What is an Automatic Radar Plotting Aid (ARPA)?
An Automatic Radar Plotting Aid (ARPA) is an advanced maritime radar system designed to improve navigation safety by automatically locating targets and predicting their future movements.
By providing real-time data on the speed, direction, and position of other vessels, ARPA significantly reduces mariners’ workload and improves situational awareness, particularly in congested or restricted waters.
ARPA was developed out of a need to improve maritime safety and efficiency. Traditional radar systems require manual target plotting, which is time-consuming and prone to human error.
The advent of digital technology in the late 20th century automated this process, driving the development of ARPA systems. These systems are designed to automatically track targets, analyze their movements, and provide valuable collision avoidance information.
Automatic Radar Plotting Aids
The International Maritime Organization (IMO) has developed specific standards that amend the requirements of the International Convention for the Safety of Life at Sea (SOLAS) for the use of appropriate automatic radar plotting aids.
The main functions of an automatic radar plotting aid (ARPA) are summarized in a statement within the IMO performance standards. This statement specifies the requirements for ARPA: “Improved collision avoidance at sea: Reduces lookout workload by enabling lookouts to automatically obtain information, enabling them to handle multiple targets with the same efficiency as manually plotting a single target.” As this statement indicates, the main benefits of ARPA are reduced workload for bridge personnel and the provision of more complete and faster information about selected targets.
A typical function of ARPA is to assess the current situation and, using computer technology, predict future situations. ARPA assesses the risk of collision and provides the operator with a proposed course of action for their vessel.
ARPA systems adhere to the following standards and provide the following functions:
1. Radar Motion Display
True and Relative Motion Display: Displays true and relative radar motion information to enhance situational awareness.
2. Target Acquisition
Automatic and Manual Target Acquisition: The system supports both automatic and manual target acquisition to ensure complete tracking of all relevant targets.
3. Digital Readout
Detailed Target Information: Provides a digital readout of the target, including:
- Direction
- Speed
- Distance
- Type
- Closest Point of Approach (CPA)
- Closest Point of Approach Time (TCPA)
- Distance and Pass Time
4. Collision Assessment
Enhanced Display: Collision assessment information is displayed directly on the Planned Position Indicator (PPI), using:
- Vector (actual or relative)
- Graphical display of the Predicted Area of Danger (PAD)
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5. Test Maneuvers
Simulation Capabilities: Supports test maneuvers, including:
- Direction Changes
- Speed Changes
- Combined Heading and Speed Changes
6. Navigation Stabilization
Automatic Terrain Stabilization: Provides automatic terrain stabilization to ensure accurate navigation.
7. Fast Processing
Higher Processing Speed: Radar information is processed significantly faster than traditional radar systems while maintaining the same limitations.
8. Data Accuracy
Dependence on Input Accuracy: The accuracy of ARPA data depends on the accuracy of input data from sources such as gyroscopes and logbooks.
Difference between RADAR and ARPA
| Feature | Radar | ARPA (Automatic Radar Plotting Aid) |
| Alerts and Alarms | Limited | Provides visual and audible collision risk alerts |
| Automation | Manual plotting required | Automatic plotting and tracking |
| Collision Avoidance | Basic visual information | Provides detailed collision avoidance information |
| Data Display | Real-time display of echoes on the screen | Enhanced display with target vectors, CPA, TCPA, and trails |
| Ease of Use | Requires constant monitoring and manual plotting | User-friendly interface with automated functions |
| Predictive Capabilities | None | Predicts future positions and movements of targets |
| Primary Function | Detects and displays the position of objects | Detects, tracks, and predicts the movement of objects |
| Target Identification | Limited, relies on visual identification | Can integrate with AIS for detailed target information |
| Target Tracking | Limited to manual observation | Automatically tracks multiple targets simultaneously |
| Vector Display | Not available | Shows true and relative vectors of targets |
Final words
In summary, the ARPA system is a revolutionary tool for maritime navigation, fundamentally improving safety and operational efficiency.
The Advanced Research Projects Agency (ARPA) is working to address the challenges faced by mariners by automating the tracking and prediction of other vessels, providing them with critical information at a glance, invaluable in crowded and complex waters.
Advances in digital technology enable ARPA to replace manual aiming with radar, significantly reducing the risk of human error and streamlining navigation operations.
ARPA displays real-time data on speed, direction, and potential collision distance, facilitating immediate decision-making and allowing mariners to simulate various navigation scenarios.
A framework established by the International Maritime Organization (IMO) highlights the crucial role ARPA plays in enhancing maritime safety. By providing mariners with smarter, faster decision-making tools, ARPA enables them to more easily monitor multiple vessels.
