| Airborne gravity is a method of determining gravity disturbances from measurements taken on an aircraft. The method investigated is the use of a strapdown INS and differential GPS. The INS measures specific force (reaction force due to gravity plus aircraft acceleration) while DGPS measures aircraft acceleration only. Therefore, by differencing the two data streams an estimate of the gravity field, contaminated by measurement noise, is obtained. The question that arises is how accurately, and with what resolution, can the INS/DGPS system determine the disturbances.; This dissertation provides a detailed analysis of strapdown INS/DGPS for the determination of gravity disturbances from an airplane using both rotation invariant scalar gravimetry (RISG) and strapdown inertial scalar gravimetry (SISG). The analysis encompasses theoretical aspects and a detailed numerical study using real data from two flight tests in September 1996 and June 1998.; Results from the September 1996 test showed a best agreement of the system estimate with an upward continued reference of 2.8 mGal and 1.1 mGal at flight heights of 4350 and 7300 metres, respectively. An analysis of crossover point differences for the lower flight showed a repeatability of 1.6 mGal. The SISG method performed consistently better than RISG. These results are near the expected resolution of the current prototype system. However, the long-term non-linear drift of the system disturbance estimates was found to be a problem. This problem could be remedied by using accelerometers with better bias stability, or by combining the airborne disturbance estimates with other sources of gravity information in the flight area. The possibility of combining multiple observations of the specific force and GPS acceleration was also investigated for the September 1996 test, however, combining multiple estimates showed little improvement over estimates with a single INS/DGPS system.; The June 1998 test compared strapdown INS/DGPS airborne gravity to the more established airborne gravity using a LaCoste and Romberg gravimeter. The two systems agreed at the 2–3 mGal level, which is near the combined expected noise levels for the two systems. The excellent agreement shows that the use of a strapdown INS/DGPS system is a promising approach to airborne gravity. |
