Altimeter and radiometer in Antartica

• Main Author: Adodo, Fifi Ibrahime
• Other Authors: Laboratoire d'études en Géophysique et océanographie spatiales (LEGOS), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Centre National de la Recherche Scientifique (CNRS), Université Paul Sabatier - Toulouse III, Frédérique Rémy, Ghislain Picard
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2018
• Subjects: Polar ice sheet; Backscattering coefficent; Polarization ratio; Surface roughness; Radar altimeter; Radiometer; Calotte polaire; Antarctique; Altimétrie radar; Radiométrie; Coefficients de rétrodiffusion; Ratio de polarisation de température de brillance; Ugosité de surface; Physique de la mesure; [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology; Antarc*; Antarctic; Antarctique*; antartic*; Ice Sheet
• Online Access: https://theses.hal.science/tel-01899498; https://theses.hal.science/tel-01899498v2/document; https://theses.hal.science/tel-01899498v2/file/2018TOU3135b.pdf

In the context of global climate changes, the Antarctic ice sheet contribution to sea-level rise is one of the main uncertainty sources. The extent and extreme meteorological conditions of this continent render remote sensing a useful tool for long term monitoring. Altimetry and radiometry observations in the microwave range reveal variations of the volume of the ice sheet and surface properties of the snowpack. Radar altimeters, provide repeated observations of the surface topography elevation, which allow the quantification of volume variations of the ice sheet. However, the penetration of radar waves in dry and cold snowpack adversely affects the estimated surface elevation. Approaches to minimize the penetration error are all based on a relationship with the backscattering coefficient. Understanding the annual and interannual variations of the backscattering coefficient is thus a key issue in order to improve the estimation accuracy of the surface elevation and to refine the ice-sheet volume trend. This thesis aims at studying the backscattering coefficients acquired by radar altimeters, which until now have received little attention. Radar altimeters on board ENVISAT (S and Ku bands) and SARAL/AltiKa (Ka band) have different sensitivities to the snowpack properties. The annual and interannual variations of the backscattering coefficient at the three bands is investigated. Sensitivity tests are carried out with an electromagnetic model to determine the prevailing snowpack properties that drive the signal. The seasonal signal is sensitive to surface density and roughness at S band, to snow temperature at Ka band and to either snow surface density and roughness or temperature depending on the location on the continent at Ku band. The seasonal signal of the backscattering coefficient is then compared with that of the brightness temperature measured by radiometers on SARAL and SSM/I. The results show a significant influence of surface roughness on brightness temperatures at Ka band, which has often been ...