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Is It Permissible to Use GPS Data to Avoid Collisions?

Felski Andrzej, Jaskólski Krzysztof

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2025

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Vol. 19 No. 2

347--354

EN

Automatic Radar with Plotting Aids is the basic means of preventing collisions at sea for many years. However, the use of the radar on a moving vessel requires image stabilization, which has been at least for the last 50 years solved by coupling with the gyrocompass and the log. In the present century, the widespread use of Global Navigation Satellite System receivers has led to the common practice of interconnecting this receiver with many other systems on ships. This is often also the case for radar, although GNSS gives information about movement related to the ground, whereas the International Maritime Organization recommends using parameters relating to water. The mandatory and widespread equipping ships with the Automatic Identification System means that this system is increasingly used in the process of collision avoidance, but also with the use of ground-referenced data. The aim of the paper is to investigate whether this is acceptable and what are the limits of this practice. This question becomes increasingly important in the context of the growing number of unmanned vessels. Not all, especially small autonomous surface vehicles will be equipped with radar and may also use AIS transmissions in collision avoidance algorithms. Studies have shown that this may pose a risk of collision. At low ship speeds, if the current speed exceeds 5 knots and the direction of the current significantly deviates from the course of one of the ships, there is a risk that the planned maneuver will not be carried out. This may mean that the closest approach distance will be significantly different from the planned one.

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Spectral analysis of compass errors based on fast fourier transform and reduction absolute errors using a pass-band finite impulse response filter

Jaskólski Krzysztof, Czaplinski Wojciech, Tomczak Arkadiusz

Polish Maritime Research

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2024

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nr 2

109--120

EN

Compass errors can be regarded as a deviation of the vessel from the expected heading. Gyrocompass errors are randomly oscillating in nature, and it is difficult to describe the behaviour of a gyrocompass sufficiently accurately using mathematical relationships. Fibre-optic gyroscopes have no mechanical components, so the variability in their indications has a different nature; the computational processes and inertial sensors used cause certain types of errors. Thus far, compass studies have focused on presenting absolute errors in the time domain. However, compasses exhibit specific characteristics in the frequency domain that affect the amplitude of their deviation. This leads to the issue of identifying the oscillatory spectrum of errors in the operation of such compasses, and how this spectrum is impacted by the dynamic movement of the vessel. We attempt to assess this phenomenon by means of measurements taken on board the training and research vessel M/S NAWIGATOR XXI. The application of a fast Fourier transform allows for calculation of the absolute compass errors in the frequency domain, meaning that the frequency of occurrence of errors can be observed as noise against the background of the useful signal. Our results confirm the value of applying a finite impulse response filter, which is used to filter out noise in the form of absolute compass errors from the useful signal background. The convolution function proposed here considerably extends the possibilities for analysing the signal spectrum in the frequency domain when testing for the accuracy of compass device indications, and enables the elimination of random errors with a low frequency of occurrence.

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Verification of the AIS service availability model based on dynamic data streams recorded from three receiving stations in the Polish coastal area

Jaskólski Krzysztof, Czapliński Wojciech

Archives of Transport

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2024

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Vol. 70, iss. 2

159--180

EN

The reliability aspects of the operation of radio navigation systems constitute a crucial element for the safety of maritime navigation.. Technological progress in ship traffic monitoring is achieved through the design of ship systems and shore infrastructure equipped with Automatic Identification System (AIS) devices. One of the issues with AIS operation is the limited availability of the service in the form of data streams with an extended data age recorded on the receiving side. Another problem is the emission and reception by ships of incomplete positional reports without navigational parameters. Such situations render the system operationally unfit in terms of processed information. Therefore, it is essential to investigate the operational characteristics of radio navigation systems and develop tools to monitor the AIS service status on the receiving side. This article presents the development of a model for the availability of an AIS for vessels based on the determined mean time of the occurrence of incomplete navigation parameter values in AIS messages and the results of research in the domain of time and frequency using a mathematical method of the Fast Fourier Transform (FFT). The study results refer to six basic navigation parameters and show a varying service availability factor for the navigation parameters under study, i.e. the latitude (LAT), longitude (LON), speed over ground (SOG), course over ground (COG), heading (HDT), and the rate of turn (ROT). The data recorded by three receiving AIS stations on the Polish coast, i.e. PLKOL, PLSZZ, and PLSWI, were used as a key source of practical knowledge on the limitations of the AIS service availability. The experiment observed interruptions in the regular transmission of data from navigation equipment in the AIS service operational zone. As a result, the functional relationship was described based on the spectral analysis of the frequency of occurrence of times between the service repair (Time To Repair, TTR), and the model was proposed to be applied to the study of other variables. The presented model is a tool that allows for improving the monitoring of vessel traffic in terms of reliability, which directly affects the improvement of maritime traffic safety.