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Change cloud maks for 250m products

Posted: Fri Jul 24, 2020 6:46 pm America/New_York
by jvaldezch
Hi forum, Is there a way to use L2gen and improve cloud mask for products at 250 m resolution?


Change cloud maks for 250m products

Posted: Mon Jul 27, 2020 2:16 pm America/New_York
by OB SeaDAS - knowles
Yes you can improve the resolution of the level2 flag mask "CLDICE", depending of course on which sensor mission you are using.  I'm guessing that you are referring to MODIS which contains 250m, 500m, 1000m bands and can be processed by SeaDAS at any of these resolutions.  The cloud flag/mask "CLDICE" is generated based on the surface reflectance band (rhos) of the sensor's longest NIR band (in the case of MODIS rhos_869).  This default band is 1km resolution.  To achieve a CLDICE mask at 250m, you can use the 250m 859nm band instead (rhos_859).  Here is an example of SeaDAS OCSSW command line operations to do this using the file A2010283180500.L1A_LAC:

$ A2010283180500.L1A_LAC

$ A2010283180500.L1A_LAC A2010283180500.GEO

$ A2010283180500.L1B_LAC

$ l2gen ifile=A2010283180500.L1B_LAC ofile=A2010283180500.L2_QKM_OC2 geofile=A2010283180500.GEO l2prod="rhos_859 rhos_869" resolution=250 cloud_wave=859 cloud_thresh=0.027 par=A2010283180500.L1B_LAC.anc

cloud_wave=859 is where you are specifying to use the 250m rhos_859 band.  l2prod is a list of your choice of products, keeping in mind that the standard OC products such as chlor_a are 1km.  You can also tweak the param "cloud_thresh" default threshold if you really wish to be more or less aggressive in the cloud flagging.  "cloud_thresh" is the threshold of the rhos band "cloud_wave" at which the CLDICE flag gets triggered.

The attached images show output results of this scene over Lake Ontario, showing band rhos_859, with mask on and with mask off.