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The gravity anomaly matching technique is one of the key technologies in gravity aided inertial navigation, which is a totally passive method to correct the accumulated system error. The gravity anomaly measurement with a gravimeter operates in the real position of a vehicle are compared with the data picked up from a gravity map with the position indicated by the inertial system. The difference contains the position error information which can be estimated in a kalman filter as well as in other system. In consideration of the nonlinearity of the gravity anomaly distribution, nonlinear filtering algorithms are applied into the gravity anomaly matching technique. The measurement noise which is the difference between the gravimeter data and the map data in the same position affect the estimating result a lot, while former studies usually use the white noise to simulate the measurement noise, which cannot represent the real situation. In this paper, the measurement noises are analyzed in detail based on the real gravimeter data and the existing gravity map. According to the applications of the shipborne inertial attitude measurement system, which moves in a relatively low speed, the characteristics of the measurement noises are discussed. Different from the former studies in which the measurement noises are simply treated as the white noise, the noise intensity and the correlation time are both considered as the parameters when modelling the measurement noise. The impact of the measurement noise on the gravity anomaly matching technique are also analyzed with different model parameters. Based on the parameter identification of the global gravity anomaly model, the frequency domain analysis are applied to the gravity anomaly signal that the shipborne inertial attitude measurement system sensed. The gravity anomaly signal along the trace are simulated as the Gauss-Markov process with different parameters, while the measurement noise are also generated independently. The impact of the measurement noise on the gravity anomaly matching technique are studied in detail with changing the parameter. Semi-physical simulations are operated with the real movement parameters of a shipborne inertial attitude measurement system and the simulated gravimeter data. With the cubature kalman filtering algorithm used in a single-axis rotation attitude & heading measurement system, the matching results show that the attitude estimation accuracy and the convergence rate improves with the measurement noise intensity decreasing, which indicates that the measuring accuracy of the gravity anomaly data should be enhanced. On the other hand, with the correlation time increasing, the filter becomes much easier to diverge, which means the resolution power of the measuring data should be improved. Methods to decrease the time correlation of the gravity anomaly data are also discussed. Simulation results show that by extending the sample time or enhancing the space frequency, the diverging of the filter can both be well restrained. The optimal parameters are existed with given accuracy of the system and the movement.

In this paper, we integrate the high-precision inertial navigation system (INS) with the GPS precise point positioning (PPP) by using the tightly-coupled architecture, which aims to obtain the preferable attitude and positioning information in the remote marine applications. The structure of INS/PPP tightly-coupled integrated navigation is presented firstly in the paper. Then, the observation model in the local geographic frame (ENU frame) is derived, where the Extend Kalman filter (EKF) is used for the information fusion. Finally, a real shipborne marine test is conducted to test the performance of INS/PPP tightly coupled integration. The experimental results show that the positioning accuracy of the integrated navigation system can be better than 10cm in the horizontal axis and 20cm for the vertical channel, and the attitude estimation error can be smaller than 1 arcsec. Besides this, the performance the tightly-coupled integration can be maintained during 100s simulated signal outages, while that performance of loosely-coupled integration will degrade significantly in such a case.

The optical method is one of the most accurate methods for the 3D angular deformations measurement. However, the measured results fluctuate around a mean value as a result of the impact of the atmospheric turbulence, and the relationship between the fluctuation and the atmospheric turbulence is unclear. In this paper, we propose an optical 3D angular deformations measurement method to analyze the optical wave propagation, and study the impact of the atmospheric turbulence. The fluctuations of the three deformation angles are calculated in different atmospheric turbulences. It is found that this optical method is not suitable for high accuracy measurement with the refractive-index structure parameter larger than 10−14 m−2/3. When the widths of the crosshairs fringes are different, the impacts of the atmospheric turbulence are nearly the same. It is also found that the impact of the atmospheric turbulence can be reduced by increasing the gray value of the image.