Sentinel-1 relative orbit offset changed for 1C?

Microwave Toolbox
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I have been computing the relative orbit of Sentinel-1 scenes using an offset. For S1C for example:

(abs_orbit - 172) % 175 + 1

As of early July (around 09/10) however, that formulare no longer yields correct results. I assume it is related to the news item here: Sentinel-1D user data opening and future plans | Copernicus Data Space Ecosystem about planned, changed orbit constellation.

My question is: Is that somewhere documented when exactly the change took effect and from which dates products were delivered with the new orbit constallation?

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Dear Stefan,

A few precision.

The relative orbit numbering didn’t change. The same relative orbit numbering is valid after/before the change of orbital node. As an example, the relative orbit #n represents the exact same ground track after and before the change.

What has changed is the relation between the absolute orbit numbering and the relative one.

The usage of a formula is however questionable as the two numbers (absolute and relative) are annotated in the manifest file (at least).

The change of orbital change of S-1C took several weeks. There have been more recent news on that:

Basically any S-1C data from the 24/06 are in the new configuration and would require a new mapping.

If you need the exact date from where a new formula is needed, you may want to use the last record of the S-1C orbit scenario file:

https://opensf.esa.int/Repo/PUBLIC/DOCUMENTATION/MISSION_DATA/ORBIT_SWATH_DATA/SENTINEL1C/OSF/S1C_OPER_MPL_ORBSCT_20241206T003425_99999999T999999_0011.EOF

I need to further check if a note was generated/ published on that which imho is not necessary as the mapping exist on the metadata.

BTW : the formula to find the new offset is
np.mod(abs_orbit - rel_orbit + 1, 175)

Nuno Miranda

Sentinel-1 Mission Manager