RADARSAT backscatter characteristics of ice growing on shallow sub‐Arctic lakes, Churchill, Manitoba, Canada

Abstract Results from an investigation on the evaluation of RADARSAT (C‐HH) imagery for monitoring ice growth and decay, and related processes of shallow sub‐Arctic (tundra and forest) lakes in northern Manitoba, Canada, are presented. Field observations on the structural and stratigraphic characteristics of snow and ice from four lake sites are used in support of the interpretation of changes in synthetic aperture radar backscatter intensity as a function of time and incidence angle (20–49°). Results show that bubble inclusions, most of which are tubular and oriented in the direction of growth, strongly influence backscatter intensity from floating ice in RADARSAT Standard beam mode imagery. It is shown that radar return can vary considerably as a function of incidence angle. Differences of as much as 6·5 dB were observed for the same ice cover when observed at steeper (20–35°) compared with shallower (35–49°) incidence angles. During the early stages of ice growth and/or when the ice volume contains a small amount of tubular bubbles, backscatter intensity from the floating ice measured at shallower incidence angles (35–49°) is similar to that observed from the grounded ice at any incidence angle (−17 to −11 dB). A strong decrease in backscatter was observed at all sites during spring thaw and was explained by the microwave signal being absorbed by the wet snow cover and by specular reflection from the standing water (ponds) on the lake ice surface. With its multiple beam mode configurations, RADARSAT offers an improved temporal coverage over ERS‐1/2, thus making it possible to determine more precisely freeze‐up and break‐up dates, and timing of bottom freezing from shallow Arctic and sub‐Arctic lakes. Copyright © 2002 John Wiley & Sons, Ltd.