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insarlab / MintPy

Miami InSAR time-series software in Python
https://mintpy.readthedocs.io
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The quality of the time series degrades as the distance from the reference point increases. #1165

Closed m1ch96 closed 3 months ago

m1ch96 commented 3 months ago

Dear developers of Mintpy

I'm trying to perform a time series analysis of my stack of 1771 interferograms processed with GMTSAR. I have followed the two examples of workflows in Mintpy: https://github.com/insarlab/MintPy-tutorial/blob/main/workflows/smallbaselineApp_aria.ipynb https://github.com/insarlab/MintPy-tutorial/blob/main/workflows/smallbaselineApp.ipynb And I loaded the data following these instructions: https://mintpy.readthedocs.io/en/latest/dir_structure/

I encountered no errors apart from the unwrap error correction (which I skipped in the end, as it is optional), and I obtained the time series of displacement along the line of sight. However, the quality of the time series obtained is very low, and they appear very scattered. The main point that I noticed is that the further the time series associated with a pixel is from the reference point pixel, the worse the quality. As an example, I attach three images with increasing distances from the reference point (the first is near, etc.). I corrected the troposphere with the ERA5 dataset and the DEM error. Point_Displacement_Time-series_near1 Point_Displacement_Time-series_medium Point_Displacement_Time-series_far

This frame is characterized by a low coherence on average (~0.10). However, I observed some other processing of this frame, and the quality of the time series obtained is not as low as mine. original_averagecoh.pdf

I also attach some other graphs that characterize this specific run. 0.10_0.15_intfpersar.pdf 0.10_0.15_network.pdf 0.10_0.15_coherenceHistory.pdf 0.10_0.15_pbaseHistory.pdf 0.10_0.15_avgSpatialCoh.pdf temporalCoherence.pdf

I tried to choose the reference point based on these criteria:

  1. Low deformation pixel
  2. High coherence
  3. Not affected by strong ionospheric streaks
  4. Close to the same elevation as the area I am studying The last point is difficult for me since my AOI covers the entire frame.

I tried several combinations of minCoherence, minAreaRatio, and reference point positions but the pattern I observe in the end is always the same: a degradation of the quality of the time series farther from the reference point position.

At the bottom, I attached my custom template. At the beginning, there are parameters that characterize my workflow and the workflow of GMTSAR.

I tried to look in the forum and here, but I was not able to find someone with a similar problem. Could the issue be attributed to the absence of the unwrap error correction phase? If you have any idea what might be causing the issue or if you need further information, please let me know.

Thanks for your attention. Michele

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