An Improved Method for Dynamic Measurement of Deflections of the Vertical Based on the Maintenance of Attitude Reference

Abstract

A new method for dynamic measurement of deflections of the vertical (DOV) is proposed in this paper. The integration of an inertial navigation system (INS) and global navigation satellite system (GNSS) is constructed to measure the body's attitude with respect to the astronomical coordinates. Simultaneously, the attitude with respect to the geodetic coordinates is initially measured by a star sensor under quasi-static condition and then maintained by the laser gyroscope unit (LGU), which is composed of three gyroscopes in the INS, when the vehicle travels along survey lines. Deflections of the vertical are calculated by using the difference between the attitudes with respect to the geodetic coordinates and astronomical coordinates. Moreover, an algorithm for removing the trend error of the vertical deflections is developed with the aid of Earth Gravitational Model 2008 (EGM2008). In comparison with traditional methods, the new method required less accurate GNSS, because the dynamic acceleration calculation is avoided. The errors of inertial sensors are well resolved in the INS/GNSS integration, which is implemented by a Rauch–Tung–Striebel (RTS) smoother. In addition, a single-axis indexed INS is adopted to improve the observability of the system errors and to restrain the inertial sensor errors. The proposed method is validated by Monte Carlo simulations. The results show that deflections of the vertical can achieve a precision of better than 1″ for a single survey line. The proposed method can be applied to a gravimetry system based on a ground vehicle or ship with a speed lower than 25 m/s.

Dynamic measurement of high-frequency deflections of the vertical based on the observation of INS/GNSS integration attitude error

“…Due to the accurate and proper modeling of the state-space, the DOV can be separated from the systematic errors. This paper is an improvement to our former research (see Dai et al, 2014). In comparison with the former research, the new method proposed in this paper can measure the DOV in the absence of star sensor, and the systematic errors are well reduced based on an accurate state-space model.…”

“…(11) and (12) that the DOV information is directly related to the attitude errors of INS/GNSS integration. The linear relationship between INS/GNSS attitude errors and DOV indicates the possibility of estimating DOV when INS/GNSS attitude errors are obtained (Dai et al, 2014).…”

An Analysis of the Attitude Estimation Errors Caused by the Deflections of Vertical in the Integration of Rotational INS and GNSS

“…In the work of Grejner-Brzezinska [5,23,24], it was shown theoretically and experimentally that DOV can introduce a tilt error of vehicles, which should be compensated or modeled for a high accuracy attitude estimation. In fact, high-precision INS/GNSS integrated navigation systems have also served as vector gravimetry to measure the DOV [25,26,27,28]. In the studies of [27,28], the attitude reference decoupled from DOV was constructed with the raw gyros data of the INS for the INS/GNSS attitude error calculation.…”

“…In fact, high-precision INS/GNSS integrated navigation systems have also served as vector gravimetry to measure the DOV [25,26,27,28]. In the studies of [27,28], the attitude reference decoupled from DOV was constructed with the raw gyros data of the INS for the INS/GNSS attitude error calculation. Subsequently, with the accurate modeling of DOV and inertial sensors, the DOV can be obtained by the difference between two sets of attitudes.…”

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

“…Besides online gravity models, en route gravity compensation methods using gradiometers are reported [4,5]. However, due to its independence from the accuracy of gravity sensitive instrumentation, gravity modeling has always been introduced into INSs [5,6]. …”