A Method of Deflection of the Vertical Measurement Based on Attitude Difference Compensation

To solve the problem of dynamic measurement of deflection of the vertical (DOV) based on the combination of the strapdown inertial navigation system (SINS) and the global navigation satellite system (GNSS), a DOV recovery method based on attitude difference compensation is proposed. The method does not need to model the unknown DOV and avoids the modeling inaccuracy error. Firstly, the attitude angles are estimated by the SINS/GNSS integrated navigation system using Kalman filter. At the same time, the attitude angles are also calculated by integrating the gyro unit of SINS with GNSS. The difference between attitude angles obtained by the two methods is made, and the horizontal attitude difference includes the DOV information and the gyro attitude error with definite characteristics. Then the DOVs in the inertial navigation system are compensated by the horizontal attitude difference with modeled gyro attitude error. The fading memory Kalman filter is used to estimate the attitude angles of INS after DOV compensation, and the attitude angles are taken as the benchmark to make a difference with the attitude angles obtained by SINS/GNSS integrated navigation system. The difference result is the DOVs along the trajectory. In order to find out the optimal fading factor, a traversal search method based on the velocity error of pure inertial solution after DOV compensation is proposed. The shipboard experiment shows that the method can recover the DOVs along the trajectory. After compensation with the recovered DOVs, the positioning error of 21.6-hours pure inertial solution of the SINS is not more than 150 meters, and the positioning accuracy is improved about 6.7 times compared with the Sandwell model compensation.