In a dual-source model, component surface temperature and are needed instead of one radiometric surface temperature used in a single-source model. Vegetation information such as leaf area index or fractional cover of vegetation is also needed. Neglecting the cavity effect in the canopy, the radiometric surface temperature can be related to component temperatures by a simple linear mixture model as the following (Norman et al, 1995 a):
e(AjTrJ(6 ,X) = fv(6)ev(A) Tv" +fs(6)es(X) T" (21)
where n 4 for spectral bands in A.=8~14|Lim and A,=10~12|.im ( Becker and Li, 1990), e, ev and es are the emissivity of the (vegetation + soil) mixture, vegetation and the soil respectively, 0 is the zenith view angle of the sensor, fv(9) and fs(0) are the fractions of vegetation and the soil in the field of view of radiometer when looking at the surface at zenith view angle (0), fs(0)=l-fv(0), is the soil fraction. fv(0) depends on the type of vegetation and the architecture of the canopy. Assuming a random canopy with a spherical leaf angle distribution (Norman et al, 1995b), where LAI is leaf area index. For nadir view, fv(0) is the fractional vegetation cover, fc. Usually, a radiometer measure surface brightness temperature Tbo(A, ,0) and Eq. (21) can be rewritten as
When the surface brightness temperature TB0(A, ,0) at two or more view angles can be obtained from the measurements of radiance, it is possible to derive Tv and Ts from TB0(^ ,0) through Eq.(23).
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