nav 6 semi final and finals.ppt

NAVIGATION VI
Operational Use of Radar/ARPA

Objectives
 At the end of the grading period, the students will
be able to demonstrates a knowledge and
understanding of the following:
• Principal ARPA System
• ARPA system display characteristics
• Methods of Displaying Information
• IMO performance standards for ARPA

Principal ARPA System
What is ARPA?
 An abbreviation for Automatic Radar Plotting
Aids. Basically an ARPA is a computerized radar
plotting system, which can perform radar plotting
manually or automatically according to operator’s
choice.
 When it works properly, ARPA is a fantastic tool in
the hands of a qualified navigator with proper
training. One prime requirement for all users of
ARPA is to have good knowledge of the principle
of manual plotting in order to understand the
information given by the ARPA.

What is ARPA?
 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:
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.

What is ARPA?
 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:
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.

Types of ARPA
 In the early days, ARPAs of broad categories existed
and were generally referred to as “stand alone”
and “integral”
a) Stand-alone ARPA
These were primarily intended as additions to
conventional radars. 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.

a) Stand-alone ARPA
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) Integral ARPA
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.

How ARPA is used?
The ARPA is connected to the radar from which it automatically
extracts data, processes it and displays it along with graphics
and possibly alphanumeric. A computer forms the heart of
the system which plots the targets and displays the vector
associated with each tracked target.
Having first set up the ARPA display (as normal radar display),
select:
a) Range scale- e.g 12 miles
b) Plot- Relative (true) bearings
c) Mode- North-up (head-up or course up)
d) Mark the targets to be tracked (using joystick and gate)
e) Set the “vector length”--- in minutes
f) Check the course and speed input

General Features
• Daylight-bright high-resolution display
• 28 inch diagonal CRT presents radar picture of 360 mm
effective diameter with alphanumeric data area around it
• User friendly operation by combination of tactile backlit
touch pads, a trackball and rotary controls
• Audio-visual alert for targets in guard zone
• Echo trail to assess targets’ speed and course by
simulated afterglow
• Electronic plotting of up to 10 targets in different symbols
(This function is disabled when ARPA is activated)

General Features
• Electronic parallel index lines
• Interswitch (optional) built in radar or ARPA display unit
• Enhanced visual target detection by Echo Average, Echo
Stretch,
• Interference Rejector, and multi-level quantization
• Stylish display
• Choice of 10, 25 or 50 KW output for X-band; 30 KW
output for S-band, either in the transceiver aloft (gearbox)
or RF down (transceiver in bridge)
• Exclusive FURUNO MIC low noise receiver

ARPA Features
• Acquires up to 20 targets automatically
• Movement of tracked targets shown by true or relative vectors
(Vector length 1 to 99 min. selected in 1 min steps)
• Setting of nav lines, buoy marks and other symbols to enhance
navigation safety
• On-screen digital readouts of range, bearing, course, speed,
CPA, TCPA,
• BCR (Bow Crossing Range) and BCT (Bow Crossing Time) of
two targets out of all tracked targets.
• Audible and visual alarms against threatening targets coming
into operator-selected CPA/TCPA limits, lost targets, two guard
rings, visual alarm against system failure and target full situation

DISPLAY CONTROLS - MODE PANEL

 HM OFF- Temporarily erases the heading marker.
 ECHO TRAILS- Shows trails of target echoes in the form
of simulated afterglow.
 MODE- Selects presentation modes: Head-up, Head-
up/TB, North-up, Course-up, and True Motion.
 GUARD ALARM- Used for setting the guard alarm.
 EBL OFFSET- Activates and deactivates off-centering of
the sweep origin.
 BKGR COLOR- Selects the background color.
 INDEX LINES- Alternately shows and erases parallel
index lines.

 X2 ZOOM- enlarges a user selected portion of picture
twice as large as normal. (R-type only)
 CU, TM RESET- Resets the heading line to 000 in course-
up mode; moves own ship position 50% radius in stern
direction in the true motion mode.
 INT REJECT- Reduces mutual radar interference
 RANGE RINGS- Adjusts the brightness of range rings.

QUIZ 1
Answer the following:
1. What is the meaning of the abbreviation “ARPA”?
2. What is ARPA?
3. What are the two types of ARPA?
(explain each in your own words)
4. How ARPA is used?

QUIZ 1
5. Give the usage of each display controls mode panel.
a. HM OFF
b. ECHO TRAILS
c. MODE
d. GUARD ALARM
e. EBL OFFSET
f. BKGR COLOR
g. INDEX LINES
h. X2 ZOOM
i. CU, TM RESET
j. INT REJECT
k. RANGE RINGS

How is numerical data relating to a particular target
found?
By using the joystick and placing the gate marker ring over
a particular target, data in numerical form relating to that
target can be obtained:
a)range and bearing
b)course and speed
c)CPA and TCPA
This data may be made to appear sequentially
simultaneously on a special data display. Alternatively,
alpha-numeric may be used to make the data appear on the
display, alongside the particular target.

What extra facilities are available in the ARPA system?
1.Trial Maneuver
It should be possible to simulate the effect to a maneuver-- “own
ship”- o- on all tracked targets. This is done by the feeding in:
a)the propose course
b)the proposed speed
c)the delay(if any)
This display can be made to indicate the effect of such a
maneuver. The method is the display may be either static or
dynamic, in which case the tracked targets and own ship are made
to move at some 30 times normal speed. “Own Ship” will of course
move at the “propose” speed in the “proposed” direction with own
ship’s handling characteristics being taken into account.

2.Operational Warning
a)CPA warnings- it is possible to set limit of CPA and TCPA
which if violated by a tracked target, whether its vector
actually reaches the warning area or not, will activate an
alarm. The offending target will be by a brighter than normal
or flashing vector or a special symbol.
b)Guard rings and zones- it should also be possible to warn
the observer if any distinguishable target closes to a range or
transits a zone chosen by the observer. The first appear will
not activate the alarm. The existence of guard rings should
not be regarded as an alternative to keeping a proper
lookout.

2.Operational Warning
c)Target lost- the ARPA should clearly indicate if a target is
lost with the last tracked position being clearly indicated.
Methods of Displaying Information
Since the first computerized radar system came on the
market and to this very day many different ways of
presenting the information has been developed, produced
and delivered. Today, regardless of graphic presentation, all
ARPA systems must be able to present target information in
form of both relative and true vectors.

Methods of Displaying Information
 Both time of vectors should be time adjustable. In addition
to displaying target information graphically, all ARPA’s also
display target information digitally on the traffic display or on
a separate screen.
 In additional a number of graphical symbols are used for
different purposes:
 Defining stationary targets
 Indicating navigational marks
 Sailing routes
 Pointing out targets that cause alarms etc.

ARPA’s Graphical Symbols
Symbols and Definition
 TV - True Speed Vector indicates the targets speed and
course.

 RV - Relative Speed Vector indicates target relative
course and speed.

 TH - Track History should be provided on request,
consisting of at least four equally spaced past positions of the
echo.

 PPC - POINT OF POSSIBLE COLLISION is the point at
which a collision could take place.

 PAD - Predicted Area Of Danger is the area to be
avoided based on CPA and TCPA setting and relative target
speed.

QUIZ 2
1. How is numerical data relating to a particular target
found?
2. What are the two extra facilities are available in the
ARPA system?
3. Give the graphical symbols and definitions of the
following:
a. TV d. TH
b. RV e. PAD
c. PPC

Area Rejection Boundaries (ARBs, AEBs)
 It is possible to place electronic lines on the
screen which eliminate automatic plotting in
selected areas. The lines are adjusted for “rotation”
and “transaction” controls. These reduced the load
on the tracker when in the proximity to a coast echo.
Alternative systems provide automatic acquisition
in zones which may be designated by range and
sector controls.

Equipment Fault in ARPA system
a.Connection with other equipment
The connection of the ARPA to any other equipment should
not downgrade the performance of that equipment. The
failure of an input from other equipment, such as log or
compass, should activate an alarm.
b.Performance tests and warnings
Self diagnosis should activate a warning in the event of
ARPA malfunction. Also means shall be available to check
the correct interpretation of data against a known solution.

What alternatives facilities are available on
ARPA system?
a.Automatic Acquisition
It is permissible for targets to automatically, as well as
manually acquired. But where automatic acquisition is
provided, the operator must be able to select the areas in
which it operates.
b.Manual Acquisition
The operator specifies the target to be subsequently tracked.
To do this, a joystick and screen marker or tracker ball and
screen marker are used. The target is entered into or
removed from the computer memory when the acquire or
cancel button is press.

What alternatives facilities are available on ARPA system?
c.Tracking and Acquisition Limits
There will may be times when targets are close to own ship but
present no real threat, and whose vectors may well clutter up the
center of the display. It may be possible therefore to set limits on
the ranges at which targets are acquired and to which they are
tracked.
d.Potential Points of Collision (PPCs)
From the basic plot of a target, it is possible to determine the
course to steer in order a collision or interception will take place.
It is possible to have these PPCs appear on the display and in
this way, allow the navigator to avoid them.

e.Predicted Areas of Danger (PAD)
It is logical step from PPCs to indicate areas around these points
into which vessel should not do in order to ensure that some
specified clearing range is maintained.
These predicted areas of danger are feature of the Sperry
Collision Avoidance System. Earlier models as appear as
ellipse is not necessarily the PPC.
f.Methods of Testing an ARPA for malfunction
These usually take the form of self-diagnostic routines with some
indicator of the unit or Printed Circuit Board which is found to be
faulty.

g.ARPA facilities
Finally the first true ARPA appeared, a system able to extract the
signal from the targets then pass them to a digital processor.
Once the data is within the processor of these equipment, a
variety of facilities will present information to the observer.
These facilities includes:
1.Relative Vectors 6. Trial Maneuver
2.True Vectors Output 7. Digital Data
3.Points of Collision 8. Navigational Lines and Limits
4.Predicted Areas of Warning 9. Operational Danger
5.History of Warning 10. Equipment
11. Rejection Boundaries

QUIZ 3
1. What is Area Rejection Boundaries?
2. What are the equipment fault in ARPA system?
3. Enumerate the alternatives facilities available on
ARPA system.

• This section gives you information about IMO requirements
for ARPA system including performance standard for gyro
and log.
Performance Standards for Automatic
Radar Plotting Aids (ARPA) Resolution
A.422 (XI)

QUIZ 4
1.Explain the concept of IMO Performance
Standards for Automatic Radar Plotting Aids
(ARPA) Resolution A.422 (XI)

Objectives
 At the end of the grading period, the students will be able
to demonstrates a knowledge and understanding of the
following:
• Theory of ARPA Tracking System
• Tracking Window
• Setting Up Maintaining Displays
• Risk of Over -Reliance on ARPA

Theory of ARPA Tracking System
 Explains processing delay and other important
limitations in the system. When operating the
ARPA in Automatic Acquisition mode, the
operator must be aware of the following tracking
system limitations:
a. Normally the sensitivity of the ARPA tracking
system is reduced when operating in Automatic
acquisition mode.

b. When the “guard ring” philosophy is used by the
ARPA tracking system, echoes can escape
acquisition because the radar at a range closer that
the distance to the inner guard ring detects them or
the echoes remain between guard rings.

c. When the “search area” philosophy is used,
echoes can escape acquisition because they
are outside the specified area or to many
echoes are picked up, resulting in system
overload.

Tracking Window
 The number of sweeps being digitized in each
tracking gate depends on the tracking
philosophy used by the actual ARPA
manufacturer. Several sweeps will always be
required.
 In order to start digitizing the analogue radar
echo is not lost by too many scans during a
specified time, as this will result in rejection of
defining the echo as a possible target and no
further processing will be executed.

Tracking Window
 To define the echo as a target of interest, a minimum
number of sweeps inside the gate must be defined
above the threshold. A good working and properly
turned ARPA tracking system should be capable of
acquiring all echoes, which can be seen by the human
eye.
 Each of the radar echoes we want to plot must be
processed like this. The different ARPA manufacturers
us different position on digitized echo as reference for
further processing. Possible target reference points are:
 The front edge
 The center
 Or the back of the digitized radar echo

Tracking Window
0 0 0 0 0
0 1 1 1 0
0 1 1 1 0
0 1 1 1 0
0 0 0 0 0
Sweep 1 2 3 4 5
 Each reference point has its advantages or
disadvantages. In our example we use the center of the
target as reference.

Setting Up Maintaining Displays
Kinds of Warnings
 Collision Warning -- audible and flashing warning
activated whenever a traced target violates the pre-
set collision criteria.
 Lost Target -- audible and flashing warning
activated whenever the system no longer can track
a target.
 System Alarm -- audible and flashing warning
activated when a pre-set limit is violated.

 The ARPA system Start Up procedure varies from
system to system however, the following points
outline the minimum of what must be checked
before an ARPA is operated in basic mode.
 Overlooking one or more of these points may cause
serious consequences:
1. Switch on the ARPA and checked that required
radar is connected and properly adjust.
2. Check that the ships connected course is feed into
system.
3. Check that the radar antenna alignment is correct, if
not, correct it.

 Overlooking one or more of these points may cause
serious consequences:
4. Check that required log is selected
5. Select required radar mode, normally True Motion,
Course Up or True Motion, North Up should be use
for traffic surveillance purposes
6. Select required range, vector length and collision
warning criteria
7. Familiarize yourself with the ARPA manufacturers
recommended start up procedures and other
recommendations.

 If navigation features are available on your ARPA
and you intend to use them, the following
additional points must be checked:
a. Date and time should be displayed correctly on the
ARPA information screen.
b. Own ships position input must be kept correct on
the ARPA at all times, otherwise all position must
be calculated by the ARPA will be incorrect.
c. In coastal areas, navigation check-points should be
marked on the ARPA in order to assist the
navigator in detecting the possible positioning error
as soon as possible.

 If navigation features are available on your ARPA
and you intend to use them, the following
additional points must be checked:
d. Special requirements pointed out by the ARPA
manufacturer
 The main purpose of the ARPA is to provide the
navigator with the possible overview of the traffic
situation at all times.

The Importance of Incorrect Speed Input
Ship B
Course/Speed
Ship C
Course/Speed
Ship D
Course/Speed
Result
Correct
El. log
1 040-2,0 210-7,0 270-5,0 Calculation
Aspect
2 032-2,4 212-6,4 272-5,0 Small
Errors
Manual
3 119-1,22 204-8,7 248-5,6 Dangerous
Errors
Doppler
4 220-0,5 213-9,5 253-7,2 Dangerous
Errors
Doppler

The Importance of Incorrect Speed Input
 The table presents ARPA calculated result as given
by four different speed input sources:
1. Electromagnetic log which gives correct speed
through water.
2. Manual speed input, miscalculated by +0.5 knots
3. Doppler log provides speed over ground without
compensating for transverse drift.
4. Doppler log provides speed over ground and
compensates for transverse drift.

QUIZ 1
1. In your own words, what are the tracking system
limitations that the operator must be aware of?
2. Enumerate the possible target reference points.
3. Enumerate and explain the kinds of warnings.
4. Give at least 3 serious consequences in overlooking
the setting up display.

Risk of Over Reliance on ARPA
Problems may occur in using ARPA
1. The risks of over-reliance on ARPA
 Appreciation that ARPA is only navigational aid and
that’s its limitations, including those of its sensors,
make over-reliance on the ARPA dangerous in
particular for keeping a look-out, the need to
comply at all times with the basic principles and
operational guidance for officers in-charged of a
navigational watch.

1. The risks of over-reliance on ARPA
Risk:
 impressive system
 no system is better that the weakest part
 the operator must be aware of the ARPA limitations
 An ARPA system in the hand of unqualified
personnel is not only dangerous, but can indirectly
be the main reason for an accident.

2. Errors and Precautions
 Errors in an ARPA system can be divided into
groups:
a. errors in sensors (radar, log, gyro, etc.)
b. errors in ARPA software
c. errors in ARPA hardware
d. errors in interpretation of the actual display
 When working with computerized systems, always
remember “Rubbish-in-Rubbish-out” simple as
that.

3. Errors in Interpretation of Display
 Here are some possible treats:
a. raster scan ARPA display “lock up”
b. mixing trial and real time information
c. wrong speed input or overlooking type of speed
input to the ARPA
d. no correction for gyro course error before input to
ARPA
e. misinterpretation of display symbols may cause
severe problems

3. Errors in Interpretation of Display
f. operating long periods in “impure presentation” may
have serious consequences
g. exclusive reliance of ARPA will sooner or later give
you a problem
 Remember that ARPA is only a navigational aid
and that its limitations including those of its
sensors, make exclusive use of ARPA dangerous.

4. Automatic Acquisition Precaution
 The majority of ARPA systems manufactured today
provide and automatic acquisition feature. This feature
may reduce the operator’s workload during busy
periods and thus contributing possibility to safe sailing.
 However, the operator should be aware of the fact that
most ARPA systems are less sensitive in auto-
acquisition mode than in manual acquisition mode. This
is one good reason not to rely on the new target
warning only, but at regular intervals visually observe
the ARPA screen to make sure that all targets are
acquired.

5. Factors affecting system performance and
accuracy:
a. Knowledge of ARPA sensor input performance-
radar, compass and speed inputs, effects of sensor
malfunction on the accuracy of ARPA data.
b. Effects of the limitations of radar range and bearing
discrimination and accuracy, the limitations of
compass and speed input accuracy on the
accuracy of ARPA data.
c. Knowledge of factors which influence vector
accuracy.

6. Tracking capabilities and limitations
a. Knowledge of the criteria for the selection of targets
by automatic acquisition
b. Factors leading to the correct choice of targets for
manual acquisition
c. Effects on tracking of “lost” targets and target
fading
d. Circumstances causing “target swoop” and its
effects on displayed data

7. Processing delay
 The delays inherent in the display of processed
ARPA information, particularly on acquisition and
re-acquisition or when target maneuvers.
8. When and how to use the operational warnings,
their benefits and limitations
 Appreciation of the uses, benefits and limitations of
ARPA operational warnings, correct setting, where
applicable, to avoid spurious interference.

9. System Operational test
a. Methods of testing for malfunctions of ARPA
systems, including functional self-testing
b. Precautions to be taken after a malfunction occur
10. Manual and automatic acquisition of targets and
their respective limitations
 Knowledge of the limits imposed on both types of
acquisition in multi-target scenarios, effects on
acquisition of target fading and target swoop.

11. When and how to use true and relative vectors
and typical; graphic representation of target
information and danger areas
a. Thorough knowledge of true and relative vectors,
derivation of targets true courses and speeds
b. Threat assessment; derivation of predicted closest
point of approach from forward extrapolation of
vectors, the use of graphic representation of danger
areas

11. When and how to use true and relative vectors
and typical; graphic representation of target
information and danger areas
c. Effects of alterations of courses and/or speeds of
own ship and/or targets on predicted closest point
of approach and predicted time to closest point of
approach and danger areas
d. Effects of incorrect vectors and danger areas
e. Benefit of switching between true and relative
vectors

12. When and how to use information on past
position of targets being tracked
 Knowledge of derivation of past positions of targets
being tracked, recognition of historic data as means
of indicating recent maneuvering of targets and as
a method of checking the validity of the ARPA’s
tracking.

13. Setting up and maintaining displays
 Selection of the time scale of vectors/graphics
a. Use of exclusion areas when automatic acquisition
is employed by ARPA
b. Performance checks of radar, compass, speed
input sensors and ARPA

14. System Operational Test
 System check and determining data accuracy of
ARPA including the trial maneuver facility by
checking against basic radar plot.

15. When and how to obtain information from ARPA
display
 Demonstrate ability to obtain information in both
relative and true motion modes of displays
including:
a. Identification of critical echoes
b. Used of exclusion areas in automatic acquisition
mode
c. Speed and direction of targets relative movement

display
including:
d. Time and predicted range at targets closest point of
approach
e. Course and speed of the targets
f. Detecting course and speed changes of targets and
Limitations of such information

display
including:
g. Effect of changes in own ship’s course or speed or
both
h. Operation of the trial maneuver

QUIZ 2
1. Give at least 5 problems that may occur in using
ARPA and explain why is it considered as a
problem.

nav 6 semi final and finals.ppt

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