The estimation of wet tropospheric correction for space altimetry using a variational approach

• Main Author: Hermozo, Laura
• Other Authors: Centre national de recherches météorologiques (CNRM), Institut national des sciences de l'Univers (INSU - CNRS)-Météo France-Centre National de la Recherche Scientifique (CNRS), Université Paul Sabatier - Toulouse III, Laurence Eymard, Bruno Picard
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2018
• Subjects: Wet tropospheric correction; Radiometer; Radiative transfer; Surface; Water vapor; Altimetry; Correction troposphérique humide; Radiomètre; Transfert radiatif; Humidité; Altimétrie; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Sea ice
• Online Access: https://tel.archives-ouvertes.fr/tel-02061448; https://tel.archives-ouvertes.fr/tel-02061448/document; https://tel.archives-ouvertes.fr/tel-02061448/file/2018TOU30026b.pdf

Space altimetry is one of the major contributors to the understanding of regional and global oceanic circulation. It currently enables to provide a map of ocean topography at higher temporal and spacial scales. A propagation delay of the altimeter signal along its path through atmospheric water vapor needs to be accounted for, and corresponds to the wet tropospheric correction. Statistical methods are currently used to estimate wet tropospheric correction. These methods are fed by brightness temperature measurements provided by a radiometer coupled to the altimeter, at two or three frequencies close to the water vapor absorption line, at 22.235 GHz. While these algorithms provide wet tropospheric correction with low uncertainties over open ocean, improvements are still needed to reduce higher uncertainties in complex oceanic areas, such as upwelling regions, and over heterogeneous surfaces, as coastal regions, sea ice or inland waters. To this end, a one-dimensional variational approach (1D-Var) is developed in the frame of this thesis. This approach accounts for atmospheric and surface variability in the surroundings of the measurements, to provide wet tropospheric correction estimates at a global scale, over various surfaces, in the context of both current and future altimetry missions, with improved instrumental technologies. We first analyze the characteristics of the 1D-Var approach and evaluate its performances. The contribution and impact of the different input parameters on retrieved atmospheric variables and wet tropospheric correction are shown through this analysis. The potential and limits of the 1D-Var approach to retrieve wet tropospheric correction over open ocean, for clear sky conditions, are evaluated. The contribution of high frequencies, typical to future altimetry missions, is also analyzed. It is fully exploited to retrieve wet tropospheric correction over coastal areas, where land contamination occurs within brightness temperature measurements. A preliminary analysis of surface emissivity ...