old data That was acquired
168:34 you know, 1975 or something. , that was using a different I
168:38 R F than we're using now. there is a D. G.
168:42 . F. That 1975 will fall and you can use that one.
168:48 that's and that data was probably reduced most certainly reduced using that that that
168:57 . Okay, so I showed these you yesterday the total field strength,
169:03 inclination and the declination. I just them here because um well I just
169:09 them here now. What this is is sort of getting a little
169:15 But this is because this is stuff people worry about. I don't
169:19 you know, I don't really worry this stuff very much. But people
169:23 and this has to do with actually question yesterday about reversing fields. So
169:28 people think that the earth field is by a geodynamic dynamo dynamo effect.
169:37 ? So so a mono polar dynamo would be something like this. We
169:45 the magnetic field going through and you a curve going through it. You
169:48 some angular rotation. And so an current in here and that would produce
169:57 magnetic field. Right? Like a oid from your days of studying
170:04 Well, what people think what a of people think, He says you
170:07 some kind of double dynamo in other , um uh it's that that would
170:14 for polarity reversals and non uniform field . Right? So you have these
170:20 tubular cyclones and whereas where they could alternating polarities right with the flow of
170:29 altar. So you have some kind colored in the in the course some
170:34 of popular flows like that. And and so this is a this is
170:42 picture by Schmidt where he simulates. your here's your reversal simulation uh A
170:51 year transition. So in this case have whatever the north pole is in
170:57 , the south poles and blue at point things are getting kind of mixed
171:02 but in the end they realign and now the blue is up here in
171:06 north and the gold is here in south and these would be the flux
171:10 that they're that they're modeling. It's very cool very cool sort of pictures
171:16 stuff. Um So does that answer question about the field reversal?
171:25 I just I just think it's an topic. There's so much like I
171:30 wanna say back and forth on it is so many different things to read
171:33 it. I like it. So would suggest reading this paper if you
171:38 . I have it if you I can send it to you,
171:43 that team. I'll make another. I will send any paper to you
171:52 you want that you said that I you. I have them all.
171:58 , okay moving on. Um This the mag sat scale or not only
172:05 . This is a very old This goes this is 1982 but it's
172:10 out for the kind of like But you can see that the inclination
172:14 45 And then plus or -45 and do the magnetic equator. And these
172:22 those same anomalies that I kept showing the big view. But these look
172:27 much better. There's just there's a bit more of a, you
172:31 a little bit more variability in wavelength stuff. So I like this one
172:35 lot better. But if you do power spectrum of this field, what
172:42 get is you get and if you know, if you plot the
172:46 of that power versus harmonic degree um you get an interesting plot, you
172:55 this very long wavelength linear feature here then it flattens out. So this
173:02 slope of the short of the, the higher degrees. That's all these
173:07 . But there is there is a wavelength, the point that you just
173:11 see in this and that's the core . So people think of the car
173:15 . So we'll look at power spectrums and we talk about anomaly source
173:22 But this is kind of a preview that because we can use the same
173:29 in local areas and kind of dissected spectrum into different death regions of the
173:38 that are being produced in the So that's a tool for interpretation that
173:44 get to. But this is kind a preview of it. So data
173:50 variations, variations in the intensity Earth at the precise is this my summary
173:57 ? No, it's not. precise processes that give that give rise
174:04 second operations are not well understood, we know that. Oh right.
174:09 is second rate. So this is this is like 100 years or 20
174:14 . I mean the Earth, the of the Earth actually dressed as the
174:22 like uh to the west, to east. Um we'll find out,
174:27 I know that just so we understand secular variation. So here's an
174:31 this is from garland. This is textbook 1979 secular change Earth from.
174:38 this is 1922.5 versus 1942. So a 20 year difference. And so
174:46 see uh let's look at this. in 22 you have this high,
174:50 it's drifting to the west. So have this high right here in the
174:56 atlantic. So there's africa and south . It's just not the coast again
175:01 20 years later it's migrated across the and it's just sitting out here north
175:08 brazil. Okay, let me see I can find another one.
175:12 so this one here over the over right, is now drifted and over
175:20 over um just north of Africa. You can find another one.
175:27 and this one here, that's right . That one is drifted as
175:33 So the field is drifting to the . Um And that's called the secular
175:42 . Which is which is this is reason why you need to retain the
175:46 . G. R. S. old because because the field is you
175:50 they re they re update the G. F. Of course your
175:53 methods get better plus the field is . So you have to continually
175:59 Right? So the you know the formula this lasagna for polynomial, it's
176:06 is rooted. Let me go You can find that formula. That
176:12 . Where is it at? But my formula that's trained magnetic. Didn't
176:29 have it? I'm sorry. One time. Please bear with me I
176:34 to find this. I thought for I had to endure for you.
176:44 I haven't. I'm gonna make a . I. G. R.
176:49 . Formula. That's that kills It's very similar though. It's very
176:56 to um Two the last word correction you can imagine. Alright. Um
177:07 here's uh here's the summary of the field change. There's external and internal
177:14 that affected. So um uh Beginning the very smallest there's pulsations down
177:26 There's things called-based journals here. Um are external recurrence of storms. Semiannual
177:35 . I see that's the 11 year . And then here you have the
177:40 change which we just talked about and over here is reversals on the order
177:44 thousands of years. So um so this includes secular magnetic experiences of
177:53 reversals. And over here it's micro storms and seasonal changes. So there's
177:59 lot of things that affect the magnetic , but you really only do one
178:04 . Now the magnetic poles move they sort of wobble, you
178:13 and uh reliable Palin genetic data are . Now Poll Rwanda is this idea
178:24 so what you do is if you a stereo net and you plot positions
178:30 south american africa, the rotation that make can be described. The rotation
178:38 any plate on the Earth can be in terms of a rotation pole,
178:45 ? That that you know to the the to the diameter of the earth
178:51 some angle. So you can describe rotation atmosphere with a pole location and
178:56 on the angle. So these dots where that hole intersects the surface down
179:05 . So there'll be another one on other side, right? And then
179:10 the plates move around. So these the relative pulls between the rotation angle
179:17 north America. South America over time described by these poll locations and some
179:24 and then over time you can reference to each other. In this case
179:30 a parent polar. So it's africa south America reference to each other.
179:36 , now there's true polar wander where reference them two. The hot
179:43 fixed reference frame. So I don't if people the idea of fixed hot
179:50 is is really being challenged a lot days. But so you would do
179:57 relative and apparent polar wander reconstruction between and south America and you do these
180:06 on the sea floor spreading anomalies as as um paleo magnetic data which which
180:15 which is detects remnant magnetization as I . And um this is just to
180:23 random and paleo Magnetics but and then can plot that um that polar motion
180:32 to each other. But then you take that and rotate that whole system
180:36 poles through the through polar under path the in the spot reference rate.
180:43 then what you can do is you do that with all the clothes,
180:46 the ocean basins and do that with all. Why am I telling you
180:50 ? So yeah, this is the bit I just want to talk about
180:55 we're talking about polls and the polls around and then of course not only
181:00 they move around but you also um plates move around and so these are
181:08 the sort of tools that people use try to keep keep track of that
181:14 sort of summarize with dated corrections, is temporal tied instrument trip, special
181:23 elevation free air train at boss for platforms and missed. I leveling or
181:31 loops and temple from magnetic journal if want secular which is which is actually
181:38 the Nigeria and then special the main and in this tie level. Um
181:46 it. Any questions was that? So this is really the summary of
181:53 magnetic field changes and the only correction the I. G. R.
181:57 . And then this last bit on wonder. Um I just wanted to
182:03 this idea to. You might have of it already but I think it's
182:06 because it is a magnetic field issue paleo Magnetics has to do with remnants
182:12 we talked about and uh it is that that has done particularly with reconstructions
182:23 and things like that. So any any questions for any of this
182:29 Not right now. I kind of to just like look through it and
182:35 cool. You can always ask me week or whatever. Oh well that
182:46 a lot. What do you What do you got you guys want
182:49 take a lunch break down and reconvene do the next lecture. Yeah that'll
182:57 . What what what what do you I'm up for anything if you want
183:02 start early to finish early? That's with me. I don't care.
183:07 you want to do like 30 minutes minutes 1215. Um Okay if you
183:19 . What about you? Is that with you man. Are you gonna
183:22 at lunch? Uh both of work me to start a year old.
183:31 you are you're taking lunch, Yeah. But I can take lunch
183:39 when you have the uh So you I'm talking I guess. Right?
183:46 . Yeah. Yeah. Fair Okay. I just wanted I didn't
183:51 didn't know if you wanted to read book over your while you were eating
183:54 something, so okay then. So it is you calling the shots?
184:01 see you in half an hour.
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