Beale, Julie Anne-Marie; (1995) Multifrequency polarimetric microwave measurements of the Greenland ice sheet. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The Greenland ice sheet is an important component of the global hydrological system and contributes to the global radiation budget. A knowledge of the extent and surface state of this ice sheet is therefore important in predicting and monitoring global climate change. This thesis shows how active and passive multifrequency polarimetric microwave remote sensing measurements may be used to provide such information. The microwave response of the four different zones of the Greenland ice sheet is investigated. The four zones are the central dry zone, the percolation zone, the soaked zone and the ablation zone towards the edge of the ice sheet (Benson, 1962). High resolution active data from the NASA/JPL AIRSAR airborne synthetic aperture radar, and lower resolution, more extensive, passive data from the Defense Meteorological Satellite Program Special Sensor Microwave Imager (DMSP SSM/I) are used. A multifrequency polarimetric matrix based computer model is developed to determine the theoretical 3D polarimetric response of simulated geophysical surfaces. This model is based on conservation of energy and predicts the polarimetric content of the reflected signal (amplitude and phase components) and the emitted energy. A method is developed to determine the dielectric constant (and hence moisture content) of imaged areas using the remotely sensed polarimetric signals. This allows classification of the different zones of the ice sheet, so providing a useful tool for mapping the extent of the different ice sheet zones. The annual variation of the polarimetric signals is investigated to determine the seasonal change of the surface state of each zone. The polarimetric data suggest that subsurface layers or other discontinuities (for example, subsurface ice layers or depth hoar) play a major role in the microwave response of the Greenland ice sheet. This should be considered in future climatological and topographical studies of ice sheets.

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