Research On GT-2A Airborne Gravity Data Processing

The basic principle and data processing method of airborne gravimetry are mentioned in this thesis,as well as more details about the FIR/IIR low-pass filter and Kalman filter designed for acquiring the gravity disturbances from observations of the airborne gravimeter,and research on the iterative/FFT methods based on Poisson's integral formula and the direct representation method used for the downward continuation of the gravity disturbances.Based on these theories and methods,we use the observations derived from GT-2A airborne gravimeter and the ground gravity data in two areas(one is a flat and another is mountainous)as the experimental data.Using these data,we can examine the algorithm designed by ourselves,compare the downward continuation methods,and evaluate the measuring accuracy of the GT-2A airborne gravimetry system.The main work and contributions in this dissertation are as following:1)Based on the basic principle of airborne gravity measurement and data processing methods,our research is focused on the design of filters using FIR,IIR and Kalman approach respectively,as well as the downward continuation methods,including the iterative/FFT methods based on Poisson's integral formula and the direct representation method.Thus,an approach for processing GT-2A airborne gravity measurements has been accomplished,which can be used to acquire gravity disturbances from the original observations and evaluate the accuracy of the results.2)The FIR low-pass filters are designed by different kinds of window functions,while the IIR low-pass filters are designed based on Butterworth and Chebyshev approach,and the Kalman filter includes the forward and backward filtering procedure.We have used all these filters to process the airborne gravimetry observations to get the gravtity disturbances,which are then compared to the results from the GTGRAV,a commercial software accompanied with GT airborne gravimetry system.The result shows that the FIR low-pass filter designed by Hamming window functions is the most reliable one among all the filters mentioned here,whose results are closest to the results from GTGRAV.The standard error of their differences is ± 1.25 mGal.3)Using the observations on cross-over point and repeat lines,we can evaluate the inner accuracy of GT-2A system.Before network adjustment the inner accuracy calculated by the discrepancies of the cross-over data is 1.39 mGal,and after network adjustment it turns to be 0.88 mGal.The inner accuracy calculated by the discrepancies of the data on the repeat lines is 0.85 mGal.Thus,the inner accuracy of GT-2A system is believed to be better than 1 mGal.4)The downward continuation of gravity disturbances is accomplished by iterative/FFT methods based on Poisson's integral formula and the direct representation method respectively.Comparing the airborne gravimetry measuring results with the ground gravity data after setting them to the same points by downward continuation,we can evaluate the outer accuracy of GT-2A system and compare the three methods for continuation.The result shows that the FFT methods is the best.In flat area the outer accuracy is 1.46 mGal.In the mountainous area the gravity disturbance from GT-2A on the height of 4000 m has the outer accuracy of 3.17 mGal,while that on the height of 4500 m is 3.36 mGal.