SNAP taking a lot of time processing sentinel-1 dual pol SAR data for H-A decomposition

BEAM-Dimap format is good solution.
My points are:

  1. When to use complex calibration
  2. No able to perform terrain correction. output is zero data (blank image). When terrain correction is not performed then I am getting the Entropy, alpha bands.

Graph 1 works fine

  1. Read
  2. Deburst
  3. Subset
  4. Multilooking

if you want to perform polarimetric analyses (as in your case) complex calibration is required.

Try SRTM 1 Sec (AutoDownload) instead of 3Sec because SNAP has problems lately, resulting in black images.

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I tried SRTM 1 sec and it works :slight_smile: Thanks a ton for this. Regarding calibration, at which point in graph I should apply this??

SNAP supports calibration after multi-looking (unless you check “output intensity”) so you can make a subset first and multi-look to reduce the data size to be processed.

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@ABraun The problem with the SRTM 3Sec has been reported somewhere.

Thank you very much

Hey thank you very much for this information, it helped a lot. I divided the graph into two parts and now it is working fine and faster also. :slight_smile:

These are the two graphs:
Graph1:

  1. Read
  2. Complex calibration
  3. Deburst
  4. Subset
  5. Multilook
  6. Write (as BEAM-DIMAP)

Graph2:

  1. Read (output of graph 1)
  2. Polarimetric speckle filtering (refined LEE 7x7)
  3. Polarimetric Decomposition (H-A dual pol)
  4. Terrain Correction (DEM : SRTM 1 Sec)
  5. Write (as tif)

Thank you all for suggestions and tips :slight_smile:

What actually the problem is? How these two DEMs are different?

SRTM 3 Sec is 90 meters and has bigger tiles https://dwtkns.com/srtm/
SRTM 1 Sec is 30 meters and has smaller tiles https://dwtkns.com/srtm30m/

the first is somehow differently accessed by SNAP and lately the download is not successful in many cases.

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Hey thanks for the info. It recalled helped a lot. I tried the graph and it is working fine :slight_smile: But can you help me explaining the difference between:

Product -> Deburst -> Output
and
Product -> split(IW1/IW2/IW3) -> Deburst -> Merge -> Output
i.e. splitting and debursting individual sub swath and then merge to combine them vs Just debursting the product. The output of both these are different.

how are they different?

I tried H-A decomposition over a subset and the values of H-A are different.

is the same color range (min max as defined in the Color Manipulation tab) applied to both images?

Color range is different in both case. The above two steps: should they be producing the same output??

to compare how similar both rasters are you can use the scatter plot tool

you can define a minimum and maximum by yourself in the color manipulation tab and apply it to both images. You can also apply the color of the first result to the second with this button grafik (select ‘no’ when asked to search for min/max)

Both should acutually produce the same result. I guess the colors are just distributed differently because of different value ranges of both products.

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Thank you for the suggestions. I will try it and get back to you :slight_smile: .

Hi, I’ve been seeing the same problem when processing decomposition step. In fact it cost 36 hours to process a whole graph(containing preprocessing and decomposition). Can I ask how much faster it get when you divide the graph into two parts? Thanks a lot!

this depends on your system’s capabilities. But often large graphs are unnecessarily slow. So if you only have to apply this processing once I recommend avoiding graphs in general. They only make sense if you want to apply some workflow on multiple images.

Thanks! By the way in other blogs someone said when applying “Polarimetric Matrices” after “Multi-looking”, you’ll get the wrong answer. I notice that you didnt do the “Polarimetric Matrices” step? and directly apllied decomposition?

SNAP allows to perform polarimetric decomposition directly on the Intensities without converting to S/T/C matrix before. As many of them include a spatial window I would not multi-look before unless you want to change the pixel resolution for a certain reason.

Thanks!!! helped a lot :smiling_face_with_three_hearts: