When performing the steps for deriving a map subsidence at the end, I am wondering whether we need to perform terrain correction before of after unwrapping? I did some experiments between unwrapping the phase after performing terrain correction and phase unwrapping before performing terrain correction. The results are shown below:
The image on the left shows the phase unwrapping which performed after the data has been terrain corrected. For the image on the right, the unwrapping phase were performed firsts and the it was terrain corrected.
We see that the difference between the two images is large. It seems that if we terrain correct the SAR image first before phase unwrapping, the results we get are very different. Why does terrain correction change the results so much?
So, is it recommended for terrain correction step to be done at the very end?