Trying to caliberate a SAR image. I am relatively new to SNAP. I did the following steps without problems.
- Orbit file
- Thermal noise filter
- Remove GRD border noise
- Calibration (Radar >Radiometric>Calibrate)
- Specle Filtering
But while doing the next step required, that is
6. Range Doppler terrain correction (Radar>Geometric>Terrain Cor.>Range Dop. Terrain cor.) ,
I get the following error - ''A problem occured during the taget product initialisation.
Message: Entire image is outside of SRTM valid area.
Please use another DEM’'
Any assistance is highly appreciated.
The error-message identifies the issue - please choose a DEM that covers your AOI, for example a Copernicus global DEM.
My area of interest is Weddell Sea, Antartica.Can I use getasse30 as my DEM for this, since I am trying to study the sea ice parametres and getasse30, that by definition is Global Earth Topography And Sea Surface Elevation at 30 arc second resolution.
Because when I use this dem , I am able to do terrain corrrection succesfully.
Yes that DEM is good enough for co-registration but I would not use it for terrain correction. If you are interested in the sea-surface trerrain correction is not even required.
Thanks. I was told that terrain correction is not really necessary but to still do it as a matter of learning, assuming it wont cause problems on sea surface if we do or dont do it . Is that right or doing terrain correction on sea surface cause unwanted hazzles? ?
Some DEMs have “no data” over the sea so it is not even possible to do the correction. You should perform the ellipsoid-correction however, and even there be aware that the scene can be shifted slightly due to geoid-ellipsoid height difference over your area of interest.
Okay. Will try that. Thank you so much.