AIRBORNE VECTOR GRAVIMETRY USING PRECISE, POSITION-AIDED INERTIAL MEASUREMENT UNITS

Vector gravimetry using a precise inertial navigation system continual ly updated with external position data, for example using GPS, is stud ied with respect to two problems. The first concerns the attitude accu racy requirement for horizontal gravity component estimation. With cov ariance analyses in the space and frequency domains it is argued that with relatively stable uncompensated gyro drift, the short-wavelength gravity vector can be estimated without the aid of external attitude u pdates. The second problem concerns the state-space estimation of the gravity signal where considerable approximations must be assumed in th e gravity model in order to take advantage of the ensemble error estim ation afforded by the Kalman filter technique. Gauss-Markov models for the gravity field are specially designed to reflect the attenuation o f the signal at a specific altitude and the omission of the long-wavel ength components from the estimation. With medium accuracy INS/GPS sys tems, the horizontal components of gravity with wavelengths shorter th an 250 km should be estimable to an accuracy of 4-6 mgal (mu g); while high accuracy systems should yield an improvement to 1-2 mgal.