Feasibility of Retrieving Stratospheric Aerosol Extinction Fields from GEO-LEO Limb Measurements: An Inversion Algorithm Approach

Kurzfassung

This paper investigates the feasibility of retrieving stratospheric aerosol extinction fields from GEO–LEO limb measurements using a dedicated inversion framework. The retrieval problem is severely ill-posed and involves a fundamentally three-dimensional observation geometry. To obtain stable solutions, variations of the extinction field in the cross-track direction are neglected, reducing the problem to the retrieval of radial and weakly horizontally varying aerosol distributions within a quasi-planar GEO–LEO geometry. Two simplified retrieval strategies are considered. In the first strategy, the radial extinction profile and the horizontal extent of the aerosol field are retrieved using external aerosol optical thickness observations as additional constraints. In the second strategy, the extinction field is represented by a parametric model and the corresponding model parameters are retrieved. To reduce the computational complexity, a simplified single-scattering forward model is adopted. The inversion problem is formulated as the minimization of a regularized Tikhonov function and is solved using a multistart optimization framework combining global random sampling, validation and selection of admissible starting points, local bounded optimization, discrepancy-principle filtering, and clustering of candidate solutions. Numerical simulations for a broad range of synthetic aerosol scenarios show that the proposed methodology is capable of reproducing the dominant aerosol structures with good accuracy. Although the retrieval problem remains strongly ill-conditioned, the effective degrees of freedom indicate that GEO–LEO limb measurements contain substantial independent information about the aerosol field and provide a promising basis for retrieving both radial aerosol extinction profiles and aspects of their horizontal structure.