Abstract
An algorithm for the retrieval of total column amount of trace gases in a multi-dimensional atmosphere is designed. The algorithm uses (i) certain differential radiance models with internal and external closures as inversion models, (ii) the iteratively regularized Gauss–Newton method as a regularization tool, and (iii) the spherical harmonics discrete ordinate method (SHDOM) as linearized radiative transfer model. For efficiency reasons, SHDOM is equipped with a spectral acceleration approach that combines the correlated k-distribution method with the principal component analysis. The algorithm is used to retrieve the total column amount of nitrogen for two- and three-dimensional cloudy scenes. Although for three-dimensional geometries, the computational time is high, the main concepts of the algorithm are correct and the retrieval results are accurate.
Highlights
To speed up the computations, the linearized spherical harmonics discrete ordinate method (SHDOM) is equipped with a spectral acceleration approach that combines the correlated k-distribution method with dimensionality reduction techniques
SHDOM is run with a solution accuracy of 10−4 and by using an adaptive grid with a splitting accuracy of 10−4, the principal component analysis with M = 4, and the derivative correction factor f Xg as in Equation (39), periodic boundary conditions, the delta-M approximation [32], and the untruncated phase function single-scattering solution
The algorithm has been applied to the retrieval of the total column amount of NO2 under cloudy conditions
Summary
We go one step further and present the main concepts of an algorithm for retrieving the total column amount of trace gases in a multi-dimensional atmosphere To achieve this goal we combine inverse models and regularization tools from inversion theory with a fast linearized version of the spherical harmonic discrete ordinate method [6]. These theoretical results are summarized, while, the accuracy and efficiency of the algorithm, used to retrieve the total column amount of nitrogen dioxide (NO2 ) for two- and three-dimensional cloudy scenes, are numerically investigated. We conclude our analysis with some recommendations for operational retrievals
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