This document describes an experimental observation comparing the capabilities of ARPA radar and AIS systems used in vessel traffic services (VTS). Two ARPA radars and two AIS units were installed at a building near the Keelung VTS center to monitor ship movements. Information from the ARPA radars including position, course, and speed was photographed every 6 minutes, while AIS data was continuously received and stored in a database. The data was analyzed to compare which information - from ARPA radars or AIS - was more accurate and useful for VTS monitoring purposes.

1. Group 4
Presented by: Genobiagon, Jayson J.

2. • Explain the capability & Limitations of ARPA
• What are the advantages of using ARPA?
• What does ARPA provide that are not on other devices?
• What are the disadvantages of using ARPA ?

3.  A marine radar with automatic radar plotting aid (ARPA) capability can create tracks using radar contacts.
The system can calculate the tracked object's course, speed and closest point of approach (CPA), thereby
knowing if there is a danger of collision with the other ship or landmass.
 Development of ARPA started after the accident when the Italian liner SS Andrea Doria collided in dense fog
and sank off the east coast of the United States. ARPA radars started to emerge in the 1960s and, with the
development of microelectronics. The first commercially available ARPA was delivered to the cargo liner
MV Taimyr in 1969[1] and was manufactured byNorcontrol, now a part of Kongsberg Maritime. ARPA-
enabled radars are now available even for small yachts.
 1 INTRODUCTION
 1.1 Automatic radar plotting aids (ARPAs) should, in order to improve the standard of collision avoidance at
sea:
 .1 reduce the workload of observers by enabling them automatically to obtain information about plotted
targets, so that they can perform as well with several separate targets as they can by manually plotting a
single target; and
 .2 provide continuous, accurate and rapid situation evaluation.
 1.2 The radar facilities provided by an ARPA display should comply with the performance standards for
radar equipment (resolution A.477(XII)) appropriate to its mode of use.
 1.3 In addition to the general requirements contained in resolution A.694(17), ARPA should comply with the
following minimum performance standards.
Explain the capability & Limitations of ARPA

4.  COMPARISON BETWEEN ARPA RADAR AND AISCHARACTERISTICS FOR
VESSEL TRAFFICSERVICES

 ARPA RADAR FUNCTIONALITY
 Basically ARPA radar is the equipment by means
 of a computer system operating in conjunction with
 radar. Radar transmitter generates very short pulses of
 radio waves. When the waves of one of these pulses
 encounter any obstacle, such as a ship or shore line, part
 of the radiated energy is reflected and received by the
 original radar. The reflected pulse constitutes a radio
 echo. The time between radiating the pulse and receiving
 the echo can be accurately measured. Therefore the
 distance between the radar and the ship is calculated.
 The direction of the ship is the direction of the pulsetransmitted [12].

5.  All radar installations should comply with IMO
 minimum requirements. The variable range marker
 should enable the range of an object to be measured with
 an error not exceeding 1.5 per cent of the maximum
 range of the scale in use, or 70 meters, whichever is the
 greater. The means provided for bearings should enable
 the bearing of a target whose echo appears at the edge of
 the display to be measured with an accuracy of plus or
 minus 1 degree or better [6].
 Traditionally when finding a target echo showing
 on radar screen, a ship officer plotted the relative motion
 of the echo in order to get target’s course, speed, the
 closest point of approach (CPA) and the time to CPA
 (TCPA) by hands. Usually that took much time to
 complete the plotting task. Owing to the error of
 remarking the echo’s bearing and distance, results of
 measurement were not very accurate. Sometimes a
 large mistake in the radar plotting might lead the office
 to take an incorrect judgment of target ship movements
 and cause navigational faults. The situation has been
 improved after ARPA radar fitted onboard. All data are
 calculated by computer and clearly showed on the ARPA
 display. The benefit is not only reduction of plotting
 time in less than 2 minutes for the whole process but
 also accuracy of the data. Furthermore, ARPA radar can
 provide navigational warning, when a ship is
approaching
 a defined dangerous area or the CPA to another ship
 is less than the limited CPA.

6. Although it is apparent that ARPA radar is a very
effective aid to navigation, especially for anti-collision,
the limitation of radar function still exists when pulses
of radio wave are transmitting. The first is that the
maximum distance of an object detected is affected by
the height of antenna and the height of object due to the
curvature of the earth. Secondarily, some objects, such
as small wooden fishing boat, may not be detected until
a short distance due to the reflecting power of the pulses
affected by the surface and material of the objects.
Thirdly, the accuracy of object’s bearing is affected by
the horizontal beam width of the pulses. In modern
marine radar the bearing discrimination is from 0.6 to 2
degrees [10]. Fourthly a more obvious effect is blind
areas and shower areas. For radar radiation a mountainous
island will cause a blind area, and objects behind the
island will not be detected on radar screen. A big ship
at close range may cause a shadow, and small objects
will not always appear on the screen, especially in a
short distance because of the reduction of the echo
energy. The shadow effect will reduce the range of a
small object detected from 4 miles to 0.5 miles [10].

7.  The loss of tracking will result in the need to reacquire
 and re-identify. Heavy rain or snow sometimes also
 affects the effectiveness of radar tracking. With modern
ARPA radar, traffic routes, fairways
 and other marks of importance can be delineated on the
 display. No matter the above limitations, ARPA radar
 currently has become required equipment for
surveillance
 of ship movements in VTS. To achieve the
 operational purpose the ARPA radar should be able to
 detect all moving or stationary targets which satisfy the
 detection criteria within VTS coverage area during all
 specified operating circumstances. Any target should
 be acquired and maintain tracking in at least 5 out of
 every 10 scans average over a period of 2 minutes [9].
 Navigation data of target ship should be displayed either
 on the VTS display using synthetic symbols near
 the ship or in tabular form in an un-used part of the VTS
 display. A failure to reacquire a target automatically in
 a limited time should be brought to the attention of the
 VTS operator. AIS FUNCTIONALITY
 Functions of the AIS should satisfy the following
 requirements: in a ship-to-ship mode for collision
 avoidance, as a means for littoral States to obtain
information
 about a ship and its cargo, as a VTS tool, i.e.
 ship-to-shore (traffic management) [8]. The AIS is a
 shipboard broadcast system operating in the VHF radio
 maritime frequencies: 161.975 MHz (channel 87B) and
 162.025 MHz (channel 88B). The universal VTS using
 self-organized time division multiple access (SOTDMA)
 technology was adopted by IMO in 1998 for high
broadcast
 rate and reliable operation. The system is characterized
 by a transmission schedule. The transmission
 time in the radio channel is divided into time slots of a
 constant length. The spacing of the time slots for a
 particular ship depends on its speed and maneuvering
 status [3]. AIS is to be capable of handling over 2,000
 time slots per minute per channel and updates as often
 as very two seconds [5].

8. The AIS should automatically provide to
appropriately
other ships and shore stations equipped static
information, dynamic information and voyage related
information. Static information, such as ship call
sign,
name and Maritime Mobile Service Identity (MMSI)
is
permanently stored in the AIS. Dynamic information,
such as ship’s position, course and speed, is collected
from ship equipment, such as GPS, gyro compass and
speed log. Voyage related information, such as ship’s
draught and hazardous cargo, is input by ship officers
in
manually each voyage. It should also receive
automatically
such information from similarly fitted ship.
The information is autonomously sent at different
update rates depending on the type of message. The
reporting interval of dynamic information is
dependent
on speed and course alteration. When a high speed
ship
is changing course, the information update interval is
2
seconds, but it is 3 minutes for the ship at anchor. The
interval of static and voyage related information is
every 6 minutes or on request [5]. Dynamic
information
must be apparently sent at a shorter interval than
others.
The status of ship movement is changing faster the
interval of update rate is shorter. Other ship can find
the
change early. Therefore AIS can provide ship officers
with sufficient additional information of the ship
encountering
that is potentially extremely valuable for
taking action to avoid collision.
Every message containing the ship identity is a
great value to VTS. Most of ship identifications
tracked
by VTS rely on approaching ships reporting their
name
and location through VHF call, and the VTS operator
then correlating this information with an unassigned
ARPA track. After VTS is fitted with AIS, as the name
implies, ship identity can be automatically and
immediately
provided that help overcome time consuming
procedure
and misunderstanding messages, inherent in the
VHF communications due to the problems of
different
languages and accents [13]. Another great benefit for
VTS is ship tracking improved. VTS receiving AIS
messages from a ship at the maximum range of the
VHF
communications usually in excess of detecting range
of
conventional radar. As a consequence, VTS can
extend
detection range and the detection is contained in AIS
messages.

9. The multiple functions of AIS on navigation safety
have had a major impact on maritime industry.
Although
there are many advantages of using AIS receiving
ship information: accurate ship position, automatic
and prompt update, good quality during adverse
weather,
reliable ship tracking without shadow effect, etc., there
are also some disadvantages in use of AIS. When a ship
shuts off the AIS, or does not fit the AIS, such as fishing
boats, the VTS operator can see the ship in sight but no
information on AIS display. Under this situation,
accurately
monitoring ship movement could not achieve
with AIS, has to use other equipment. If the operation
still concentrates on the AIS display and neglects
existence
of the ship, it will be a seriously critical time.
Another problem is that ship equipment in conjunction
with AIS, such as GPS or gyro compass, has trouble so
that the information delivering to VTS and other ships
is incorrect or inaccurate. EXPERIMENTAL
OBSERVATION
For surveillance requirements VTS must realize
ship movements within the severed area. In VTS center,
maneuvering information of ships can be detected
actively
by ARPA radar without the need of transmission
by other equipments from target ships, and
receivedpassively by AIS because required data have to
rely on
AIS transmitting from target ships. But the latter can
provide ships identity and voyage data automatically.
As a VTS operator, facing the two sets of information
obtaining from ARPA radar and AIS what should be
read first needs a careful consideration. It is necessary
to compare which of these two sets of data is more
important, useful and accurate for VTS.
Although the effectiveness of receiving data is
related to VTS location and ship pattern within the
area,
it is impossible to use the equipment in VTS for the
comparison, which must operate uninterrupted for
navigation
safety. Therefore it was decide to complement
this study by means of experimental observation for
obtaining a comprehensive understanding of the
effectiveness
of data from ARPA radars and AIS fitted in the
building of Merchant Marine Department (MMD),
National
Taiwan Ocean University (NTOU). In the
observation, two ARPA radars of JRC maker and two
AIS of Nauticast maker were used. The building facing
ocean is one mile east off Keelung VTS center. Ships
moving within Keelung approaches can be scanned by
the ARPA radar and identified by the AIS fitted in the
building. Use of the equipments at NTOU provided a
unique opportunity to compare present VTS operations
in Keelung harbor.

10.  Wave lengths of the two ARPA radars were 3 cm
 (X-band) and 10 cm (S-band) respectively.
Therefore
 during the period of the observation, screens of
the two
 radars were controlled in 6 miles and 24 miles
 respectively. The maximum number of ship
targets
 detected by the ARPA radars was 6 in manual
acquire,
 and information including bearing, distance,
course and
 speed of three targets could be displayed each
time. The
 information was photographed at 6 minute
internal by a
 digital camera, and then keyed and stored in a
computer.
 Latitude and longitude of target position had to
be
 calculated according to its bearing and distance
from
 the known position of MMD building, as shown
in Table
 1.
 One of the two AIS equipments was fixed in the
 building, and another one was a portable. Both
AIS
 were connected with a computer. All received
information
 automatically transferred and stored in the
computers
 with ACCESS data base format, as shown in
Table
 2. Because the information of any target ship was
received
 every 2 seconds, the stored information was a
 large quantity. There were many repeated
information
 or the information with small change for the
same
 target. Therefore the original files of the
information in
 data base had to be sorted out in accordance
with the
 MMSI of target ships. For the comparison with
ARPA
 radar information, each hour was divided into 10
time
 points so that the information was read in 6
minute

11.  Table 1. Example of ARPA radar information in the observation
 Obs. no Time Latitude Longitude Bearing Dist. Course Speed
 R0128001 2005/1/28 09:06:00 26.45001231 118.5283896 326 3.5 199 8.9
 R0128002 2005/1/28 09:06:00 22.59564993 124.9850697 342 4.1 154 0
 R0128003 2005/1/28 09:06:00 22.04544107 124.6067301 028 4.2 300 9.3
 R0128004 2005/1/28 09:06:00 29.10156108 122.871236 051 4.1 118 2
 R0128005 2005/1/28 09:06:00 30.18180072 120.946747 038 5.1 145 0.3
 Table 2. Example of original AIS information in the observation
 Index Time MMSI Navigational Position Longitude Latitude SOG COG True
 status accuracy heading
 1 2005/1/28 08:42:21 351056000 Default Low 121.752 25.148 0 150 241
 2 2005/1/28 08:42:22 352388000 Under way Low 121.752 25.145 0 248 511
 using engine
 3 2005/1/28 08:42:23 416337000 Under way High 121.75 25.143 0 103 234
 sailing
 4 2005/128 08:42:23 538090053 Not under Low 121.73 25.334 0 229 96
 command
 5 2005/1/28 08:42:25 416207000 Under way Low 121.751 25.154 0 47 279
 sailing
 Table 3. Example of sorted AIS information in the observation
 Index Time MSSI Lat. Long. Speed Course Heading Distance
 2125 2005/01/28 09:00:00 1130504 121.778 25.149 0 0 511 0.549295003
 2124 2005/01/28 09:00:00 215300000 121.724 252.0 12 51 130 3.9665911.6
 2128 2005/01/28 09:00:00 309764000 121.617 25.368 16 269 227 15.86499307
 2126 2005/01/28 09:00:00 351056000 121.752 25.148 0 178 241 1.063393154
 2127 2005/01/28 09:00:00 352388000 121.752 25.145 0 284 274 1.116407184

12.  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: 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.
 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
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 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)
 3.3.3 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.

13.  3.3.5 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)
 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*. In this regard:
 * Refer to IEC 872M : Marine Automatic Radar Plotting Aids (ARPAs)
 .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*. In this mode,
relative vectors including those of the targets used for ground referencing should be displayed when requested.
 * Refer to IEC 872M : Marine Automatic Radar Plotting Aids (ARPAs)
 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.

14.  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 symbols* on the display.
 * Refer to IEC 872 : Marine Automatic Radar Plotting Aids (ARPAs)
 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 symbols* on the display.
 * Refer to IEC 872 : Marine Automatic Radar Plotting Aids (ARPAs)
 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*.
 * Refer to IEC 872 : Marine Automatic Radar Plotting Aids (ARPAs)
 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:
 .1 present range of the target;
 .2 present bearing of the target;
 .3 predicted target range at the closest point of approach (CPA);
 .4 predicted time to CPA (TCPA);
 .5 calculated true course of the target; and
 .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 maneuver
 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 alpha-numeric data. The simulation should be indicated with the relevant symbol* on the display.
 * Refer to IEC 872 : Marine Automatic Radar Plotting Aids (ARPAs)
 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 ° of roll.
 3.8.2 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).

15.  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 ARPA can be assessed periodically against a known solution. When a test
programme is being executed, the relevant test symbols* should be displayed.
 * Refer to IEC 872 : Marine Automatic Radar Plotting Aids (ARPAs)
 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.

16. Automatic Radar Plotting Aid

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