Research On Advance Data Processing Technology For Air-sea Gravimetry

Marine and Airborne gravimetry are the two effective techniques for obtaining gravity field information.At present,in the case that the accuracy of air-sea gravimetry instruments is not significantly improved.It has great theoretical and practical significance to carry out research on the processing techniques.Based on the previous studies,this paper focuses on the design methods of FIR,IIR and wavelet threshold filtering in gravity anomaly or gravity disturbance signal extraction,as well as the free-air correction of gravity disturbance reduction,spherical harmonic coefficient method and a new method for Searching intersection points.The main research contents and results of the thesis are summarized as follows:1.Based on Newton's second law of motion,the mathematical models of air-sea vector and scalar gravity measurement are derived in detail.The observation equations of gravity measurement system in local horizontal coordinate system and carrier coordinate system are given respectively.The air-sea gravity measurement is summarized one by one.Various corrections were made and numerical calculations and analysis were carried out.2.The fine filtering technique of sea and air gravity measurement data is studied.The FIR,IIR and wavelet threshold filtering are analyzed.The various filtering methods are verified and compared by using the measured data.?1?Two FIR low-pass filters for marine gravimetry are designed using the best uniform approximation and the frequency sampling for eliminating noise.In the same design parameters,the best uniform approximation method gets better low-pass filtering results than that of the frequency sampling method.Lastly,the true marine gravimetry data are processed by the designed low-pass filter and the accuracy of gravity anomaly is in good agreement with the window function filter.?2?Based on the strapdown marine gravity real data,the effectiveness of using wavelet threshold in filtering marine gravity anomaly is checked.Different wavelet,different threshold techniques and different decomposition level are tested.Results show that the db6,db7,db8,db9,db10,sym6,sym7,sym8,sym9,sym10,coif3,coif4 and coif5 are the thirteen wavelets suit for marine gravimetry,and the wavelet decomposition level can be taken to 8 or9 layers.The filtering effect by rigrsure threshold is better.When the wavelet is decomposed into the 8th and 9th layers,the result of the wavelet threshold filtering agrees well with the filtering result using the Butterworth low-pass filter with 0.005 Hz and 0.0033 Hz cut-off frequency,but the result of the wavelet threshold filtering is more smoothing than the Butterworth low-pass filter.And the RMSE of the difference between the two filtering results is within 0.25 mGal.Wavelet threshold filtering is easier to decompose the noise component than the Butterworth low-pass filter,which can eliminate gravity distortion more effectively.3.The precise reduction method of air-sea gravity measurement data is studied.The study explores the method of using the Earth's gravity field model to calculate the gravity disturbance observation at the route height to the average flight height surface,and the method of returning the sea surface gravity anomaly observation value to the geoid.At present,the free-air corrections is incomplete.Based on this fact,we propose spherical harmonic coefficient method,which is a one-step reduction method of gravity disturbance,and its correctness is verified by the Somigliana formula.Then analyze the influence of different free-air correction formulas on gravity disturbance reduction with the reference of spherical harmonic coefficient method.The results show that NGS-improved third order free-air correction has the highest accuracy,H&M free-air correction takes the second place,and the second-order formula widely adopted by Chinese scholars^?has lower accuracy.Therefore,we recommend to use the spherical harmonic coefficient method or the NGS-improved third-order formula to improve the accuracy of airborne gravimetry when at1 mGal or better accuracy of airborne gravimetry or high-altitude surveying.4.The accuracy evaluation technology in the air-sea gravity measurement line network was studied.At present,there are shortcomings such as slow search speed,low correct rate and poor applicability of the conventional search methods in airborne gravity measurement data processing.Based on this fact,we propose the sliding window solve method that the main line point is regarded as the search center and the main and sub line points are searched in a certain size of search box,the adjacent measuring points detected in the main and auxiliary lines form a line segment,and the intersection and discrepancy are determined using the determinant method,projection method and area method.Through practical examples,the sliding window solve method is discussed and analyzed from the aspects of search time and accuracy.The results show that the proposed method is simple and efficient,where the searching efficiency of cross-point is improved and the workload is reduced significantly.