Local and Ellipsoidal Incidence angle of Sentinel-1


I know this topic may have been already discussed but lately I am aware of the confusion between local (affected by terrain) and ellipsoidal incidence angle (projected to flat ellipsoid surface).

Through literature,the Sigma0 value of the radar backscattering has been always demonstrated as
Sigma0= Beta0*sin (ellipsoidal incidence angle) and thus corresponding to the reflection from the surface area of the ellipsoid.

Following this equation, one could say that the value Sigma0 derived from SNAP for S1 images is linked to ellipsoidal incidence angle and not the local incidence angle (affected by terrain elevation and slope)

For this reason, the question is: Can someone use the Sigma0 value accompanied with the local incidence angle or it should be only used along with the ellipsoidal incidence angle for a given application?

I know that over flat surface the local and the ellipsoidal incidence angle may not widely differ (2 to 3 degrees) but one should know what is more scientifically used for SAR application.

Yes, you can use Sigma0 with the local incidence angle and people have been doing that for decades. if you want to reduce/remove local incidence-angle effects on SAR images you should perform Radiometric Terrain Flattening (RTF).

Hi. I wanna extract incidence angle for soil roughness evaluation purposes. I confused due to various incidence angle option in SNAP. Could any one help me which of them should I extract for my purpose?

if you are about to terrain correct the data, you can select “Projected local incidence angle”

@ABraun Could you please expand on why “Projected local incidence angle” is better than “Local incident angle” for terrain correction? Intuitively (as non expert) I would have thought that Local incident angle is the angle between the SAR beam and the terrain, derived from orbit information and DEM surface. So this angle would have been my guess to use for terrain correction? Thanks