Sentinel-1: Repeated data, separate files, different date and time

  • 26 April 2024
  • 6 replies
  • 4 views

I have found locations for which there is a morning pass and an evening pass with the opposite look angles (one ascending, one descending), but for every date that they occur, the contents of the files are duplicated. In other words, the EO Browser lists the two different files with two different date/times, but the underlying data is exactly the same, and is the data from the earlier morning pass.
I’m talking about Sentinel-1A and Sentinel-1B.
It’s even worse than that. If you search for Ascending only, you get the Descending data commingled with the Ascending data. There is no separating the two passes in EO Browser.


6 replies

Can you provide some more specific examples, e.g. with locations and dates and links to EO Browser, so that we can check?
Are you working on “AWS” or “EOCloud” dataset?

Boston, MA
Oct 12, 2019, 10:48 and 22:43
Sep 18, 2019, 10:48 and 22:43
Sep 6, 2019, 10:48 and 22:43
I retrieved data from both AWS and EOCloud.
Filtered on Asc and Desc, always get the combined set which you can see graphically, two overlapping rectangles with a clear stitch line. Can’t separate the data sets.

Also, I wanted to triangulate the interference, but you can see in the combined data set where the interference from the descending pass is chopped at the stitch line.

Let me clarify a little. The image data is overlaid for the later pass, and not necessarily “duplicated”. There is no way to access the imagery for the earlier (descending) pass. It’s true of EOCloud and AWS. The preview in EOCloud correctly shows the scanned region, and you can see, for example, the interference pattern from the tip of Cape Cod into the middle of the state, but when you display the imagery it always includes both passes and the descending pass is overwritten by the ascending data (I believe).

I’ve downloaded the SLC data. Just to complicate things further, I found that VV and VH were flipped (or something like that) in the 10:48 descending pass Oct 12. Regardless of the cause, clearly the VV and VH do not make sense in the Level-1 SLC. On the other hand, in EOBrowser the polarization’s look correct as can be seen in the portions of the descending pass that aren’t overwritten by the ascending pass. I’ll check the Level-1 GRD in the morning.

Now I understand the issue, thank you for that.
This is a consequence of the initial design of the EO Browser, which was based on the assumption that “there is rarely more than one acqusition on the same date”, which was true then, but no longer… The search functionality can seaprate between ascending and descending and if you follow the “link”, you can download relevant source files for ascending and descending. When switchng to visualizaiton however, EO Browser only sets the “date” and then the latest of the acqusitions is shown.
You can work around this issue if you use Sentinel Hub OGC service rather than EO Browser - there you can set more details and separate these two acqusitions in you favorite GIS tool.

I am not sure you will be able to do an interferometry as this usually requires the use of SLC, not GRD.

Yes, thank you for the response. No, you cannot do traditional phase interferometry from GRD, agreed. Thank you for pointing out the EO Browser behavior, that explains it. I do think the data was corrupt in the SLC, but I haven’t been able to revisit that file to prove it, so forget about that.

Lastly, most important for today, Sentinel-1B made an unscheduled collection over Boston yesterday, Oct 30. That strip is on the “12 day” schedule, how do I determine there will be a schedule change? In addition, Sentinel-1A made an unscheduled collection over New York City on Oct 23, on a descending pass that doesn’t even exist on the schedule for that region of earth. Not all the way to New York City, my mistake. But a collection over central Massachusetts that almost includes Boston, but nonetheless did indeed collect on my region of interest. A collection that does not appear in the recent past, perhaps ever, as far as I can tell. A schedule deviation. Where do I find these schedule deviation plans?

Never mind. I see the KML schedules. I’ve downloaded them before, but forgot. OK, so all questions answered.

Press on, keep flying.

Please contact Copernicus support (eosupport@copernicus.esa.int) for this question and share with this community the answer once you get it.

An alternative option is to reigster to notification service, which triggers the event every time a new product is ingested and you cross-check it against your AOI.

https://registry.opendata.aws/sentinel-1/

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