2

The file name convention for the Sentinel-1 mission is MMM_BB_TTTR_LFPP_YYYYMMDDTHHMMSS_YYYYMMDDTHHMMSS_OOOOOO_DDDDDD_CCCC, where

  • MMM: mission identifier (S1A, S1B)
  • BB: mode/beam (IE/EW/WV)
  • TTT: product type (SLC, GRD, OCN)
  • R: resolution class ((F)ull, (H)igh, (M)edium)
  • L: processing level (1,2)
  • F: product class ((S)tandard, (A)nnotation)
  • PP: polarization (SH, SV, DH, DV)
  • YYYYMMDDTHHMMSS: start time / end time
  • OOOOOO: absolute orbit number
  • DDDDDD: mission data take ID
  • CCCC: unique product ID

Is there any way to quickly find out whether the orbit was ascending or descending from the absolute orbit number?

3

For the quick and dirty way to find out if it is ascending or descending, it is easier to look at the start (or end) time. For instance, in Belgium, you get the ascending images at around 5 PM and the descending ones at around 6 AM. So, in the string YYYYMMDDTHHMMSS, if the first H is 1, I know for sure that the image has been taken on an ascending orbit. The time is in GMT, so you need to adjust it based on the timelines if you are not at the same longitude.

If you want to make sure, you can use gdalinfo to open the safe file

gdalinfo yourS1folder.SAFE/manifest.safe 

and look at the ORBIT_DIRECTION in the metadata

EDIT: if you know roughly where you are, some regions have specific acquisition plans with ascending only, descinding only or both, as you can see from the image below from ESA sentinel website, valid since february 2018.

enter image description here

  • Great solution, but you still need to know when the satellite passes your ROI in which orbit. Let's see if there is a more automatic solution applicable if you have only the file name, no metadata. – Michael Jun 20 '18 at 13:03
  • it is true that it is ROI dependent, but the sentinels 1 are sun synchronous, so if you know the longitude, you can guess the ascending and descending times with enough precision. Also note that some parts of the world are only capture in ascending or descending orbits. – radouxju Jun 21 '18 at 5:26
0

You can't get ascending or descending from the orbit number alone: One relative orbit aka "path" on https://vertex.daac.asf.alaska.edu can be both ascending and descending.

Below are screenshots from the ASF website of path 85 on the same day: first ascending, then descending. While I'd also really like a way to look at the filename and get asc/desc, it might require some extra ad-hoc ways to look at the orbit and time of acquisition (like mentioned above) to get the direction.

Ascending path 85 Descending path 85

I was also looking for the answer for a long time, then finally decided to download a bunch of the .xml info files for some paths to find the pattern. I saw that each path had both ascending paths and descending- I guess ESA labels one full polar revolution of the satellite around Earth as an absolute orbit path, so that once it goes over the north pole (maybe south pole?) the orbit number is the same but direction flips from ascending to descending.

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