GRAVITY-FIELD APPROXIMATION USING AIRBORNE GRAVITY GRADIOMETER DATA

A set of airborne Gravity Gradiometer Survey System (GGSS) data was used in combination with the OSU89B geopotential model to predict gravity anomalies and deflections of the vertical. The gradiometer data were collected during an airborne survey of the GGSS in the Texas/Oklahoma area. Nineteen flight tracks were in our disposal for further analysis. These tracks resulted from 54 initial distinct tracks from which a processing was performed by the Analytic Sciences Corporation. In order to assess the quality of the GGSS measurements, a first crossover analysis was carried out. The results showed large discrepancies at the crossing points between East-West (EW) and North-South (NS) tracks. The least squares collocation method and the fast fourier transform technique were used to produce gravity anomalies and deflections of the vertical referred to geoid surface from second-order derivatives measured at the flight level. The predicted gravity values were then compared to "truth-based" point free air gravity anomalies with a standard deviation (s.d.) of the differences at the level of 3 mGal in the best cases. Presumably, improved GGSS data would have given improved predictions of surface gravity values. The predicted deflections of the vertical were compared to "truth-based" values at a small number of ground stations. The very low accuracy of this prediction (s.d. = 5.62 arc sec for xi and 6.78 for eta) should be studied in combination with the inherent characteristics of the gravity field and the validation of GGSS data in the test area.