Inversion for Limb Infrared Atmospheric Sounding

Kurzfassung

Recently, several new generation instruments for far infrared and microwave remote sensing of the Earth’s atmosphere have been launched, and enables us to observe the atmospheric composition based upon the thermal emission technique. These new technologies and observational data pave the way for more dedicated atmospheric research missions in the future. The impetus for my thesis is the growing interest in robust inversion algorithms for solving nonlinear inverse problems arising in atmospheric remote sensing. A retrieval code PILS (Profile Inversion for Limb Sounding) which allows for high resolution radiative transfer computations and the reconstruction of atmospheric parameters from infrared and microwave limb sounding measurements is presented. The employed forward model simulates physically realistic limb emission spectra in an efficient manner, by taking into account the instrument performance and the measurement characteristics. In particular, automatic differentiation (AD) techniques providing a rapid and reliable implementation of exact Jacobians, are a special optimization feature of the forward model. The inversion methodology is essentially based on a nonlinear least squares framework with adaptive (direct and iterative) numerical regularization approaches. The performance of these regularization techniques relies on the design of the regularization parameter choice methods and the a posteriori stopping rules. The characterization of the retrieval error, including the smoothing error, the noise error, and the model parameters error, assesses the accuracy of the regularized solution. An intercomparison between PILS and the retrieval code developed by the Netherlands Institute for Space Research (SRON), dealing with radiative transfer and inversion calculations with predefined input, aims to clarify the correctness and consistency of the implementations. Small differences in the forward model mainly result from continuum absorption and the integration of the radiative transfer equation. The possible causes of discrepancies in the retrieval results are the consequences of the different inversion methods employed (regularization, a priori information) and discretization. Retrieval results pertaining to trace gas retrievals from balloon-borne measurements by TELIS (TErahertz and submillimeter LImb Sounder) are discussed by analyzing both synthetic and real radiance spectra. A sensitivity study of hydroxyl radical (OH) retrieval is used to evaluate the inversion performance of PILS and to reveal the initial expectation of TELIS's measurement capabilities (e.g. critical error sources, data quality). Furthermore, retrieval results of ozone (O3), hydrogen chloride (HCl), carbon monoxide (CO), and OH from the winter fights during 2009--2011 are presented to assess the performance of the TELIS 1.8THz channel and to judge the reliability of PILS by comparing with the data products obtained by the TELIS 480--650 GHz channel and other limb sounders. These observations offer opportunities for the scientific community to make an extensive investigation into the stratospheric chemistry and dynamics, and to study the atmospheric environment over the polar region of the Northern Hemisphere.