Research On Error Estimation Of Precise Strapdown Airborne Gravimeter

Airborne gravimetry is the method to map the regional and local gravity field on air-plane. Compared to the classic method, it has the advantage of high speed, wide area, lowcost, and it is able to carry out the gravity survey in those special zones, such as desert-s, glaciers, swamps and virgin forests, where inconvenient traffic and uninhabited areasmake the ground gravity could not be available. It can obtain quickly and economical-ly the gravitational field of large area with the characteristic of uniform distribution andgood accuracy. Strapdown airborne gravimeter has the merits of small size, light weight,low cost, high reliability and low power consumption, and it will play a huge role in theairborne gravity surveys.In the completion of863projects“Airborne gravity exploration systems devel-opment and integration”, combined with the strapdown airborne gravimeter SGA-WZwhich was developed by the National University of Defense Technology, the thesis car-ried out in-depth researches in strapdown airborne gravimeter error analysis, device errorestimation, the lever arm estimation and precision assessment. Main results are summa-rized as follows:Firstly, It carried out in-depth study in the principle of strapdown airborne gravime-ter, including mathematical model and its main source of error, posed the requirementsof components to achieve the goal of1mGal/1km. It contains the sensor accuracy, theaccuracy of GPS, the time synchronization accuracy, the temperature control accuracyand the vibration system. In the sensor accuracy, it gives details of the horizontal andvertical accelerometers, level and azimuth gyroscopes. In the mean time, it distinguishesthe accelerometer scale factor temperature coefficient, quantization error and the second-order nonlinearity error. It provides specific indicators and reference for development ofstrapdown airborne gravimeter.Secondly, constant speed and straight course makes ordinary15state filter does notmeet the observability conditions during the airborne surveys. In analysis of the rela-tionship between the the vertical gyro drift and level accelerometer bias, it proposes thestepwise parameter solidification algorithm to get a better estimation of the sensor error.Simulation results show that, the repeated line precision of SPS is0.56mGal/2km whilethat of generic method is0.77mGal/2km for, SPS has an improvement of approximately 27%. Experimental results show that, SPS algorithm accuracy is1.10mGal/6km, whilethat of generic method is1.34mGal/6km, SPS algorithm has a better improvement ofapproximately17.9%. Simulation and experiments show that the the SPS algorithm caneffectively get a good estimation of the gyro drift, thereby increases the accuracy of hori-zontal accelerometer bias, which ultimately improves the accuracy of the airborne gravitysurvey.Thirdly, it analyzes the mechanism of the lever arm error referred to strapdown air-borne gravimeter and points out the need to achieve the accuracy of the lever arm errorwhich requires10cm. Extended Kalman filter is applied and analyzed, a detailed deriva-tion of observation equation is derived. Analysis of he observability of the lever arm wasthen carried out which shows that two or more different angular movement in differentdirections can make the lever arm completely observable. The simulation results showthat two or more different angular movement in different directions can make the lever ar-m vector completely observable, while single direction angular motion can not guaranteethe lever arm vector in global aspect which means the convergence of the lever arm vec-tor can not be kept. Experimental results show substantial lever arm vector analysis andextended Kalman filter is an effective and feasible way to estimate the lever arm vector.Fourthly, traditional accuracy assessment method of airborne gravity measurementsis crossover point and repeat line inconsistency. But it can not effectively assess the pre-cision of a single measuring line. It proposes a method assessment of strapdown gravitymeter for a single line measurement accuracy which was bases on the DoHab assessmentmethod. Two sets of actual airborne gravity flight experiment were used to validate theDoHab method. Comparison results show that the DoHab method is better than ordi-nary method in distinguishing the degrees of the deviation. The DoHab method couldeffectively distinguish two single lines with quite different precision. The paper makesan exploration and study on the quality control methods to improve strapdown airbornegravimeter while ensuring the accuracy of the airborne flight surveys.