Atmospheric correction for ATSR thermal channels single channel method

Space-borne radiometers measure brightness temperature at the top of the atmosphere, TB(A,, 0), not the surface brightness temperature, Tbo(^ ,0). At wavelength and zenith view angle the radiances measured by the radiometers on the satellite are from three contributions: (1) emittance from the land surface that is attenuated by the atmosphere between the surface and the sensor, (2) the downwelling atmospheric emittance to the surface and then reflected by the surface to the sensor, (3) upwelling atmospheric emittance. With this concept, the radiative transfer equation in thermal bands can be written as

B(Tb(A,,0)) = e(X ,8)B(Trad(A. ,Q))x(k 6) + UJikV + W W.6) (24)

where B is Planck function, e (X ,0) is the surface emissivity, x( X,Q) is the total atmospheric path transmittance, IatmT(X,0) is the upwelling atmospheric emittance, IreA) is reflected downwelling atmospheric emittance by the sur face. Neglecting the reflected downwelling atmospheric emittance, Eq.(24) can be rewritten in terms of brightness temperature

One can get the corrected brightness temperature at the surface, TBo(^,Q), by inverting the Planck's function B(TBo(A,,0)) in Eq.(25), knowing the total atmospheric path transmittance and the atmospheric emittance at different wavelengths and zenith view angles which can be computed using a radiative transfer model such as MODTRAN.

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