Research On The Methods Of Acceleration Estimation Based On Starfire Differential Gps System With Strapdown Gravimeter

The shipborne gravimetry using strapdown gravimeter has been carried out by using a system which is based on the combination of a Strapdown Inertial Navigation System(SINS) and receivers of Global Positioning System(GPS) being used in differential mode (DGPS).The basic theory of shipborne gravimetry is that gravimeter (or accelerometer) senses the total acceleration including gravity signal, inertial acceleration and other accelerations, and GPS determines the vertical acceleration of the moving-base, then the signal of gravity anomaly will be yielded if vertical acceleration can be subtracted from total acceleration with some corrections. Therefore, the accurate determination of acceleration by using GPS is one of the key problems. There are mainly two approaches estimating the acceleration of moving-base, the position differentiation method and carrier phase direct method. Both methods need to erect the reference station on the ground, not only enhanced the cost of operation, moreover, some regions are unable to erect the reference station, which limited the gravity campaign, especially when the measuring ship is far from the GPS base stations. So it is important and significant to study how using a single GPS receiver to determine the vertical acceleration precisely.In this paper, the method of acceleration estimation based on StarFire Differential GPS System,low-pass filtering of the observed data and low-order integral coefficient differentiators were studied. The main work and innovations of this paper are summarized as follows:1. The two main methods using GPS to determine acceleration of moving-base were studied and analyzed, and the accuracy of acceleration in theory is given in different filtering intervals. The propagation characteristics of the differential expressions are analyzed, which provide a theoretical basis to the digital differentiator preference and low-pass filter design.2. The low-order integral coefficient differentiators were compared and analyzed. Frequency characteristics and the error of frequency in different orders were studied. Through simulation, the optimal differentiator for acceleration determination was selected. The FIR low-pass filter is designed based on the Chebyshev best uniform approximation theory by combining the noisy characteristics of gravity measurements.3. The method of evaluating the accuracy of acceleration was created. The accuracy of positioning was evaluated. The precision of acceleration determination is evaluated by using different filtering intervals in static and kinematic respectively. The results showed that under static, the accuracy of vertical acceleration is 0.5121mGal with 200s FIR low-pass filtering. Under kinematic, the accuracy of vertical acceleration is 0.5736mGal with 200s FIR low-pass filtering. The accuracy of accelerations using different differentiators was also studied, and the optimal differentiator was given.