Pass direction and Relative orbit


I would like to ask you why Sentinel-1 has two relative orbits for first pass direction and only one relative orbit for second pass direction.

I was watching some scenes and seen this principle. E.g. Descending pass direction was changing relative orbit no. 124 and 22, while ascending has only no. 73 or another place has relative orbit no. 73 and 146 for ascending and no. 22 for descending pass…

So Why is that? What is the principle behind this…

Thank you!!!

Your question is not fully clear but the S-1 is described here:


I will try it go give it another way. Simply, what I am asking is how many relative orbits (passes of satellites with monitoring) can be over one specific place (in Europe). I would say two. One pass for ascending mode and one pass for descending mode. However, I was observing that same places have three relative orbits (three different passes) and I am asking how it is possible? I don’t see the answer in links which you have sent it to me…

Thank you!

Hi, For our site in the SE UK, there are 4 possible S1 IW images per cycle. There are 2 ascending and 2 descending. For the 2 ascending, our site is imaged at different range (across-track) locations in the 400 km IW swath (and the same for the 2 descending images). If you open an Google Earth kml file i n the second link above, it should become clearer why a given site is imaged several times for orbit cycle.


Aaaaa great I see it now! The Google Earth helped a lot!

Thanks Peter!