Retrieving aerosol height from the oxygen A band: a fast forward operator and
sensitivity study concerning spectral resolution, instrumental noise, and
surface inhomogeneity
Hyperspectral radiance measurements in the oxygen A band are sensitive to the
ver- tical distribution of atmospheric scatterers, which in principle allows
to retrieve aerosol height from future instruments like TROPOMI, OCO2, FLEX,
and CarbonSat. Discussed in this paper is a fast and flexible forward operator
for the simulation of hy- perspectral radiances in the oxygen A band and,
based on this scheme, a sensitivity study about the inversion quality of
aerosol optical thickness, aerosol mean height, and aerosol type. The forward
operator is based on a lookup table with efficient data com- pression based on
principal component analysis. Linear interpolation and computation of partial
derivatives is performed in the much smaller space of expansion coefficients
rather then wavelength. Thus, this approach is computationally fast and at the
same time memory efficient. The sensitivity study explores the impact of
instrument design on the retrieval of aerosol optical thickness and aerosol
height. Considered are signal to noise ratio, spectral resolution, and
spectral sampling. Also taken into account are surface inhomogeneities and
variations of the aerosol type