The client needed bathymetric information (i.e. water depth) before spring breakup of the ice. The information was required for the planning of a shipping route that would accommodate the deep draft of the large cargo vessels that were intended to traverse the lake. A multi-week ground penetrating radar (GPR) survey was carried out, on the ice, under severe winter conditions. At regular intervals, a hole was augered through the ice, and the GPR measured depths were checked against a depth sounding tape.