Sensitivity and information content of aerosol retrievals from the advanced very high resolution radiometer: Radiometric factors

The sensitivity of aerosol optical depths τ1 and τ2 derived from the Advanced Very High Resolution Radiometer (AVHRR) channels 1 and 2, centered at λ1 = 0.63 and λ2 = 0.83 μm, respectively, and of an effective Ångstrom exponent α, derived therefrom as α = -ln(τ1/τ2)/ln(λ1/λ2 ), 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, Δτi and Δαi, are parameterized empirically as functions of τi, radiometric errors, and Sun and view geometry. In particular, the α errors change in approximately inverse proportion to τ and are comparable with, or even exceed, typical α signals over oceans when τ