To achieve high Strapdown Inertial Navigation System (SINS) alignment accuracy within a short period of time is still a challenging issue for underwater vehicles. In this paper, a new SINS initial alignment scheme aided by the velocity derived from Doppler Velocity Log (DVL) is proposed to solve this problem. In the stage of the coarse alignment, the velocity of DVL is employed to reduce the impact of the linear motion. With a backtracking framework, the fine alignment runs with the data recorded during the process of the coarse alignment and thus will speed up the overall alignment process. In addition, by using this new scheme, it is equivalent to length the alignment time for both coarse and fine alignments, so the accuracy of the alignments will be improved. In order to reduce the volume of the data that has to be recorded, a new model for SINS fine alignment is derived in the inertial reference frame which makes it feasible for real time applications. The experimental results are presented for both unaided static and in-motion alignment using DVL aiding. It is clearly shown that the proposed method meets the requirement of SINS alignment for underwater vehicles.

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A Fast SINS Initial Alignment Scheme for Underwater Vehicle Applications

In-motion alignment of Strapdown Inertial Navigation Systems (SINS) without any geodetic-frame observations is one of the toughest challenges for Autonomous Underwater Vehicles (AUV). This paper presents a novel scheme for Doppler Velocity Log (DVL) aided SINS alignment using Unscented Kalman Filter (UKF) which allows large initial misalignments. With the proposed mechanism, a nonlinear SINS error model is presented and the measurement model is derived under the assumption that large misalignments may exist. Since a priori knowledge of the measurement noise covariance is of great importance to robustness of the UKF, the covariance-matching methods widely used in the Adaptive KF (AKF) are extended for use in Adaptive UKF (AUKF). Experimental results show that the proposed DVL-aided alignment model is effective with any initial heading errors. The performances of the adaptive filtering methods are evaluated with regards to their parameter estimation stability. Furthermore, it is clearly shown that the measurement noise covariance can be estimated reliably by the adaptive UKF methods and hence improve the performance of the alignment.

A novel scheme for DVL-aided SINS in-motion alignment using UKF techniques

Fuzzy adaptive integration scheme for low-cost SINS/GPS navigation system

The Position and Orientation System is integrated measurement equipment for airborne remote sensing system. The calibration of gyro biases is an effective way to reduce azimuth misalignment and navigation error of strapdown inertial navigation system (SINS). According to the analytic-coarse-alignment principle, the sensitivities of Euler angles with respect to inertial sensor biases are analyzed uniquely. The errors of Earth rotation rate in body frame caused by initial misalignment are obtained. Based on the transformation model of gyro biases, a novel analytic calibration of gyro biases with arbitrary double position is proposed. The simulation and experiment results show that the method can accurately calibrate the gyro biases, improve the precision of initial alignment and inertial navigation for SINS, and verify the efficiency of the proposed method.

Error Analysis and Gyro-Bias Calibration of Analytic Coarse Alignment for Airborne POS

As one type of autonomous navigation system, the inertial navigation does not need to receive any external information. Relying on the data measured by gyroscope and accelerometer, it could solve the motional parameters of position, velocity, and attitude via navigation computer, which is the most important navigation system for the OTV.

INS/GNSS Integrated Navigation Technology

In order to solve the strapdown inertial navigation system (INS) alignment problem under the marine mooring condition, the rapid strapdown INS fine alignment method is proposed. This method uses the gravity in the inertial frame to deal with the lineal and angular disturbances. Also the forward and backward processes for strapdown INS calculation and filter estimation are designed. Making use of the forward and backward processes to repeatedly process the saved inertial measurement unit (IMU) data sequence could quickly obtain the initial strapdown attitude matrix. Simulation and trial test validate the performance of the proposed rapid fine strapdown INS alignment.

Rapid Fine Strapdown INS Alignment Method under Marine Mooring Condition

A novel algorithm for marine strapdown gyrocompass based on digital filter

Conventional attitude algorithms for strapdown inertial navigation system (SINS) use angular increment as algorithm input. However, these algorithms do not address the issue of angular rate which is the output of modern-day gyro. The integration of angular rate for the purpose of getting angular increment degrades the algorithm performance inevitably. To solve this problem, a generalized method for improved coning algorithms is proposed. The improved coning algorithms use angular rate as algorithm input and estimate the coning term with the cross product of angular rates. Simulations are carried out under coning motion. While angular rate is used as algorithm input, the accuracy of attitude computation can be improved effectively by using improved coning algorithms as compared with conventional ones.

Generalized Method for Improved Coning Algorithms using Angular Rate

The transversal coordinate system has been proposed to solve the problem of navigation in the Polar Region for a strapdown inertial navigation system (INS). However, it is assumed that the Earth is a perfect sphere in the transversal coordinate system, which is not accurate for a high-precision INS. To solve this problem, we consider the Earth as a reference ellipsoid and then deduct its radii of curvature in our transversal coordinate system. In addition, with the aid of the Bessel geodetic projection method, transformations of navigation quantities from a local-level coordinate system to our transversal coordinate system are derived based on the reference ellipsoid. Numerical results indicate that our method based on the reference ellipsoid performs better than the method based on a reference sphere.

Yueyang Ben

Papers

Rapid Fine Strapdown INS Alignment Method under Marine Mooring Condition

A novel algorithm for marine strapdown gyrocompass based on digital filter

Generalized Method for Improved Coning Algorithms using Angular Rate

Transversal Strapdown INS Based on Reference Ellipsoid for Vehicle in the Polar Region

System reset of transversal strapdown INS for ship in polar region