The brightness temperatures over the southeastern Libyan Desert (21¿--23¿N; 28¿--29¿E) from the NOAA-16 Advanced Microwave Sounding Unit-A (AMSU-A) were investigated for the months of January and March 2001. Angular distributions of the data from each month show remarkably stable patterns. The stable pattern of angular distributions can be potentially useful for postlaunch calibration and validation of the AMSU-A instrument, if a long-term trend of the angular distributions can be established. Angular distributions from the three window channels (channels 1, 2, and 15 with frequencies centered at 23.8, 31.4, and 89 GHz, respectively) and one near-surface sounding channel (channel 3 at 50.3 GHz) were simulated with a parametric model using the radiative transfer equation and a soil dielectric-emissivity model that generates the required soil emissivity as a function of zenith angle. The simulated results agree well with the data over the Libyan Desert area. The best-fit results indicate that radiation sensed by each channel comes from different thermal sampling depth and that these window channels could be used for temperature sounding in soils. The effect of spacecraft roll error on the angular distribution was also investigated. It was found that 1¿ roll error would produce a left-right asymmetry of 2.6 K in the angular distribution.