GRACE's warts – new peer reviewed paper suggests errors and adjustments may be large

Below is a GRACE satellite map. The Earth looks like a warty ball, with red bumps and blue pits that represent measured fluctuations in the planet’s gravity. Note Greenland in the red. We’ve covered GRACE before, suggesting it may not be a good tool to measure ice loss in Greenland. See this WUWT story.

Image: National Academies Press

The red spots represent measurements where Earth’s gravity is stronger. The blue ones are where it is measured to be weaker. The universal force of gravity itself does not vary, but the pits and bumps are a local indication that Earth’s mass distribution isn’t smooth and uniform. As seen on the image above, tectonic mountain building in South America produces red zones; elsewhere, tectonic movements produce thin, blue, ones.

Even more interesting is the fact that the map changes over time, Earth as we know is not static.

CO2 science reviews this new paper, which suggests that for sea level rise and ocean mass, the signal to noise ratio is high low and adjustments further complicate the issue. It also suggests some studies aren’t appropriately correcting for these issues. For example, GRACE measurements related to Greenland and West Antarctica (which we also criticized in WUWT here and here):

“…non-ocean signals, such as in the Indian Ocean due to the 2004 Sumatran-Andean earthquake, and near Greenland and West Antarctica due to land signal leakage, can also corrupt the ocean trend estimates.”

Ocean Mass Trends (and Sea Level Estimates) from GRACE Reference

Quinn, K.J. and Ponte, R.M. 2010. Uncertainty in ocean mass trends from GRACE. Geophysical Journal International 181: 762-768.

Background

The authors write that “ocean mass, together with steric sea level, are the key components of total observed sea level change,” and that “monthly observations from the Gravity Recovery and Climate Experiment (GRACE) can provide estimates of the ocean mass component of the sea level budget, but full use of the data requires a detailed understanding of its errors and biases.”

What was done

In an effort designed to provide some of that “detailed understanding” of GRACE’s “errors and biases,” Quinn and Ponte conducted what they describe as “a detailed analysis of processing and post-processing factors affecting GRACE estimates of ocean mass trends,” by “comparing results from different data centers and exploring a range of post-processing filtering and modeling parameters, including the effects of geocenter motion, PGR [postglacial rebound], and atmospheric pressure.”

What was learned

The two researchers report that the mean ocean mass trends they calculated “vary quite dramatically depending on which GRACE product is used, which adjustments are applied, and how the data are processed.” More specifically, they state that “the PGR adjustment ranges from 1 to 2 mm/year, the geocenter adjustment may have biases on the order of 0.2 mm/year, and the atmospheric mass correction may have errors of up to 0.1 mm/year,” while “differences between GRACE data centers are quite large, up to 1 mm/year, and differences due to variations in the processing may be up to 0.5 mm/year.”

What it means

In light of the fact that Quinn and Ponte indicate that “over the last century, the rate of sea level rise has been only 1.7 ± 0.5 mm/year, based on tide gauge reconstructions (Church and White, 2006),” it seems a bit strange that one would ever question that result on the basis of a GRACE-derived assessment, with its many and potentially very large “errors and biases.” In addition, as Ramillien et al. (2006) have noted, “the GRACE data time series is still very short,” and results obtained from it “must be considered as preliminary since we cannot exclude that apparent trends [derived from it] only reflect inter-annual fluctuations.” And as Quinn and Ponte also add, “non-ocean signals, such as in the Indian Ocean due to the 2004 Sumatran-Andean earthquake, and near Greenland and West Antarctica due to land signal leakage, can also corrupt the ocean trend estimates.”

Clearly, the GRACE approach to evaluating ocean mass and sea level trends still has a long way to go — and must develop a long history of data acquisition — before it can ever be considered a reliable means of providing assessments of ocean mass and sea level change that are accurate enough to detect an anthropogenic signal that could be confidently distinguished from natural variability.

References

Church, J.A. and White, N.J. 2006. A 20th-century acceleration in global sea-level rise. Geophysical Research Letters 33: 10.1029/2005GL024826.

Ramillien, G., Lombard, A., Cazenave, A., Ivins, E.R., Llubes, M., Remy, F. and Biancale, R. 2006. Interannual variations of the mass balance of the Antarctica and Greenland ice sheets from GRACE. Global and Planetary Change 53: 198-208.

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For information, GRACE consist of two satellites, which follow each other and their mutual distance is measured with extremely high precision. The idea of GRACE is, that when passing more mass beneath, stronger gravity delays the leading satellite and the distance shrinks a bit and vice versa.

Djon

Anthony,
“CO2 science reviews this new paper, which suggests that for sea level rise and ocean mass, the signal to noise ratio is high and adjustments further complicate the issue. ”
I don’t think “high” is the adjective you intended to use in that sentence. A high signal to noise ratio is a good thing – much more signal than noise.

REPLY:
thanks for pointing out my error. You are correct, fixed, Anthony

chris y

Anthony- “…the signal to noise ratio is high and adjustments further complicate the issue.”
I think you meant to say the signal to noise ratio is low, or poor.
It is very difficult to measure changes in total ice volume when the changes are in the low ppm/year, and the uncertainties are in the ppm/year. On the other hand, it creates lots of opportunities for interpretive shenanigans to support a policy position.

Enneagram

The force of gravity itself does not vary
It does!, as the image itself shows it. It can be, say, 9.79, 9.81, (acceleration in m/sec.sq.)
REPLY: I agree, poor wording. I was talking about it in the broader sense, I’ll make it clearer. – Anthony

Roger Knights

IOW, GRACE is GROSS.

Jerry

“The force of gravity itself does not vary, but it is an indication that Earth’s mass distribution isn’t smooth and uniform.”
Sure it varies. That’s exactly what the map shows. That’s what the satellites are measuring.
REPLY: I wasn’t clear with the original sentence, a bob-boo on my part due to starting the post, getting interrupted by a phone call, and coming back to it. I’ve clarified it now. – Anthony

There is strong correlation between North Atlantic Temperature anomaly and the gravity/magnetic anomaly in the Hudson Bay region.
http://www.vukcevic.talktalk.net/NATA.htm

Zeke

They don’t even know the neutral density of the atmosphere at that altitude, so the drag could vary considerably.
Environmentalists have attempted to use the GRACE satellites to claim water levels in Indian aquafers could no longer sustain rice crops.
With GRACE like that, who needs ill favor?

George E. Smith

“”” Enneagram says:
July 20, 2010 at 2:27 pm
The force of gravity itself does not vary
It does!, as the image itself shows it. It can be, say, 9.79, 9.81, (acceleration in m/sec.sq.) “””
Not according to my Physical Chemistry Book.
It says that ( g ) is 9.80665 and THAT IS AN EXACT VALUE ! ( ms^-2 )
But what of the surface of the ocean; is it in hydrostatic equilibrium.
Gravity is supposed to be stronger at the poles since one is closer to the earth center; so does water run “downhill” from the equator; does the rotation create a equatorial hill that water runs off or dows all that shape the surface to a gravitationally level surface so water doesn’t tend to run anywhere ?

Reed Coray

When attempting to quantify the gravitational effects of the Earth as a function of position (i.e., model the Earth’s gravitational effects), measurements are made of entities that are affected by the Earth’s gravitation. A model is then constructed that couples quantitative values of the model parameters to those measurements. Values for the model parameters are then estimated that in some sense “best fit” the measurements. Three commonly used “best fit” criteria are: (1) weighted-least-squares (WLS), (2) maximum likelihood (ML), and (3) minimum variance (MV). As I understand it, provided the errors associated with the measurements are zero mean and Gaussianly distributed with known standard deviations, all three “best fit” criteria will produce the same estimates of the model parameters. However, if the measurement errors aren’t Gaussian with known standard deviations, the three “best fit” criteria will give different estimates of the model parameters.
No matter which “best fit” criterion is used, when estimating the values of model parameters from a set of measurements, all models contain three kinds of parameters: (1) model parameters that are exactly known (called constants), (2) model parameters that are treated as known but are in fact estimates (often called “Q-parameters” or “consider parameters”), and (3) model parameters (sometimes called “P-parameters”) whose values are to be estimated from the measurements. Examples of constants are the speed of light in a vacuum, pi, e, etc. Examples of Q-parameters are the total mass of the Earth, the force on an orbiting object from the solar wind, the force on an object from friction, the mass and position of the moon, etc. In theory, the state of knowledge of the Q-parameters can be expressed as a correlation matrix. In practice, it is sometimes the case that the diagonal elements of the Q-parameter correlation matrix are known fairly well, but many off-diagonal terms are unknown. The model Q-parameters will have various effects on the measurements–ranging from negligible to significant. For example, an error in the position of Pluto may have a negligible effect on the measurements while an error is the solar wind may have a significant effect.
When using measurements to estimate P-parameters values, the Q-parameters are often treated as constants–i.e., uncertainties in their values are ignored. This is a common practice and works in many applications. However, when characterizing the accuracy of the P-parameter estimates (i.e., quantifying the P-parameter uncertainties), it is often critical to include the Q-parameter uncertainties. Ignoring these uncertainties often leads to P-parameter estimated errors that are significantly smaller (better) than their actual errors.
For the GRACE system to generate estimates of the change in ice volume over areas of the Earth’s surface, a model must exist that couples ice-change to the measurements made by the GRACE system. Because in practice it is often impossible to treat every component of a model as a P-parameter, expect the GRACE system model that relates model parameter values to GRACE system measurements will undoubtedly contain both constants and Q-parameters. Any discussion of the accuracy of the GRACE system in estimating the change in ice volume must include a discussion of all model Q-parameters. Maybe they have, but I doubt it. Experience has taught me (a) a full treatment of Q-parameter effects on P-parameter estimates is seldom performed, and (b) that without such a treatment, reported P-parameter accuracies are often meaningless.
Bottom line, given the preponderance of funding to find any evidence that supports global warming, at this point in time I’m skeptical that the GRACE system can determine, for example, Greenland ice loss/gain to any meaningful accuracy.

Mike McMillan

The universal force of gravity itself does not vary, but the pits and bumps are a local indication that Earth’s mass distribution isn’t smooth and uniform. . . . Even more interesting is the fact that the map changes over time, Earth as we know is not static.
Gravity is a curvature of space-time that just looks like a force. The GRACE satellites use a 1-dimensional distance to map a 4-dimensional entity, and that takes a lot of assumptions plugged into computers to get answers. Gravity field changes measurable at the resolution you get with GRACE take geological time scales, and the satellites have been up only a brief time. The only map changes you will see are increased resolution as more passes build up the database.
If you want to measure the force aspect of gravity directly, you can use gravimeters, which have much higher accuracy, one millionth of a ‘g’ for a coffee can sized portable one. I recall that they can tell the difference between the top and the bottom of a step ladder.
GRACE has the advantage of quick worldwide coverage, but it’s measuring the field several hundred miles above the earth, hundreds of miles away from the Greenland ice cap. Only a surface based gravimeter survey could provide the accuracy needed to measure ice cap mass changes.

Jim G

Anthony,
Gravity is a curvature of space-time in the presence of mass, not a “force”, as I am sure you are aware. The curvature varies with the mass since there is no elemental force of gravity as was believed by Newton. If we think of it properly, there is no mistake. Of course mass is also itself relativistic, rest mass visa vi mass in motion and the energy/mass imparted to such a system. So, the entire analysis per GRACE is somewhat more complicated and less enlightening, to me at least, particularly given the signal to noise situation involved per the above. Not sure any of this GRACE stuff is of much practical use or can really be shown to have any effect on climate.

Alan Simpson

I may be being terribly dim here but aren’t these coupled satellites measuring, (allegedly) changes in gravity?
What effect does the recent “unprecedented” collapse of the Ionosphere / Thermosphere have on the measurements?
Even, leaving aside the paper’s criticisms, it appears the data is of no use to measure ice anywhere.
I bet I f’d up the strike thing again. Sigh.

Zeke

“Gravity is a curvature of space-time that just looks like a force.”
Actually “gravity is due to radially oriented electrostatic dipoles inside the Earth’s protons, neutrons and electrons.” Therefore, “If the electric field within the Earth changes, the amount of this dipolar distortion will change and the force of its gravity will change.”
Hope that helps.
“Electric Gravity” and “Newton’s Electric Clockwork Solar System,” by Wal Thornhill

latitude

“GRACE-derived assessment, with its many and potentially very large “errors and biases.”
So NASA spends $100 million putting two tinker toys in orbit
and the data they send back really means nothing
Maybe social services wasn’t such a bad idea after all.

Alex Buddery

@ Zeke the Sneak July 20, 2010 at 3:04 pm
Why would they need to know the neutral density of the atmosphere? How would that affect one satellite and not the other?

GeoFlynx

From the paper you cite by Quinn and Ponte –
“Perhaps the most significant development of recent years is the realization that mass contributions from land ice have contributed to contemporary SLR much more than assumed just five years ago. Related to this finding is the fact that large polar ice sheets appear to be much more sensitive to surface warming than previously realized, such that surprisingly large dynamical changes are now being observed on the Greenland and West Antarctic ice sheets.”
There is nothing in this paper that appears very encouraging from a denier’s point of view. I am surprised you chose it as an example of “doubt and error” in the climate community.
REPLY: “GeoFlynx” if you call me a “denier” again, I will ban you.
Trollbox for you until you apologize
– Anthony

Enneagram

This is from the “flintstones universe”, directly from “The Twilight zone”:
Gravity is a curvature of space-time that just looks like a force

mike sphar

In 50 – 100 years or so, maybe this will have produced enough data to tell us something. Or not. I won’t be hear except in component form. So I won’t care and will never know.

Enneagram

Zeke the Sneak says:
July 20, 2010 at 4:01 pm
“Gravity is a curvature of space-time that just looks like a force.”
You are right. Excuse them, they are a production “Hanna-Barbera”, Characters of the Flintstones Universe, they believe in a universe made out from round stones and where phantoms like anti-matter, black holes exist. However their time is over.

John Trigge

So, as these satellites are travelling around the Earth, how do they account for the gravity effects of the moon, planets, sun, etc?
Even if the more distant objects have no or little effect, surely the moon must have to be accounted for if they are measuring gravity to such fine tolerances.

d

Great article and i love how the readers dont let you get away with anything!!!!
REPLY: thanks, our readers, with the exception of a few trolls, are generally pretty sharp- Anthony

Thanks for the discussion. Reed Coray and Mike McMillan give a clear description, that for that too. My experience with gravity is confined to mineral and petroleum exploration. Useful tool but not in any way, shape or form definitive. I have often wished it was so but it is not. No geophysical remote sensing tool to data has replaced direct measurements. Given the gravity texture of the underlying structures and the scales at which they exist, combined with the texture of the surface and attempting to map on near continent wide basis; I think it will be a long, long time before any results like ice thickness from GRACE can be trusted.

George E. Smith

“”” Zeke the Sneak says:
July 20, 2010 at 4:01 pm
“Gravity is a curvature of space-time that just looks like a force.”
Actually “gravity is due to radially oriented electrostatic dipoles inside the Earth’s protons, neutrons and electrons.” Therefore, “If the electric field within the Earth changes, the amount of this dipolar distortion will change and the force of its gravity will change.” “””
That’s wonderful; we know that electrostatic forces can both attract and repel; so if your theory is correct; then one must be able to get gravity to push, as well as pull.
If that were the case; then we really wouldn’t need any energy at all.
We know how to completely shield from the EM forces; but so far we haven’t found any gravity shields. Gravity does have infinite range like EM does.

Billy Liar

Does the GRACE team also have contemporaneous high accuracy surface atmospheric pressure measurements to compensate for the inverse barometer effect on the sea surface level? Come to think of it they would also require contemporaneous surface wind measurements in order to work out how the wind has piled the water up against coasts etc.
I’m willing to bet they model this if they bother correcting at all. Another source of some (relatively) big errors ( 1 millibar = 1 cm change in sea level).

woodNfish

I think the important thing to remember in all this “expert knowledge” that is pushed on us everyday is that these so-called experts are only specialists, not really experts, and they know a lot less than they let on.
Their fancy and expensive tools help them learn a bit more, but they still don’t know it all, and each and every one of them suffer from tunnel vision. Everything they say should be viewed with skepticism. It is foolish to do otherwise.

Zeke

Alex Buddery says:
July 20, 2010 at 4:05 pm
@ Zeke the Sneak July 20, 2010 at 3:04 pm
Why would they need to know the neutral density of the atmosphere? How would that affect one satellite and not the other?

As you know the two GRACE satellites fly in tandem, measuing minute accelerations between them. This assumes that the acceleration was due to gravitational forces acting on the first sattelite.
However, important questions concerning the density of the thermosphere and nongravitational accelerations need to be addressed. Satellite drag could vary with solar activity or Joule heating in the 120-600 km region. Thank you.
read more here:
http://lws-trt.gsfc.nasa.gov/trt04_Crowley.pdf

Zeke

George E. Smith says:
July 20, 2010 at 4:20 pm
“That’s wonderful; we know that electrostatic forces can both attract and repel; so if [this] theory is correct; then one must be able to get gravity to push, as well as pull.”
The Electric Gravity theory does not say that gravity itself is electrostatic force. It says that subatomic particles are distorted by the electrostatic force, with the inner pole positive and the outer pole negative. In this way, they all weakly line up. “Since the particles are free to rotate, their dipoles will line up and the weak dipole force of each particle will add up to produce the effect of gravity.”

Agile Aspect

In general relativity, gravity is a pseudo-force in the sense it doesn’t accelerate it follows geodesics in spacetime.
In Newtonian gravity, i.e, in the framework where objects accelerate, F_gravity= G*M*n/r^2 where G is the universal gravitational constant.
The force of gravity varies on the Earth because the mass is not homogeneous and it’s not a sphere.
The F_gravity=m*g equation where g is a constant assumes the earth is homogeneous, uniform and spherical, and all the mass can be concentrated at the center (which is close enough for undergraduate physics courses.)
g is not a universal constant.

sky

Reed Coray says:
July 20, 2010 at 3:38 pm
“Experience has taught me (a) a full treatment of Q-parameter effects on P-parameter estimates is seldom performed, and (b) that without such a treatment, reported P-parameter accuracies are often meaningless. ”
I agree totally! And this applies not just to GRACE measurements. In many cases, even the distinction between P and Q parameters is blurred to get the “results” that agenda-driven “science” is looking for. This leads to a lot of hoopla (and hooey) about noise subjected to oh-so-sophisticated treatment.

Dr A Burns

The article fails to tell the whole story from Church and White 2006:
http://www.agu.org/pubs/crossref/2006/2005GL024826.shtml
“Here, we extend the reconstruction of global mean sea level back to 1870 and find a sea-level rise from January 1870 to December 2004 of 195 mm, a 20th century rate of sea-level rise of 1.7 ± 0.3 mm yr−1 and a significant acceleration of sea-level rise of 0.013 ± 0.006 mm yr−2. This acceleration is an important confirmation of climate change simulations which show an acceleration not previously observed. If this acceleration remained constant then the 1990 to 2100 rise would range from 280 to 340 mm, consistent with projections in the IPCC TAR. ”
Has anyone bought and studied this paper ?

Paul Callander

Just a small point but the 2004 Indian Ocean earthquake was the Sumatra – Andaman earthquake not Sumatra – Andean as it is quoted twice in the article. I note it is in quotes in both cases so is the error yours, Anthony, or in the original?

Robert

Interesting that you guys are still citing amazing grace despite being refuted
[snip]
Lets not let ice dynamics and glaciology get in the way of the “real” science, shall we?
Grace matches up well with all the other methods of estimation for ice losses.

intrepid_wanders

Okay,
Maybe it can not measure sea ice to any useful degree, but that OP picture is just a “quick render”.
Click to the evil Potsdam Institute:
http://icgem.gfz-potsdam.de/ICGEM/ICGEM.html
Once the fugly, bumpy globe pops up, click to move the globe to the area you want to view, then change the “boost” to 5000 or 2000 and the “grid” to 0.2deg.
When the java finishes rendering the object it should be pretty respectable (But slow…)
When you zoom in on an area of area of interest, you can turn the “boost” back up to see more detail. I am not sure if it is a tool, but it is not too bad.

Owen

What about the GPS measurements of crustal uplift that support GRACE measurements of the loss of ice mass? Nothing like two independent methods cross validating each other.

pat

O/T but pertinent:
20 July: The Atlantic: IPCC Chief Says Grassroots Must Lead on Climate Action
Rajendra Pachauri, the occasionally controversial head of the Intergovernmental Panel on Climate Change said that climate action would have to bubble up from the bottom, rather than coming down from on high.
“I really think the time has come for us to build from bottom to top. There is enough initiative in different countries that all this will bubble up and perhaps lead to an accord,” Pachauri told The Atlantic during a break at the Clean Energy Ministerial meeting convened by the Department of Energy. “I think the drive really has to come from communities, from the grassroots level, and the public at large.”…
But no international accord has come together, and climate legislation remains stalled in Congress. Maybe that’s why Pachauri is sounding the grassroots note: twisting the arms of national leaders just hasn’t worked
http://www.theatlantic.com/science/archive/2010/07/ipcc-chief-says-grassroots-must-lead-on-climate-action/60120/

dp

I get the feeling we’re going to see another “trick” to make the data look the way they want it to look.

H.R.

Amazing GRACE alooking down,
you’re checking gravity.
We thought you were the boss
but not if earth’s not round.
We’ll all just wait and see.

Mike McMillan

Dr A Burns says: July 20, 2010 at 5:10 pm
. . . a 20th century rate of sea-level rise of 1.7 ± 0.3 mm yr−1 and a significant acceleration of sea-level rise of 0.013 ± 0.006 mm yr−2. This acceleration is an important confirmation of climate change simulations which show an acceleration not previously observed. If this acceleration remained constant then the 1990 to 2100 rise would range from 280 to 340 mm, consistent with projections in the IPCC TAR.”

The CSIRO paper abstract indicates an unending increase in sea-level rise rate is needed to prove TAR correct, and that we’re all doomed, grant please. But a one foot rise in more than a century is not going to put the Maldives or Holland out of business.
Since 1993, the Jason/Topex satellites have measured an unaccelerated rise rate of 3.2mm/year, which will give us the bottom of the CSIRO rise by 2100. If the IPCC TAR used sophisticated climate models to predict what a grade schooler could have found with straightedge, I can’t see what we’re paying them for.
Neither does a 13 hundredths of a mm acceleration rate teased out of noisy ancient tide records stand up to the quality of the Jason/Topex ongoing series, which doesn’t show any overall acceleration.

John from CA

As Agile Aspect points out, g isn’t a constant.
Yet, though the oceans as mass are fluid, they principally occupy the same space within tidal changes and currents until a glacial.
Isn’t the magnetic core principally responsible for changes in the gravitational field and polarity flips from N to S?

Robert

Wait a sec? you snipped all the evidence refuting this one? including the 3 skeptical science posts this past week on this very subject? There was nothing offensive in the comment, THAT is censoring to try and keep from getting refuted. I expected better than that.
REPLY: Robert, Anthony here. Not sure what you are referring to. I’m a bit out of the loop on this, when did this happen? I just approved one below, is that what you are referring to? – Anthony
UPDATE: I now see the comment above, snipped by another moderator. Not sure why. But links have been provided by John Cook below. -Anthony

Robert

http://www .skepticalscience.com/Part-Three-Response-to-Goddard.html
Now are you going to snip the above website? I think that when a response on a similar subject has been shown then I have every right to present it. There are certainly lots of people who post links that get through, why does this one not? Is it because it refutes the amazing grace analysis and has not/cannot be responded to because it is correct?
[Reply: You are putting up other blogs to do your arguing for you. -1 for laziness. Make your own arguments here. ~dbs, Mod.]

MinB

Thanks, Anthony, for this post. This topic drew out new commenters which is great and reminded me of the paucity of my scientific knowledge. I’m inspired to learn more.

Note that this study applies to measurements of ocean mass, not land ice. There are multiple measurements of ice loss from Antarctica and Greenland – both GRACE satellite data and a number of other independent measurements which all find consistent rates of ice loss. Some good summaries of the full body of evidence can be found at:
[snip. repeatedly flogging your blog is at least immodest. ~dbs, mod.]

HR

The GRACE satellites travel through the thermosphere (500km above ground) and Solomon recently showed large unexpected changes in the thermosphere over recent years. Does anybody with the appropriate brain power know whether this will have any effect on the satellites?
REPLY: Well for one thing, less drag as the thermosphere shrinks, more drag as it expands -Anthony

HR

Anthony Watts says:
July 20, 2010 at 7:17 pm
Antony are you looking for nefarious actions here? The quest for morale authority by both sides of this debate is one of it’s less appeals aspects.
REPLY: Huh, no, Just curious. I don’t know much about Skeptical Science, I don’t know if it is university funded, privately funded, NGO sponsored, or if John just does it all on his own like I do with WUWT. Since he seems to have some things that would cost serious money, like that iPhone app, it’s an honest question. – Anthony

GeoFlynx

Sorry Anthonthy- no insult intended. What does your group wish to be called?
REPLY: skeptics

HR

“Well for one thing, less drag as the thermosphere shrinks, more drag as it expands ”
Thanks for the reply. But it just highlights I asked the wrong question. I meant if it has any affect on the data?