A compact high-resolution radar for determining snow accumulation rates

Abstract

Rising sea level has important humanitarian and economic implications. Scientists are rigorously investigating the contribution of glacial ice sheets to sea-level rise. Knowledge of the mass balance of the ice sheets is important in understanding their dynamics. The accumulation rate of snow on ice sheets is an important variable in determining this mass balance. The accumulation rate is currently determined using ice cores and pits. This is a tedious method to obtain coverage over the entire ice sheet due to the limited number of samples that can be acquired. The only practical means of obtaining coverage over a large area would be by means of remote sensing. We have developed a wideband radar to map the isochronous layers in the ice sheet This will help reduce the uncertainty associated with sparse sampling of the ice sheet. We built a compact FM-CW radar that operates from 500 to 2000 MHz with range resolution of about 10 cm. Both the transmitter and receiver were housed in a single Compact PCI chassis. We used a YIG oscillator to generate the FM signal. The performance of an FM-CW is usually degraded by the nonlinearity of the source. We linearized the sweep of the YIG oscillator by means of a phase-locked loop (PLL). We have successfully tested the radar in the lab and we will be performing tests during the 2004 summer field experiments at the Summit camp in Greenland. We successfully tested a connectorized version of this radar during the 2003 field experiments at the North Greenland Ice Core Project (NGRIP) camp. We were able to map the internal layers up to a depth of about 150 m over a 5-km transect. We also conducted detailed snow pit studies at several spots over the transect for correlating the visually determined layers with the radar determined layers. We will present the radar design, laboratory test results of its performance, results from the experiments at Summit and a comparison of the radar data with information derived from ice cores and snow pits.