Add Orbit field in the EO extension

[p3dr0]

This field is defined as:

• orbit (or orbit_number) : number : A number identifying the acquisition orbit

Use cases of how orbit would be used to be added here.

[m-mohr]

In the Copernicus Open Access Hub it is one of the primary fields for searching. So I'm +1 to add it to EO and SAR extension (and later put it in something like a sat extension, which also extracts platform, constellation, instrument etc.)

One thing to think about is relative vs. absolute orbit number.

[p3dr0]

I remember using the relative orbits a while ago with ENVISAT MERIS and AATSR but now with Sentinel I mostly use orbit number and direction (ascending and descending)

[m-mohr]

We added absolute_orbit and pass_direction to the SAR extension, therefore I think this is solved?