Interferometric radar observations of Glaciar San Rafael, Chile

Interferometric radar-observations of Glaciar San Rafael, Chile, were collected in October 1994 by NASA's Spaceborne Imaging Radar C (SIR-C) at both L- (24 cm) and C-band frequency (5.6 cm), with vertical transmit and receive polarization. The C-band data did not yield good geophysical products, because the temporal coherence of the signal was significantly reduced after 24 h. The L-band data were, however, successfully employed to map the surface topography of the icefield with a 10 m uncertainty in height, and measure ice velocity with a precision of 4 mm d(-1) or 1.4 m a(-1). The corresponding error in strain rates is 0.05 a(-1) at a 30 m horizontal spacing. The one-dimensional interferometric velocities were subsequently converted to horizontal displacements by assuming a flow direction and complemented by feature-tracking results near the calving front. The results provide a comprehensive view of the ice-flow dynamics of Glaciar San Rafael. The glacier has a core of rapid flow, 4.5 km in width and 3.5 degrees in average slope, surrounded by slower-moving ice, not by rock. Ice velocity is 2.6 m d(-1) or 0.95 km a(-1) near the equilibrium-line altitude (1200 m), increasing rapidly before the glacier enters the narrower terminal valley, to reach 17.5 m d(-1) or 6.4 km a(-1) at the calving front. Strain rates are dominated by lateral shearing at the glacier margins (0.4-0.7 a(-1)), except for the terminal-valley section, where longitudinal strain rates average close to l a(-1). This spectacular longitudinal increase in ice velocity in the last few kilometers may be a fundamental feature of tidewater glaciers.