Differences between "Coregistration" and "DEM-Assisted Coregistration"

Hi there!

Under the “Radar----Coregistration” button, there are two optional function:

(1) Coregistration
(2) DEM-Assisted Coregistration

My questions are:

A: What are the differences between the two ways of coregistration?

B: I am using ALOS-2 L1.1 SLC data to do offset tracking analysis, I want to use SNAP to firstly do image coregistration, and than move to other software to perform offset tracking. Which way of coregistration in SNAP should I choose?

PS: I am using an interferometric pair of SLC data. Same orbit, same look angle etc.

Thanks for any help!

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The difference between the two coregistration is that the first one (coregistration) is based on a double cross correlation of images (coarse then finer). It has the advantages of needing no external input.

The DEM-Assisted Coregistration is based on orbit files and DEM. I suggest you to read the following article which clearly explain the method : impact of dem-assisted coregistration on high-resolution sar interferometry
The idea is to find an analytical expression of the pixel’s shift between the images caused by the topography. It thus requires an external DEM.

For you second question I don’t know. The first method gives you “poor” results. However, if the orbits are not precise enough, the second one cannot help you much.