This is the RTK GPS system that we used to map the glacier, kindly loaned by Leica. Our method was to walk all round the glacier taking GPS co-ordinates and snow depth measurements, to within 10cm accuracy. We could then create a 3-dimensional image of the glacier surface to compare to previous years, to see if the glacier was advancing or retreating. The GPS system comprises a base station and a rover. This photo only shows the base station, mounted on a tripod with a red battery and a blue radio. The radio communicates with the rover. Alone, the rover can only take co-ordinates to an accuracy of approximately 30m. Because the base station is stationary it is able to calculate its position to the required accuracy. The data from the rover is then processed relative to the base station position to ultimately produce GPS co-ordinates accurate to 10cm.