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what‘s the unit of rayleigh reflectance #178

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bodhifan opened this issue Feb 12, 2023 · 2 comments
Open

what‘s the unit of rayleigh reflectance #178

bodhifan opened this issue Feb 12, 2023 · 2 comments
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@bodhifan
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bodhifan commented Feb 12, 2023

Hi, thanks for your excellent work. I have a question: what's the unit of Rayleigh reflectance?
Here is the sample code to get Rayleigh reflectance:

from pyspectral.rayleigh import Rayleigh
viirs = Rayleigh('Suomi-NPP', 'viirs')
import numpy as np
sunz = np.array([[32., 40.], [31., 41.]])
satz = np.array([[45., 20.], [46., 21.]])
ssadiff = np.array([[110, 170], [120, 180]])
refl_cor_m2 = viirs.get_reflectance(sunz, satz, ssadiff, 'M2')
print(refl_cor_m2)
[[ 10.45746088 9.69434733]
[ 10.35336108 9.74561515]]


from the results, It is mostly like irradiance contributed by Rayleigh scattering.

@adybbroe adybbroe self-assigned this Feb 15, 2023
@adybbroe
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What you calculate is a reflection - the contribution to the observed due to Rayleigh scattering and aeorosl absorption. The units are in percent (%).
I realize that is not overly clear, but can be guessed from the documentation here though:
https://pyspectral.readthedocs.io/en/latest/rayleigh_correction.html

We have not come around to use pint (https://pypi.org/project/Pint/) or something like that yet, which would make this explicit.

@bodhifan
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Thanks for your reply. Another question. Where is it to set aerosol parameters if Rayleigh correction relates to aerosol? Such as aerosol optical depth.

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