The Impact of Radar Distance Measurement Accuracy on the Accuracy of Position Fixing in VTS Systems

Abstract

The main source of information on the situation across the sea basins used by operators of shipping monitoring systems is a network of coastal radar stations. Presently, it is possible to gather navigational information from many individual radar stations simultaneously, which may be used for improving the accuracy of vessel position fixing. However, without making other estimates, we obtain an inconsistent image comprising multiple echoes of the same ship, and as such it is impossible to say which echo presents the vessel on the move. Another problem is the method of performing radar observations, which significantly affects the accuracy of position fixing. The estimated radar distance is encumbered with a gross error in the case of large vessels, as the position of a large vessel is not the same as the position of the edge of the radar echo to which the estimation is made. In this paper, the authors present a method to adjust the measured radar distance. The proposed method may be automated easily, which would significantly enhance VTS positioning processes.

A Method of Increasing the Accuracy of Radar Distance Measurement in VTS Systems for Vessels with Very Large Dimensions

“…We are, therefore, able to describe the effective reflection surface of the radar beam. For the purposes of further considerations, let us assume, similarly to [11], that the aspect is the angle between the course line of the vessel observed in the VTS system and the vessel bearing line, determined from the coastal position of the radar station (Figure 2). We can obtain bearings and distances using the marine radar.…”

“…Such an approximation allows for a relatively precise adjustment of the real shape of the hull as a radar echo for the purposes of the model proposed in this article. In [11], the authors assumed the vessel as a combination of a half ellipse and a rectangle; however, it seems that adopting the vessel as an ellipse generates a problem related to measuring the distance of very large vessels (e.g., L > 200 m).…”

“…To determine the distance d P −P by which the radar distance should be corrected (d R ), the ellipse equation should be used. Assuming, as in [11], that the center of the local co-ordinate system coincides with the center of the ellipse, the ellipse equation takes the form:…”

“…The authors became interested in the problem of the quality of the radar observations used, e.g., measured radar distances to echoes, which are generated by very large vessels, e.g., MAERSK class container vessels [10]. Earlier publications, e.g., [11], defined the problem of radar distance measurement error using VTS edge radars, and, in order to eliminate it, approximation of the shape of the vessel's hull with two geometric figures, a half ellipse and a rectangle, was proposed. However, this is not the correct approach to measuring the distance to the radar echo; therefore, this article generalizes the considerations made earlier in such a way that the radar echo is treated as an ellipse.…”