High resolution velocity profiles through ice cover

Abstract

During February 2004, SonTek/YSI and Environment Canada deployed acoustic Doppler profilers (ADPs) through the ice at Fort Simpson in the North West Territories. The deployments were used to develop the logistics, hardware and software for water velocity measurements through ice cover. High precision velocity profiles were taken just under the ice to study the near-ice boundary layer. The field site was the Mackenzie River near Environment Canada's Fort Simpson office. The river was over 1 km wide and had approximately 1 m of ice cover at this location. A motorized ice auger cut holes at a number of positions to allow measurements to be taken over a two day period. Unique velocity profiles, that included the near-ice and the near-bottom boundary layers, were acquired with two different Mini-ADPs, 1.5 and 3.0 MHz. The placement and blanking distances of the Mini-ADPs limited their ability to measure the velocities nearest the ice. For this a third Mini-ADP was employed. The PC-ADP was placed at the ice-water interface where it acquired 50 cm long, high resolution (1.6 cm) profiles of the near-ice boundary layer. These were used to determine the friction velocity within the boundary layer and the roughness length scales of the ice's undersurface