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by yxhss » Tue Mar 21, 2023 4:10 am America/New_York
Hi, I am new to SeaDAS and remote sensing. I am currently doing a project to predict chlorophyll a in Case 2 water .
So I realized Near infrared red band is very important parameter in detecting chlorophyll. I ran the l2gen and I have clicked the "products"tab to add the Rrs_865,but I still only got band 1-4 Rrs.
Is there any way i can get Rrs of Near infrared red band in l2gen ?If not, is there any way i can do ocean color atmospheric correction to get visible band and Near infrared red band?
One thing to keep in mind is that the NIR Rrs is that the atmospheric correction applied to OLI use the 865nm and 1609nm bands. The basic assumption for the atmospheric correction algorithm (well, the aerosol retrieval portion) is that the NIR bands have zero contribution from the water - thus the entire signal is from the atmosphere. We know this assumption breaks down in turbid waters, so there is a "NIR correction" to account for non-negligible water leaving radiance in the NIR. When you ask the code to return Rrs for the NIR bands, you are not getting a "measured" signal, but rather the result of the bio-optical model to estimate the NIR contribution to the total signal in these waters (which is removed from the signal to satisfy the basic assumption and retrieve the aerosol contribution).
If you change the processing to use 1609 and 2201nm for the atmospheric correction (by setting aer_wave_short=1609 and
aer_wave_long=2201), then Rrs_865 would be "retrieved" and not modeled. No guarantees on how valid the retreival would be though...
by yxhss » Thu Mar 23, 2023 3:27 am America/New_York
Thank you for your replying! I change the processing to use 1609 and 2201nm for the atmospheric correction and i can get NIR band.But i dont think the retrieval results are necessarily accurate compared with in-situ measurement data...