Design for an Airborne GPS-Inertial Surveyor

Abstract

The Aerial Profiling of Terrain System (APTS), designed and built at C.S. Draper Laboratory under the sponsorship of the US Geological Survey, achieved accuracies of 60 cm horizontal and 15 cm vertical in terrain profiling. APTS used a high accuracy inertial navigation system periodically updated by measurements from a laser tracker, which used surveyed retroreflectors located on the ground. A laser profiler fixed to the IMU measured distance to the terrain along a known direction. With a full constellation of Global Positioning System (GPS) satellites soon to be available, comparable accuracies could be achieved with a medium-accuracy inertial navigator updated by differential carrier-phase GPS measurements. Additional flexibility could be provided by gimballing the profiler. For appplications in which precise survey of ground points is desired, improvements in the laser tracker would make it possible to acquire retroreflectors that are genuinely unsurveyed. The design provides for the inclusion of additional optional sensors such as imaging devices, and for the use of the surveyor as a test bed for other navigation systems. The design incorporates technology capable of recording data at rates of several megabits per second.