The Order of DEM Creating Steps

Great, thanks for the quick response.

Here’s an example from an area where I am working. The image below is the phase with only the Goldstein Phase Filtering performed:

Here’s the same area with Multilooking performed:

Running the multilooking seems to have put the image back into Slant range if I am correct. Is that typical behavior?

the opposite is the case. All interferometry is performed in slant geometry until terrain correction. Applying multi-looking corrects for pixels of different sizes due to the incidence angle and makes them all squared.

Have a look at this comparison:

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Excellent, thank you for the detailed info.

I hope I am not hijacking the thread here. Feel free to split or move this if necessary.

Is it incorrect to perform Topographic Phase Removal when processing to Generate DEMs? I see @musicnerd did not include that step.

yes[quote=“dhill269, post:9, topic:5771”]
Is it incorrect to perform Topographic Phase Removal when processing to Generate DEMs?
yes. This is only if you want to detect subsidence or uplift (differential interferometry) and absolute heights don’t matter. But if you are interested in the topography itself, topographic phase removal must not be applied.

As long as the questions are addressing the same subject I see no need to split.

Thank you very much for this. However, after applying colour ramp, when I try to export in hillshade window, it gives an error that saying the file have one band only. It requires three bands. How did you get over this issue? I know this is not related to here, but it annoyed me a bit. :slight_smile:

Thanks again. Performing the Topographic Phase Removal is likely what has been causing me issues.

I will also provide my processing steps below as they may help others:

1. S1 TOPS Coregistration

(Only IW2 swath, Bursts 1-3, VV band only)

Output RGB image (RGB: Intensity Apr 10, Intensity Apr 22, N/a):

2. Interferogram Formation

(Default options used)

Phase image:

Coherence image:

3. S1 TOPS Deburst

(Default options used)

Phase image:

Coherence image:

4. Goldstein Phase Filtering

(Default options used)

Phase image:

Coherence image:

5. Multilooking

(Default options used)

Phase image:

Coherence image:

6. Snaphu Export, unwap and import

(8 processors, 20x20 row and colums, MCF, TOPO)

Phase image:

Unwrapped phase image:

7. Phase to Elevation

Elevation image:

The resulting elevation looks really wacky but I suspect this is simply due to very low coherence between the two images.

Here’s the coherence image for comparison:

The low coherence areas have very wacky elevation as we would expect.

Here is a histogram of the coherence showing that generally the values are quite low.

My study site is located in Canada and the images were acquired in April. My hunch is that the snow cover at that time is what is causing the low coherence. This is probably further exacerbated by the forest cover in much of the area. I will look into using some images from a difference season to compare results.


please friends how can i solve this problem in dem

this is natural data
i have big differences

Can you post a screenshot of the coherence image?

that is it >> i have mini project about this one please help me

i did subset to the image after Interferogram … that is right or no

you need better coherence for interferometry. Only areas with high coherence can be used later.

Please have a look at these answers:



getting interferometric DEMs in tropical areas is nearly impossible with C-band data because it is scattered ad the canopy and coherence is lost after a few seconds. Even with bistatic data (e.g. TanDEM-X) this is a challenge. So getting a DSM of the canopy is also not possible.

Unless you have P-band data (wavelenghs of ~74 cm) these canopies are not penetratable.

When are the exact dates of your two images?

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thank you very much for your answer

the number of GCPs for the coregistration is not possible in slc product

this is the date >>>>

no need the dem for all the area i have shown only for this area

that low vegetation as you see…

as stated, you should use the S1 TOPS coregistration instead of splitting the bands before.

Don’t apply Orbit Files or split the bands manually. This is all combined in the Sentinel-1 TOPS Coregistration. Use the SLC zip files as inputs and let the module to the rest.


i know but My laptop is advance but this process took long time to finish in this step S1 TOPS coregistration … so… when can i do subset to my specific study area that i need …

second Q can i extract the dem for this area …

and how can i increase the GCP by S1 TOPS coregistration …