Marine Target Identification Device Low Speed CPA TCPA Stabilization
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Solution Overview
Problem
Existing automatic identification systems (AIS) for marine traffic control face challenges in accurately predicting the closest point of approach (CPA) and time to closest point of approach (TCPA) when ships are stopping or moving at low speeds, due to positioning errors leading to unreliable alarm generation and repeated alarms.
Innovation Solution
A target identification device and method that replaces the course over ground (COG) with a direction oriented towards the target when the speed over ground is below a certain threshold, allowing for reliable CPA and TCPA calculations, thereby preventing random variations and repeated alarms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If GPS positioning is used to calculate SOG and COG, then position information can be obtained, but positioning errors cause random variations in SOG and COG when the ship is stopping or moving at low speed
Solution Approach 1:
The patent changes the parameter used for calculation based on ship speed. When ship speed is below a threshold, it switches from using GPS-derived SOG and COG to using relative motion parameters (relative speed and relative bearing) calculated from AIS position data. This parameter substitution resolves the reliability issue by avoiding GPS error amplification at low speeds while maintaining calculation accuracy.
2Reliability
If CPA and TCPA are calculated using GPS-derived SOG and COG, then collision warning can be provided, but repeated alarms occur when the ship is stopping or moving at low speed
Solution Approach 1:
The patent switches calculation parameters based on ship speed threshold. At low speeds, it uses relative motion parameters from AIS data instead of GPS-derived parameters, which eliminates the random variations that cause repeated alarms. This ensures stable and reliable collision warning performance across all operating conditions.
3Ease of operation
If the difference vector is short when the ship is stopping or moving at low speed, then positioning errors become significant, but using GPS positioning is necessary for obtaining SOG and COG
Solution Approach 1:
The patent introduces an intermediary calculation method using AIS relative position data. Instead of directly using GPS-derived parameters, it calculates relative speed and relative bearing from successive AIS position reports, which serves as an intermediary that avoids the amplification of GPS errors at low speeds while still providing the necessary motion parameters for CPA and TCPA calculation.
Data Source
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Figure 3A~4B
AI summary
A target identification device in a user object includes: a user information obtaining part and a target information obtaining part obtaining a position, a speed over ground and a course over ground of the user object and a target object; a processor that calculates a CPA distance and a TCPA with respect to the target obj ect relative and the user object, based on the positions, the speeds over ground and the courses over ground of the user object and the target object. The processor replaces the course over ground of the user object with a direction toward the target object and calculates the CPA and the TCPA when the speed over ground of the user object is a low speed determination value or less.