3.1.1 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.
3.2.1 Target acquisition may be manual or automatic. However,
there should always be a facility to provide for manual for 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 indicated on the
3.2.2 Automatic or
manual acquisition should have a performance not inferior to that which could be
obtained by the user of the radar display.
3.3.1 The ARPA should be able to automatically track,
process, simultaneously display and continuously update the information on at
- 20 targets, if automatic acquisition is provided, whether automatically or
- 10 targets, if
only manual acquisition is provided.
3.3.2 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 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.
3.3.3 Provided the target is not subject to
target swop, the ARPA should continue to track an acquired target which is clearly
distinguishable on the display for 5 out of 10 consecutive scans.
3.3.4 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.
3.3.5 The ARPA should be able to display on request at least
four equally time-spaced past positions of any targets being tracked over a period
of at least eight minutes.
3.4.1 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 adopted by IMCO
3.4.2 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 adopted by IMCO
should not affect the integrity of the basic radar presentation.
3.4.3 The display on which ARPA information is presented should
hue an effective diameter of at least 340 mm.
3.4.4 The ARPA facilities should be available on at least the
following range scales:
- 12 or 16miles;
- 3 or 4miles.
3.4.5 There should be a
positive indication of the range scale in use.
3.4.6 The ARPA should be capable of operating with a relative
motion display with "north-up and either "bead-up" or "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 his display
either true or relative motion. There should be a positive indication of the
display mode and orientation in use.
3.4.7 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. In this regard :
- ARPA presenting predicted information in vector form only should have the
option of both true and relative vectors;
- an ARPA which is capable of presenting target course and speed
information in graphic form should also, on request, provide the target's true
and/or relative vector:
displayed should either be time-adjustable or have a fixed time-scale;
- a positive indication of the
time-scale of the vector in use should be given.
3.4.8 The ARPA information should not obscure radar information
insuch a manner as to degrade the process of detecting 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.
3.4.9 Means should be provided to adjust independently the
brilliance of the ARPA data and radar data, including complete elimination of the
3.4.10 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 or 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 observers'
ability to maintain a proper lookout. Facilities to adjust the brightness should
should be made to obtain quickly the range and hearing 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 one minute an indication of the target's
motion trend and display within three minutes the target's predicted motion in
accordance with paragraphs 3.4.7,3.6,3.8.2 and 3.8.3.
3.4.13 After changing range scales on which the
ARPA facilities are available or resetting the display, full plotting information
should be displayed within a period of time not exceeding four scans.
3.5 Operational warnings
3.5.1 The ARPA should have the capability to warn the observer with a
visual and/or audible signal of any distinguishable target which closes to a range
or transits a zone chosen by the observer. Thetarget causing the warning should be
clearly indicated on the display.
3.5.2 The ARPA should have the capability to warn the
observer with a visual and/or audible signal of any distinguishable target which
is predicted to close to within a minimum range and time chosen by the observer
The target causing the warning should be clearly indicated on the display.
3.5.3 The ARPA 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.
3.5.4 It should be possible to activate or
do-activate the operational warnings.
3.6 Data requirements
3.6.1 At the request of the observer the following
information should be immediately available from the ARPA in alphanumeric form in
regard to any tracked target
- present range to the target ;
- present bearing of the target ;
- predicted target range at the closest point of approach (CPA);
- predicted lime to CPA (TCPA);
- calculated true course of target ;
- calculated true speed of target.
3.7 Trial manoeuvre
The ARPA should be capable of simulating the effect on all
tracked targets of an own ship manoeuvre without interrupting the updating of target
information. The simulation should be initiated by the depression either of a
spring-loaded switch, or of a function key, with a positive identification on the
3.8.1 The ARPA should provide accuracies not less than those
given in paragraphs 3.8.2 and 3.8.3 for the four scenarios defined in Appendix2.
With the sensor errors specified in Appendix3, the values given relate to the best
possible manual plotting performance under environmental conditions of plus and
minus ten degrees of roll.
3.8.2 An ARPA should present within one minuteof steady stale
tracking the relative motion trend of a target with the following accuracy values
(95 per cent probability values) .
| Data /
| 1||11||2.8||1.6 |
| 4||15||1.5 ||2.0|
3.8.3 An ARPA should present within three minutes of steady
state tracking the motion of a target with the following accuracy values (95 per
cent probability values).
| Data /
| 2||2.3||0.3||n.a.||n.a.||2.8|| 0.8|
| 3||4.4||0.9||0.7||1.0||3.3|| 1.0|
| 4||4.6||0.8||0.7||1.0||2.6|| 1.2|
3.8.4 When a tracked target, or own ship, has completed a
manoeuvre, the system should present In a period of not more than one minute an
indication of the target's motion trend, and display within three minutes the
target's predicted motion, in accordance with paragraphs 3.4.7, 3.6, 3.8.2 and
3.8.5 The ARPA should
be designed in such a manner that under the mosts favourable conditions of own
ship motion the error contribution from the ARPA should remain insignificant
compared to the errors associated with the inputs sensors, for the scenarios of
3.9 Connexions with other equipment
3.9.1 The ARPA should not degrade the performance
of any equipment providing sensor inputs. The connection of the ARPA to any other
equipment should not degrade the performance of that equipment.
3.10 Performance tests and warnings
3.10.1 The ARPA should provide suitable warnings
of ARPA malfunction to enable the observer to monitor the proper operation of the
system Additionally test programmes should be available so that the overall
performance of ARPA can be assessed periodically against a known solution.
3.11 Equipment used with ARPA
3.11.1 Log and speed indicators providing inputs to ARPA
equipment should be capable of providing the ship's speed through the water.