How to derive Lw from Rrs product

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guorz
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How to derive Lw from Rrs product

by guorz » Mon Jun 27, 2022 5:50 am America/New_York

I wanna derive Lw from Rrs product, found this formula on Rrs algorithm description page:
Rrs(λ)=(Lw(λ)/(F0fscos(θs)tds)fb(λ)fλ
F0 = extraterrestrial solar irradiance (Thuillier et al. 2003)

fs= adjustment of F0 for variation in Earth-Sun distance

fb = bidirectional reflectance correction

fλ = correction for out-of-band response

but I have no idea how to get fb and fλ, any idea?

Thanks!
RG

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OB General Science - guoqingw
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Re: How to derive Lw from Rrs product

by OB General Science - guoqingw » Mon Jun 27, 2022 1:40 pm America/New_York

Hi RG,

Do you mind sharing a little detail about why you want to get Lw? If you meant to obtain the nLw (normalized water-leaving radiance, some products use it as standard L2 data), there is a simple equation: nLw = Rrs*F0, and you can find F0 here: https://oceancolor.gsfc.nasa.gov/docs/rsr/rsr_tables/

Please let us know.
Guoqing

guorz
Posts: 16
Joined: Wed Apr 19, 2017 1:22 pm America/New_York

Re: How to derive Lw from Rrs product

by guorz » Mon Jun 27, 2022 10:49 pm America/New_York

Hi Guoqing,

Thanks for your anwser!

The reason why I want to get Lw is I'm trying to calculate Lt(the formula below), and will calculate Lr,La,Lg,Lwc through corresponding model and look-up table, but unable to get in-situ Lw data for my study area, so I'm thinking about derive it from Rrs, seems that I should use Lw here,right?

L_t (λ)=L_r (λ)+L_a (λ)+T(λ) L_g (λ)+t(λ) L_wc (λ)+t(λ)L_w (λ)

Thanks,
RG

OB General Science - guoqingw
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Re: How to derive Lw from Rrs product

by OB General Science - guoqingw » Tue Jun 28, 2022 1:10 pm America/New_York

The easy way to get Lw is using the l2gen of SeaDAS. Other parameters including brdf can also be obtained from l2gen.
Guoqing

guorz
Posts: 16
Joined: Wed Apr 19, 2017 1:22 pm America/New_York

Re: How to derive Lw from Rrs product

by guorz » Tue Jun 28, 2022 9:53 pm America/New_York

got it thanks!

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