Understanding RAW Bursts

Microwave Toolbox
1

Hi everyone,

I’m just getting started with Sentinel-1 IW-mode RAW data. After unpacking an RAW product, my .SAFE folder contains these .dat files of very different sizes. I am assuming each file corresponds to a sub-swath, but I’m not clear on:

  1. What exactly is inside each .dat file? Is each file one “burst,” or does it hold multiple bursts for that subswath?
  2. Why do the file sizes vary so much? Does it reflect number of bursts, or something else?
  3. How can I pick the right bursts or files to reconstruct just my area of interest? Is there a recommended way to read the annotation XML to find burst offsets and timing?

Any pointers on how to interpret these .dat files, map bursts correctly, and choose which data to process first would be much appreciated. Thanks!

Screenshot 2025-05-27 at 7.51.36 PM
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2

Hei

See this - https://sentiwiki.copernicus.eu/__attachments/1673968/COPE-GSEG-EOPG-TN-15-0005%20-%20Sentinel-1%20Level-0%20Data%20Decoding%20Package%202020%20-%201.3.pdf?inst-v=96021aea-734a-44d2-9ca8-2228c7de7290

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As you can see there are ‘annot’ and ‘index’ described for those files. I’d recommend to follow the links given in this topic - Sentinel-1 TOPSAR (IW) Level-0 Data Processor There are preprocessing, decompression etc functionality already developed.

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3

To make it fast:

  • the .dat file contains the information -source packets- from the SAR instrument. The SAR processing can be done only with this one, if wanted
  • the -index.dat file is added by the ground segment as a helper. Being the Sentinel-1 FDBAQ encoding being of variable bitrate, it implies to read the .dat file sequentially. The index files gives you pointers to the .dat file that allows to skip source packets (every second from memory but not sure ). This is helpful if you seek for extra efficiency in the I/O like we were doing at the time of developing the processor.
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