An Online Gravity Modeling Method Applied for High Precision Free-INS

The gravity disturbance vector is one of the major error sources in high-precision and long-term inertial navigation applications. Specific to the inertial navigation systems (INSs) with high-order horizontal damping networks, analyses of the error propagation show that the gravity-induced errors exist almost exclusively in the horizontal channels and are mostly caused by deflections of the vertical (DOV). Low-frequency components of the DOV propagate into the latitude and longitude errors at a ratio of 1:1 and time-varying fluctuations in the DOV excite Schuler oscillation. This paper presents two gravity compensation methods using the Earth Gravitational Model 2008 (EGM2008), namely, interpolation from the off-line database and computing gravity vectors directly using the spherical harmonic model. Particular attention is given to the error contribution of the gravity update interval and computing time delay. It is recommended for the marine navigation that a gravity vector should be calculated within 1 s and updated every 100 s at most. To meet this demand, the time duration of calculating the current gravity vector using EGM2008 has been reduced to less than 1 s by optimizing the calculation procedure. A few off-line experiments were conducted using the data of a shipborne INS collected during an actual sea test. With the aid of EGM2008, most of the low-frequency components of the position errors caused by the gravity disturbance vector have been removed and the Schuler oscillation has been attenuated effectively. In the rugged terrain, the horizontal position error could be reduced at best 48.85% of its regional maximum. The experimental results match with the theoretical analysis and indicate that EGM2008 is suitable for gravity compensation of the high-precision and long-term INSs.

Section: Real-time Gravity Compensationmentioning

confidence: 99%

“…Thus it is reasonable to take advantage of the EGM2008 for gravity compensation in INSs. A few studies based on the theoretical analysis and simulation on such methods indicate that it is effective to compensate gravity induced INS errors with the aid of EGM2008 [5,23,24,25]. …”

Section: Introductionmentioning

confidence: 99%

Gravity Compensation Using EGM2008 for High-Precision Long-Term Inertial Navigation Systems

Han

et al. 2016

“…However, due to the disadvantage of low measuring precision, a single MEMS inertial sensor is not sufficient to achieve satisfactory precision. On the other hand, high accuracy attitude angles can be obtained by MEMS gyroscope which performs correction using the geomagnetic and gravity vectors and where the conventional attitude reference system has the same combination mode [ 1 , 2 , 3 , 4 , 5 , 6 ]. Although the gravity vector can effectively modify the attitude angle information [ 7 ], the geomagnetic vector used to correct the heading angle cannot accurately point to the geographical North pole because of magnetic declination.…”

Section: Introductionmentioning

confidence: 99%

A Novel Attitude Determination System Aided by Polarization Sensor

Wei

Chu

et al. 2018

This paper aims to develop a novel attitude determination system aided by polarization sensor. An improved heading angle function is derived using the perpendicular relationship between directions of E-vector of linearly polarized light and solar vector in the atmospheric polarization distribution model. The Extended Kalman filter (EKF) with quaternion differential equation as a dynamic model is applied to fuse the data from sensors. The covariance functions of filter process and measurement noises are deduced in detail. The indoor and outdoor tests are conducted to verify the validity and feasibility of proposed attitude determination system. The test results showed that polarization sensor is not affected by magnetic field, thus the proposed system can work properly in environments containing the magnetic interference. The results also showed that proposed system has higher measurement accuracy than common attitude determination system and can provide precise parameters for Unmanned Aerial Vehicle (UAV) flight control. The main contribution of this paper is implementation of the EKF for incorporating the self-developed polarization sensor into the conventional attitude determination system. The real-world experiment with the quad-rotor proved that proposed system can work in a magnetic interference environment and provide sufficient accuracy in attitude determination for autonomous navigation of vehicle.

“…Nowadays, with the release of ultra-high degree global Earth gravitational models, such as the EGM2008, horizontal gravity disturbances can be precisely calculated based on these spherical harmonic models (SHMs), and the effect of horizontal gravity disturbance on INS can be compensated. The compensation method based on SHM is preferable, because only some software updates of INS are needed to obtain the horizontal gravity disturbance, instead of using a costly gradiometer [ 16 , 17 ]. In this paper, calculation of the horizontal gravity disturbance based on SHM is described in detail.…”

Section: Introductionmentioning

confidence: 99%

A Model of Gravity Vector Measurement Noise for Estimating Accelerometer Bias in Gravity Disturbance Compensation

Tie

Cao

Chang

et al. 2018

Compensation of gravity disturbance can improve the precision of inertial navigation, but the effect of compensation will decrease due to the accelerometer bias, and estimation of the accelerometer bias is a crucial issue in gravity disturbance compensation. This paper first investigates the effect of accelerometer bias on gravity disturbance compensation, and the situation in which the accelerometer bias should be estimated is established. The accelerometer bias is estimated from the gravity vector measurement, and a model of measurement noise in gravity vector measurement is built. Based on this model, accelerometer bias is separated from the gravity vector measurement error by the method of least squares. Horizontal gravity disturbances are calculated through EGM2008 spherical harmonic model to build the simulation scene, and the simulation results indicate that precise estimations of the accelerometer bias can be obtained with the proposed method.