KUP 22: Awareness of principal types of ARPA, their display characteristics, performance standards and the dangers of over-reliance on ARPA

Learning objective:
1. Understand the principal types of Automatic Radar Plotting Aids (ARPA) and their respective display characteristics.
2. Gain knowledge of the performance standards set for ARPA systems, ensuring compliance with international regulations.
3. Recognize the potential dangers and limitations of over-reliance on ARPA, including issues related to system accuracy, processing delays, and situational awareness.
4. Develop the ability to critically assess ARPA information to ensure safe navigation and effective decision-making.

Content

Automatic Radar Plotting Aid (ARPA) is a vital tool for enhancing situational awareness and collision avoidance at sea, allowing vessel operators to track, plot, and analyze the movements of surrounding vessels. This module covers the key aspects of ARPA performance, display characteristics, and system limitations, as well as the potential risks of over-reliance on these systems. Through this learning content, participants will gain the necessary knowledge and skills to effectively operate ARPA, interpret radar data, and make informed navigational decisions to ensure safety at sea.

Types of ARPA Systems

Two principal types: standalone ARPA, which is an add-on to conventional radar, and integral ARPA, which integrates radar and computer systems into one display unit.

• a) Stand-alone ARPA. They provided all of the ARPA facilities but derived their data from “host” radar. This was an attractive means of upgrading the ship’s radar system without incurring the expense of removing the existing radar and installing a new ARPA system.
• Stand-alone equipment had to be interfaced to a variety of existing equipment and while it was the less expensive and more expedient of the two alternative, it was never the solution and so, today, most of the ARPA’s being fitted into the “integral” category. Stand-alone ARPA works in two ways; The radar system receives all the raw data and transmits all these data to ARPA for processing. This may work, but having these two units doing the work of a single one convinced the ship owners that the dawn of new age in the electronic navigation has come and they must be able to adopt to the new system provided by this advancement in science.
• b) In the modern integral ARPAs, a computer, usually referred to as the processor, is incorporated in the radar/ARPA system so that the ARPA data can be displayed on the same screen as the conventional radar data. The main operational advantage is that the radar and ARPA data are readily comparable. In practical terms, it is much better than the same manufacturer is responsible for the design, testing, installation and functioning of the system. Gradually the trend has been for all ARPA development to follow this form, although there is still a small group who continue to develop stand-alone modules [1].

Performance Standards and Limitations

PERFORMANCE STANDARDS [2]

1. Detection
   Where a separate facility is provided for detection of targets, other than by the radar observer, it should have a performance not inferior to that which could be obtained by the use of the radar display.
2. Acquisition
   1. Target acquisition may be manual or automatic for relative speeds up to 100 knots. However, there should always be a facility to provide for manual acquisition and cancellation: ARPA with automatic acquisition should have a facility to suppress acquisition in certain areas. On any range scale where acquisition is suppressed over a certain area, the area of acquisition should be defined and indicated on the display.
   2. Automatic or manual acquisition should have a performance not inferior to that which could be obtained by the user of the radar display.
3. Tracking
   1. The ARPA should be able automatically to track, process, simultaneously display and continuously update information on at least 20 targets, whether automatically or manually acquired.
   2. If automatic acquisition is provided, description of the criteria of selection of targets for tracking should be provided to the user. If the ARPA does not track all targets visible on the display, targets which are being tracked should be clearly indicated with the relevant symbol* on the display. The reliability of tracking should not be less than that obtainable using manual recordings of successive target positions obtained from the radar display.
      * Refer to IEC 872M : Marine Automatic Radar Plotting Aids (ARPAs)
   3. The ARPA should continue to track an acquired target which is clearly distinguishable on the display for 5 out of 10 consecutive scans, provided the target is not subject to target swop.
   4. The possibility of tracking errors, including target swop, should be minimized by ARPA design. A qualitative description of the effects of error sources on the automatic tracking and corresponding errors should be provided to the user, including the effects of low signal-to-noise and low signal-to-clutter ratios caused by sea returns, rain, snow, low clouds and non-synchronous emissions.
   5. The ARPA should be able to display on request with relevant symbol* at least four equally time-spaced past positions of any targets being tracked over a period appropriate to the range scale in use. The time-scale of the past position plot should be indicated. The operating manual should contain an explanation of what the past position plots represent.
      * Refer to IEC 872M : Marine Automatic Radar Plotting Aids (ARPAs)

Safe Use of ARPA

A typical ARPA gives a presentation of the current situation and uses computer technology to predict future situations. An ARPA assesses the risk of collision, and enables operator to see proposed maneuvers by own ship. While many different models of ARPAs are available on the market, the following functions are usually provided [3]:

1. True or relative motion radar presentation.
2. Automatic acquisition of targets plus manual acquisition.
3. Digital read-out of acquired targets which provides course, speed, range, bearing, closest point of approach (CPA, and time to CPA (TCPA).
4. The ability to display collision assessment information directly on the PPI, using vectors (true or relative) or a graphical Predicted Area of Danger (PAD) display.
5. The ability to perform trial maneuvers, including course changes, speed changes, and combined course/speed changes.
6. Automatic ground stabilization for navigation purposes. ARPA processes radar information much more rapidly than conventional radar but is still subject to the same limitations. ARPA data is only as accurate as the data that comes from inputs such as the gyro and speed log.

Recommendation

References

1. NAVIGATION VI Operational Use of Radar/ARPA. https://www.slideshare.net/slideshow/nav-6-radar-arpa/43602952
2. Human Environment and Transport Inspection, Ministry of Infrastructure and Water Management. “823(19) Performance standards for automatic radar plotting aids (ARPA”s)”. https://puc.overheid.nl/nsi/doc/PUC_2510_14/
3. National Geospatial-Intelligence Agency. “CHAPTER 5 — AUTOMATIC RADAR PLOTTING AIDS (ARPA) – Radar Navigation and Maneuvering Board Manual“. Maritime Safety Information.