Theory, Methods And Applications Of Airborne Gravimetry

In this dissertation the theories and methods for the airborne gravimetry are investigated in detail with the emphasis on four aspects, on the basis of three groups of real data from Hanzhong, Datong and Harbin tests using the first Chinese Airborne Gravimetry System (CHAGS). They are the data filtering, airborne gravimeter observation processing, the precise determination of the vertical acceleration and the estimation of the airborne gravity disturbance vector. Furthermore, we also focus on the precise determination of the local geoid by using airborne gravity data. The main works and contributions are summarized as follows.1. On the basis of the Newton's second law of motion, the gravity equations relevant to the stabilized systems and the strapdown systems for the airborne vector gravimetry and those related to the stabilized systems, the rotation invariant system and the strapdown systems for the airborne scalar gravimetry are established.2. For the local coordination of the airborne gravimeter and the GPS antenna phase center, the lever arm corrections with respect to the GPS position, velocity and acceleration are formulated. The test results indicate that only the lever arm corrections for the free-air corrections and the vertical accelerations are required to be taken into account in reality.3. In view of the dependence of the accuracy and resolution for the airborne gravimetry, one new concept to determine the cutoff frequency of the lowpass filter that based on the spectral windows for the airborne gravimetry and the internal accuracy (e.g. crossover errors) under different filter length is advanced.4. Instead of using the traditional filters in airborne gravimetry, viz. the 6x20s resistor-capacitor (RC) filter and the 300s Gaussian filter, we design the Finite Impulse Response (FIR) filter and the cascaded Butterworth filter that can be suited for various operation conditions. Aiming to reduce the length of the FIR filter, a technique involved in a cascaded FIR filter is suggested to filter the raw airborne gravity.5. The spectral properties of the stabilized platform tilt angle and the horizontal acceleration correction are investigated and analyzed. The amount of the pre-filtering of the horizontal acceleration correction is derived, which matches the platform period. With this amount the potentially systemic biases due to the imperfection of the horizontal acceleration correction can be reduced significantly.6. The dependence of the beam scale factor (K-factor) on the amount of the filtering applied to the data is discussed. Four methods for calibrating the K-factor are developed, and the results show that the accuracy of the airborne gravity anomalies is improved about 0.2~0.4mGal by using of the new K-factor.7. The cross-coupling corrections for the L&R gravimeter are computed as a linear combination of 5 so-called cross-coupling monitors, the weight factors (coefficients) determined from marine data by factory may not be optimal for airborne application. In this paper, these coefficients are recalibrated to minimize the difference between airborne data and upward continued surface data (external calibration) and to minimize the errors at line crossings (internal calibration) respectively. An integrating method to simultaneously recalibrate the above mentioned coefficients and the K-factor is also presented. Numerical results show that the systemic errors in the airborne gravity anomalies can be greatly reduced using any of the recalibrated coefficients.The systemic error is reduced from 4mGal to 1mGal in Datong test. Since the internal calibration requires only the survey to be well structured, with a large and well-distributed number of line crossings, and it doesn't require any of external information, it will be useful and valuable.8. The main factors that impact on the precise determination of the vertical acceleration using GPS are the residual atmospheric and orbit errors, multipath errors, measurement noise and the errors due to changes in the satellite cons...