Rapid Variations of the Static Data Transmitted within AIS Message 5

For over a decade now the Automatic Identification System (AIS) has been considered an important improvement of both the watchkeeping duties at sea and the vessel traffic surveillance activities worldwide. The on-board AIS equipment is used for broadcasting the dynamic data describing the vessel movement vector as well as the static parameters related to her voyage or hull dimension. The reporting intervals of the AIS transmissions depend on the data validity periods which are shorter for continuously changing dynamic AIS parameters and longer in case of less frequently altering static AIS variables. This work focuses on cases of static AIS parameters like the GNSS reference point which were detected to be changing at a high rate, despite the fact that the settings like this are only allowed to be modified during the configuration phase of an AIS transponder. The AIS data received at the DLR reference station in Rostock are analysed and provide a statistical overview of this phenomenon

Interdependencies between Evaluation of Collision Risks and Performance of Shipborne PNT Data Provision

The highest priority for safe ship navigation is the avoidance of collisions and groundings. For this purpose the concept of ship domain has been introduced to describe the surrounding effective waters which should be kept clear of other ships and obstacles. In the last decades a large variety of ship domains have been developed differing in the applied method of their determination as well as in the modelled shape, size, and safety areas. However, a ship domain should be adjusted in real time to enable a reliable evaluation of collision risks by the officers of the watch. Until today in the discussions about modelling and utilization of ship domains it has been mostly unnoticed that the performance of vessel’s position (P), navigation (N), and timing data (T) ultimately determines the accuracy and integrity of indicated ship domain. This paper addresses this question and starts with a comprehensive analysis of AIS data to prove the violation of ship domains in the maritime practice. A simulation system has been developed to enable for the first time to investigate how far inaccuracies in PNT data result into a fault evaluation of collision risks. The simulation results have shown that there is a non-negligible risk of not detecting a collision, if inaccuracies of sensor data remain unnoticed

Interdependencies between Evaluation of Collision Risks and Performance of Shipborne PNT Data Provision

The highest priority for safe ship navigation is the avoidance of collisions and groundings. For this purpose the concept of ship domain has been introduced to describe the surrounding effective waters which should be kept clear of other ships and obstacles. In the last decades a large variety of ship domains have been developed differing in the applied method of their determination as well as in the modelled shape, size, and safety areas. However, a ship domain should be adjusted in real time to enable a reliable evaluation of collision risks by the officers of the watch. Until today in the discussions about modelling and utilization of ship domains it has been mostly unnoticed that the performance of vessel’s position (P), navigation (N), and timing data (T) ultimately determines the accuracy and integrity of indicated ship domain. This paper addresses this question and starts with a comprehensive analysis of AIS data to prove the violation of ship domains in the maritime practice. A simulation system has been developed to enable for the first time to investigate how far inaccuracies in PNT data result into a fault evaluation of collision risks. The simulation results have shown that there is a non-negligible risk of not detecting a collision, if inaccuracies of sensor data remain unnoticed

Occurrence of Unknown Sensor Data within AIS Dynamic Messages

For more than a decade, the Automatic Identification System (AIS) has contributed to increasing the safety of navigation at sea. Despite the benefits of the system, AIS messages shared between vessels and the AIS dynamic data transferred to the Portable Pilot Units may contain unknown values of sensor data if the sensor data on board becomes either unavailable or undeliverable for any reason. In this paper, an experiment is conducted to analyse the performance of an AIS transponder during a virtual sea voyage. By altering the sensor data rate it is possible to cause the AIS transponder to output AIS messages with unknown sensor data. After performing the experiment, a generic approach is used in order to establish a correlation between the sensor data rate and the relative occurrence frequency of AIS unknown values. This leads to the formulation of a simple equation which describes the interdependence between the interval of sensor data provision, the age of the sensor data allowed by the AIS transponder and the percentage of unknown data within the AIS data output

EKF Based Trajectory Tracking and Integrity Monitoring of AIS Data

This work presents a novel approach for integrity monitoring of AIS data. Currently, the AIS is a valuable source for maritime traffic situation assessment but not suited for collision avoidance, as it is prone to failures and not capable of indicating the level of data integrity. To tackle this, an EKF was designed to track vessel trajectories, which allows for failure detection based on residual monitoring. For the latter, two methods for hypotheses testing were implemented, namely chi-squared and GLR tests. In addition, the IMM framework was adopted for mixing the state estimates of two different process models, the CV and CTRV. The designed filter will be validated on behalf of simulated and real-world AIS data

Assessment of Possible Misidentification of AIS Transponders within AIS Data due to Bit Inversions of MMSI

For almost two decades now, the automatic identification system (AIS) has contributed to increasing the safety of navigation at sea. In addition to that, the system can provide valuable data for surveillance of maritime traffic on a global scale. For reliable tracking the movement of vessels with AIS, it is important to correctly identify the craft. Nowadays, such identification is based entirely on the maritime mobile service identity (MMSI). Despite extensive research being done on the subject of anomalies detectable within the AIS, with emphasis on spotting and correcting erratic vessel movements, a possibility of accidental falsification of MMSI leading to incorrect track reconstruction of a vessel has so far been neglected. This study focuses on analysing hypothetical situations when the MMSI of an AIS transponder on board a vessel is altered within the transponder software and a valid AIS data message is sent with a false MMSI which accidentally belongs to a completely different vessel. Since such MMSI transformation leaves no traces, an assessment of a speed-based plausibility is additionally proposed to figure out how many MMSI-based injections of false AIS track points can be detected