Quality Control (QC) for each step to determin subsidence

Hello everyone;
How can I control quality of each step in SNAP software to decide pass or fail that step?
for example how can I find out ,if “Apply orbit” pass or fail ?
Or “Back Geocoding” works fine ? ( any logfile or method )
etc.
If there is any method, how can I interpret it.

Thanks.

let’s go through the single steps

  1. TOPS Split: If the output has only VV and a smaller extent, it worked
  2. Apply Orbit File: Check under Metadata > Abstracted Metadata > Orbit State Vectors . The number of entries (orbit_vector1, orbit_vector2) should have increased.
  3. BackGeocoding: Create an RGB image to check if the two images are correctly aligned (example)
  4. Enhanced Spectral Diversity: Open View > Tool Windows > Radar > InSAR Stack Tool and check the RMSE of the coregistration.
  5. Interferogram generation: You can visually check if the inteferogram has good quality (visible fringes, little noise, no trends) and if the coherence is sufficiently high throughout the image. Low coherence indicates phase decorrelation (bad quality). Also select “output elevation” to check the quality of the DEM which is used for topographic phase removal. If it has gaps or errors, the topographic phase will be estimated incorrectly as well.
  6. Unwrapping: Also mostly checked visually - are all areas unwrapped correctly, are there any artefacts (introduced by tiling, check the last page of this tutorial)
  7. Phase to displacement: How does the overall displacement pattern look - does it have overall trends superimposing local displacement. Is the displacement band normalized correctly? See page 25 of this tutorial for an example.
  8. Range Doppler Terrain Correction: Not much to check here - it’s simply a geocoding based on a DEM. Again, does the result look plausibe?

Most of the steps do not result in a right or wrong output or deliver a numeric quality indicator. It is rather the task of the user to question if the processed intermediate products make sense and if they are free of visual errors before proceeding to the next step.

1 Like

HI Dear ABraun

Thanks for your fast reply.

For Back Geocoding , I think it’s very hard to determine co-registration quality all over images with this method.
But I have another question .I need to build a stack of sentinel 1a images for PS method in an urban area ( SNAP+StaMPS). In the Interferogram formation , I have a green patern ( attached image ) at the end of the bursts. To solve this problem, is it necessary to use "spatial subset from view " for each interferogram (all stack interferograms)??
Please let me know if you have another advice.

Thanks

you can remove it from the product with the spatial subset, yes. But only after debursting and also the extent of all products for the StaMPS export must be exactly the same. That means the stack of intensities must be cropped accordingly.