Influence of aerosol vertical profile variability on retrievals of aerosol optical thickness from NOAA AVHRR measurements in the Baltic region

The expected influence of variability in atmospheric aerosol profiles on retrievals of aerosol optical thickness (AOT) from NOAA AVHRR measurements is analysed. In particular, the bias in the AOT retrieval due to the assumption of a climatological aerosol profile in the retrieval algorithm is studied. The bias is defined as the difference between AOT retrieved with an algorithm using a climatological aerosol profile, and the actual AOT employed in the calculations of radiances at the top of the atmosphere (TOA). The TOA radiances are simulated by means of the MODTRAN code for different aerosol profiles. Atmospheric conditions and solar and satellite angles used in the bias simulations are typical of the Baltic region. In the simulations, the maximum absolute value of the bias amounts to nearly 40% in channel 2 and 14% in channel 1 of AVHRR.