Using External DEM 10x10m

As I mentioned I reprojected into WGS84 before start the processing.

yes, I meant using which tool, which resampling, which other parameters?

Dear Andreas,
Thank you for reply. For the case I report here I’d like to use DEM having 10x10m spatial resolution. The file was reprojected in QGIS and works fine there and with other software too.
One possibility for this issue could be the small area covered by this DEM. Could you advise please.

Best regards.

this still doesn’t answer my question :slight_smile:

How did you do it in QGIS? This is essential because there are some error sources I could think of.

Dear ABraun, sorry for the delayed reply. In QGIS I used Raster->Projections->Warp dialog and setting appropriate parameters -tr switch. After processing I got 30x30m file and worked fine with SNAP.
Actually the problem was the size of DEM tiles (4x4 km). I started with only two tiles (32 and it didn’t work, but getting more (12 - 192 it worked fine even without reprojection.

I have similar problem, I also mentioned it in here, Source of the post

The tiles cover the AOI have been downloaded from here source :

Both are opened in QGIS and then exported as geotiff WGS84 (geographic coordinates) and mosaic both tiles, Would you please to bring my attention to any not correct step!

The problem is, the slave is empty aftermath corr.

I tested the workflow for your data and it seems to work:

My guess is that the reprojection of the 2m DEM data to WGS84 has not been correct and now SNAP treats it somehow wrong.
As the elevation data is a asc file with no metadata you have to make sure that you select assign the correct coordinate reference system (UTM 35 N) before you reproject.

Edit: It took 135 minutes (16 GB RAM) but it worked. The upper image is with topographic phase removal based on the 2m DEM, the second is without.


Thanks a lot, but it seems for me stacked in QGIS, I did two times, but same results. Would you please to clarify the steps of QGIS, because I reproject it in both cases but slave is still empty.

no matter what QGIS thinks about the projection of the data (it assumes WGS84 after loading, but it is not), you have to select the correct UTM zone in the reprojection module (here it is 35N) as the source CRS and WGS84 as the target reference system.

1 Like

I did exactly same before and now , but still the slave is empty, I’ll send you the DEM, and both S1 identifier, as private message, hope you have time, many thanks in advance. I also tried up 10 m *asc,. but still similar empty slave. But using GETASS30 autodownload, there is no problem.

just for clarification: After which step is the slave empty?
First I thought you wanted to use the 2m DEM for the topographic phase removal (because this was the problem in the topic you linked).
I don’t think it makes sense to use a 2m DEM for the back-geocoding of S1 SLC data. Especially if the covered area is much smaller than the S1 data. Use GETASSE30 and it works.

1 Like

Both tiles of the DEM covers the only first burst, which covers the AOI, The slave is empty after TOPSAR corr. GETASSE30 works, but doesn’t implement the demand, I explained to you, the goal only to test the DEM for the further processes.

if the coregistration was completed, you could still use the 2m DEM in later steps. Or do I miss your point?

Do you think preparing data to StaMPs, the tested DEM - 2 m, could be use, though the slave image is empty, throughout the single corr. (only two images)?

The corr. , is completed perfectly, but getting an empty slave, points out to problem, even the DEM covers the one burst of AOI.

I don’t understand why you don’t use GETASSE for the coregistration. It makes no difference.

I’d like to continue with one DEM, to retrieve the possible scatterers points, for single object, I mentioned to you. I think GETASSE, has less resolution to the object, therefore, how it’s possible to subtract the elevation phase to get the displacement of this object!

As I mentioned earlier, I’d like to test this DEM, from the first step and using to the end, But

Do you think I could use different external DEM in STaMPS, ? Since last time I used the default one, which I think it’s SRTM 3sec.

yes, you can use GETASSE for the coregistration (completely fine), but later use the 2m DEM for the topographic phase removal (here it makes sense to have a high resolution DEM).
But you might want to resample it to 10x10 meters, for instance, because it really takes a lot of time to perform topographic phase removal and for PSI you need more than 20 products.

Thanks a lot, that what I was talking about,

But still, is it possible in StaMPs to use an external DEM!

why not? You include it in the stack by checking it in the interferogram operator. StaMPS later doesn’t care where it comes from.

I’ll give trial and let see, but, tremendous thanks Andy,