Negative dem elevation values

Ok sir and what should be approx perpendicular baselines for these kinds of terrain…
Like i have selected 65 to 70meters for this terrain
and 24 days temporal

I have to work with Sentinel data only as per the project given
And i Cant change the broad study area, But yes can shift in that Uttarakhand Region only., though it would be difficult to find the area in Uttarakhand with Little or no vegetation, But will try to see any area with Minimum Vegetation

So i have to start again now with Final & Fresh ,because of short of time

Therefore, i am asking more information about Baselines

for Sentinel-1, values over 100 meters are more suitable according to the ESA guidelines
Have a look at this document -> Section 1.3 Selecting images for InSAR DEM generation

And for most areas, 12 days are available. Have a look at the observations scenario:

About your study area: Whoever gave you the task to build a DEM based on Sentinel-1 must have no idea on the limitations of this kind of data and I personally think such tasks shouldn’t be given by supervisors.

Ohke sir i will see the dataset with
Least Vegetation
And Baseline above 100 meters with 12 or 24 days

Actually Sir
My task is to Fuse the Ascending and Descending InSAR pair DEMs.

And other Dems also , If required For Good elevation values

I did for both Ascending & Descending But didnt get Good results

to evaluate your elevation information, you can select the “elevation” checkbox in the terrain correction step and have both the InSAR DEM and the SRTM used for terrain correction in one product and compare. This idea is illustrated at more detail here: Making interferogram for TANDEM-X bistatic mode

Yes sir ,This i did with previous Dems also,
SRTM comparision with INsar
Where i didnt get good results with Sentinel dataset…
Now willl try again

As per your guidelines
Thankyou so much sir


Hello Sir,

My colleague made them covering New Delhi and Harayana Region, which is plain area only
Then also the values are very high in Positive as well as Negative
Why is it so happening in other area also . I dont have the product name right now, so have uploaded the screenshot of the area to get some idea.


same reasons as above. Temporal decorrelation, low coherence, not enough fringe patterns, unwrapping errors, atmospheric disturbances, unsuitable perpendicular baselines…

Sentinel-1 is not the best base for DEM generation. Please have a look at these explanations

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ok fine sir…I will forward these tutorial to my colleague also to read.

After discussions and all , now I AM FINALLY making DEM using Sentinel only of the RAJASTHAN area which is like desert area, having least vegetation in North INDIA

And the data i got of Ascending pass with baseline as 108 meters and -36 days temporal
Descending pass: 113 metrers baseline and same -36 days temporal. of April-may dry season

As i was not getting good baseline with least temporal days so have chosen this

And 36 days will not cause much change to the topography of the Terrain so thatswhy i chose same temporal for both, since finally i have to fuse the two DEMs

I hope this will give me better results??

the conditions sound good by now - good luck with it!
It would be nice if you can share the results in here.

If you can share the product IDs I can shortly check the interferogram of the image pair if you want.

Yes sir Sure

And sir I should use SRTM 1sec DEM only ?

Product ID, write now i am not having sir , i have asked my friend to forward from institute…
I will give you in some time

for Range Doppler Terrain Correction it is the best choice. For comparison in your study area, I don’t know which of the freely available ones is the most accurate.



These are the product sir

Descending (phase masked with low coherence)

Ascending (phase masked with low coherence)

Coherence looks not bad but I miss topographic features which match in both images. Many of them look quite random and typically “wave-like”, such as in the top of descending and in the bottom of desecending interferogram. These structures are very likely caused by InSAR errors and do not represent topography.

Thankyou sir

So what should I do

I can proceed to generate DEM out of this?

As i have to fuse both passes , so will i be able to get satisfactory results after fusion?

Because mainly i have to do that and get good results from DEM fusion

you can try but based on the quality of the interferogram I have doubts that the results will be good. If you fuse two images and the quality of an area is good in one image and bad in the other, it will still be a bad fusion.

You find some good results on how interferograms should look to get usable results: The Order of DEM Creating Steps

But these are one of the very few where it really worked. You should talk to your supervisor and explain that Sentinel-1 is not a good source for DEM processing. Otherwise you might raise unrealistic expectations which you technically cannot fulfill.

Ok sir…and can you also tell me the value of Coherence you used for masking

And also sir . i should apply topographic phase removal in this case or not?

And i am thinking to generate DEM for 1 swath first…Because full will take time including merging etc…

If you want to extract topographic features (make a DEM) you must not apply it.

The threshold was 0.1, quite low. Testing for one swath makes sense.

oke sir…
Thankyou very much…

if any issue i will let you know once