Seasonal clill1.atic forcing of alpine glaciers revealed with orbita l synthe tic aperture radar

The evolut ion of four dynamic radar glacier zones at the surface of an alpine icefield in British Columbia is monitored using a time series of 35 First European Remote Sensing Satellite ( ERS-I ) synthetic aperture radar (SAR) i mages acquired from 1992 to 1994 . These zones result from changing wetness and textural properties, and ap­ pear to represent: (I) cold snow with no l iquid water present; (2) a n initial melt front with an upper boundary near t he ele\'ation of t h e 0° i sotherm; (3) metamorphosed, rapidly melting fi rst-year snow with a rough or pilted surface; and (4) bare ice. This interpretation is aided by tem perature and runoff data, a i r p hotographs and field measurements of snolVpack properties acqu i re d simultaneously w i t h two ERS-I SAR scenes, ice-surface elevations dcri\'ed from I: 50 000 topographic m aps and simu lations of radar backscatter from a geometric optics model of surface scatteri ng. Meltwater production is afTccted by the de\'e!opment of zones (2), (3) and (4), which form, migrate up-elevation and d i sappear each year bet ween April and September.