Thank you for the reply.
The data is located at north-east Black Sea region of Turkey.
Is Hillshade a function in toolbox? I looked for it but I couldn’t find.
I will try to produce another DEM of the same area.
Regards
1 Like
these are probably not the worst conditions for InSAR. Coherence will probably be low at the north end where the green coastal area begins.
Hillshading is not available in SNAP but can be done in QGIS, for example. Make sure that you select a projected coordinate system instead of WGS84 in the terrain correction module in order to retrieve correct hillshading.
nice example:
5 Likes
I’m wondering why you included Step 5 - Multilooking in your process. I am very new to InSAR so I’ve been following along the tutorial here: http://sentinel1.s3.amazonaws.com/docs/S1TBX%20Stripmap%20Interferometry%20with%20Sentinel-1%20Tutorial.pdf
They suggest here doing Topographic Phase Removal then the Goldstein Phase Filtering. Now that tutorial I believe is for deformation analysis - are these steps different for DEM generation?
Thanks!
1 Like
multi-looking is not obligatory in SAR processing, but reduces file size and, to a certain extent, speckle effects. If your interferogram doesn’t contain much speckle and you have the computing capacity, you can as well skip multi-looking.
2 Likes
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:
1 Like
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?
[/quote]
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. 
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.
6 Likes
Can you post a screenshot of the coherence image?
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:
2 Likes
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?
1 Like
thank you very much for your answer
the number of GCPs for the coregistration is not possible in slc product
this is the date >>>>
