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This paper presents the development and results of two wideband radar systems used to map near surface internal layers in glacial ice and estimate accumulation rate. The surface-based system operates at 1.25 GHz with a 10 cm resolution, while the airborne system operates at 750 MHz with a 60 cm resolution. The radar data collected matched qualitatively with core data, and accumulation rates were computed from radar data. The estimated accumulation rates were found to be consistent with core data. The paper concludes with future work and improvements to the radar systems.
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S. Gogineni, P. Kanagaratnam, R. Parthasarathy, V. Ramasami & D. Braaten The University of Kansas Wideband Radars for Mapping of Near Surface Internal Layers to Estimate Accumulation Rate
Outline • Introduction • Background • Systems Description • Results • Conclusions
Introduction • Sea level rose by about 15 cm over the last century. • Thermal expansion of the ocean • Melting of mountain glaciers • Contribution from polar ice sheets • There is a large uncertainty in polar ice sheets’ contribution. • Accurate mass balance determination is essential to determining their contribution. • Volumetric method • Flux method
Introduction • Volumetric method • Measure change in surface elevation • Satellite radar and laser Altimeters • NASA ICESAT -- January 03. • ESA CRYOSAT -- 2003 or 2004. • Interpretation of the data from these missions requires additional information. • Spatial and temporal variation of accumulation rate.
Introduction • Flux approach • Measure net input and ouput • Snow accumulation • Ice loss • Melting • Calving • Both methods need information on the accumulation rate. • Snow pits and ice cores • Limited coverage
Introduction—GREENLAND ACCUMULATION MAP Cores or pits on the Greenland ice sheet. Small variance where there are large numbers of cores or pits. Large variance in areas with significant change Difficult to operate in margins of the ice sheet Bales et al., 2001
Introduction— Systems • We developed two radar systems to map near-surface internal layers for estimating accumulation rate. • Surface-based system • Center frequency = 1.25 GHz • 10 cm resolution • Airborne system • Center frequency = 750 MHz. • 60 cm resolution
We used surface-based measurements to determine optimum radar parameters Constraint No interference to navigation and communication equipment System specifications Systems—Airborne Radar
Installation of Radar System in Aircraft Radar backend RF section
Results—Matching with core data • We simulated idealized radar response using core data • Matched layers qualitatively. • Radar data were collected in 2002 and core data in 1995. We had to account for this difference. • A source of error.
Results –Tracking layers • Using the simulated response at the core site, we identified a few layers and tracked them
Results— Accumulation rate • We computed accumulation rate from radar data as Lowest accumulation rate during 1983-1990 = 0.3045 0.017 m yr-1 Highest accumulation rate 1979-1983=0.3904 0.027 m yr-1) We found the water equivalent accumulation rate to be 34.9±5.1 cm/yr. Estimate from core data is 34.57 cm/yr.
Conclusions • We designed and developed two wideband radars for mapping near surface internal layers in glacial ice. • We showed that we can estimate accumulation rate. • Data will be distributed through the web in about six months. • More accurate simulations • System point spread function • Incorporate volume and surface scattering— noise. • Develop data inversion algorithms
