Study of passive remote sensing of the atmosphere and surface ice Executive summary and final report

Abstract

A radiative transfer model to compute brightness temperatures in the microwave frequency range for polar regions including sea ice, open ocean and atmosphere has been developed. The calculation of the sea-ice reflectivity is incorporated by the 'many layer strong fluctuation theory' model of Grenfell and Stogryn. The surface reflectivity of the open water is computed with three scale model of Schrader. Both surface models supply the bistatic scattering coefficients, which define the lower boundary for the atmospheric model. The atmospheric model computes the gaseous absorption of water vapour and oxygen by the Liebe model. Cloud hydrometeors are considered by Mie- or Rayleigh-scattering. The radiative transfer model has been validated for SSM/I frequencies using six test cases. The ground truth data (surface and atmosphere) has been observed during the ARKTIS'88 and ARKTIS'93 experiments. The simulated brightness temperatures are compared to collocated SSM/I measurements. The validation exhibits shortcomings of the sea-ice model for 37 GHz. The actual reasons for these deviations are unknown, but a possible explanation is an artificial oscillation of the reflectivity as function of frequency and ice-layer thickness. An empirical correction of the reflectivity for this frequncy has been derived and its application gives consistent comparison results between the simulated and observed brightness temperatures within the accuracy range. (orig.)207 refs.Available from TIB Hannover: RN 3292(297) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman