Radiometric Terrain Flattering

Hi there,
I just pre-processing Sentinel 1 data for an area in Canada. I did thermal noise removal, apply orbit file and calibration and now I am doing Radiometric terrain flattering with SRTM 1Sec HGT (Autodownload) . I could do it for some of data, but for the rest of this it gives an error like this:

A problem occurred during processing the target product processing.
**type: OperatorException **
Message: java.lang.ArrayIndexOutOfBandsException

Could you please help me through this?

I have to also say that for Sentnel 1B IW ones also it says the DEM resolution is low! The best I can do based on the list is SRTM 1sec! What should I do then?

Some other thing I need to add: I used Aster 1sec GDEM as well to check. The process goes and compeleted, but the final image is uniform dark gray!

Hi @marifo,

Is your study area inside the coverage area of SRTM?

Hi Yes I have its SRTM. but it is near the shoreline (near Hudson bay). do you think this can influence it. and what should i do?

I would suggest to visually check the quality of your dem. Rigth click on the product -> add Elevation band. Your dark grey image could still contain valid pixel values, you can check in the Pixel info tab. cheers.

In Processing Parameters, if you have the re-grid toggled on, can you try toggling it off?

That solved the problem for me a while back (although I cannot recall if my error message was the same as yours).

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I am trying to perform RTF correction on ALOS-2 datasets. I first converted HH intensity value to beta naught then I performed RTF correction, but I am getting this error. Kindly guide me what’s the meaning of this error and how to solve it.

Kind Regards

Is your DEM projected in WGS84?
May I ask where the 12m DEM comes from? You named it “dem_alos_12m_geo” which reminds me of the RTC products by ASF. In case that it is a side-product of ALOS PALSAR orthorectification it is probably only a resampled version of SRTM. The elevation information is not better.

I am telling you this because you could then just use the SRTM 1ArcSec DEM and avoid probable errors caused by the external DEM.

Yes, I get it from RTC products by ASF and it’s projected to WGS84. Thank you for your correction, I also have TanDEM-X 12m DEM for my study area. I can use it. Right now I try to use SRTM 1sec (Auto Download) DEM and I unchecked “Re-grid Method”. It was executed successfully but the result is all zero pixels as shown in the figure below.

is your area outside the SRTM region?


@ABraun my study area is north of Pakistan and it’s under SRTM coverage. I tried RTF correction using following DEMS.

  1. SRTM 1 sec (Auto Download)
  2. SRTM 1 sec (as External DEM)
  3. TanDEM-X 12m (as External DEM)

But I am getting the same error, the resultant image contains all zero values.

does the Beta0 image look correct?
Which steps were applied until the Radiometric Terrain Flattening?

Yes, Beta0 image looks correct as shown below. I just clipped original image to a small subset then convert to Beta0 and apply Radiometric Terrain Flattening.

that is strange, should work actually.
Do you have the latest version of SNAP installed?

Yes I am using SNAP 6.0

Is there any particular prerequisite besides converting to beta naught in order to perform terrain flattening?

No, this is the only requirement. You could maybe try the SRTM 3 Sec also

Hi @ABraun I already tried with SRTM 3 sec but still getting the same result.

I can’t think of an explanation for that, sorry.