I’m a new Sentinel user and I’m confused about S1A orbitology. Pulling IW SLC data from the Alaska Satellite Facility portal (https://vertex.daac.asf.alaska.edu) for a small ROI, I’m seeing both Ascending and Descending orbits for the same Path Number, with similar-looking ground footprints. I can see how an orbit that precesses would hit a spot on the ground with alternating Ascending/Descending orbits, but wouldn’t the footprints look different, with the rhombuses (rhombi?) skewed to opposite directions?
Below are the ground footprints for two IW collects in September 2015 (spaced 12 days apart), along with the SLC file names. The 9-17 collect is marked as Descending in the ASF metadata CSV file, while the 9-29 collect is marked Ascending. I’d expect one of these to be horizontally-flipped with respect to the other, but that’s not the case. Can anyone explain or point me to the documentation that explains why this is the case?
Data received prior to 12/9/2015 may have an incorrect orbit direction shown in the search results granule description. A fix for this was delivered at that time, so all newer data will have the correct direction in the description. The older data will have to be re-ingested for the fix to take affect, but this hasn’t been done yet.
The orbit direction for a granule is correctly rendered on the map when you mouse-over the search results. (Ascending orbits are oriented lower right to upper left and descending orbits upper right to lower left.) And the correct orbit diction is described in the XML Metadata file.
I hope this helps and I apologize for the confusion.
I appreciate Bill’s prompt reply and everyone’s comments here.
