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fnemina / pyOSOAA

pyOSOAA is a python interface for the Ocean Successive Orders with Atmosphere - Advanced (OSOAA) radiative transfer.
GNU General Public License v3.0
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How to compute whitecaps reflectance? #24

Closed ghost closed 5 years ago

ghost commented 5 years ago

I see your case study. Simple radiative transfer equation: 𝜌𝑡 = 𝜌𝑟 + 𝜌𝑎 + 𝜌𝑟𝑎 + 𝜌𝑔 + 𝑡𝜌𝑤. But no whitecaps reflectance included. How to compute whitecaps reflectance?

fnemina commented 5 years ago

OSOAA has no option to add automatically the reflectance for the whitecaps from the wind speed. However the parameter SEA.SurfAlb can be used to add a lambertian reflectance for the simulation.

This reflectance can be calculated using different models. This calculation can then by an input in the surfalb atribute of the SEA class in the pyOSOAA.

If you want I could create a method to do this automatically in pyOSOAA were you input the wind speed and get the corresponding surface albedo.

ghost commented 5 years ago

图片

fnemina commented 5 years ago

Hello Qiao Feng

You can the path reflectance from by subtracting the water leaving radiance from the toa radiance. I've made a jupyter notebook with an example for this.

PathReflectance.zip

You can also check this here.

For the diffuse transmittance, in the case where you ignore aerosols it can be approximated by the expression you wrote above. There taur is the Rayleigh Optical Thickness and the expression with the cosines is the total airmass for a plane atmosphere. It's basically the same that for the direct transmitance but the optical thickness is divided by 2. You can check it here in the paragraph after equation 6. Otherwise if you consider aerosol it is more difficult to calculate.

Best regards, Fran

ghost commented 5 years ago

Thank you very much. pyOSOAA is very useful. I love it.