Upgrate Earth gravimetric recipes for SWOT data #272
Conversation
|
Given the large differences in some of the grid's scale factor, I would be more comfortable to see what we are loosing with quantization to uint16. Again, a simple test is to compare the original floating point values at some nodes (obtained with |
A comment on the grid factor. I believe that for earlier recipes, the scale was intended a range of 2^15 values. That is partly why I was so hesitant with this issue. |
|
2^15 if for signed ints (1/2 negatives & 1/2 positives). 2^16 is for unsigned ints |
|
I see, But I don't know why was set to signed ints. I don't know why we didn't saw that. |
|
Maybe Paul checked that current scales were enough to maintain the FAA up to the microGal, but I'm not so sure about the deflections. |
|
Guys,
I can see the thread of your conversation but I am not sure I understand what the original issue was.
Dave Sandwell’s “img” files use two-byte signed integers for deflections of the vertical inmicroradians times 10, that is, 10^-7 radian, and gravity anomalies in milliGals times 10 (that is 10^-6 m /s^2). For vertical gravity gradient I think there is also a multiple of 10, maybe it is Eotvos times 10, but I would have to check.
This scaling does not completely fill the maximum possible range of a signed two-byte integer (+/- 32767).
W
… On Apr 16, 2025, at 3:20 PM, Joaquim ***@***.***> wrote:
joa-quim
left a comment
(GenericMappingTools/gmtserver-admin#272)
Maybe Paul checked that current scales were enough to maintain the FAA up to the microGal, but I'm not so sure about the deflections.
—
Reply to this email directly, view it on GitHub, or unsubscribe.
You are receiving this because your review was requested.
<#272 (comment)> <https://github.com/notifications/unsubscribe-auth/APUT6GLMXYLAV4Q5RTHPEGL2Z2UPTAVCNFSM6AAAAAB3ITGDEOVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDQMJQGUZTEOBYG4>
joa-quim
left a comment
(GenericMappingTools/gmtserver-admin#272)
<#272 (comment)>
Maybe Paul checked that current scales were enough to maintain the FAA up to the microGal, but I'm not so sure about the deflections.
—
Reply to this email directly, view it on GitHub <#272 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/APUT6GLMXYLAV4Q5RTHPEGL2Z2UPTAVCNFSM6AAAAAB3ITGDEOVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDQMJQGUZTEOBYG4>.
You are receiving this because your review was requested.
|
|
Walter, This issue started when we realized that the new SWOT grid has a larger amplitude (SWOT minimum is ~400 mGal lower than the V32 version). Though a bit surprising, that is not the issue. The issue was that with the new SWOT's range Federico had a doubt on what would be a good scaling factor ... and conversations started. See #271 for more details. |
|
OK,
The only comment I can make is that the gravity field of the Earth has not suddenly developed anomalies with an extra 400 mGal.
Rather what I think is happening is that there are bad data values at the edges of SWOT swaths and these are not being fully edited before SWOT is getting turned into gravity.
w
… On Apr 16, 2025, at 3:46 PM, Joaquim ***@***.***> wrote:
joa-quim
left a comment
(GenericMappingTools/gmtserver-admin#272)
Walter,
This issue started when we realized that the new SWOT grid has a larger amplitude (SWOT minimum is ~400 mGal lower than the V32 version). Though a bit surprising, that is not the issue. The issue was that with the new SWOT's range Federico had a doubt on what would be a good scaling factor ... and conversations started. See #271 for more details.
—
Reply to this email directly, view it on GitHub, or unsubscribe.
You are receiving this because your review was requested.
<#271> <#272 (comment)> <https://github.com/notifications/unsubscribe-auth/APUT6GIUQJI475QRWO27ZUL2Z2XQFAVCNFSM6AAAAAB3ITGDEOVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDQMJQGU4TAOBWGY>
joa-quim
left a comment
(GenericMappingTools/gmtserver-admin#272)
<#272 (comment)>
Walter,
This issue started when we realized that the new SWOT grid has a larger amplitude (SWOT minimum is ~400 mGal lower than the V32 version). Though a bit surprising, that is not the issue. The issue was that with the new SWOT's range Federico had a doubt on what would be a good scaling factor ... and conversations started. See #271 <#271> for more details.
—
Reply to this email directly, view it on GitHub <#272 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/APUT6GIUQJI475QRWO27ZUL2Z2XQFAVCNFSM6AAAAAB3ITGDEOVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDQMJQGU4TAOBWGY>.
You are receiving this because your review was requested.
|
|
Walter, we are not talking about outliers.
|
|
Joaquim,
Isn’t that location on the Antarctic ice?
I have no idea what the true gravity field is doing there but if it went from -500 to +500 mGal over such a short distance, wouldn’t that be surprising, and probably not physical? Is there a real situation that could generate such an anomaly gradient?
Anyway, I am not trying to argue about the truth of any particular anomaly, only to say that the gravity anomaly, if expressed in integers representing 10^-6 m/s^2, should easily fit in a two-byte signed integer.
Highest regards,
Walter
… On Apr 16, 2025, at 6:33 PM, Joaquim ***@***.***> wrote:
joa-quim
left a comment
(GenericMappingTools/gmtserver-admin#272)
Walter, we are not talking about outliers.
diffs_faa.jpg (view on web)
—
Reply to this email directly, view it on GitHub, or unsubscribe.
You are receiving this because your review was requested.
<https://github.com/user-attachments/assets/05c5a704-0b4f-4119-91af-3a0951d11f9d> <#272 (comment)> <https://github.com/notifications/unsubscribe-auth/APUT6GJCD5NX3SOXA7QEK7L2Z3LEJAVCNFSM6AAAAAB3ITGDEOVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDQMJQHE3DKMZTGU>
joa-quim
left a comment
(GenericMappingTools/gmtserver-admin#272)
<#272 (comment)>
Walter, we are not talking about outliers.
diffs_faa.jpg (view on web) <https://github.com/user-attachments/assets/05c5a704-0b4f-4119-91af-3a0951d11f9d>
—
Reply to this email directly, view it on GitHub <#272 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/APUT6GJCD5NX3SOXA7QEK7L2Z3LEJAVCNFSM6AAAAAB3ITGDEOVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDQMJQHE3DKMZTGU>.
You are receiving this because your review was requested.
|
|
Walter, you are right that it's on the Antarctica shore but I think you misunderstood what the figure represents. It shows the grid differences between the SWOT and previous V32 FAA's. I've added the coastline to make it clear.
Yes, no doubt. The discussion was only on what new value (if any) should we use as scale for these new grids. Easter truce in Washington? Cheers
|
|
More I look at this more I think that this SWOT anomalies cannot be right. This is 3 times the amplitude of the anomaly across the Chile trench. @dsandwell
|
|
Thanks for find the anomaly. This is probably an ishelf where there is a step in the ocean height due to ice. V32 is probably more accurate so I would use V32 around Antarctica. THere are some other issues with SWOT gravity related to the outer edges of the swaths. It will take a while to fix all of these. |
|
Glad to having contributed with something 👍 |
|
Well, back to the subject of scale. I agree that the resolution of the data should be higher than that of the measurement. But I think it would be convenient to use a scale that maximizes the number of values. |
This PR is only to upgrade the recipes to use the SWOT grids (in this link https://topex.ucsd.edu/pub/global_grav_1min_SWOT/) instead of this ones (https://topex.ucsd.edu/pub/global_grav_1min/).
In the four recipes I change the precision (or scale) and offset. I also change the SRC_FILE, REF and DOI.
I think that only important thing that I want your approval is for the SRC_TITLE of each recipe.
See discussion on #271