Performance Standards of ARPA
1. Detection: If a separate facility is provided for the detection of targets, other than by the Radar, its performance should not be inferior to that which could be obtained by the use of the radar display.
- 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
- The automatic or manual acquisition should have a performance not inferior to that which could be obtained by the radar display indicated on the display.
- The ARPA should be able automatically to track, process, simultaneously display and continuously update the information on at least 20 targets, whether automatically or manually acquired.
- If an Automatic Acquisition is provided, a 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.
- 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.
- 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.
- The ARPA should be able to display on request with a 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.
- The display may be a separate or integral part of the ship’s Radar. However, the ARPA display should include all the data required to be provided by a radar display in accordance with the performance standards for navigational radar equipment.
- The design should be such that any malfunction of ARPA parts producing data additional to information to be produced by the radar as required by the performance standards for navigational equipment should not affect the integrity of the basic radar presentation.
- The ARPA facilities should be available on at least 3, 6 and 12 nautical mile range scales, and there should be a positive indication of the range scale in use.
- ARPA facilities may also be provided on other range scales permitted by resolution A.477(XII) and, if provided, should comply with these standards.
- The ARPA should be capable of operating with a relative motion display with “North-Up” and “Course-Up” azimuth stabilization. In addition, the ARPA may also provide for a true motion display.
- If true motion is provided, the operator should be able to select for the display either true or relative motion. There should be a positive indication of the display mode and orientation in use.
- The course and speed information generated by the ARPA for acquired targets should be displayed in a vector or graphic form which clearly indicates the target’s predicted motion with relevant symbols*, In this regards:
- an ARPA presenting predicted information in vector form only should have the option of both true and relative vectors.
- There should be an indication of the vector mode selected and, if true vector mode is selected, the display should show whether it is sea or ground stabilized;
- an ARPA which is capable of presenting target course and speed information in the graphic form should also, on request, provide the target’s true and/or relative vector;
- vectors displayed should be time-adjustable;
- a positive indication of the time-scale of the vector in use should be given; and
- if stationary targets are being used for ground reference, this fact should be indicated by the relevant symbol’. In this mode, relative vectors including those of the targets used for ground referencing should be displayed when requested.
- The ARPA information should not obscure the visibility of radar targets. The display of ARPA data should be under the control of the Radar Observer. It should be possible to cancel the display of unwanted ARPA data within 3 secs.
- Means should be provided to adjust independently the brilliance of the ARP A data and radar data, including the complete extinction of the ARPA data.
- The method of presentation should ensure that the ARPA data are clearly visible in general to more than one observer in the conditions of light normally experienced on the bridge of a ship by day and by night.
- Screening may be provided to shade the display from sunlight but not to the extent that it will impair the observer’s ability to maintain a proper look-out. Facilities to adjust the brightness should be provided.
- Provisions should be made to obtain quickly the range and bearing of any object which appears on the ARPA display.
- When a target appears on the radar display and, in the case of automatic acquisition, enters within the acquisition area chosen by the observer or, in the case of manual acquisition, has been acquired by the observer, the ARPA should present in a period of not more than 1 min an indication of the target’s motion trend, as discussed above.
- After changing range scales on which the ARP A facilities are available or resetting the display, full plotting information should be displayed within a period of time not exceeding one scan.
5. Data Requirements:
- The observer should be able to select any tracked target to obtain data. Targets selected should be marked with the relevant symbol* on the Radar Display. If data is required for more than one target at the same time each symbol should be separately identified, for example with a number adjacent to the symbol*.
- Following data for each selected target should be clearly and unambiguously identified and displayed immediately and simultaneously in alpha-numeric form outside the radar area:
- Present range of the target
- present bearing of the target
- predicted target range at the closest point of approach (CPA)
- predicted time to CPA (TCPA);
- calculated true course of the target; and
- calculated true speed of the target.
- The display of the calculated true course and speed of the target should include an identification of whether the data provided is referenced to sea or ground stabilization.
- When data for several targets are displayed, no fewer than two items listed above should be displayed simultaneously for each target selected. If the items of data are displayed in pairs for each target, the groupings should:
- Range and Bearing
- CPA and TCPA
- Calculated true course and speed
- The ARPA should provide accuracies not less than mentioned below for the four scenarios defined in Appendix 2.
- With the sensor errors specified in Appendix 3, the values given relate to the best possible manual plotting performance under environmental conditions of ±10 degrees of roll.
- An ARPA should present within one minute of steady-state tracking the relative motion trend of a target with the following accuracy values (95% probability values).
- An ARPA should present within three minutes of steady-state tracking the motion of a target with the following accuracy values (95% probability values).
- The ARP A should be capable of simulating the effect on all tracked targets of an own ship maneuver with or without time delay before maneuver without interrupting the updating of target tracking and display of actual target alpha-numeric data. The simulation should be indicated with the relevant symbol* on the display.
- The operating manual should contain an explanation of the principles underlying the trial maneuver technique adopted including, if provided, the simulation of own ship’s maneuvering characteristics.
- It should be possible to cancel a trial maneuver at any time.
8. Sea and Ground Stabilization
- The ARPA should be capable of sea and ground stabilization.
- Log and speed indicators providing inputs to ARPA equipment should be capable of providing the ship’s speed through the water in the fore and aft direction.
- The ground stabilized input may be provided from the log, from an electronic position-fixing system, if the speed measurement accuracy is in accordance with the requirements of Resolution A 824(19), or from tracked stationary targets.
- The type of input and stabilization in use should be displayed.
9. Operational Warnings:
- The ARPA should have the capability to warn the observer with a visual and audible signal of any distinguishable target which closes to a range or transits a zone chosen by the observer.
- The target causing the warning should be clearly indicated with relevant symbols· on the display.
- The ARPA should have the capability to warn the observer with a visual and audible signal of any tracked target which is predicted to close within a minimum range and time chosen by the observer.
- The target causing the warning should be clearly indicated with relevant symbols* on the display.
- The ARP A should clearly indicate if a tracked target is lost, other than out of range, and the target’s last tracked position should be clearly indicated on the display It should be possible for the observer to activate or de-activate the audible warning signal.
*- Refer to IEC 872: Marine Automatic Radar Plotting Aids (ARP As)