Greetings,

I want to generate an L2 image in Seadas from an Aqua L1A file that I ordered via the 'Level 1 and 2 Browser' from the the main OceanColor Web page.  The SeaDAS L2 generation code needs and an Aqua L1B file, and the L1B generator needs a geo file but I didn't receive any geo file with my order - unless it was one of files in the 'ancillary_files' directory.  

Where do I get the geo files, or do I already have them (I downloaded everything in the ancillary directory)?   I couldn't find any info on MODIS Aqua L2 generation on the Seadas site.

Thanks for the help.
Tim

Tim,

Rather than distribute geolocation files, which are as large as the L1A files themselves, we distribute the attitude and ephemeris files from which geolocation can be generated.  The way seadas is currently set-up, you must have the appropriate att/eph files in the appropriate directory, and then you can run:

  process->MODIS->Aqua->geolocate 

and

  process->MODIS->Aqua->aqua_l1bgen

to get the geolocation and L1B files required for processing to L2.  You can check the HELP button for the above processes for further instruction.  The tricky part is getting the right att/eph files into the right place so seadas can find them.  They are all available from:

    ftp://oceans.gsfc.nasa.gov/MODISA/ATTEPH/

or in monthly tarball form from:

    ftp://samoa.gsfc.nasa.gov/seadas/seadas/   

in files called seadas_modisae*.tar.gz.  If you grab a tarball and extract it into the top-level seadas directory, the files will go into the correct seadas subdirectory, which is:

    seadas/data/modisnpp/atteph/yyyy/ddd/   where yyyy and ddd are the year and day number

This may seem a little cumbersome, but the advantage is that you don't need to store geolocation files, which are large (and may change), or L1B files, which WILLchange as the calibration evolves. In production, we regenerate geolocation and L1B every time we reprocess an L1A to L2, and then we discard the GEO and L1B files.

I have talked to the SeaDAS lead (Mark) and he will work on providing some instruction on the website for this process.

-- Bryan

P.S.:  Nicolai Tesla is alive and well, and living in a Volcano in South America.

Tim,

If you go to:

http://seadas.gsfc.nasa.gov/doc/geolocate/geolocate.html

and

http://seadas.gsfc.nasa.gov/doc/aqua_l1bgen/aqua_l1bgen.html

you will find a little more information on attitude and ephemeris
files and aqua l1bgen processing.

Regards, Mark