# Calculate Backscatter coefficient by SNAP

By using the radiometric calibration module

Thanks, sir. Here are my procedures:

1. Radar->Radiometric->S-1 Thermal noise removal;
2. Radar->Apply Orbit File;
3. Radar->Calibrate->(Processing Parameters: Output Beta0 band);
4. Radar->Radiometric Terrain Flattening;
5. Radar->Geometric->Terrain Correction->Range-Doppler Terrain Correction.

Is there anything wrong? Moreover, the result of pixel value after Step 5 is the EXACT backscattering coefficient? Thank you!

BTW, my data is S1A_IW_GRD…

I see nothing wrong with that.
You will still have some radiometric inaccuracies, maybe resulting from topography and the quality of the DEM in the terrain flattening step.

Excuse me, sir. What can I do more to obtain the exact backscattering coefficients? And, in my Step 3, the output result is Beta0 band. Should I output the Sigma0 band? What is the difference among Beta0, Sigma0 and Gamma0 band?

the only thing I can think of is to use digital elevation models of higher spatial resolution and quality.

Regarding your second question, you need Beta0 as an input for Terrain Flattening - please have a look here:

After Step 5, the output band is “Gamma0_VV” or “Gamma0_VH”?

VV and VH are different polarizations of the microwave, they are not related to the calibration process.

Yes. I wonder after Step 5, the output band is “Gamma0”?

This is the result after Step 5:

Terrain Flattening converts Beta0 to Gamma0

Yeah, I got it. Thank you very much. I really appreciate your help.

I think for GRD products, the first thing is to perform calibration for GRD data and generate the sigma0 of VV/VH data; then covert the sigma0 of VV/VH data to backscattering coefficients product in dB.

Are you doing it in SNAP ,all the 5 steps??

LOL, I took me a lot of reading also to realize that radiometric calibration is back-scatter coefficient.

Sigma0 is the normalized radar cross section (often named backscatter coefficient, calibrated with calibration constant and global incidence angle)
Beta0 is the radar brightness (only the calibration constant is applied, incidence angle is not included)

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Thanks Doc, so many some little things to understand and master in radar analysis unlike optical analysis

Dear ABraun,

I read through these conversations and I am wondering to know that there is any possibility to get the backscatter coefficient (Sigma0) as a final product in decibel after Terrain flattening and Terrain correction?

Greetings,
Karlmarx

hello, I am a new user to SNAP. Can any body tell me that how to calculate backscatter coefficient(steps). and how many data needed to calculate this?

I suggest using ASF’s Radiometric Terrain Correction (RTC) service directly, they will generate the results (geocoded in dB scale) ：
https://asf.alaska.edu/asf/on-demand-sentinel-1-rtc-is-now-available-at-10-m-pixel-spacing-and-in-db-scale/