CPA Calculation Method based on AIS Position Prediction

Abstract

The information on the Closest Point of Approach (CPA) of another vessel to own ship is required in a potential collision situation as it helps determines the risk to each vessel. CPA is usually calculated based on the speed and direction of the approaching ship neglecting the Change Of Speed (COS) and the Rate Of Turn (ROT). This will make the CPA less useful. To improve the CPA calculation, Automatic Identification System (AIS) information containing the Speed Over Ground (SOG), Course Over Ground (COG), COS and ROT is used. Firstly, a model using these four factors is built to predict ship positions better. Secondly, a three-step CPA searching method is developed. The developed CPA calculation method can assist in informing the navigation decisions and reducing unnecessary manoeuvres. Through the analysis of a real collision scenario, this paper shows that the proposed method can help identify and warn of anomalous ship behaviours in a realistic time frame.

AIS-Based Multiple Vessel Collision and Grounding Risk Identification based on Adaptive Safety Domain

“…. (17) The grounding risk function GR i x p , y p for the ith vessel is defined through the same manner of CRs i , as depicted in Figure 8, in which the risk factor decays at the same rate in the forward direction but at twice the rate in the remaining three directions…”

“…The longitudinal, lateral and spatial risk functions for collision and grounding, respectively, are shown in Figure 7. Notice that the same vessel domain ( Figure 5) and risk evaluation parameters Equation (6) are used for collision and grounding risk evaluation, however, with different spatial functions (Equations (16) and (17) and Figure 7). The main advantage here is to ensure memory-efficiency such that each AIS message in combination with vessel dimensions is mapped into 14 single-precision floating-point numbers (vertices' x-y coordinates defined by Equation (11) and four parameters of Equation (6)).…”

“…These methods need to perceive all risky situations in their first stage which is very important for navigation safety. Risk identification was considered in Reference [16] based on Automatic Identification System (AIS) data and the Closest Point of Approach (CPA) [17] as well as distance at CPA and time to CPA parameters. These are typically based on assumptions of linear tracks, constant speed and course and neglect vessel dimensions and maneuverability.…”

Development of Navigator Behavior Models for the Evaluation of Collision Avoidance Behavior in the Collision-Prone Navigation Environment

“…The calculation of the distance of the CPA requires complex procedures and formulas, which have already been reported in various references [33,34]. Using the formulas in [35], dCPA(t) was calculated using the following procedure:…”

“…Distance measures D(λ Fail , λ Success ) or D(λ Success , λ Fail ) between models λ Fail and λ Success have a dissimilarity concept with respect to model distance. Several interpretations of the model distance exist in terms of such as cross entropy, divergence, and discrimination of information [28,35]. The MD Success is a measure result of how well the model λ Fail matches observations generated by model λ Success , relative to how well model λ Success matches observations generated by itself.…”