nav 6 radar arpa

PRELIM

NAVIGATION VIOperational Use of Radar/ARPA

ObjectivesObjectives At the end of the grading period, the students will be able

to demonstrates a knowledge and understanding of the following:

• Fundamental Principle of Radar• Safe Distance

• Radiation Hazards and Precaution

• Characteristics of Radar Sets and Factors Affecting Performances

• Factors External to the Radar Set Affecting Detection• Factors Causing Faulty Interpretation• Performance Standards Resolution 477(XII)

Fundamental Principle of Radar

• RADAR- derived from the phrase RADIO DETECTION AND RANGING.

A short burst of electro magnetic energy transmitted and hit to an object and then

return, since the velocity of the propagation is known it would be easy to

calculate because the distance to the object as long as it can measure time from

which the transmission started until the echo return.


On Board Ship the RADAR has two main tasks: To function as an aid to prevent collision, as

with the help of RADAR one can “SEE” in fog and darkness.


On Board Ship the RADAR has two main tasks: To assist in navigation, particularly at landfalls

and when navigating in coastal waters.

Characteristics of Radar Sets and Factors Affecting Performances

RADIO WAVES are Electro magnetic Waves motion consist of crest and trough.


• Wavelength- is a distance between a successive crest of waves, electromagnetic waves of a length between 0.1-30000 mm are known as radio waves.

• Frequency- are other way of measure of waves motion, which indicates the number of crest that pass a fix of initial time.

• Frequency and Wavelength are two terms closely associated.


LOW FREQUENCY HIGH FREQUENCYEach type has their advantages and disadvantages. For example a short wave length is preferred in shipboard radar system because there Is a relationship between the size of the antenna and the Horizontal Beam width, the larger width of the scanner the smaller is the angular beam width for the same wavelength.


LOW FREQUENCY HIGH FREQUENCY

Most marine radar transmit is:X Band (3 cm) - 9000 MHZC Band (5 cm) - 5000 MHZS Band (10 cm) - 3000 MHZ

Marine Radar Component

ANTENNA

TRANSCEIVER TRANSMITTER

MAGNETRON

MODULATOR

TRIGGER

POWER TRANSFORMER

DISPLAY

RECEIVER

MIXER

1ST AMPLIFIER

EQUALIZER

VIDEO AMPLIFIER

RADAR BLOCK DIAGRAM


RADAR ANTENNATransmit and receive in an concentrated

beam and a motor turns the antenna in rotation, the signal, which are amplified the signal becomes visible to the operator in form of a radar picture.


Two types of RADAR ANTENNA:

SLOTTED WAVE GUIDE TYPE


Two types of RADAR ANTENNA:

PARABOLIC TYPE


RECEIVERThe incoming signal is fed to a series of

amplifier and further to detect or demodulator for which smoothes the signal, the main task of the receiver is to amplify the reflected (incoming echoes) weak echoes and make them suitable for transmission to the indicator.


TRANSMITTERIt is the trigger pulses to the modulator and

converted the inputs into a high frequency oscillation thru magnetron. A high frequency oscillation are fed via wave guide or into a coaxial cable to the transmitter/receiver switch.


DISPLAYA radar echoes are display in a cathode ray

tube (CRT). Several types of CRT are utilized like A-SCAN or Short Persistent Tube, Plan Position Indicator or PPI, Raster Scan Display.

A-SCAN or short persistent tube, the strength of an echo derived from its amplitude.


P.P.I DISPLAY

Marine Radar ComponentDISPLAYPPI is a long persistent tube, the trace is

rotated around in unison with the rotation of the scanner and echoes previously recorded are retained during a period of at least one scanner revolution.

Marine Radar ComponentDISPLAYRASTER SCAN DISPLAY. Normally a

rectangular screen with dimension in the ratio 4:3 consisting of; example 1024 horizontal lines and 1280 vertical line or picture elements (pixel)

The radar provides all echoes information in Cartesian form (i.e. range, bearing). Before the information can be displayed the information must be recalculated into X-Y coordinated by a processor.


RASTER SCAN DISPLAY

Marine Radar ComponentDISPLAYThe advantage of raster scan is that, it can

be viewed in daylight without a visor, and the capacity for the additional graphic information is almost unlimited compared with the PPI.

The disadvantage of the raster scan is that even the best raster scan display available today, cannot match the resolution of the old PPI.

Factors External to the Radar Set Affecting Detection

RADAR SCAN & RADAR SWEEPRadar Scan- it is a one complete 360

degrees rotation of the antenna (during one scan normally thousand sweeps are generated and transmitted)

Radar Sweep- is the transmission of one radar pulse only.


PULSE REPETITION FREQUENCY (PRF)Define as the number of pulses transmitted

per second.Long pulse is equals to low PRFShort pulse equals to high PRF

LONG PULSE- means more power and longer range but less resolution in range.

SHORT PULSE- means a weaker pulse, less radar range but better resolution in range.


RADAR RANGE DEPEND MAINLY IN DIFFERENT PARAMETERS

Vertical Beam WidthSelected Pulse LengthHeight of AntennaInstallation of AntennaShip’s Trim

Safe DistanceIMPORTANT RADAR RANGE

PARAMETERSAntenna HeightHeight of the TargetSize of the TargetTarget Reflecting AreaMaterials of the TargetShape of the TargetWeather Condition

Safe DistanceFOLLOWING PARAMETERS MUST TAKEN INTO

ACCOUNT: Transmitted Peak Power Wavelength Pulse Length Antenna Gain Noise Figure Number of Pulses Per Scan Wave Guide Loss Display Parameters

Safe DistanceRANGE DISCRIMINATION

The ability of radar to discriminate between two small object close together in the same bearing.

Effecting range discrimination are:Select Pulse LengthThe size of the spot

If possible short pulse and short range should be selected and focused, brightness carefully adjusted.

Safe DistanceBEARING DISCRIMINATION

The ability of radar to discriminate between two small object close together at the same range but different bearing.

Bearing discrimination depends on:Horizontal Beam WidthThe spot size

Correct focusing and brightness setting will improve the bearing discrimination.

Safe Distance

BEARING AND RANGE DISTORTIONThe radar’s possibility to reproduce on area

or a ship correctly and to discriminate between close lying targets is limited and varies with different types of radar.

The discriminating ability in range is usually 25-75 meters, however the accuracy is lower on long range.

Safe Distance

BEARING AND RANGE DISTORTIONThe discriminating ability laterally is usually

1-2 degrees.Radar sets with a wavelength of 3 cm have

a better discriminating ability compared with the 1 cm wavelength.

Radiation Hazards and Precaution

MAGNETIC COMPASSThe magnetic compass must have a safe

distance from the radar. Nowadays, although most ships are equipped with zero compass, the magnetic compass is still the master compass on all ships and thus should be taken good care of.

Normally the safe distance varies between 1 and 5 meters.


RADIATIONMarine radar transmits energy of varying

strength in form of short pulses or bursts. Pulse power can produce biological changes not obtained with constant wave transmission. At short distance, transmission from marine radars may pose a health hazard, follow the instruction from the radar manufacturer closely and don’t take any chances.


RADIATIONWhen working close to a radar antenna,

make sure that a warning signal has been placed on the radar console. Clearly telling everybody that no start up should be attempted before the work on the antenna is completed or cancelled.


RADIATIONWhenever the air humidity is abnormally

high which it is in fog, rain, snow and hale, a reduction in radar detection range should be expected.

Some disturbances of radar picture:SeaRain

These disturbances maybe serious so refer to the radar manual for more details.


NORMAL TRANSMISSION OF RADAR WAVES

Radar conditions at approximately 10-15% greater that the distance to the optical horizon said to have normal transmission of radar waves.

Generally, normal conditions exist in areas with cold air masses. The longer the wavelength, the greater is the tendency to bend round objects. Hence you can expect the 1 cm radar to have greater range that the 3 cm radar.


SUB-REFRACTION When warm, moist air remains over cold water,

the air is cooled from below creating a fog. Temperature end humidity will increase with altitude and the radar wave will bend upwards; decreasing the radar range is called sub-refraction.


DUCTING With conditions of light wind and low clouds over

cold water we often get a condition called “ducting”. That is, when radar beam is reflected several times between the fog and sea surface. The radar range can be increased considerably.

Ducting can be expected to take place when temperature inversion exist and the atmosphere is calm.


RADAR BLACKOUTWith conditions of considerable ground fog, we can

get a total radar blackout: All radar waves are reflected from the top of the

fog. Stationary warm air masses located on top of cold

sea. If the height of the fog is less that the height of the

radar antenna, a total reflection of the radar signal from the top of the fog may take place.


SEA CLUTTER Sea clutter echoes are caused by reflection of the

radar pulse against the sea waves. The reflection is specular and conditions for the pulse to return to the scanner are favorable near the ship. At longer ranges the beam will be deflected away from the ship.

Marine radars are equipped with rejection systems to minimize the effect of sea clutter. This control is often named “Anti Clutter Sea” or “STC”.


RADAR SHADOW As we have seen, the radar waves transmit in a

straight line. A radar coastline echo (or any other objects) appearance will be determined by the topography. The radar picture can be quite different from the map.

Another important reason for the difference between sea map and the radar image is the radar range and bearing discrimination parameters, i.e. how much the radar “magnifies” the echo in range and bearing.


CENTERING ERRORS The sweep center, which on the PPI indicates own

ship, must coincide exactly with the cursor center of rotation to achieve a correct bearing.

Another important reason for the difference between sea map and the radar image is the radar range and bearing discrimination parameters, i.e. how much the radar “magnifies” the echo in range and bearing.

The Use of Radar in Navigation

Interpretation of the Radar Picture The radar picture is a plain picture of the ships

surroundings. Only long training and experience can teach you to interpret the radar picture quickly and accurately as well as to identify different targets.

Use of radar to assist in navigation can be divided into 3 categories:

Making Landfall Coastal Navigation Pilotage


LANDFALL NAVIGATIONLandfall by radar may give surprises.

Always remember: initial radar fixes are often not reliable at long ranges and when approaching land the picture may change completely.


COASTAL NAVIGATIONCoastal navigation requires experience and

vigilance all the time. The range accuracy of the radar is generally better than the bearing accuracy. When bearings has to be taken, choose isolated targets of relative small size.


PILOTAGEFor navigation in narrow waters, radar is

great device. The navigator must know radar shadows. Knowledge is essential in order to distinguish clearly between stationary and moving objects.


RADAR REFLECTORS The purpose of radar reflector is to direct as much

as possible of the reflected radar energy back to the radar antenna, which means stronger echoes on the PPI.

RADAR BEACONS Racon signal appears in PPI and provides bearing

and range of target.


THREE MOTION COMPONENTS The targets relative course and speed is the targets

motion in relation to own ship during the echoes movements across the PPI on a relative motion display.

The targets true course and speed is the targets true motion during the period of observation. This corresponds to the echoes movements across the PPI on a true motion display.

The own ships course and speed are your ships true motion during the period of observation.


MULTIPLE ECHOES Multiple echoes can be created by reflection between

own ship and an object before the scanner finally collects its energy. We will see a line of targets on the same bearing and with equal distance between them.

True echo is the one closest to own ship. The shapes of multiple echoes are less defined that that of the original echo and they are weakening in intensity outwards. Reduction of gain and clutter will remove the false echo before the true echo.


SIDE ECHOES The side lobes cause side echoes. The effect of side

echoes will only be observed at short ranges. Nearby target are picked up by the side lobes as well as by the main lobe. Anticlutter will normally remove side echoes.

It is impossible to design a scanner without side lobes although the construction of an aerial affects the magnitude of side lobes. However, today many slotted wave guide scanners have almost eliminated the visual effect of side echoes.


BLIND SECTORS Antenna not placed at the ships highest point.

Structures above antenna will create blind sector in radar screen. Objects within these sectors will normally be invisible in the screen. It is relatively easy to plot the blind sectors if this is done during the period with a lot of sea clutter. The blind sectors can be seen as distinctly dark sectors in the sea clutter area. Plot each sector on a plotting sheet and place this so it can easily be seen from the radar observed position.


HEADING MARKER ERRORS When the heading marker on the radar screen does

not exactly tally with the ships heading, or in other words, when the echo from a target straight ahead does not lie exactly on the heading line, then we have a heading marker error.

Heading Marker error may have serious effects on the radar picture and has been the cause of many collisions.


FALSE ECHOES If the radar signal is reflected from objects on board in

such a way that the pulse hits a target, we may receive a false echo at almost the same distance as to the real target but on a different bearing. This false echo will often be located on own ships blind sector.

The navigator should know exactly where own ships blinds sectors are located. This is important in order to take actions to minimize the effect of the blind sectors.


RAIN SQUALLS AND SHOWERS Rainsqualls and showers appear on the screen as a

wooly mass. An intense rainstorm can be detected up to 25 miles Thunderstorms give excellent echoes Rain and clutter and targets beyond the rain area

will obscure echoes inside the rainstorm


WEATHER CONDITION During weather conditions including heavy rain, thunderstorms

etc., the S-band is a better choice than X-band radar. False echoes and disturbances

Own ships antenna receives signals from another radar Fan shaped broken lines emanating from the center of the

screen Most radar equipments contain radar interference rejection

circuits to eliminate this disturbance False echoes and disturbances on the radar screen may

have many different appearances and causes. Some faults can affect the accuracy, so whenever disturbances are observed be especially aware of this possibility.


SYMBOLS FOR RADAR CONTROL

1. Radar Off

2. Radar On

3. Radar Stand By

4. Aerial Rotating

5. North-up Presentation

6. Head-up Presentation

7. Heading Marker Alignment

8. Range Selector

9. Short Pulse

10.Long Pulse

11.Gain


12.Tuning

13.Anti Clutter Rain Minimum

14.Anti Clutter Rain Maximum

15.Anti Clutter Sea Minimum

16.Anti Clutter Sea Maximum

17.Scale Illumination

18.Display Brilliance

19.Range Rings Brilliance

20.Variable Range Marker

21.Bearing Marker

22.Transmitted Power Monitor


SYMBOLS FOR RADAR CONTROL There are seven main controls that determine the

performance of the radar:

• standby/transmit

• brilliance

• gain

• tuning

• range

• anti sea clutter control (STC)

• anti rain clutter control (FTC)

Symbols For Radar Control

Standby/Transmit The standby/transmit switch usually has three positions

labelled ‘off’, ‘standby’, and ‘transmit’. Turning the switch to standby will activate the radar set, however it doesn’t come on immediately as the magnetron needs a few minutes to warm up before it can transmit. The radar will have some form of visual signal to indicate when this period is expired. The radar can then be switched to ‘transmit’ and on some sets a short or long pulse can be selected at this time, normally long pulse would be selected. A long pulse will be more likely to show an echo from a weak target or a target at a longer range. A short pulse will achieve better definition on short ranges.


Standby/Transmit As well as its main function of giving the magnetron time to

warm up, in ‘standby’ mode the scanner is not rotating (on most sets) and is a way of conserving power and prolonging the life of the magnetron while keeping the set ready for immediate use. It is a good practice at sea to leave the radar on ‘standby’ at all times as this will prevent condensation forming inside the radar set.


Brilliance The brilliance control on an analogue radar controls the

brightness of the rotating trace and will also affects the brightness of the displayed echo so it needs to be adjusted so that the trace itself is just visible, to give a good contrast between echo and background.

On a raster scan display the brilliance control regulates the brightness of the picture, making it bright enough for daylight viewing or dim enough so as not to impair the operators night vision.


Gain The gain control may appear to have a similar function as the

brilliance control in that operating it makes the picture brighter or darker. This similarity however, is only superficial as the gain control has a completely separate function and it is important not to confuse the two.

The gain control affects the receiver and not the display as the brilliance does. Turning up the gain will increase the amplification of the incoming signal, making weak echoes look stronger, but confusing the display with background speckle or noise, similar to the background crackling of an ordinary radio. Turning down the gain will reduce the sensitivity of the receiver and reduce the speckle but care must be exercised that this is not overdone as weak or distant echoes may be lost


Tuning The tuning control can be compared to the tuning control

of an ordinary radio, in that it tunes the receiver to the frequency of the transmitter. Poor tuning adjustment may not be easily recognised on the screen. Tuning slightly out will eliminate some very weak echoes, but still produce a clear picture of the stronger ones. Hence the importance of frequent fine tuning of the set.


Range The range control regulates the range at which the set

operates. It simply changes the size of the area on the display and hence the scale. You would change the range of the radar just as you would change charts for passage planning or close-in piloting. The choice of range would depend on what you are using the radar for, and your locality. For coastal navigation you might select a range of 6 or 12 miles so that appropriate coastal features will be displayed, for collision avoidance a range of 12 miles or 24 miles may be appropriate, for pilotage into a confined anchorage a range of ½ a mile may be needed.


Sea Clutter Control (STC) The radar beam will bounce echoes off the sea around the ship,

particularly if the weather is a little rough. This result will be a bright sunburst pattern in the middle of the screen which will be more pronounced in the upwind direction. You could reduce this by turning down the gain, the down side to that solution however, is that the echoes of more distant targets will be lost as well.

The solution is the sea clutter control. It works by reducing the receiver gain for a few microseconds after each pulse is transmitted, then gradually restores it to its former level. It works very well, but its use requires care. Too much sea clutter control will result in the loss of close range targets. At sea the sea clutter control must be continually monitored and adjusted.


Rain Clutter Control (RTC) The rain clutter control will reduce the interference on the

screen due to the rain and increase the chance of seeing targets within rain showers. The effect on returning echoes from rain on the screen is usually no more than a transparent smear, looking a little like cotton wool, but it can be dense enough to conceal other echoes within the shower. In a tropical downpour however, the rain can completely block out all echoes, at times requiring the operator to stop the vessel.


Rain Clutter Control (RTC) The rain clutter control works by making use of the fact

that the returning echo from rain is different from the returning echo of a solid object. The returning echo from rain is much longer and very much less dense than the echo from a solid object. The rain clutter circuitry works by passing on to the receiver only the leading edge of a returning echo. This does not affect the returning echo from a solid object like a ship, but drawn out, weak returning echoes from the rain however, will be weakened considerably.

Setting Up Radar Display

START UP SEQUENCE Radar ON/OFF Radar Standby

Scanner ON/OFF

Setting Up Radar DisplayCHOICE OF RADAR PRESENTATION Many factors may influence a navigator’s choice of radar

presentation. Availability of equipment and own experience will naturally be deciding factors, but it is important that navigator is aware that he is not completely free in his selection of radar presentations.

A navigator on a ship equipped with True Motion Radar, operating in an area with dense traffic is obliged to utilize True Motion radar presentation in order to avoid additional problems in a possible collision case. The reason for this is that True Motion presentation is considered to be, and is the best choice under such conditions. Most navigators who use their equipment correctly will soon obtain the needed experience to choose the presentation that provides the simplest and most accurate information at anytime.

Setting Up Radar DisplayMEASUREMENT OF RANGE The range accuracy of radar is generally high. Range can be

measured on radar with reference to fixed range rings equally spaced around own ships position on the radar screen. For more accurate measurement of range, most modern radars provide a variable range ring that can be positioned in any range on the screen.

The Variable range ring should regularly be checked for accuracy against the fixed range rings, which are normally most stable. With a variable range ring more accurate measurements can be taken. Fixed range rings can be used when the need for high accuracy is not important.

Setting Up Radar DisplayBEARING ACCURACY The bearing accuracy of massive radars is normally not so high Beam with distortion, which can be partly eliminated by

reduction in gain. Heading marker error, which can be determined by various

methods Centering error, which can easily be corrected Error due to yawing of own ship Error due to parallax when viewing the display Always read and follow the radar manufacturer recommendations

for use and maintenance of the radar equipment. This will save you time and money and ensure proper use of equipment.

Marine Radar Performance Specification

Performance Standards for Radar Equipment Resolution A.477(XII)

MIDTERM

ObjectivesObjectives At the end of the grading period, the students will

be able to demonstrates a knowledge and understanding of the following:

• Construct the relative motion triangle• Determine course, speed and aspect of other

ships• Determine the closest point of approach (CPA)

and time to closest approach (TCPA)• Determine the effect of course and speed changes• Report Radar Plot data

PLOTTINGPurpose of Plotting1. It can show whether danger of collision exists, how close

will pass the target and how much time there is left before this will take place.

2. Approximate determination of the course and speed of the other vessel, so that sensible avoiding action can be taken when needed.

Manual plotting in connection to radar means to mark one or more echoes within a specific time interval and thus decide the target’s movement in relation to own ship.

The objective of plotting is to obtain the clearest possible picture of the situation.

PLOTTINGThe Plotting Process Detection- recognition of the presence of the

target. Selection- choosing of target requiring closer

observation Tracking- the process of observing changes in

target position Plotting- the whole process of detection,

selection, tracking, calculation of targets parameter

PLOTTINGTarget Aspect The aspect is defined as the angle of view

however, in connection with plotting we will use the term “Calculated Aspect” in order to distinguish between the two.

It can be defined as the angle between the target ships heading and bearing to own ship, as seen from the target ship.

In connection with plotting and use of radar and ARPA, we had better define what we receive from these systems as calculated aspect.

PLOTTING

Target Aspect

Target Ship

Aspect Red 40

Own Ship

Aspect B measured from dead to a head to 180 degrees on either side of the ship.

PLOTTING

Relative Aspect Relative speed is defined as the target speed

relative to own ship, as deducted from a number of measurements of its range and bearing on the radar, expressed as an angular distance from own ships heading.

PLOTTINGPlotting Triangle Knowledge of the speed triangle is essential for

understanding the principles used in plotting.

R

E

M

R - M = Echo Line/Relative TrackE – M = Target Ship Course and SpeedE – R = Own Ship Course and Speed

PLOTTINGHeading Defined as the direction in which the bow of a

vessel is pointing, expressed as an angular distance from north.

North

Heading 45

45 degrees

PLOTTING

Relative Bearing If the relative bearing of an approaching target

remains the same over time, collision danger is observed.

Relative Bearing of Target 030 degrees

Own Ship Heading

PLOTTING

True Bearing On merchant ships, true bearing is mainly used

for position fixing.

North

True Bearing 300 degrees

PLOTTING

Bearing On a ship bearing can be relative or true in

connection with traffic surveillance, relative bearing are often used.

True North

Relative Bearing

Ship’s Heading 015 degrees

Relative Bearing

PLOTTING

CPA (Closest Point on Approach) CPA must not be mixed with the point where the

target crosses own ship’s heading, often referred to as BCP (Bow Crossing Point)

Bow Crossing Point

CPA

TCPA

PLOTTING

TCPA (Time Closest Point on Approach) TCPA is the time estimated as measured along

the echo line form its present position to the closest point on approach.

Bow Crossing Point

CPA

TCPA

PLOTTINGManeuvering Board Plotting can be done with head up or north up

however, regardless of selected radar presentation it is advantageous to plot with north up.

True Plotting Gives a natural and easily understood picture of the

course of events. Can be done directly in the chart if the scale is

large enough to give a clear picture. Gives an easily understood picture of the situation

PLOTTING

Relative Plotting Own ship is considered a fixed point. Plotting

must be done with high accuracy and great care. Heavy traffic can make manual plotting

impossible.

PLOTTING

Electronic Plotting Today many modern radars are equipped with

an electronic plotting feature. Used together with EBL (Electronic Bearing Lines) is very good tool in the hands of a qualified navigator. These radar features make plotting direct on the radar display very convenient and replace the need for reflection plotter or plotting sheets.

PLOTTING

Errors in Manual Plotting Even small errors in one or several of these

parameters can cause large and dangerous errors in the plot calculations. Always check these parameters as thoroughly as possible in order to reduce the possibilities for “nasty surprises” during manual plotting work.

PLOTTING

Sources of Errors in Manual Plotting Bearing Error Distance Error Error in timing between plots Error in speed Gyro Error Relative Speed Maneuvering of own vessel Unstable steering, yawing, etc.

Errors in Manual Plotting

Collision Danger The usual method of deciding whether a collision

danger is present is taking several bearings. This is time consuming, and it requires that many bearings have to be taken.

A dangerous situation can quickly emerged by taking a few inaccurate bearings from a comparatively long distance and then “forgetting” the target if the CPA is considered large enough.


Errors in Distance Measurement An error in distance measurement, as in bearing

error, can produce grave results when judging the traffic situation.

Errors in Timing A timing error between two plots will result in

calculation of incorrect target course, speed and time to CPA.


Errors in Speed An error on speed causes incorrect calculation in

the same manner as error timing. However, we must remember that in all plotting where we wish a picture of aspect, own vessels speed through the water must be utilized. Never make corrections due to current or drift. In connection with plotting, speed through water should be used.


Gyro Error Make it a habit to always correct the gyro for

known gyro error target with low speed.

Factors That Affects Manual Plotting Unstable Steering Maneuvering of Own Ship The Technical Exactness of the Equipment Rough Weather Conditions Target Relative Speed The Navigator’s Experience and Lack of Plotting Practice

VHF (Very High Frequency)Communication

Importance of VHF Communication A way to make ones intentions clear to another

vessel. To arrive at an unambiguous decision about

avoiding tactics. Broadcasting a general information report to

ships in the vicinity. Use of VHF is not explicitly advocated in the

rules, but implicitly (“by all available means”) its use is recommended.


VHF Communication Report Content Time Position Course Speed Maneuvers


Three Basic Steps to Remember in Using VHF: Identification (Own ship name, call sign, type) Ascertainment of Movements and Intensions

(time, position, course, speed, etc.) Disengagement (indicating both vessels have

recognized the action completed)Sea speak is the official maritime language initiated by

Captain F.F. Weeks and later adapted by IMO. The center principle of Sea speak is that receiver should be alerted to the type of message that follows, at the beginning of the message.


Sea Speak Type of Message Question- indicates that the following message

is of interrogative character. Answer- indicates that the following message is

the reply to previous question Request- indicates that the content of the

following message is asking for action from others with respect to the ship.

Information- indicates that the following message is restricted to observed facts.


Sea Speak Components Intention- indicates that the following informs

other about immediate action to be taken. Warning- indicates that the following message

informs other traffic participants about danger. Advice- indicates that the following message

implies the intention of the sender to influence the recipient by a recommendation.

Instruction- indicates that the following message implies the intention of the sender to influence the recipient by regulation.

Relative Radar Plotting Symbols

Symbols are signs, letters, or abbreviations used to replace words. They are used in mathematics and certain sciences to good advantage by reducing the amount of space required explaining a thing. Since symbols take the place of words and, they form a language of their own her here is a list that is used in Radar Plotting.


CPA - Closest Point of Approach. DRM - Direction of relative movement e - point of origin of the own ship e-m - Contact's vector e-r - Own ship's initial vector e-r' - Own ship's final OC - Own ship's initial course. m - The head of the relative motion vector (r-m)

also the head of the contact's vector (e-m).


RML - Relative Motion Line. SRM - Speed of Relative Movement. TCPA- time closest point of approach NCPA- new closest point of approach ST- actual target’s true speed CT- true course of target mx- point of execution AC- collision avoidance course AS- collision avoidance speed ROCS- resume ownership course and speed


NRML - New Relative Motion Line the Relative Motion Line after own ship has maneuvered.

r - The head of own ship vector (e-r). r-m - The relative motion vector. M1 - First plotted position of contact

SEMI FINAL

ObjectivesObjectives 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 SystemWhat 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.

Principal ARPA SystemWhat 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.

Principal ARPA SystemWhat 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.

Principal ARPA SystemTypes 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.

Principal ARPA Systema) 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.

Principal ARPA Systemb) 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.

Principal ARPA SystemHow 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

Principal ARPA System

Principal ARPA SystemGeneral 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)

Principal ARPA SystemGeneral 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

Principal ARPA SystemARPA 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

Principal ARPA SystemARPA Features• Electronic plotting of up to 10 targets in different symbols (This

function is disabled when ARPA is activated)

• Electronic parallel index lines

• Interswitching (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; 30kw output for S-band, either in the transceiver aloft (gearbox) or RF down (transceiver in bridge)

• Exclusive FURUNO MIC low noise receiver•

Principal ARPA SystemDISPLAY CONTROLS - MODE PANEL

Principal ARPA SystemDISPLAY 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.


DISPLAY CONTROLS - MODE PANEL 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.

Principal ARPA SystemHow 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 TCPAThis 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.

Principal ARPA SystemWhat extra facilities are available in the ARPA system?1.Trial ManeuverIt 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.

Principal ARPA SystemWhat extra facilities are available in the ARPA system?

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.


What extra facilities are available in the ARPA system?

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 InformationSince 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.

Principal ARPA SystemMethods 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 targetsIndicating navigational marksSailing routesPointing out targets that cause alarms etc.

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

ARPA’s Graphical SymbolsSymbols and Definition RV - Relative Speed Vector indicates target relative course and speed.

ARPA’s Graphical SymbolsSymbols and Definition TH - Track History should be provided on request, consisting of at least four equally spaced past positions of the echo.

ARPA’s Graphical SymbolsSymbols and Definition PPC - POINT OF POSSIBLE COLLISION is the point at which a collision could take place.

ARPA’s Graphical SymbolsSymbols and Definition PAD - Predicted Area Of Danger is the area to be avoided based on CPA and TCPA setting and relative target speed.


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 systema.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.

Principal ARPA SystemWhat 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.

Principal ARPA SystemWhat 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 Warning9. Operational Danger

5.History of Warning 10. Equipment

11. Rejection Boundaries


• 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 (XII)

FINALS

ObjectivesObjectives 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 BCourse/Speed

Ship CCourse/Speed

Ship DCourse/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.

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 heed 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





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





g. Effect of changes in own ship’s course or speed or both

h. Operation of the trial maneuver

nav 6 radar arpa

Education

radar picture

help of radar

shipboard radar system

performancesradio waves

electromagnetic waves

affecting detectionfactors

successive crest of

electro magnetic waves