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UNIT 4

NAVIGATION

RADAR

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RADAR is an acronym for Radio

Detection and Ranging.

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Radar determines distance to an

object by measuring the timerequired for a radio signal to travel

from a transmitter to an object and

return.

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It is a system used to preventcollision, determine position, the

course and speed of other vessels.

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The Principle of Radar 

 As the radar antenna rotates, thetransmitter sends out a series of very short pulses every degree.

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When the pulse strikes a reflectingobject or surface, it is reflected to

the RADAR aerial and passed to

the radar receiver.

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The pulse is displayed on a cathode

ray tube.

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When an echo returns, the image

on the cathode-ray tube brightens.

Thus a spot of light appears on thetube at a distance from the centre

proportional to the time pulse takes

to go out and back.

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By measuring the time difference

between the transmission andreceipt of these waves, the RADAR

can calculate an object’s distance

or range.

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The strength of signal

The strength of return signals varies

depending on

the reflectivity of the surface of thereflecting object

its distance

atmospheric conditions..

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From vertical surfaces such ascliffs, ships, buildings there will be

strong reflection.

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Metal objects are the best

reflectors.

Wood and plastic produce weaker 

reflections than metal.

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RADAR systems are;

continuous-wave (CW), frequency modulated (FM),

Doppler radar 

optical radar which transmits verynarrow signal beams of laser lightinstead of radio waves.

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ARPA

 ARPA is an acronym for Automatic

Radar Plotting Aid.

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It is a combination of a traditional radar 

display with a computer driven plotting

device.

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The system receives target information

input from the ship's radar system, andown ship course and speed information

from the ship's electronic navigation

equipment.

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1- What is RADAR used for?

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2-What is the function of transmitter?

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3- What happens when an echo returns?

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4- On what is the pulse displayed?

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5- What does the strength of signals

depend on?

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6-What are the main radar types?

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7- What are the main components of 

radar system?

Fill i th bl k ith th d b l d k

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Fill in the blanks with the words below and make

any changes if necessary

send out- distance-transmitter-detection-collision-receive -

weather - electromagnetic 

1-RADAR is a ……………………. system which is used to locateand identify objects. 

2- Radar can detect objects out of the range of sight and works in

all ………………… conditions. 3- Radar relies on sending and ……….electromagnetic radiation. 

4- Radar system is composed of: a …………………., an antenna,a receiver, and a display unit. 

5- The antenna sends the signals out as ………………. radiation. 

6- RADAR can calculate an object’s ……………………. or range.7- The radar system is mainly used for avoiding …………………

8- The transmitter……… short pulses of radio frequency energy. 

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What does RADAR stand for?

a. Radio Direction at Random 

b. Radio Direction and Ranging 

c. Radio Detection and Ranging 

d. Radio Direction and Reckoning 

e. Radio Detection and Reckoning

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What does RADAR stand for?

c. Radio Detection and Ranging 

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Which is not a RADAR type?

a. continuous wave 

b. frequency modulated c. GPS 

d. Doppler  e. optical

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Which is not a RADAR type?

c. GPS