Sentinel 1 relative orbit from filename


#1

Apologies in advance for the question not being directly SNAP or S1tbx related. I need to filter some filenames before parsing the files into SNAP.

I came across a little formula (https://scihub.copernicus.eu/news/News00014) to calculate the relative orbit number from a Sentinel-1 product names absolute orbit number:

Relative Orbit Number = mod (Absolute Orbit Number orbit - 73, 175) + 1

I find this works for Sentinel-1A but not Sentinel-1B. For example both with relative orbit number 30:
S1A_IW_GRDH_1SDV_20170909T175748_20170909T175813_018302_01EC88_98A1
mod (018302 - 73, 175) + 1 = 30
S1B_IW_GRDH_1SDV_20170903T175659_20170903T175724_007231_00CBEF_874B
mod (007231- 73, 175) + 1 = 159

I would rather do this calculation on the filename rather then read from metadata files if possible. Does anyone now if there is a formula that works for Sentinel-1B?

Many thanks in advance


S1 slice number from filename?
TopSAR coregistration questions (help!)
#2

Hi, The equation Relative Orbit Number = mod (Absolute Orbit Number orbit - 73, 175) + 1 is only applicable to S1-A. The corresponding equation for S1-B is

Relative Orbit Number = mod (Absolute Orbit Number orbit - 27, 175) + 1

so for your S1-B example, orbit 7231 gives a relative orbit of 30 as expected.


#3

Thank you Peter, works perfectly.
Would you mind linking your source if you have one?


#4

The source of these equations is myself!! I am a member of the Mission Performance Centre and so I derived these equations as part of my work.


#5

haha ok that works for me! :stuck_out_tongue:
Sorry wasn’t questioning authenticity was just curious if I poorly googled and/or if it is publicly documented!


#6

Thank you for that formula, Peter. Do you know where I might download a map or image identifying the Sentinel-1 relative orbits? I’ve scoured the internet but have come up empty-handed.


#7

Hi, I am not aware of a map as such. However you can determine the relative orbit of planned acquisitions such as shown in the image below. The Google Earth planning files can be found at https://sentinel.esa.int/web/sentinel/missions/sentinel-1/observation-scenario/acquisition-segments. Clicking on a given acquisition will give the details window including the relative orbit.


#8

Thank you, Peter. I’ll look into assembling a map from the planning files.


#9

Peter and others,

This is also a non-snap related question but I’m not sure where else to look. I am interested in understanding the relative orbit number a bit better. To try to control incidence angle in my analysis as much as possible I’m starting with an analysis only looking at images from the same relative orbit number. Oddly, this results in a 6 month gap of images in late 2015 (S1A only, clearly) and another gap in early 2017. Is there a reason why images from a particular relative orbit would be missing for large chunks of time over a given area? Is there a better parameter to use to filter for coincident or mostly coincident images over time?
Best
Corinne