Hello, I am trying to obtain the sigma nought values using a single SLC image ( ascending mode). I follow the further steps:
Imporing the .zip file in SNAP
Applying S1 Thermal Noise Removal
Applying Orbit File
Calibration
S1 TOPS deburst
Speckle Filtering ( Single Product Speckle Filtering)
Multilooking
Terrain Correction-> Range Doppler Terrain Correction-> in the processing parameters am trying to use an external dem instead of the SRTM (I had projected my DEM in WGS84 and i exported as geotiff with a pixel resolution of 0.2m) In the no data values it has the value 0.0. I run the process and the result image has null values ( black image).
I don’t know what I am doing wrong. Can you help me with this?
I have noticed that your DEM resolution is 0.2m. In my opinion it is too high resolution for Sentinel-1 data, especially for big area. I have never seen that somebody used 2500 more precise (50*0.2 m = 10m)^2 DEM than final product. This may cause more errors that 10-20m resolution DEM.
Of course, a lot depends on the terrain. On flat terrain you can choose a lower resolution DEM than on mountainous terrain.
The error may be due to a calculation problem. I would follow @ABraun advice to try default SRTM.
I tried to use the SRTM but there is a difference in the final results, especially in the map of local incidence angle, that’s why I need my DEM with the specific resolution. I managed to obtain first results by subsetting the image in the exact area of my DEM and changing the coordinate system of my DEM from WGS84 to WGS84/UTM zone 36N ( for Cyprus) and it works. Thank you!