Dears,
I’m need apply the Radiometric Terrain Flattening in a lot of Sentinel-1 images within Google Earth Engine.
But in GEE the Sentinel-1 GRD data are currently with Orbit File applied, Terrain Corrected and converted to dB. After this processing is possible write ab algorithm to apply RTF with efficiency?
My bests regards.
No, it would have to be added at their input stage. I proposed that they add flattening during input already years ago, but so far AFAIK they have preferred to stay with the GTC products you’re familiar with.
A recent publication on Angular-Based Radiometric Slope Correction for Sentinel-1 by Andreas Vollrath et al, 2020
Check out the complementary material on github here:
The Vollrath et al solution is not the same as terrain flattening. Rather it is some empirical angle correction factor depending on 2 assumed terrain types.
For terrain flattening, the correction is (also) based on the normalization for pixel area. One would expect pixel area to be a constant depending only on SAR viewing configuration and local DEM derived slope angles. That suggests you would need to derive that only once and provide it as a reference layer (ignoring small difference in SAR viewing config between orbit passes).