Radiometric & Geometric Correction Workflow

Giova · September 15, 2020, 12:19pm

Hi everyone,
to find my corner reflectors by S1 SLC, I have tried to do this workflow:

TOPSAR-Split (VV polarisation)
Apply-Orbit-File
Calibration (output beta0 band)
TOPSAR-Deburst
Terrain-Flattening (default parameters)
Speckle-Filter (default parameters)
Terrain Correction (default parameters)
Then I covert the gamma0 linear to dB.

But I have some questions about this workflow.
I see some papers that use sigma0 band instead gamma0 band to find the corner reflectors, so to do this I need to select as output the sigma0 band in the step 3 and to delete the step 5 (because it converts sigma0 band to dummy); first quesiton: which is the difference between gamma0 and sigma0 and which is better for my goal?

Second question: @ABraun I’ve tried to use SAR simulation terrain correction instead terrain correction, but the graph builder show the following error message: “Source product should include a simulated intensity band.”. Do you know why?

Every suggestion is welcome, thanks in advance.

ABraun · September 15, 2020, 12:55pm

please have a look here: Difference Sigma, Gamma and Beta nought?

are you sure you used this tool?

Because actually, simulation of an intensity band is part of the operator.

mengdahl · September 16, 2020, 1:09pm

Technically speckle-filtering should take place before TF so you should swap 5. and 6.

arnab · November 26, 2020, 9:38pm

How about the “Border Noise Removal” discussed in the article below?

ABraun · November 27, 2020, 6:26am

I wouldn’t consider it mandatory, only if you have this kind of noise and want to get rid of it.

zephyr · November 27, 2020, 10:08am

Hello.

I tired doing the SLC steps for generating gamma0 bands for VV and VH. However, the resulting bands are empty. Do you know any further step I need to do for this?

Thanks!

ABraun · November 27, 2020, 10:23am

after which step is the product empty?

zephyr · November 27, 2020, 10:44am

After range doppler terrain correction
here’s the screenshot:

mengdahl · November 27, 2020, 11:12am

Are the images OK of after the TF step? Empty images in TC sometimes result from missing DEM issues.

zephyr · November 28, 2020, 9:18am

checked the results of TF and it was empty too… I found the problem now, wrong DEM.
Thanks a lot!!!

Ognjen · December 30, 2020, 12:54pm

Hi, thanks for your explanations and links, they really helped me.
Could you please link the source when specifying changes like this:

" NOTE : Since SNAP 8, conversion to Beta0 prior to Terrain Flattening is no longer required, because it has been integrated into the TF operator."

Because I think this has not been implemented yet:

I’m using SNAP 8

Best,
Ognjen

ABraun · December 30, 2020, 1:42pm

It’s possible that the help menu hasn’t been updated yet(@jun_lu), but the issue is marked as resolved

Ognjen · December 30, 2020, 7:44pm

Yes, but it says “Fix versions: 9.0.0.0”

Does it mean it won’t be included unti SNAP 9 or maybe I misunderstood?

ABraun · December 31, 2020, 10:53am

According to my understanding, this is already included in the current version. At least I have tested with SNAP 8 and it worked.

jun_lu · January 5, 2021, 2:33pm

For some reason the functionality is not in SNAP 8. We will issue a module update as soon as possible.

eyeinsky · February 10, 2021, 10:13am

You might consider “forcing” beta0 calibration as preparation to terrain flattening, to avoid follow-down errors.

ABraun · February 10, 2021, 10:29am

that is how it was solved until SNAP 7, you get an error message that Beta0 is required as an input. The idea for improvement is to check if the data is uncalibrated and include Beta0 computation within the Terrain Flattening step.

florian.beyer · June 8, 2021, 11:18am

It is not fixed in Version 8. For both in graphical model builder and snappy, I get “dummy” after TF, when I input other bands than beta0.

navv37 · August 6, 2021, 5:56am

Is this possible now. In the support document it says that the input can be a T3 C3 or C2 matrix but I am still getting the error.

Thanks

manojiitkgp09 · October 12, 2021, 3:08pm

Hi,

I applied terrain flattening to the raw asset using the following pipeline xml(1) and then added the processed asset in google earth engine. However I can see the processed asset being shifted a little (2)(as shown below in earth engine code editor output screenshot). I have also attached the xml(3) without terrain flattening which works fine.

Regards
Manoj