Abstract
An aided Inertial Navigation System (INS) is increasingly exploited in precise engineering surveying, such as railway track irregularity measurement, where a high relative measurement accuracy rather than absolute accuracy is emphasized. However, how to evaluate the relative measurement accuracy of the aided INS has rarely been studied. We address this problem with a semi-analytical method to analyze the relative measurement error propagation of the Global Navigation Satellite System (GNSS) and INS integrated system, specifically for the railway track irregularity measurement application. The GNSS/INS integration in this application is simplified as a linear time-invariant stochastic system driven only by white Gaussian noise, and an analytical solution for the navigation errors in the Laplace domain is obtained by analyzing the resulting steady-state Kalman filter. Then, a time series of the error is obtained through a subsequent Monte Carlo simulation based on the derived error propagation model. The proposed analysis method is then validated through data simulation and field tests. The results indicate that a 1 mm accuracy in measuring the track irregularity is achievable for the GNSS/INS integrated system. Meanwhile, the influences of the dominant inertial sensor errors on the final measurement accuracy are analyzed quantitatively and discussed comprehensively.
Highlights
The integration of a Global Navigation Satellite System (GNSS) and an Inertial Navigation System (INS) has been widely used in weapon guidance, aviation engineering, and land mobile mapping to provide accurate georeferencing(Liu et al, 2020; El-Sheimy and Youssef, 2020)
The results show that 1 mm accuracy is achievable in vertical and horizontal track irregularity measurements with a navigation-grade Inertial Measurement Unit (IMU) aided by a carrier-phase differential GNSS and the Nonholonomic Constraint (NHC)
The statistical values of the measurement errors from both the semi-analytical and simulation approaches are listed in Table 2, which demonstrates that the consistence between these two methods is better than 85%
Summary
The integration of a Global Navigation Satellite System (GNSS) and an Inertial Navigation System (INS) has been widely used in weapon guidance, aviation engineering, and land mobile mapping to provide accurate georeferencing(Liu et al , 2020; El-Sheimy and Youssef , 2020). The second kind of applications pays more attention to the absolute accuracy, which is dominated by the mid-term and longterm error components, while the railway track irregularity measurement, a typical precise inertial surveying application, is more concerned with the temporal or spatial relative measurement accuracy, like the smoothness of the estimated trajectory, as illustrated in Fig. 9 in the appendix We would expect the apparatus corrupted by error process y have better accuracy in measuring railway track irregularities, as depicted in the lower panel and discussed in the appendix This example reveals that the covariance matrix or the propagation models of the aided INS navigation errors do not contain the information describing the temporal correlation characteristics, which determine the relative measurement accuracy. For the research on precise railway track irregularity measurement by an aided INS, the following two questions are often asked
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