The program l1agen_seawifs needs a file called elements.dat to calculate the navigation information that is included in the L1A output product. The data in elements.dat are orbit position and velocity elements produced by l1agen_seawifs, using onboard GPS data and a high order orbit propagation model, and are used to meet navigation accuracy (goal is 1 pixel). The elements.dat file is needed as input to navigation algorithms in order to initialize the GPS filtering methods in l1agen_seawifs.
To obtain the best navigation, users should download the most recent version of elements.dat from the oceans.gsfc.nasa.gov ftp site every 2 or 3 days if l1agen_seawifs is run regularly. If l1agen_seawifs is run on an occasional basis, the elements.dat file should be downloaded before running the program. The most recent elements.dat file may be used for any previously collected L0 data.
Running l1agen_seawifs will automatically update the elements.dat file.
If l1agen_seawifs is run on a daily basis, a fairly accurate elements.dat file
can be maintained. However, it is still recommended to download elements.dat
every 2 or 3 days since it is derived using a larger number of GPS data and
may incorporate occasional navigation corrections. (Users will be notified of
any navigation corrections.)
The elements.dat file is available from:
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