Fine-Resolution Mapping of Near-Surface Internal Layers

Parathasarathy, R., Kanagaratnam, P., Akins, T., Wulte, J., Braaten, D., Jezek, K., and Gogineni, P.

Abstract:

Knowledge of the mass balance of the Greenland Ice Sheet is necessary to assess its contribution to the rising sea level. The accumulation rate of snow on ice sheets is an important variable in determining this mass balance and in interpreting data from ICESAT and CRYOSAT missions. Using a small number of ice pits and cores to determine accumulation rate is unreliable, due to the small number of samples. In order to reduce this uncertainty, we have developed a wideband radar to generate a continuous profile of the isochronous layers in the ice sheet. Such a profile can be used to estimate long-term accumulation rate with reduced uncertainty. We built a wideband FM-CW radar that operates from 500 to 2000 MHz with range resolution of about 10 cm. We used a YIG oscillator to generate this signal. Since FM radar performance is affected by any non-linearity in the YIG oscillator, we developed a method for correcting any non-linearity in the YIG oscillator by using it in a phase-locked loop configuration. We simulated the performance and built a prototype radar. We tested the radar during the 2003 field season at North GRIP, and collected data over a long transect of 5 km. We collected radar data in conjunction with detailed snow pit studies at several locations along the radar tracks. Also we extracted a 15 m core for isotope analysis. Our preliminary results show that we can map layers to a depth of about 150 m with about 10 cm resolution. We will present the design considerations, laboratory test results of radar performance, results from experiments at NGRIP and comparison of the radar data with information derived from snow pits.

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