EXPERIMENTAL ASSESSMENT OF A NON-DEDICATED GPS RECEIVER SYSTEM FOR AIRBORNE ATTITUDE DETERMINATION

The use of a non-dedicated GPS receiver system for attitude determinat ion was assessed in airborne mode through a test conducted at Sandia N ational Laboratories. Four independent NovAtel GPSCard(TM) receivers w ere installed in Sandia's Twin Engine Otter with two antennae mounted on the fuselage and two on the wing tips at separations of 6 to 18 m. A strapdown INS was also on board the aircraft in order to provide an independent attitude reference at rates between 4 and 10 Hz. During th e multi-day test, GPS measurements were recorded at rates between 1 an d 10 Hz. Carrier phase measurements were post-processed using a double -difference approach developed at The University of Calgary in which i nteger ambiguities were resolved in seconds using the known antenna se parations as constraints. The tracking capability of the system is dem onstrated under dynamics consisting of roll and pitch angles up to 60 and 35 degrees, respectively. Comparisons between the GPS and INS atti tude angles are presented and show agreement at the several-arcminute level. Conclusions are made with respect to system accuracy and perfor mance in an operational airborne environment.