l2gen on LANDSAT 8,why I cant get NIR band?

Use this Forum to find information on, or ask a question about, NASA Earth Science data.
Post Reply
yxhss
Posts: 2
Joined: Wed Feb 01, 2023 4:36 am America/New_York
Answers: 0

l2gen on LANDSAT 8,why I cant get NIR band?

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?

Filters:

OB SeaDAS - xuanyang02
Subject Matter Expert
Subject Matter Expert
Posts: 657
Joined: Tue Feb 09, 2021 5:42 pm America/New_York
Answers: 1
Been thanked: 2 times

Re: l2gen on LANDSAT 8,why I cant get NIR band?

by OB SeaDAS - xuanyang02 » Tue Mar 21, 2023 4:57 pm America/New_York

I did l2gen on LC08_L1TP_114036_20190122_20200829_02_T1_MTL.txt, and got 7 bands including Rrs_865.

Make sure Rrs_865 or Rrs_nnn shows up as l2prod in the Parfile textArea in l2gen GUI

# PRIMARY INPUT OUTPUT FIELDS
ifile=/Users/*/Scenes/OLI/run/LC08_L1TP_114036_20190122_20200829_02_T1/LC08_L1TP_114036_20190122_20200829_02_T1_MTL.txt
ofile=/Users/*/Scenes/OLI/run/LC08_L1TP_114036_20190122_20200829_02_T1/LANDSAT8_OLI.20190122T015917.L2.OC.nc

# SUITE
suite=OC

# PRODUCTS
l2prod=Kd_490 Rrs_865 Rrs_vvv angstrom aot_865 chlor_a

Screen Shot 2023-03-21 at 4.47.07 PM.png
Screen Shot 2023-03-21 at 4.47.07 PM.png (93.23 KiB) Not viewed yet

OB.DAAC - SeanBailey
User Services
User Services
Posts: 1474
Joined: Wed Sep 18, 2019 6:15 pm America/New_York
Answers: 1
Been thanked: 5 times

Re: l2gen on LANDSAT 8,why I cant get NIR band?

by OB.DAAC - SeanBailey » Wed Mar 22, 2023 3:40 pm America/New_York

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...

Sean

yxhss
Posts: 2
Joined: Wed Feb 01, 2023 4:36 am America/New_York
Answers: 0

Re: l2gen on LANDSAT 8,why I cant get NIR band?

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...

Post Reply