Abstract
In this study, we improve the matching accuracy of underwater gravity matching navigation. Firstly, the Iterative Optimal Annulus Point (IOAP) method with a novel grid topology is proposed for breaking through the inherent grid structure limit of the canonical gravity matching algorithm and enhancing its underwater gravity matching accuracy. The theory of IOAP is as follows: (1) small-annulus matching and positioning mechanism on the tracking starting point is developed by employing the starting point and drift error of the INS (Inertial Navigation System), the fixed rotation angle, etc. The optimal matching location of the starting point is obtained by matching and comparing the matched points in this small-annulus grid, which contributes to heightening the initial-position error insensitivity of the algorithms. (2) Variable-angle three-layer annulus matching and positioning mechanisms on the tracking ending point were constructed by using the optimal matching location of the starting point and combining the tracking direction-and-distance information of the INS and the cumulative drift error, etc. It is used to generate the annulus matching points with the ring-type grid topology. (3) The optimal matching position of the ending point in this annulus is obtained by iteratively calculating the evaluation index value of the matching points and following the evaluation index optimal rule. Secondly, we comprehensively consider the main performance evaluation indexes of the underwater gravity matching algorithms, such as the statistical indicators of the matching accuracy, the average matching time and the matching success rate, and take them as a basis of the pros and cons of the matching analysis. Furthermore, under conditions that include different scale searching regions or different reference-angle ring radii, the statistical results verify that the IOAP had a different matching ability and better robustness. Finally, several trajectories with the starting points from different areas and the ending points in different gravity ranges are tested and compared to carry out the numerical simulations. These results indicate that the IOAP has many advantages, such as a high matching accuracy and strong positioning applicability in different gravity regions. Compared with the TERCOM (terrain contour matching algorithm), its average matching accuracy was the highest, increased by 40.39%.
Highlights
The Inertial Navigation System [1] (INS) is the core navigation system for realizing the autonomous navigation of underwater vehicles
Different from the previous studies, this paper was inspired by the matching grid topology of the TERCOM and the drift error characteristics of the Inertial Navigation System [1] (INS), and our main research motivation is the reconstruction of matching grid topology for innovatively proposing the iterative optimal annulus point method (IOAP) with a novel grid topology that aims at improving the matching accuracy of gravity-aided navigation on underwater vehicles
According to the real sailing speed and direction and sampling time interval ∆t of the underwater vehicles, a tracking sequence P1k P2k · · · PLk of the matching point PLk is extracted from the gravity map and its corresponding nearest neighbor gravity sequence g1base g2base · · · gbase is calculated, which results in computing the mean square difference (MSD) value of this matching point PLk, denoted by MSDk
Summary
The Inertial Navigation System [1] (INS) is the core navigation system for realizing the autonomous navigation of underwater vehicles. Different from the previous studies, this paper was inspired by the matching grid topology of the TERCOM and the drift error characteristics of the INS, and our main research motivation is the reconstruction of matching grid topology for innovatively proposing the iterative optimal annulus point method (IOAP) with a novel grid topology that aims at improving the matching accuracy of gravity-aided navigation on underwater vehicles. Considering the relative sensitivity [20] of gravity matching algorithms such as the SITAN and ICCP to the initial error of the tracking starting point, the Matching Positioning strategy of the tracking Starting Point in small annulus (SPMP) was established to improve, to a certain extent, the insensitivity (robustness) of the IOAP to the gravity matching initial error It is centered around the underwater vehicle position indicated by the INS and uses a certain drift error and rotated angle to span a matched grid area with small annulus topology (termed as small annulus) for covering the real position of the tracking starting point with a probability one. It can provide the position information of the tracking starting point for further ascertaining the tracking ending point position guided by the INS sailing direction and distance
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