Is Sentinel-1 GRD product Sigma0 or Gamma0 in Google Earth Engine? [closed]

Question

I am using Sentinel-1 SAR GRD imagery with IW and EW swaths from ESA through Google Earth Engine.

• Is the pre-processed Sentinel-1 GRD product that I access through GEE is Sigma0 or Gamma0 or Beta0?

• Also how can I convert from Sigma0 to Gamma0?

Answer 1

1. As written in the first line of Sentinel-1 pre-processing description, Sentinel-1 GRD image collection represents sigma0 in dB.
2. To convert sigma0 to gamma0, you can use the following trigonometric properties (reference; slides 34-36):

sigma0 = beta0 * sin(theta) ... where beta0 is the square of raw digital number

gamma0 = beta0 * tan(theta)

thus,

gamma0 = sigma0/cos(theta)

You can implement the above expression in Earth Engine to obtain gamma0.

Link to full code.