Study On Gravity Aided Technologies In Shipborne Attitude Measurement With Ring Laser Gyro

Attitude measurement technique plays an important role in many fields such as the sea-based aerospace measurement and control,and the shipborne missile launching system.As the popular applications of the ring laser gyro on the surface ships and the underwater working platforms,the inertial attitude measurement becomes an important way to measure the attitude in oceanic applications.High accuracy inertial attitude measurement is significantly disturbed by the gravity disturbance.Meanwhile,long endurance measurement precision is hard to be maintained due to the system noise which is accumulated with time.The combination of the oceanic gravity information and the Attitude &Heading Measurement System(AHMS)provides a novel thinking for the development of the passive,all-weather and high-precision attitude measurement on sea surface.In this paper,the real-time acquisition and compensation of the high frequency component of the deflections of the vertical(DOV)and the nonlinear filtering algorithm for the gravity anomaly map matching were studied based on the analysis of the development bottleneck of the gravity-aided inertial attitude measurement.How to reduce the influence of the gravity disturbance on the attitude measurement and how to prevent the system error divergence utilizing the gravity anomaly were analyzed.A gravity vector aided AHMS method is proposed in order to improve the inertial attitude measurement accuracy.The effectiveness of the proposed method is verified by both simulations and experiments.The main work and the research achievements are as follow:(1)The mechanism of the effect of the gravity disturbance on the inertial attitude measurement was deeply analyzed.The analytical results of the gravity induced AHMS attitude error was derived in detail based on the inertial attitude error equation.Meanwhile,the frequency domain characteristic of the attitude error induced by the gravity disturbance was analyzed by the covariance analysis.The results indicate that the high frequency components of the DOV mainly affect the attitude for vehicles moving in a relatively low speed,which provides a clearer research direction to further reduce the attitude error induced by the gravity disturbance.(2)In a view of the demand that the gravity compensation needs high resolution DOV data,on one hand,the error analysis of the existing global gravity model was studied.A more accurate gravity map was obtained based on the map refinement method.On the other hand,the methods of estimating the DOV on-line were studied.Two realtime modified schemes on attitude observation method were proposed to acquire high frequency DOV data,which are the model-selection based self-adaptive delay feedback method(SDF)and the Q-adjusting based attitude observation method(Q-AOM).The results show that both methods can acquire the DOV estimation accuracy which is comparative with the post processing results.(3)The gravity direct compensation based on the gravity map and the gravity filtering compensation based on the DOV estimation were studied based on the data preparation acquired by the gravity map refinement and the high frequency component of the DOV real-time estimation technology.The error characteristics of the map compensation were analyzed and the indexes of the DOV influencing on the attitude error were proposed in order to judge whether the effective compensation can be realized and confirm proper extracting frequency of the DOV,and finally improved the attitude measurement accuracy;For the gravity filtering compensation,the DOV model was built and the compensation was done with the DOV estimation in the AHMS/GNSS.Experiments utilizing the shipborne survey data were done and the results show that the gravity map compensation based on the high-frequency DOV can improve the attitude accuracy in rough terrain area effectively,and the gravity filtering compensation method based on the DOV estimation on-line can provide higher attitude accuracy in the AHMS/GNSS.(4)The gravity anomaly map matching method based on the Cubature Kalman Filter(CKF)was studied in order to reduce the attitude error induced by the accumulated system error.The influences of the system noise and the observation noise on the algorithm were analyzed.The gravity anomaly measurement data accords well with the gravity map by the data preprocessing.With optimizing the observation noise with higher spatial resolving power,the results indicate that the method can effectively avoid the CKF divergence,and the long-term attitude accuracy of AHMS working in autonomous mode can be well maintained.(5)The gravity vector aided AHMS method was proposed based on the DOV compensation and the gravity anomaly map matching.The attitude error induced by the gravity disturbance and the system error was comprehensively reduced.The DOV estimated by AHMS/GNSS were treated as the output of the gravity gradiometer.The experiment results show that the attitude accuracy acquired by the gravity vector aided AHMS method was higher than that of AHMS without aiding.