The antennas of the radar are situated at the rear end of the sleigh. They send impulses into the ice, which are reflected by different properties in the ice and return the impulse signals to the antennae. Data can be plotted as a radio-echogram, from which you can read out thickness of the ice, the rock under the ice and different layers of ice in the ice sheet. Radar measurements from flyovers work in much the same way as the sleigh radar. Each radar can be adapted to focus on different properties, such as the shift from ice to bedrock, ice layer, melt layer etc.