Earthdata Forum

Hi all,

I am currently working on a long term time series with MODIS nFLH and ocean color. I am using this parameter to calculate the quantum yield of fluorescence. For this I need the senz data product.
Since this is not a standard product I am processing from L1.
I am happy to download all the standard OC products I need at L2/L3, but was wondering if there is anyway to speed up the L2gen process for senz. My assumption was that doing L2gen for senz alone vs together with OC would not change the speed as the rate limiting step is the atm corrections.

After talking with Bruce Monger he suggested asking here if I can turn off the atm correction in l2gen and just output senz.
Is this something I can possibly do?

Thank you!
Jonathan Sherman

Hi Jonathan,

   You may try setting aer_opt to -99 (AERNULL) in the input .par file. The setting will skip the aerosol calculation, which takes most of the atmospheric correction time.  Please let me know if it works.

Best,
Minwei

Thank you Minwei.
I will give it a try soon and let you know.
Jonathan

Setting atmocor=0 will skip the atmospheric correction.  If all you want in your L2 file are geometries, this will be the most efficient way to process to L2.  However, if all you need is access to the geometries, there's no need to use l2gen.  The MODIS GEO file has it..all l2gen would do for you is copy that to a L2 formatted file.

Sean

Hello,
   I have a question about  MODIS L1/L2 data. Is it possible to use MODIS 250m data to derive L2 (Rrs, Rhot, Ch-a, and SST)?  Would SeaDAS/OCSSW/l2gen work for that?
Thank you.
Amita

Hi Amita,

   MODIS 250m data alone doesn't work to derive L2. You may need 1000m and 250 m data to generate L2 with a spatial resolution of 250m.

Best,
Minwei

Also, see this page.

https://oceancolor.gsfc.nasa.gov/docs/modis_hires/

Norman

The MODIS instruments only contain 2 bands at 250m (645nm and 859nm).  These are not blue/green or IR bands so it rules out the SST and chlor_a algorithms.  You do have options regarding fine tuning atmospheric correction.  You can use l2gen to process the 645 and 859 band products to 250m (rhot_645, rhot_859, rhos_645, rhos_859, Rrs_645, and Rrs_859, etc.).  If you process chlor_a to 250m using l2gen you will get an interpolated result for this product.

Danny

Thanks Danny.
Amita