An investigation into acceleration determination for airborne gravimetry using the Global Positioning System

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This thesis investigates the determination of acceleration using the NAVSTAR Global Positioning System (GPS) for airborne gravimetric applications. Particular attention is placed on the development and implementation of an observing model which will accurately measure accelerations using the second time derivative of the GPS carrier phase. This development follows from the work performed by Kleusberg et al [1989] and Kleusberg [1989]. The position and velocity requirements for airborne gravimetry have been met using GPS observing and processing techniques. However, the separation of the airborne acceleration due to air pockets, wind gusts, etc., from the observed gravity still remains to be resolved to the 1 to 2 mGal accuracy requirements. As a means towards determining accelerations to this accuracy level, this thesis develops a model in which the accelerations are obtained by utilizing the second time derivative of the GPS carrier phase. Carrier phase data was collected from pairs of GPS receivers located at fixed points. Three different types of GPS receivers available to the market today were used for data analysis. Spectral analysis techniques in determining acquired acceleration accuracy were applied to computed accelerations from these data sets. Low-pass filters were applied to the acceleration data in order to separate the high frequency receiver measurement noise from the low frequency acceleration data. The implications and handling of GPS data contaminated by selective availability is addressed. Results show that for carrier phase observations over a fixed baseline of less than 100 metres differential techniques can give accelerations which meet the 1 to 2 mGal accuracy requirements. Recommendations for the continuation of this research are given as well.