A Study On Infrared Hyperspectral Measurements And Its Applications On Cloud Detection, Cloud-Clearing And Atmospheric Sounding Profile

The thesis firstly studies how to objectively define a cloud mask at the relatively low spatial resolution of a high-spectral resolution atmospheric infrared sounder using high-spatial resolution imager cloud mask information co-located within the sounder instrument footprint.Secondly, we study the retrieval of atmospheric profiles of temperature, moisture and ozone, together with surface emissivity and skin temperature retrieval, from measured infrared sounder radiances under clear sky (cloudless) conditions. Profiles retrieved via a statistical eigenvector regression retrieval algorithm are used as the first guess for a physical retrieval method. Single term variational analysis is applied to the Radiative Transfer Equation (RTE) to first obtain an iterative form for temperature and water vapor mixing ratio weighting functions, then the Newtonian ? nonlinear iteration method is applied to the RTE to retrieve simultaneously profiles and surface values. By this method sounding accuracy is improved (to less than 1 K in temperature and better than 10% in humidity in the troposphere) with a vertical resolution of 1 km. This level of accuracy meets the requirements for data to be assimilated into numerical weather prediction systems.We also study the retrieval of the atmospheric profiles, cloud top pressure and effective spectral emissivity from infrared sounder radiances under cloudy conditions, assuming that two adjacent sounder footprints have the same atmospheric temperature and moisture profiles and the same cloud-top height. An optimal cloud-clearing algorithm is developed that, on a single sounder footprint basis, retrieves the infrared sounder clear sky spectral radiances from the high spatial resolution multi-band imager infrared clear radiances combined with the infrared sounder spectral radiances under cloudy conditions. Observational data are provided by the AIRS (Atmospheric InfraRed Sounder) and MODIS (Moderate Resolution Imaging Spectroradiometer) instruments, which fly on the AQUA polar orbiting platform as part of the Earth Observing System (EOS) of National Aeronautics and Space Administration (NASA). The AIRS cloud-cleared radiance spectrum is spectrally reduced to mimic all MODISinfrared spectral bands within the AIRS spectral range. These aggregated measurements, MODIS-like in spectral coverage but at the spatial resolution of AIRS, are expressed as brightness temperatures and are compared with MODIS clear sky brightness temperature observations within all successfully cloud-cleared AIRS footprints. For most MODIS infrared spectral bands under clear sky conditions, the bias and the standard deviation between MODIS observations and MODIS-simulated-from-AIRS observations is less than 0.25 K and 0.5 K, respectively, over both water and land. This thesis also describes the use of the MLEV (Minimum Local Emissivity Variance) technique for simultaneous retrieval of cloud top pressure and effective spectral emissivity from high-spectral resolution radiances.Finally, we discuss the AIRS measurement artifact due to detector array misregistration, which affects the subsequent cloud-clearing and cloud properties retrieval.