Navigation NAU 102 Radar Navigation

Radar Display Interpretation Before you can use any radar target for navigational fixing purposes, you must identify the object on a navigational chart and correlate it with its radar image. Before you can use any radar target for navigational fixing purposes, you must identify the object on a navigational chart and correlate it with its radar image. Misidentification of radar targets used for navigational purposes can lead to disaster. Misidentification of radar targets used for navigational purposes can lead to disaster.

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Radar Display Interpretation Natural Targets: Natural Targets: Land Land - Distant land echoes can be distinguished from ship echoes by their greater size and regularity of paint with each scanner sweep. - Distant land echoes can be distinguished from ship echoes by their greater size and regularity of paint with each scanner sweep.Distant land Distant land - Most land echoes are concentrated 2 to 3 miles from the coastline. - Most land echoes are concentrated 2 to 3 miles from the coastline. - Cliffs give a strong thin echo line visible at great ranges. - Cliffs give a strong thin echo line visible at great ranges.Cliffs - Slopes give a weaker, wider echo line visible at lesser ranges. - Slopes give a weaker, wider echo line visible at lesser ranges.Slopes

Radar Display Interpretation Land Land - The highest point of a hill may not be the point detected at the greatest range. - The highest point of a hill may not be the point detected at the greatest range. - Land/water boundaries like sand bars and reefs awash usually give good echoes. - Land/water boundaries like sand bars and reefs awash usually give good echoes.sand bars sand bars - Even water lapping on a gently sloping mud bank, not conspicuous by eye, may be easily distinguished on a radar display. - Even water lapping on a gently sloping mud bank, not conspicuous by eye, may be easily distinguished on a radar display.

Radar Display Interpretation Artificial Land Targets Artificial Land Targets - Large artificial coastal structures like breakwaters are easily recognizable on the radar display. - Large artificial coastal structures like breakwaters are easily recognizable on the radar display. - If buildings are present, any received long range echoes are more likely to come from them than any natural target. - If buildings are present, any received long range echoes are more likely to come from them than any natural target. - At close range, the quite fine details of a town may be seen, especially at 3-cm wavelengths. - At close range, the quite fine details of a town may be seen, especially at 3-cm wavelengths. - Streets, roads and railway lines may be picked out because of adjacent walls, fences and light standards. - Streets, roads and railway lines may be picked out because of adjacent walls, fences and light standards.

Radar Display Interpretation Artificial Land Targets Artificial Land Targets - Bridges make excellent targets but cast pronounced radar shadows behind them. - Bridges make excellent targets but cast pronounced radar shadows behind them.

Radar Display Interpretation Buoys Buoys - Echoes vary in brightness unless at short range when it is said to be firm or solid. - Echoes vary in brightness unless at short range when it is said to be firm or solid. - Aspect constantly changing due to wind and waves. - Aspect constantly changing due to wind and waves. - Waves can shadow the buoy. - Waves can shadow the buoy. - Low height may put buoy below vertical beam lobes. - Low height may put buoy below vertical beam lobes.

Radar Display Interpretation Beacons and Rocks Beacons and Rocks - Can be distinguished from buoys by possessing firmer echoes. - Can be distinguished from buoys by possessing firmer echoes. - Most rocks are of sufficient size to display some apparent shape not solely due to the radar set characteristics. - Most rocks are of sufficient size to display some apparent shape not solely due to the radar set characteristics. - Rocks, beacons and ships may be distinguished from buoys by temporarily reducing gain. The buoy echo should drop out first. - Rocks, beacons and ships may be distinguished from buoys by temporarily reducing gain. The buoy echo should drop out first.

Radar Display Interpretation Racons Racons - An electronic means of enhancing a particularly important navigational aid for identification on a radar display. - An electronic means of enhancing a particularly important navigational aid for identification on a radar display. - Similar to the transponder used in commercial aircraft to identify a particular aircraft to the air traffic controller. - Similar to the transponder used in commercial aircraft to identify a particular aircraft to the air traffic controller.

Radar Display Interpretation Racons Racons - A racon device is a small transceiver. - A racon device is a small transceiver. - Upon receiving an interrogating pulse from a transmitting vessel, (after a certain time delay) an enhanced identification pulse is transmitted by the racon at the same frequency and registers on the display as a Morse code signal. - Upon receiving an interrogating pulse from a transmitting vessel, (after a certain time delay) an enhanced identification pulse is transmitted by the racon at the same frequency and registers on the display as a Morse code signal.

Radar Display Interpretation Racons Racons - The racon reply pulse will be superimposed radially outward from the target on which it is located. - The racon reply pulse will be superimposed radially outward from the target on which it is located. - The racon will be received for between 2 and 7 successive sweeps of the antenna. - The racon will be received for between 2 and 7 successive sweeps of the antenna.

Radar Display Interpretation Racons Racons - If the target echo is too weak to be visible, approximate range to the target can be obtained from the inner edge of the racon symbol. - If the target echo is too weak to be visible, approximate range to the target can be obtained from the inner edge of the racon symbol. - The angular width of the racon symbol is a good representation of the horizontal beam width of your radar. - The angular width of the racon symbol is a good representation of the horizontal beam width of your radar.

Radar Navigation Techniques Significance of radar navigational information varies with the circumstances in which the radar is used. Significance of radar navigational information varies with the circumstances in which the radar is used. 3 broad classifications of circumstances: 3 broad classifications of circumstances: 1. Making landfall after an ocean passage 1. Making landfall after an ocean passage 2. Coasting 2. Coasting 3. Navigation in pilotage waters 3. Navigation in pilotage waters

Radar Navigation Techniques Making Landfall: Making Landfall: - The care with which a navigator takes when making a landfall will depend on the confidence he has in his position prior to landfall and the character of the coast he is approaching. - The care with which a navigator takes when making a landfall will depend on the confidence he has in his position prior to landfall and the character of the coast he is approaching. - The first priority when approaching land in thick weather is to identify without a doubt some land feature and fix a position from it. - The first priority when approaching land in thick weather is to identify without a doubt some land feature and fix a position from it.

Radar Navigation Techniques Making Landfall Making Landfall - Positive identification becomes easier the nearer a vessel draws to land. - Positive identification becomes easier the nearer a vessel draws to land. - At long ranges the actual coastline may lie below the radar horizon. - At long ranges the actual coastline may lie below the radar horizon. - It may be necessary to identify some inland topographical object. - It may be necessary to identify some inland topographical object. - This may prove very difficult. - This may prove very difficult.

Radar Navigation Techniques Making Landfall Making Landfall - Landmarks which are visually conspicuous may not be so to radar. - Landmarks which are visually conspicuous may not be so to radar. - Advance preparation and careful chart inspection will aid in the identification process. - Advance preparation and careful chart inspection will aid in the identification process. - It is unlikely that positive identification can be made of a single long-range echo paint on the PPI. - It is unlikely that positive identification can be made of a single long-range echo paint on the PPI.

Radar Navigation Techniques Making Landfall Making Landfall - Normally, at least three positively identified long- range echoes are needed for position fixing confidence using radar alone. - Normally, at least three positively identified long- range echoes are needed for position fixing confidence using radar alone. - Accurate fixing at long-range may prove impossible but may not always be needed. - Accurate fixing at long-range may prove impossible but may not always be needed. - Nevertheless, the farther out a navigator can accurately fix his position, the better. - Nevertheless, the farther out a navigator can accurately fix his position, the better.

Radar Navigation Techniques Coastal Navigation Coastal Navigation - At about 8-15 miles offshore, depending on topography, the radar image of a coastline should begin to resemble that of a chart. - At about 8-15 miles offshore, depending on topography, the radar image of a coastline should begin to resemble that of a chart. - Fixing a vessel’s position accurately becomes possible at these ranges. - Fixing a vessel’s position accurately becomes possible at these ranges.

Radar Navigation Techniques Coastal Navigation Coastal Navigation - The descending order of accuracy in radar fixes is: - The descending order of accuracy in radar fixes is: 1. Radar range and visual bearing of a single object. 1. Radar range and visual bearing of a single object. 2. Radar ranges of several (3) radar conspicuous objects. 2. Radar ranges of several (3) radar conspicuous objects. 3. Radar range and bearing of a single object. 3. Radar range and bearing of a single object.

Radar Navigation Techniques Coastal Navigation – fixing methods Coastal Navigation – fixing methods 1. Radar range and visual bearing 1. Radar range and visual bearingRadar range and visual bearingRadar range and visual bearing - An object high and steep-to toward the observer should be selected for range accuracy. - An object high and steep-to toward the observer should be selected for range accuracy. - Use of visual bearings when possible greatly enhances fix accuracy over radar bearings. - Use of visual bearings when possible greatly enhances fix accuracy over radar bearings.

Radar Navigation Techniques Coastal Navigation – fixing methods Coastal Navigation – fixing methods 2. Radar ranges 2. Radar rangesRadar rangesRadar ranges - If possible, select (3) prominent isolated objects separated in bearing by at least 45 deg. - If possible, select (3) prominent isolated objects separated in bearing by at least 45 deg. - Due to beam width distortion, try to select points of a coastline at right angles to the line of sight. This will often be the part of the coast nearest the vessel. - Due to beam width distortion, try to select points of a coastline at right angles to the line of sight. This will often be the part of the coast nearest the vessel. - Steep-to points are given preference over gently sloping areas to better locate the source of the returned echo. - Steep-to points are given preference over gently sloping areas to better locate the source of the returned echo.

Radar Navigation Techniques Coastal Navigation – fixing methods Coastal Navigation – fixing methods 3. Radar range and bearing 3. Radar range and bearingRadar range and bearingRadar 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 both - Object selected must be very prominent, isolated or both - Reduce gain to minimum possible to enhance bearing accuracy. - Reduce gain to minimum possible to enhance bearing accuracy. - Tangent bearings are undesirable due to beam width distortion. - Tangent bearings are undesirable due to beam width distortion.beam width distortion.beam width distortion.

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