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Navigation VI STCW Table A-II/1 RADAR NAVIGATION What is RADAR? The word radar is an abbreviation for Radio Detection And Ranging Radar is an electromagnetic systems used for detection and location of objects such as aircraft, ship, vehicles, people, natural environment etc. 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 NAVIGATION Landfall 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 NAVIGATION Coastal 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.

It 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. DISPLAY A 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 PPI 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. RASTER 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. The 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

PILOTAGE For 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. Fundamental Principle of Radar Transmitter generates and transmits electromagnetic wave (sine or pulse). A portion of it is reflected back by the target (object you want to identify). The radiated portion is collected by the radar antenna and processed. One antenna can be used for both transmission and reception 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. Fundamental Principle of Radar 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. -To assist in navigation, particularly at landfalls and when navigating in coastal waters.

RADAR SCAN & RADAR SWEEP Radar 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 PRF Short 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 Width Selected Pulse Length Height of Antenna Installation of Antenna Ship’s Trim

Fundamental Principle of Radar 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.

Marine Radar Component RADAR ANTENNA Transmit 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: RECEIVER The incoming signal is fed to a series of amplifier and further to detect or demodulator for which smoothen 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. TRANSMITTER

IMPORTANT RADAR RANGE PARAMETERS Antenna Height Height of the Target Size of the Target Target Reflecting Area Materials of the Target Shape of the Target Weather Condition FOLLOWING PARAMETERS MUST BE TAKEN INTO ACCOUNT: Transmitted Peak Power Wavelength Pulse Length Antenna Gain Noise Figure Number of Pulses Per Scan Wave Guide Loss Display Parameters RANGE DISCRIMINATION The ability of radar to discriminate between two small object close together in the same bearing. Effecting range discrimination are: Select Pulse Length The size of the spot If possible short pulse and short range should be selected and focused, brightness carefully adjusted.

BEARING 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 Width The spot size Correct focusing and brightness setting will improve the bearing discrimination. BEARING AND RANGE DISTORTION The 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. BEARING AND RANGE DISTORTION The 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 COMPASS The magnetic compass must have a safe distance from the radar. Nowadays, although most ships are equipped with gyro 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. RADIATION Marine 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. When 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. Whenever 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: Sea Rain 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. 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 subrefraction. 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 BLACKOUT With 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. 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. 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 own ship during the echoes movements across the PPI on motion display. -The targets true course and speed is the targets true motion period of observation. -The own ships course and speed are your ships true motion period of observation.

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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. 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. Anti sea clutter will normally remove 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. 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. 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 Sband 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 equipment contains radar interference rejection circuits to eliminate this disturbance

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. 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. 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.

SYMBOLS FOR RADAR CONTROL Radar Off Radar On Radar Stand By Aerial Rotating North-up Presentation Head-up Presentation Heading Marker Alignment Range Selector Short Pulse Long Pulse Gain Tuning Anti-Clutter Rain Minimum Anti-Clutter Rain Maximum Anti-Clutter Sea Minimum Anti-Clutter Sea Maximum Scale Illumination Display Brilliance Range Rings Brilliance Variable Range Marker Bearing Marker 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)

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. 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. 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. 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.

Setting Up Radar Display START UP SEQUENCE Radar ON/OFF Radar Standby Scanner ON/OFF

CHOICE 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. MEASUREMENT 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 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 BEARING 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. PLOTTING Purpose of Plotting 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. 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. The 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 Target Aspect The aspect is defined as the angle of view however, in connec...