Sentinel-1 SLC product shift

Microwave Toolbox
1

I am downloading few sentinel-1 SLC product for InSAR analysis.

As I search the CDSE catalogue for best matches of SLC products, covering the same location and having the same orbit-flight-direction I can see that closest products could be of S1A and S1C satellite platforms.

Consecuently the corresponding 3 Subswats of two products have a considerable Nort-South shift. Now Lets say I want to use IW1 of both products and my AOI covers 5 Bursts. How should I select them and prepare them for co-registration?

SLC-shifts
SLC-shifts580Ă—448 92.9 KB

2

Topsar split operator has parameters that allow you to specify the bursts index or wktAoi as well as polarisation. It will extract the subswath and bursts inside the selected subswath, then you can perform your other operations on the extracted subswaths. WktAoi is probably the parameter you would like to use, as it will automatically selects the bursts from a subswath, so you do not need to check manually which bursts covers your area of interest. I do not see that parameter in the UI - I usually run the graph from the XML file, so it looks something like this:

<node id="TOPSAR-Split">
  <operator>TOPSAR-Split</operator>
  <sources>
    <sourceProduct refid="Read"/>
  </sources>
  <parameters>
    <subswath>IW2</subswath>
    <selectedPolarisations>VV</selectedPolarisations>
    <firstBurstIndex>1</firstBurstIndex>
    <lastBurstIndex>9999</lastBurstIndex>
    <wktAoi>POLYGON((21.0 52.1, 21.3 52.1, 21.3 52.3, 21.0 52.3, 21.0 52.1))</wktAoi>
  </parameters>
</node>
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3

Thanks for sharing this. Using wktAoi to select the bursts automatically sounds much easier than checking them manually. The XML example is helpful too, especially for anyone running the processing graph outside the SNAP UI.

4

Thanks.

Indeed modifying the .xml file is the most flexible way to take.

Here in this snippet I can see that “firstBurstIndex“ and “lastBurstIndex” are set to 1 and 9999.

The number of Bursts in each Subswat is only 9. Therefore when setting those values to 3 and 7, I could successfully select the 5 middle Swats of IW2. Not sure why such large range is set here in this example?!

As you mentioned using wktAOI, requires that this polygon to be defined in advance and to be given as an input variable to the graph.

5

Glad that it helped! I set “firstBurstIndex“ and “lastBurstIndex” to 1 and 9999 because it is just placeholder values since the operator will ignore these values and use AOI to select the correct bursts for processing.

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