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Up Topic Products and Algorithms / Satellite Data Products & Algorithms / Rayleigh corrected reflectance (locked)
- By wtaicken Date 2007-10-31 14:49
Has anyone derived MODIS rayleigh corrected reflectance using Seadas. It was suggested I use MODIS values of Lt - Lr to obtain a rayleigh corrected radiance, and then convert that to reflectance. Does that sound feasible?

Any advice gratefully received.

regards

Will
- By seanbailey Date 2007-10-31 15:01
Use rhos. 

MSl12 has an output product, rhos_nnn (where nnn is wavelength - e.g. rhos_412)
This product is TOA reflectance minus Rayleigh reflectance.

Sean
- By wtaicken Date 2007-11-01 06:20
Hi Sean, thanks for that. I did get some seadas feedback previously about rhos_nnn ..........."There is no product that is simply Rayleigh-corrected reflectance.
The rhos product is quasi-surface reflectance (surface + aerosol)."

So I wasn't sure if it was atmospherically corrected or not. That was why I was initially deriving Lt-Lr.

Can you clarify, thanks

regards

Will
- By seanbailey Date 2007-11-01 11:36
Will,

What do you mean by  'atmospherically corrected'?
Removing Rayleigh is a partial atmospheric correction, so in that
sense Lt-Lr is 'partially' atmospherically corrected.
 
As for rhos, it does not remove aerosol reflectance, but does make
adjustments for various atmospheric transmittances, hence the
seadas group's remark that it is a  quasi-surface reflectance.

Here's what it is :

    rhos = PI / F0 / mu0  * (Lt / tg_sol / tg_sen - Lr)  / t_sol / t_sen / t_o2 / t_h2o

   (the t's are the various transmittances, mu0 is cosine solar zenith, F0 is extraterrestiral irradiance)

If you want a product that is simply total reflectance minus rayleigh reflectance, you'll need to
make your own ala:

    rhot-r = PI / F0 / mu0  * (Lt - Lr) 

Sean
Up Topic Products and Algorithms / Satellite Data Products & Algorithms / Rayleigh corrected reflectance (locked)

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