Coregistration & Coherence problem

For an unexpected reason I had to run the coregistration and coherence estimation of two SLC IW Sentinel1 products with VV polarization. They are two spatial and temporal consecutive frames ( red and blue swaths in the image). Probably it is not such a meaningful operation but I had to look into it and I need some explanation about the results.

The coregistration has been performed after typical preprocessing:

  • Apply orbit
  • calibration
  • topSAR split

and then starting with the subswath:

  • back-geocoding
  • topSAR deburst
  • topSAR merge

The result of the coregistration was the intensity of the master product, but the intensity of the slave contains only NO-DATA pixels.

when computing the coherence ( after the back-geocoding for each subswath)
the final result is unexpectedly a matrix with all valid values.
So how these two behaviours can be explained for the same pair of products?? I supposed the coherence would had been with only NO-DATA values.
Help me @ABraun @lveci @mengdahl @marpet

Thanks in advance!!

It’s not clear what you have attempted. You need two acquisitions from the same track , taken at different time-periods (time difference is multiple of 6/12 days).

What are the temporal baselines of all the four coherence images?

The temporal baselines are
ALos2 before pair - 99 days
ALos2 after pair - 57 days
Sentinel 1 before pair - 12 days
Sentinel 2 after pair - 120 days

Well fo S-1 you should use 12 days also after the event. I don’t know what went wrong with ALOS2 after but the coherence-image does look suspicious.

@mengdahl the closest image for S1 is the 120 days.
is there a co-registration parameter that can be tuned to decrease the effect of large temporal baseline.

The acquisition scenario must have changed, a pity. Are you sure there are no images from another track for example? The temporal decorrelation cannot be compensated for in processing as the actual scatterers on the ground have changed/moved.

@mengdahl Yup I enquire with ESA too and they confirmed that the area was not monitored for long time.
I understand this. Thank you for the help.