The Airborne Topographic Mapper (ATM) was a scanning LIDAR developed and used by NASA for observing the Earth’s topography for several scientific applications, foremost of which was the measurement of changing arctic and antarctic icecaps and glaciers. It typically flew on aircraft at an altitude between 400 and 800 meters above ground level, and measured topography to an accuracy of better than 10 centimeters by incorporating measurements from GPS (global positioning system) receivers and inertial navigation system (INS) attitude sensors.