navigation nau 102 radar navigation. radar display interpretation before you can use any radar...

NavigationNavigation

NAU 102NAU 102Radar NavigationRadar Navigation

Radar Display InterpretationRadar Display Interpretation

• Before you can use any radar target for Before you can use any radar target for navigational fixing purposes, you must identify navigational fixing purposes, you must identify the object on a navigational chart and correlate it the object on a navigational chart and correlate it with its radar image.with its radar image.

• Misidentification of radar targets used for Misidentification of radar targets used for navigational purposes can lead to disaster.navigational purposes can lead to disaster.

Don’t Run Aground in Oregon!Don’t Run Aground in Oregon!


• Natural Targets:Natural Targets:• LandLand - - Distant land echoes can be distinguished from ship

echoes by their greater size and regularity of paint with each scanner sweep.

- Most land echoes are concentrated 2 to 3 miles from the - Most land echoes are concentrated 2 to 3 miles from the coastline.coastline.

- - Cliffs give a strong thin echo line visible at great ranges.

- - Slopes give a weaker, wider echo line visible at lesser ranges.


• LandLand - The highest point of a hill may not be the - The highest point of a hill may not be the

point detected at the greatest range.point detected at the greatest range. - Land/water boundaries like - Land/water boundaries like sand bars and

reefs awash usually give good echoes. - Even water lapping on a gently sloping - Even water lapping on a gently sloping

mud bank, not conspicuous by eye, may be mud bank, not conspicuous by eye, may be easily distinguished on a radar display.easily distinguished on a radar display.


• Artificial Land TargetsArtificial Land Targets - Large artificial coastal structures like breakwaters - Large artificial coastal structures like breakwaters

are easily recognizable on the radar display.are easily recognizable on the radar display. - If buildings are present, any received long range - If buildings are present, any received long range

echoes are more likely to come from them than any echoes are more likely to come from them than any natural target.natural target.

- At close range, the quite fine details of a town may - At close range, the quite fine details of a town may be seen, especially at 3-cm wavelengths.be seen, especially at 3-cm wavelengths.

- Streets, roads and railway lines may be picked out - Streets, roads and railway lines may be picked out because of adjacent walls, fences and light standards.because of adjacent walls, fences and light standards.


• Artificial Land TargetsArtificial Land Targets

- Bridges make - Bridges make excellent targets but excellent targets but cast pronounced radar cast pronounced radar shadows behind them.shadows behind them.


• BuoysBuoys - Echoes vary in brightness unless at short - Echoes vary in brightness unless at short

range when it is said to be range when it is said to be firmfirm or or solid.solid. - Aspect constantly changing due to wind - Aspect constantly changing due to wind

and waves.and waves. - Waves can shadow the buoy.- Waves can shadow the buoy. - Low height may put buoy below vertical - Low height may put buoy below vertical

beam lobes.beam lobes.


• Beacons and RocksBeacons and Rocks - Can be distinguished from buoys by possessing - Can be distinguished from buoys by possessing

firmer echoes.firmer echoes. - Most rocks are of sufficient size to display some - Most rocks are of sufficient size to display some

apparent shape not solely due to the radar set apparent shape not solely due to the radar set characteristics.characteristics.

- Rocks, beacons and ships may be distinguished - Rocks, beacons and ships may be distinguished from buoys by temporarily reducing gain. The from buoys by temporarily reducing gain. The buoy echo should drop out first.buoy echo should drop out first.


• RaconsRacons - An electronic means of - An electronic means of

enhancing a particularly enhancing a particularly important navigational aid important navigational aid for identification on a for identification on a radar display.radar display.

- Similar to the transponder - Similar to the transponder used in commercial used in commercial aircraft to identify a aircraft to identify a particular aircraft to the particular aircraft to the air traffic controller.air traffic controller.


• RaconsRacons - A racon device is a small - A racon device is a small

transceiver.transceiver. - Upon receiving an - Upon receiving an

interrogating pulseinterrogating pulse from a from a transmitting vessel, (after a transmitting vessel, (after a certain time delay) an certain time delay) an enhanced identification enhanced identification pulse is transmitted by the pulse is transmitted by the racon at the same frequency racon at the same frequency and registers on the display and registers on the display as a Morse code signal.as a Morse code signal.


• RaconsRacons - The racon reply pulse - The racon reply pulse

will be superimposed will be superimposed radially outward from radially outward from the target on which it the target on which it is located.is located.

- The racon will be - The racon will be received for between 2 received for between 2 and 7 successive and 7 successive sweeps of the antenna.sweeps of the antenna.


• RaconsRacons - If the target echo is too - If the target echo is too

weak to be visible, weak to be visible, approximate range to the approximate range to the target can be obtained target can be obtained from the inner edge of the from the inner edge of the racon symbol.racon symbol.

- The angular width of the - The angular width of the racon symbol is a good racon symbol is a good representation of the representation of the horizontal beam width of horizontal beam width of your radar.your radar.

Radar Navigation TechniquesRadar Navigation Techniques

• Significance of radar navigational Significance of radar navigational information varies with the circumstances information varies with the circumstances in which the radar is used.in which the radar is used.

• 3 broad classifications of circumstances:3 broad classifications of circumstances:

1. Making landfall after an ocean passage1. Making landfall after an ocean passage

2. Coasting2. Coasting

3. Navigation in pilotage waters3. Navigation in pilotage waters


• Making Landfall:Making Landfall:

- The care with which a navigator takes when - The care with which a navigator takes when making a landfall will depend on the confidence making a landfall will depend on the confidence he has in his position prior to landfall and the he has in his position prior to landfall and the character of the coast he is approaching.character of the coast he is approaching.

- The first priority when approaching land in thick - The first priority when approaching land in thick weather is to identify without a doubt some land weather is to identify without a doubt some land feature and fix a position from it.feature and fix a position from it.


• Making LandfallMaking Landfall - Positive identification becomes easier the - Positive identification becomes easier the

nearer a vessel draws to land.nearer a vessel draws to land. - At long ranges the actual coastline may lie - At long ranges the actual coastline may lie

below the radar horizon.below the radar horizon. - It may be necessary to identify some - It may be necessary to identify some

inland topographical object.inland topographical object. - This may prove very difficult.- This may prove very difficult.


• Making LandfallMaking Landfall

- Landmarks which are visually conspicuous may - Landmarks which are visually conspicuous may not be so to radar.not be so to radar.

- Advance preparation and careful chart inspection - Advance preparation and careful chart inspection will aid in the identification process.will aid in the identification process.

- It is unlikely that positive identification can be - It is unlikely that positive identification can be made of a single long-range echo paint on the PPI.made of a single long-range echo paint on the PPI.


• Making LandfallMaking Landfall

- Normally, at least three positively identified - Normally, at least three positively identified long-range echoes are needed for position fixing long-range echoes are needed for position fixing confidence using radar alone.confidence using radar alone.

- Accurate fixing at long-range may prove - Accurate fixing at long-range may prove impossible but may not always be needed.impossible but may not always be needed.

- Nevertheless, the farther out a navigator can - Nevertheless, the farther out a navigator can accurately fix his position, the better.accurately fix his position, the better.


• Coastal NavigationCoastal Navigation

- At about 8-15 miles offshore , depending - At about 8-15 miles offshore , depending on topography, the radar image of a on topography, the radar image of a coastline should begin to resemble that of a coastline should begin to resemble that of a chart.chart.

- Fixing a vessel’s position accurately - Fixing a vessel’s position accurately becomes possible at these ranges.becomes possible at these ranges.


• Coastal NavigationCoastal Navigation

- The descending order of accuracy in radar fixes - The descending order of accuracy in radar fixes is:is:

1. Radar range and visual bearing of a single 1. Radar range and visual bearing of a single object.object.

2. Radar ranges of several (3) radar conspicuous 2. Radar ranges of several (3) radar conspicuous objects.objects.

3. Radar range and bearing of a single object.3. Radar range and bearing of a single object.


• Coastal Navigation – fixing methodsCoastal Navigation – fixing methods 1. 1. Radar range and visual bearing - An object high and steep-to toward the - An object high and steep-to toward the

observer should be selected for range observer should be selected for range accuracy.accuracy.

- Use of visual bearings when possible - Use of visual bearings when possible greatly enhances fix accuracy over radar greatly enhances fix accuracy over radar bearings. bearings.


• Coastal Navigation – fixing methodsCoastal Navigation – fixing methods 2. 2. Radar ranges - If possible, select (3) prominent isolated objects - If possible, select (3) prominent isolated objects

separated in bearing by at least 45 deg.separated in bearing by at least 45 deg. - Due to beam width distortion, try to select points of - Due to beam width distortion, try to select points of

a coastline at right angles to the line of sight. This a coastline at right angles to the line of sight. This will often be the part of the coast nearest the vessel.will often be the part of the coast nearest the vessel.

- Steep-to points are given preference over gently - Steep-to points are given preference over gently sloping areas to better locate the source of the sloping areas to better locate the source of the returned echo.returned echo.


• Coastal Navigation – fixing methodsCoastal Navigation – fixing methods 3. 3. Radar range and bearing - Least accurate of the 3 radar fixing methods- Least accurate of the 3 radar fixing methods - Has the advantage of being quick and easy to obtain- Has the advantage of being quick and easy to obtain - Object selected must be very prominent, isolated or - Object selected must be very prominent, isolated or

bothboth - Reduce gain to minimum possible to enhance bearing - Reduce gain to minimum possible to enhance bearing

accuracy.accuracy. - Tangent bearings are undesirable due to - Tangent bearings are undesirable due to

beam width distortion.


• Coastal Navigation

- Question: In the following example, at what - Question: In the following example, at what time could the navigator have obtained a time could the navigator have obtained a very accurate fix using 3 radar ranges?very accurate fix using 3 radar ranges?

navigation nau 102 radar navigation. radar display interpretation before you can use any radar...

Documents

radar image

pronounced radar shadows

land distant land echoes

ship echoes

target echo

good echoes

firmer echoes

received long range