I have generated DEM from Sentinel InSAR data. It gives relative heights (Data have negative elevation). I just want to know How to get the actual absolute elevation of my study area from this DEM.
I have attached the DEM file
Maybe I can clarify with this figure: On the left, you see an interferogram of a bistatic TanDEM-X image pair (two images acquired at the same time). This is how an interferogram must look like for the correct and reliable extraction of elevation.The coherence is high throughout the image with some lower values at backslopes and the lowlands along the coast. But the phase variation is strongly linked to the topography of the area.
On the right, you see an interferogram of the same area, but with Sentinel-1 images (6 days apart). It contains no topographic information (because of temporal decorrelation and a comparably short perpendicular baseline of 65 meters). The coherence is accordingly low and the interferogram variation is not related to topography. No valid DEM can be derived from such data.
this error cannot be removed, it is in the data. The workflow is correct, but the data is bad.
I have merged your topics into one.
Please have a look at the documents I have posted above. You find answers on why there are negative values and what is the cause. You cannot extract canopy heights from Sentinel-1 data because of the decorrelation of the phase.