3
Performance Standards
3.1 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.
3.2 Acquisition
3.2.1 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: ARPAs 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.
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 Tracking
3.3.1 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.
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 with the relevant symbolfootnote 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 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.
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 with relevant symbolsfootnote at least four equally timespaced 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.
3.4 Display
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.
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 should not affect the integrity of the basic radar
presentation.
3.4.3 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.
3.4.4 ARPA facilities may also be provided on other range scales permitted by
resolution A.477(XII) and, if provided, should comply with these standards.
3.4.5 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.
3.4.6 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.footnote In this regard:
-
.1 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;
-
.2 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;
-
.3 vectors displayed should be time-adjustable;
-
.4 a positive indication of the time-scale of the vector in use should be
given; and
-
.5 if stationary targets are being used for ground referencing, this fact
should be indicated by the relevant symbol.footnote In this mode, relative vectors including those of the
targets used for ground referencing should be displayed when requested.
3.4.7 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 s.
3.4.8 Means should be provided to adjust independently the brilliance of the ARPA
data and radar data, including complete extinction of the ARPA data.
3.4.9 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.
3.4.10 Provisions should be made to obtain quickly the range and bearing of any
object which appears on the ARPA display.
3.4.11 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, and display
within 3 min the target’s predicted motion in accordance with 3.4.6, 3.6, 3.8.2 and
3.8.3.
3.4.12 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 one scan.
3.5 Operational warnings
3.5.1 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 symbolsfootnote on the display.
3.5.2 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 symbolsfootnote 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 for the observer to activate or de-activate the
audible warning signal.
3.6 Data requirements
3.6.1 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.footnote
3.6.2 The 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:
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.1 present range of the target;
-
.2 present bearing of the target;
-
.3 predicted target range at the closest point of approach (CPA);
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.4 predicted time to CPA (TCPA);
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.5 calculated true course of the target; and
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.6 calculated true speed of the target.
3.6.3 The display of the data in 3.6.2.5 and 3.6.2.6 should include an
identification of whether the data provided is referenced to sea or ground
stabilization.
3.6.4 When data for several targets is displayed, no fewer than two items listed
in 3.6.2 should be displayed simultaneously for each target selected. If the items of
data are displayed in pairs for each target, the groupings should be 3.6.2.1 with
3.6.2.2, 3.6.2.3 with 3.6.2.4, and 3.6.2.5 with 3.6.2.6.
3.7 Trial manoeuvre
3.7.1 The ARPA should be capable of simulating the effect on all tracked targets
of an own-ship manoeuvre with or without time delay before manoeuvre without
interrupting the updating of target tracking and display of actual target alphanumeric
data. The simulation should be indicated with the relevant symbolfootnote on the display.
3.7.2 The operating manual should contain an explanation of the principles
underlying the trial manoeuvre technique adopted including, if provided, the simulation
of own ship’s manoeuvring characteristics.
3.7.3 It should be possible to cancel a trial manoeuvre at any time.
3.8 Accuracy
3.8.1 The ARPA should provide accuracies not less than those given in 3.8.2 and
3.8.3 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.
3.8.2 An ARPA should present within 1 min of steady state tracking the relative
motion trend of a target with the following accuracy values (95% probability
values).
| Scenario
|
Data
|
Relative
course
(degrees)
|
Relative
speed
(knots)
|
CPA
(nautical
miles)
|
| 1
|
11
|
2.8
|
1.6
|
| 2
|
7
|
0.6
|
—
|
| 3
|
14
|
2.2
|
1.8
|
| 4
|
15
|
1.5
|
2.0
|
Note 1: In steady state tracking both own and target ship follow straight line
course at constant speed.
Note 2: Probability values are the same as confidence levels.
3.8.3 An ARPA should present within 3 min of steady state tracking the motion of
a target with the following accuracy values (95% probability values).
| Scenario
|
Data
|
Relative
course
(degrees)
|
Relative
speed
(knots)
|
CPA
(nautical
miles)
|
TCPA
(min)
|
True
course
(degrees)
|
True
speed
(knots)
|
| 1
|
3.0
|
0.8
|
0.5
|
1.0
|
7.4
|
1.2
|
| 2
|
2.3
|
0.3
|
—
|
—
|
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 1 min an indication of the target’s motion
trend, and display within 3 min the target’s predicted motion, in accordance with 3.4.6,
3.6, 3.8.2 and 3.8.3. In this context, a ‘‘manoeuvre of own ship’’ should be deemed to
consist of an alteration of course of ±45° in 1 min.
3.8.5 The ARPA should be designed in such a manner that under the most favourable
conditions of own ship’s motion the error contribution from the ARPA should remain
insignificant compared to the errors associated with the input sensors, for the
scenarios of appendix 2.
3.9 Connections with other equipment
3.9.1 The ARPA should not degrade the performance of any equipment providing
sensor inputs, and the connection of the ARPA to any other equipment should not degrade
the performance of that equipment. This requirement should be met whether the ARPA is
operating or not. Additionally, the ARPA should be designed to comply with this
requirement under fault conditions as far as is practicable.
3.9.2 The ARPA should provide an indication when any input from an external
sensor is absent. The ARPA should also repeat any alarm or status messages concerning
the quality of the input data from its external sensors which may influence its
operation.
3.10 Performance tests and warnings
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 ARPAs can be assessed periodically against
a known solution. When a test programme is being executed, the relevant test
symbolsfootnote should be displayed.
3.11 Sea and ground stabilization
3.11.1 The ARPA should be capable of sea and ground stabilization.
3.11.2 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.
3.11.3 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.
3.11.4 The type of input and stabilization in use should be displayed.