DEM for terrain correcting... what do I need to consider?

I am terrain correcting RADARSAT-1 data using Alaska Satellite Facility’s MapReady (I can’t use SNAP for processing this imagery).

Unfortunately, unlike with SNAP, you have to find your own DEM for this. With SNAP you select the needed DEM from a drop-down menu in Terrain Correct and never give it another thought. I’m not sure what I need to consider with selecting the DEM. Does it need to cover the area of the Radarsat image entirely? Does it just have to overlap with the image?

Any advice on resources or considerations when picking the right DEM for terrain correcting an image would be very helpful.

Thank you

You can only terrain correct over a DEM, so it needs to cover your area of interest.

Thank you for your reply. Does it need to cover the entire area of the SAR image? Right now I have a bunch of smaller DEMs that fall within the spatial extent of the SAR image. But I don’t have any DEM big enough to cover the entire area.

If you process your image with each of the DEMs separately, you will end up with three terrain-corrected products , each covering the area of the used DEM. So no need for a DEM that covers the whole scene.

ps. what is the Radarsat-product SNAP cannot handle?

Thank you for your help. The problem with radarsat data from ASF is that it’s processed by the JPL precision processor, which is different from the ESA. So radarsat data obtained from ASF need to be processed in MapReady, wheras you can use SNAP for radarsat data provided by ESA. The problem is I am using a lot of radarsat data, and I believe ESA still has a cap on the number of images you can download from them.