I see a lot of you guys are asking about sentinel orbits in sarproz, and I feel the necessity to explain it a bit better.
Q: What are the orbits used for Sentinel?
A: First of all, there are three types of sentinel orbits.
The first is the built-in orbits that comes with your sentinel image. This one is the least precise orbit and is strongly advised NOT to use.
The second and third orbits requires external orbits files. The second is called restituted orbits, and the third is called precise orbits.
Restitute orbits come with a lower accuracy with a std of around 10m. However restitute orbits are published in real-time, meaning you can download the restitute orbits for sentinel just a couple of hours ago.
Precise orbits are much more accurate. The std is around 2.5m. The precise orbits are only published after 20 days. This means, if today is the 20th of August then the most updated precise orbits you can get is the 1st of August.
Q: What do I need to do to select Sentinel Orbits?
A: Nothing. Sarproz will automatically select orbits. For images in the recent 20 days, the software will automatically download restitute orbits from our ftp site and read it. For images older than 20 days, the software will automatically download precise orbits. In the case where there’s no internet connection, or our two ftps are down, the software will read the built-in orbit files.
Q: Where are the orbit files downloaded to?
A: In the same directory you placed your processing sentinel data, there will be a folder called ORBITS. The downloaded orbits will be stored in the following convention: ORBITS/S1A(S1B)/yyyy/mm/aux_poeorb(aux_resorb)/*.EOF. aux_poeorb stores the precise orbits and aux_resorb stores the restitute orbits.
Q: What if my PC does not have internet connection or cannot access your ftp site?
A: You can manually download the orbit files and stores in the corresponding folder as described above. The way sarproz does is to scan the local folder for orbit files first. If no corresponding orbit files can be found locally then the software will go online to download the files.
Q: If one image takes the restitute orbits now, when after 20 days the precise orbits become available, will the software automatically update it?
A: Only if you re-run the whole SLC data import process.
Q: How do I know what orbit files are used for each image data?
A: Currently, you can assume that all images within 20 days use restitute orbits and all older images use precise orbits, unless you do not have local orbit files, nor do you have internet connection to download orbit files. Very soon we will add a message in the log in your data import process to tell you which kind of orbits will be used in your data processing step.