Retrieving aerosol height from the oxygen A band: a fast forward operator and sensitivity study concerning spectral resolution, instrumental noise, and surface inhomogeneity

摘要

Hyperspectral radiance measurements in the oxygen A band are sensitive to thevertical distribution of atmospheric scatterers, which in principle allowsthe retrieval of aerosol height from future instruments like TROPOMI, OCO2, FLEX, andCarbonSat. Discussed in this paper is a fast and flexible forward operatorfor the simulation of hyperspectral radiances in the oxygen A band and, basedon this scheme, a sensitivity study about the inversion quality of aerosoloptical thickness, aerosol mean height, and aerosol type. The forwardoperator is based on a lookup table with efficient data compression based onprincipal component analysis. Linear interpolation and computation of partialderivatives is performed in the much smaller space of expansion coefficientsrather than wavelength. Thus, this approach is computationally fast and, atthe same time, memory efficient. The sensitivity study explores the impact ofinstrument design on the retrieval of aerosol optical thickness and aerosolheight. Considered are signal to noise ratio, spectral resolution, andspectral sampling. Also taken into account are surface inhomogeneities andvariations of the aerosol type.