GPS PHASE ACCELERATIONS FOR MOVING-BASE VECTOR GRAVIMETRY

For airborne gravimetry using INS and GPS, the accelerations from both systems are differenced to yield the gravity acceleration. Usually, t he GPS acceleration is determined by first solving for the position of the vehicle relative to a base station and subsequently taking two ti me derivatives of the vertical component. An alternative method is to time-differentiate the observed phases directly, thus avoiding the cyc le ambiguity problem that must be solved for positioning and that is f raught with (certainly not insurmountable) difficulties in the event o f a cycle slip. Due to the largely unpredictable receiver-clock errors and the imposition of the Selective Availability degradation, doubly differenced (in space) phase accelerations are used to obtain the rela tive vehicle accelerations. Test results for stationary receivers show that the acceleration vector can be determined from phase acceleratio ns to an accuracy of 1 mgal for 40-s averages. The mathematical formul ation of the acceleration determination also highlights certain other advantages over traditional methods, such as the avoidance of the Eotv os correction, although a similar kind of velocity effect must be dete rmined.