SHORT-PULSE RADAR DETECTION OF GROUNDWATER IN THE SAGAVANIRKTOK RIVER FLOODPLAIN IN EARLY SPRING

Short-pulse radar operating in the UHF band was used to search for unfrozen water beneath ice blisters and within the gravels of the Sagavanirktok River floodplain near Prudhoe Bay, Alaska. The investigations were carried out in early April 1991, when daily mean air temperatures still were below -20-degrees-C. The radar pulse spectrum was centered near 400 MHz and the radar time range was set to cover about 10 m depth. The flat, snow-covered surface allowed good antenna-ground coupling, and the ice and gravels provided a low-loss propagation medium that allowed detail of the gravel structure to be seen in the data. Grids of several traverses were profiled at three sites, all within an area of about 0.5 km2 .Unfrozen water was inferred from the strength and polarization of the radar reflections. One site contained a large icing blister beneath which an extensive reservoir was mapped and seen to extend several tens of meters beyond the mound. Data from two other sites indicated taliks 5-7 m deep near a frozen mound and within the gravels. One of the profiles extended 700 m across the floodplain and revealed other high-reflectivity targets, which were presumed to be water, within about 7 m of the surface; a deeper sounding confirmed this depth limit. It is concluded that taliks exist in the floodplain throughout the winter and are a probable source for the numerous icing mounds seen along most Arctic rivers east of Prudhoe Bay.