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.