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:
- Radiometric calibration
- Single Product Speckle Filter
- DEM Assisted Coregistration with XCorr
- Range-Doppler Terrain Correction
- Spatial Subset to my Study Area
does this make sense?
I would be very grateful if you would add some improvements!
Thanks in advance,
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 .
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.
Thank your very much for your suggestions. Does the Thermal noise removal and Apply Orbit file are the necessary steps?
I performed the SLC data using SNAP
1 TOPSAR Deburst
2 Calibration to Sigma0
3 Speckle filtering
4 Range Doppler Terrain Correction
For the radiometric calibration results, the VV is right, but the VH is incorrect.
Thermal noise is not present in every product. In case you don’t rely on highly accurate radiometric values you can also skip it.
The orbit file adds information about the geometric location of your product. If you want to combine it with other data it can improve the position accuracy.
Your suggested workflow is sufficient for most applications.
Why do you think calibrated VH is not correct?
Thanks for your reply, I follow your suggestion to perform the Sentinel-1A data using SNAP. In the previous results, when the radiometric calibration was performed, the results of VV polarization are zeros, only the VH polarization is correct. Can you supply an email for me, thus I can transform the results to you.
sorry, I can’t help you outside this forum.
But indeed, zeroes as an output are obviously wrong. Was the data correct/complete before radiometric correction?
Sorry, the results of VH is correct, but the calibrated VV are zeros.
Yes, before the radiometric calibration both of the intensity of VV and VH are correct. When the radiometric calibration was implemented, the calibrated VV are zeros, and the calibrated VH is correct.
I can’t think of a reason why this could happen.
Is it zero or no data /nan?
What order should I take steps in ?I’ve seen one of the above threads says that it should be good after orbit to apply thermal noise removal in order to decrease radiometric variation between subswath.
Thanks for your reply .Do you mean orbit before thermal noise removal is better ?What are the differences between the various epolynomial degrees and which is recommended?
Thank you for help
I really don’t know, sorry. Try it out and compare the outcomes.