Coherence steps between sub-swaths

Microwave Toolbox Problem Reports
#1

Hi all,

During coherence processing I’ve come across a strange issue where the coherence has a noticeable step between 2 sub-swaths of the same image (see screenshots below) which occurs in both the VV and VH polarisations.

snap_cc_wide
snap_cc_wide1383×397 294 KB

snap_cc_zoom
snap_cc_zoom675×563 248 KB

The processing chain used to produce this image (large graph for illustrative purposes, I’ve been processing in smaller steps for efficiency), with TOPSSplit done separately in advance:

snap_graph

Removing the flat-earth phase correction during coherence estimation as suggested in another post, does not fix this issue. Any suggestions would be very helpful!

Thanks

#2

in case your data consists of several bursts, I recommend applying Enhanced Spectral Diversity after the BackGeocoding. Can’t tell if this causes the differences between the sub-swaths, but at least you will get better coregistration in general.

#3

Thanks for your reply, unfortunately applying ESD doesn’t fix the issue, there is still a step in coherence between the sub-swaths

#4

@estebanaguilera do you have an idea what could cause these differences?

#5

Maybe try the ThermalNoiseRemoval operator?

#6

Hmm thermal noise correction is a scalar correction - how could it improve coherence?

#7

@mengdahl, indeed, if the correction applies a (spatially) smooth scaling, it shouldn’t have any noticeable effect.

I can try to reproduce the problem. @cmoore_ne would you mind sharing the product names and graph file (xml)? Feel free to anonymize the paths.

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#8

Thanks all for giving this your attention! @estebanaguilera, product names & details below:

S1B_IW_SLC__1SDV_20200526T175757_20200526T175824_021756_0294AB_8B38
S1A_IW_SLC__1SDV_20200601T175825_20200601T175852_032827_03CD65_34CF
S1A_IW_SLC__1SDV_20200601T175850_20200601T175917_032827_03CD65_D271

Using S-1 Slice Assembly to merge the 20200601 scenes, then TOPS Split to extract the IW2 and IW3 sub-swaths (bursts 1-9 for 20200526, bursts 6-15 for 20200601). The split SLC images then read into the xml graph (without ESD so the processing will be the same as for the images above):S1_proccessing_3-8.xml (8.1 KB)

#9

I checked the xml file and I can see that different parameters were used to compute the coherence:

<cohWinAz>3</cohWinAz>
<cohWinRg>10</cohWinRg>

<cohWinAz>2</cohWinAz>
<cohWinRg>10</cohWinRg>

Could you try using the same values?

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#10

That’s fixed it, thank you! I was just using the default values for square pixel, and didn’t check that it was giving different window sizes…

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