Radiometric & Geometric Correction Workflow

Do you have a suggestion as to where in my workflow it is best to perform this step, or does it not matter that much?

I would suggest:

  1. Calibration to Beta0
  2. Terrain Flattening (produces Gamma0)
  3. (Speckle Reduction)
  4. Terrain Correction
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Thank you! If anyone has an argument for a different order, especially in the context of polarimetric processing, I would love to hear that or view any literature you have on it as well.

For others who are interested in this topic, my workflow (adding in polarimetric processing) is looking like:

(Orbital Correction)
Calibration
Terrain Flattening
Speckle Reduction
Polarimetry
Terrain Correction

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talking about polarimetry it could be different. Terrain Flattening requires Beta0 as an input. But, according to my understanding, polarimetry only works on the i and q parts of the image. I’m not sure if it can be done in SNAP as it is suggested in the PDF above.

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Do u think the terrain flatterring also works for the water mask studies?

And a quick Q which is not related to this subject (sorry), do u know by any chance how to independently save “a virtual band” obtained from a bandmath as geotiff?

Thanks

as water bodies are always flat and have low backscatter (excluding waves, ice cover or oil/sand particles) I doubt that terrain flattening has a larger effect.

Regarding the virtual band: Right click > convert band and then menu > file > save.

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Just a suggestion but it should be good after orbit to apply thermal noise removal in order to decrease radiometric variation between subswath.

Be carefull because it’s usefull for data acquired after the end of november.

Best

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Can anyone confirm whether this is the case and a flattened image can’t be processed for polarimetry?

Currently a flattened image is only producing gamma0 intensities.
We need to see how we can change it to allow you to still create a
polarimetric matrix.

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Do you mean image improvement from thermal noise removal is most important during fall/winter months? Excuse my ignorance, I haven’t had the chance yet to look into thermal noise removal at all.

Sorry, if I said after novembre it’s just because calibration of sentinel 1 was improved at the end of 2015 november.

Consequently, after this time the thermal noise metadata is now relevant.

I hope now my answer is more clear…
Best

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thanks for the clarification. Do you have any source where I can read about this improvement?

Yes, it’s here

https://sentinel.esa.int/web/sentinel/news/-/article/improved-radiometric-calibration-of-sentinel-1-tops-products

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Hey together,

i want to preprocess Sentinel-1 SLC images for a subsequent agricultural classification.
I am an absoulute beginner in working with SAR-Data, so i would like to apologize for any bad mistake.
My suggestion for the preprocessing steps and the order:

  1. Radiometric calibration
  2. Single Product Speckle Filter
  3. DEM Assisted Coregistration with XCorr
  4. Range-Doppler Terrain Correction
  5. Spatial Subset to my Study Area

does this make sense?
I would be very grateful if you would add some improvements!

Thanks in advance,
best regards,
Phil :slight_smile:

are you sure you are using SLC data? In this case you would need to perform TOPSAR Deburst after Calibration in order to remove the black stripes.

Coregistration is only needed when you work with multiple datasets at once.

You could also make a subset earlier in order to save computing time .

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I try to obtain the backscatter coefficient of Sentinel-1A using SNAP. Is the radiometric calibration the first step?

depends on the level of your product. Have you downloaded SLC or GRD data?

SLC, IW mode, VV and VH polarization

If I perform TOPSAR Deburst, Filtering and radiometric calibration, the results of VH polarization is Ok, but the values of VV polarization are zeros.

for SLC data I would suggest

  1. TOPS Split
  2. Apply Orbit file
  3. Thermal Noise Removal
  4. Calibration to Beta0*
  5. TOPSAR Deburst
  6. Radiometric terrain flattening
  7. (Speckle filtering)
  8. Range Doppler Terrain Correction

If you don’t need the phase information you can also download it as a GRD product and only apply the following:

  1. Apply Orbit file
  2. Thermal noise removal
  3. Calibration to Beta0
  4. Radiometric terrain flattening
  5. (Speckle filtering)
  6. Range Doppler Terrain Correction

or (if you don’t have much topography):

  1. Apply Orbit file
  2. Thermal noise removal
  3. Calibration to Sigma0
  4. (Speckle filtering)
  5. Range Doppler Terrain Correction
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