Global climate change is currently a major environmental and political issue. The rise in sea level has been strongly correlated with global climate change. Now there is considerable uncertainty in the present-day and future roles played by polar ice sheets in sea level rise. An accurate determination of the mass balance of polar ice sheets is essential to quantify their role in sea level rise. Snow accumulation rate is an important parameter in mass balance computation of polar ice sheets. Currently this is determined by dating ice cores and analyzing stratigraphy of snow pits. Retrieving and analyzing ice cores and digging snow pits are, however, time-consuming, expensive and tedious. In addition, the sparse sampling of ice cores and snow pits has resulted in uncertainty of about 24% in the accumulation rate maps. This dissertation explores the possibility of conducting high-resolution mapping of near-surface isochronous layers in the ice sheet with aircraft radar to estimate long-term accumulation rate.

Our approach to the development of an operational airborne radar system was five fold. We first obtained the physical and electrical properties of an ice core and modeled it using the transmission line method. We performed a simple electromagnetic simulation to determine the optimum radar parameters for a ground-based system. Second, we developed an ultra-wideband Frequency-Modulated-Continuous-Wave (FM-CW) radar to operate over the frequency range from 170 to 2000 MHz. We tested the radar at the North Greenland Ice Core Project (NGRIP) camp and successfully mapped the internal layers for the top 300 m of the ice sheet. We analyzed the frequency response of the internal reflections from these measurements to determine the optimum frequency of operation for an airborne radar system. Third, we used surface- and volume-scattering models to determine the effects of clutter on the return from internal layers. Our modeling results indicated that we should be able to detect the near-surface inter-annual layers from an aircraft. We then developed a 600-900 MHz prototype airborne radar system and tested it over the Greenland ice sheet. Our results show that it is indeed possible to map the internal layers with high resolution from an aircraft. Finally, we addressed the problems associated with the prototype system and used a CAD tool to optimize the radar performance. We also developed a target simulator to test and calibrate the radar. The system is now ready for routine measurement of internal layers over the polar ice sheets.