Deriving Atmospheric Temperature and Instrumental Pointing from Millimeter/Sub-millimeter Limb Sounding Measurements

Abstract

The purpose of this work is to investigate the potential to retrieve atmospheric constituent distributions and instrumental pointing from limb sounding measurements in millimeter and sub-millimeter spectral ranges. The retrieval process is performed with the optimal estimation method (OEM) which incorporates the a priori knowledge independent of the measurement. Emphasis is put on the retrieval of the atmospheric temperature profile and instrument pointing correction. The standard approach for microwave limb sounding instruments is to derive information on the atmospheric temperature and pointing correction from oxygen emission lines. Nevertheless, other emissions, e.g.,ozone emissions, can also deliver accurate temperature and instrumental pointing information. To demonstrate that, a rigorous error analysis, including both statistical and model parameters error, is carried out. The MASTER instrument, studied by the European Space Agency, is used as a realistic example for a state-of-the-art limb sounding instrument. However, the presented method of analysis can be applied to any other millimeter/sub-millimeter limb sounding instruments, e.g.,EOS/MLS or Odin instruments. Moreover, in order to establish the measurement performance of the SMILES instrument, simulations of the entire observing and retrieval processes are performed. Linear retrieval simulations provide a set of the statistical errors needed for a general error characterization, while nonlinear retrieval simulations are carried out in order to test the retrieval for more realistic situations.