Abstract
A spectral acceleration approach for the spherical harmonics discrete ordinate method (SHDOM) is designed. This approach combines the correlated k-distribution method and some dimensionality reduction techniques applied on the optical parameters of an atmospheric system. The dimensionality reduction techniques used in this study are the linear embedding methods: principal component analysis, locality pursuit embedding, locality preserving projection, and locally embedded analysis. Through a numerical analysis, it is shown that relative to the correlated k-distribution method, PCA in conjunction with a second-order of scattering approximation yields an acceleration factor of 12. This implies that SHDOM equipped with this acceleration approach is efficient enough to perform spectral integration of radiance fields in inhomogeneous multi-dimensional media.
Highlights
The retrieval of trace gas products from UV/VIS spectrometers is strongly affected by the presence of clouds
The spherical harmonics are employed for computing the source function including the scattering integral, while the discrete ordinates are used to integrate the radiative transfer equation spatially
Before presenting some numerical results, we describe an implementation of spherical harmonics discrete ordinate method (SHDOM) that is devoted to the retrieval of atmospheric trace gas concentrations from space-borne spectral measurements of radiation reflected through the Earth’s atmosphere
Summary
The retrieval of trace gas products from UV/VIS spectrometers is strongly affected by the presence of clouds. For the forward-model simulation of satellite measurements from instruments with high spatial resolution, it is important to account for the sub-pixel cloud inhomogeneity, or at the least, to assess this effect on the radiances at the top of the atmosphere, and so, on the retrieval results. SHDOM adopts (i) both spherical harmonics and discrete ordinates representation of the radiance field during different parts of the solution algorithm, and (ii) a sort of successive order of scattering solution method (Picard iteration [3]). The spherical harmonics are employed for computing the source function including the scattering integral, while the discrete ordinates are used to integrate the radiative transfer equation spatially. To achieve higher accuracy with a limited amount of memory, an adaptive grid is implemented By this technique, regions where the source function is changing more rapidly have a higher density of grid points
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