Research On Filtering Technique Of Strapdown Airborne Gravimetry Data

Surveying the Earth's gravity field refers to an important domain of Geodesy,involving deep connections with Earth Sciences and the area of military application.Airborne gravimetry,which can fill the gap between satellite observations and terrestrial gravity field measurements at spatial resolution of several kilometers over large areas,is an efficient way to map the earth gravity field.Since airborne graivimetry is carried out in a very dynamic envirement,the signal noise rate of the gravimetry data is extreme low.How to extract gravity disturbance from such noisy data is one of the key steps in airborne gravimetry.In this paper,based on the strapdown airborne graimeter SGA-WZ,we focus on the filtering technique of strapdown airborne gravimetry data.Following is the main contribution of this paper:First,analyze the basis principle of strapdown airborne gravimetry.From the results of simulation in both ideal and dynamic envirement,it is clear that the virbration of engine and the natrue motion of the aircraft are the main isuses which will impact on the accuracy of airborne graivmetry data.In order to estimate dynamics of the aircraft,an estimation expression is designed.Second,the main drawback of the low pass filter in airborne gravimetry is founded after comparing with different sets of filtering data.When analyzing on the sample type of airborne gravimetry data,it is fact that the filtered datum are not in the same resolution because of the variable velocity of aircraft.A new method with the same sample rate on the space is suggested.Then since there are strong relationship of the gravity disturbance between the data in the same line but different flights,the wavenumber correlation filter is used to improve the accuracy of the repeated gravimetry data.Third,in order to conquer the drawback of lacking data-adaptive technique,based on the multi-scale character of the gravity disturbance,wavelet anaysis is employed to extract gravity disturbace from the raw gravimetry data.A method using wavelet shirink thresholding technique combined with the estimation expression of flight dynamics is used first.Then according to the different shapes of wavelet coefficients of the noise and gravity disturbance in airborne gravimetry data,a maximum module method is carried out to improve the accuracy of airborne gravimetry data.At last,emperical mode decomposition(EMD)is taken as a new filtering method to estimate gravity disturbance which can conquer the drawback of irregular sample data in space.The low pass filter based on EMD is analyzied.Some techniques on dertermining the critical point,such as wavelet analysis,the distribution of the power destiny of IMF and the self correlation function are used.Wavelet shrink threshold technique is also used to filter the IMFs..