Comparison of Aircraft Attitude Determination by GPS, INS, and Airborne Laser: Preliminary Results

A GPS attitude determination system was flown in conjunction with a Laser Ring Gyro Inertial Navigation Unit (INU) and the NASA designed and built conically scanning Airborne Topographic Mapping Lidar (ATM). Several flights were conducted, with the purpose to determine the relative accuracy of the GPS system compared to the INU, using the ATM as a standard. This was accomplished by flying over the relatively calm water of the gulf of Mexico. Using precision range measurements to the sea surface provided by the ATM, simple geometry provides an accurate determination of attitude.

The INU system uses optical gyroscopes and accelerometers to determine the attitude angles, while GPS units utilize an array of four antennae with known geometry and signals from satellites to determine a "most- likely" solution. Tests were conducted with two available commercial GPS units, a Trimble Advanced Navigation System (TANS) and an Ashtech Attitude Determination Unit (ADU). In this paper we present preliminary results from this comparison.