Modeling angular effect in AVHRR brightness temperatures over black surface

Brightness temperatures t_i(m) in AVHRR channels i=3 (3.7 μm), 4 (10.8 μm), and 5 (12 μm) were calculated for a variety of viewing directions 1⩽m⩽3 (m=secθ; θ is the satellite zenith angle), and a set of surface-atmosphere conditions (-2⩽t_s⩽35°C, 0.2⩽W⩽5.4 g·cm^-2 ; t_s and W are the surface temperature and the integral-water vapor amount). Assumption of a black surface is used to analyze the atmospheric effect and provide a background for further incorporation of the surface reflectance. t_i(m) are approximated with the polinomial t_i(m)=a₀ⁱ +a₁ⁱ·m+…+a_jⁱ ·m^j (j=1, 2, and 3, for linear, quadratic, and qubic fits, respectively). The information content of the fit parameters is analyzed