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 trans mit and receive polarization. The C-band data did not yield good geoph ysical products, because the temporal coherence of the signal was sign ificantly reduced after 24 h. The L-band data were, however, successfu lly 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 interferom etric velocities were subsequently converted to horizontal displacemen ts by assuming a flow direction and complemented by feature-tracking r esults near the calving front. The results provide a comprehensive vie w of the ice-flow dynamics of Glaciar San Rafael. The glacier has a co re of rapid flow, 4.5 km in width and 3.5 degrees in average slope, su rrounded 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), increa sing rapidly before the glacier enters the narrower terminal valley, t o reach 17.5 m d(-1) or 6.4 km a(-1) at the calving front. Strain rate s are dominated by lateral shearing at the glacier margins (0.4-0.7 a( -1)), except for the terminal-valley section, where longitudinal strai n rates average close to l a(-1). This spectacular longitudinal increa se in ice velocity in the last few kilometers may be a fundamental fea ture of tidewater glaciers.