Sensitivity and information content of aerosol retrievals from the Advanced Very High Resolution Radiometer: radiometric factors

The sensitivity of aerosol optical depths tau(1) and tau(2) derived from the Advanced Very High Resolution Radiometer (AVHRR) channels 1 and 2, centered at lambda(1) = 0.63 and lambda(2) = 0.83 mum, respectively, and of an effective Angstrom exponent et, derived therefrom as alpha = -In(tau(1)/tau(2))/In(X,/(2lambda)), to calibration uncertainties, radiometric noise, and digitization is estimated. Analyses are made both empirically (by introduction of perturbations into the measured radiances and estimation of the respective partial derivatives) and theoretically (by use of a decoupled form of the single-scattering approximation of the radiative transfer equation). The two results are in close agreement. The errors, Deltatau(i) and Deltaalpha(i) are parameterized empirically as functions Of tau(i), radiometric errors, and Sun and view geometry. In particular, the a errors change in approximately inverse proportion to T and are comparable with, or even exceed, typical alpha signals over oceans when T < 0.25. Their detrimental effect on the information content of the AVHRR-derived size parameter gradually weakens as T increases. (C) 2002 Optical Society of America.