Aerosol retrievals are made operationally at NOAA/NESDIS from the Advanced Very High Resolution Radiometer (AVHRR) onboard the afternoon National Oceanic and Atmospheric Administration (NOAA) satellites, and experimentally at NASA/Langley Research Center from the Visible and InfraRed Scanner (VIRS) onboard the Tropical Rainfall Measuring Mission (TRMM) satellite. The two radiometers are nearly identical in their scanning geometry, and the relative simplicity of the measurement scheme. In particular, both instruments have only two spectral channels (out of total five), useful for aerosol studies. These are centered at l₁=0.63 and l₂=0.83 mm for AVHRR/2, and l₁=0.63 and l₂=1.61 mm for VIRS. The two parameters being retrieved are aerosol optical depth in the two channels, t₁ and t₂, and Angstrom exponent derived therefrom as a=-ln(t₁/t₂)/ln(l₁/l₁).

This paper describes recent status of the retrievals, and remaining problems. The emphasis is on the statistical analyses of large volumes of satellite data. Satellite retrievals are quality controlled, and examined if physically realistic and self-consistent. Retrievals of t₁ and t₂ are checked if spectrally coherent. Retrievals of a are tested if reveal a 1/t trend, and increase in scatter, indicative of systematic and random errors, respectively. Probability distribution functions are shown to be log-normal for t₁ and t₂, and normal for a. Parameters of the respective fits in the VIRS and AVHRR data are compared. Information content of satellite-derived size parameter, a, is analyzed by introducing a signal-to-noise ratio (SNR), h. The SNR is shown to be well approximated as h~t/t_o. The critical values of t_o, at which signal in a is comparable to its noise, are compared for the two different sensors.