Ultra-wideband Radiometry for Internal Ice Sheet Temperature Measurements: Modeling and Experiments
Abstract:The internal ice sheet temperature profile is an important parameter in ice dynamics as it influences ice deformation and motion. At present knowledge of the temperature profile is limited since it is measured in a few boreholes in Antarctica and Greenland or modeled. Techniques for remotely sensing internal temperature have to be demonstrated. To address this challenge, the Ultra Wide Band Software Defined Radiometer (UWBRAD) is being developed to provide 0.5-2 GHz nadiral measurements of ice sheet brightness temperature.
This study presents results from a UWBRAD forward model comparison between the coherent model (CM) and DMRT-ML model, in order to assess the relevance of varying emission physical mechanisms in the 0.5-2 GHz range. CM computes the thermal emission of a stratified medium from the fluctuation dissipation theorem. Scattering effects are not considered, but CM includes all coherent interactions among layers. Because density fluctuations cause internal reflections that exhibit coherent effects, CM predictions are strongly sensitive to density fluctuations. DMRT-ML in contrast is incoherent, and solves the radiative transfer equation using the discrete ordinate method so that scattering effects are included. However, simulations varying DMRT-ML parameters have shown that scattering effects are negligible in this frequency range. Model results show that coherent reflections become important in the brightness temperature across the 0.5-2 GHz band (10s of K) when the correlation length of density fluctuations is short (a few centimeters). The model predictions are similar when the correlation lengths exceed 10 cm.
The project will conduct experiments with a 4-channel (0.5, 0.94, 1.38, 1.74 GHz) prototype in November, 2015 at Dome C, Antarctica. The system will observe the ice sheet at 45o incidence from a tower. Results from the modeling studies, the Dome C experiment, and preliminary assessment of retrieval performance will be provided in the presentation.