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OOW Oral Study > Radar & Arpa > Flashcards

Radar & Arpa Flashcards

1
Q

What is is multi-path error?

A

Multi-path is when a radio wave bounces back from i.e a mountain, back to the boat but the radar is transmitting and can’t pick up the signals, the radio wave therefore bounces of the ship back to the mountain and then back to the ship again where the radar can receive. This will make your target on your display at double the distance at the same bearing as the radio wave have travelled double the distance at the same bearing.

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2
Q

What is side lobe error?

A

Side lobe is created from electromagnetic energy leaking from the side of the scanner. This creates lobes besides the main beam, these lobes can pick up targets at close range and therefore create false targets either side of the real target in the shape of a semi circle or sometimes even full circle. (cock n’ balls)

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3
Q

What does a radar do?

A

Measures the time it takes for a radio wave to be transmitted, reflected and received through the Echo Range Principle and divides it by 2 to get a distance to a target and display it on a screen.

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4
Q

What is bearing discrimination?

A

Radar’s ability to differentiate between 2 targets on different bearings at the same range.

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5
Q

Name the 5 factors that affect the reflective properties of targets.

A

MASTS

Material
Aspect
Size
Texture
Shape

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6
Q

What is Minimum range and what is it affected by?

A

The ability to detect and display echoes in close proximity to the radar.

Pulse length
Vertical beam width and height of antenna.

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7
Q

What’s subrefraction?

A

Cold polar air over warm sea deflect beam upwards. 40% range reduction.

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8
Q

What’s super refraction?

A

Increase of radar range when warm air is over cold air.

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9
Q

What is ducting?

A

Temperature inversion.
Can increase radar range to 400nm if antenna is in duct

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10
Q

Radar beam characteristics?

A

Horizontal beam width
0.5-2.0 degree

Vertical beam width
20-30 degree

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11
Q

When would you select a longer range? (3 factors)

A
  1. If you are concerned about distant weather
  2. You want to acquire a target further than your current range
  3. Wish to take a range of a distant object
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12
Q

Considerations when using different ranges

A

Shorter range will be better for navigating and will have reduced range and bearing discrimination

Generally would have to increase pulse length when going to longer ranges which would increase range and bearing discrimination but would also let you potentially see upcoming targets/weather

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13
Q

Characteristics of X band?

A

X band (3cm wavelength, 9GHz)
Ability to detect a 9GHZ SART
Improved small target detection
Higher resolution image due to high frequency, improving coastline identification during navigation

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14
Q

What radar mode to be in for collision avoidance?

A

Sea stabilised - Relative motion display

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15
Q

Explain blind and shadow sector

A

There is no radar performance in a blind sector, the beam is completely blocked. Some performance is possible in a shadow sector, especially when using S band

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16
Q

How do you setup a radar?

A

Big Randy Girls take cock hard
1. Brilliance (set the brightness for your display)
2. Range (go to a suitable range)
3. Gain (turn up until you get white speckles)
4. Tuning (tune the receiver to get the best display, this is normally done automatic)
5. Heading (check so heading marker is not off, if it is means radar could be compromised)

17
Q

What are the radar components?

A

Power source, Transmitter (magnetron), T/R Cell (duplexer), Antenna (Scanner) (Also a motor to drive the antenna), Receiver/Amplifier, Display/PPI (Plan position indicator)

18
Q

What are 8 IMO requirements for ARPA?

A
  1. ARPA must be able to track at least 20 targets automatically and 10 manually.
  2. ARPA should be able to display history - minimum of 4 positions over at least 8 minutes
  3. ARPA should indicate lost targets
  4. ARPA should have a trial manoeuvre function
  5. Range and bearing info must be quickly available for objects appearing on an ARPA display.
  6. Data requirements are Target Range, Bearing, Predicted CPA, Predicted TCPA, True Course and True Speed
  7. ARPA data should be clearly visible to more than one person on the bridge during the day and at night.
  8. ARPA must provide laid down accuracy within 1 and 3 minutes.
19
Q

What are some ARPA alarms?

A
  1. A selected target breaches user defined CPA/TCPA limits
  2. A tracked target is lost
  3. An input failure (Gyro, speed etc.)
  4. A target enters the guard zone (that isn’t already being tracked)
  5. Picture freeze
20
Q

What is the order of information from ARPA?

A
  1. Target range, Bearing, Predicted CPA, Predicted TCPA, True course, True speed
21
Q

Name some problems with ARPA (6 factors)

A
  1. ARPA will not question any faulty data inputs from own vessel i.e speed, heading - this will change the vector triangle calculation therefore giving potentially dangerous incorrect data
  2. Range and bearing discrimination still exists
  3. Ice, small targets and floating objects may not appear and remain undetected
  4. False echoes may give rise to false situations
  5. Lost targets, in sea state or rain banks
  6. Target swap (when a target plotted by an ARPA loses its ‘tag’ to another passing vessel or static radar target)
  7. Over-reliance in the technology
22
Q

What checks would you conduct on your radar before departure?

A

EBL, VRM & Performance monitor

23
Q

How would you check your radar?

A

Performance monitor - visual check of power output (see if circle is the same or decreasing)

24
Q

How often should you check your radar?

A

Every watch and before departure

25
Q

Characteristics of S band?

A

S band (10cm wavelength, 3GHz)
Improved target detection in heavy weather
Improved longer range detection
Improved sea clutter response

26
Q

What is ground stabilised radar?

A

Speed and Heading from GNSS
Course and speed over ground
Best suited for coastal Navigation
Set and Drift visually shown
Difficulty in determining true aspect of vessel
A fixed target will appear stationary

27
Q

What is sea stabilised radar?

A

Speed and Heading from Gyro and Log
Course and speed through the water
Best suited for collision avoidance
Does not account for set and drift
True aspect of vessel easily determined
Fixed target will have a vector direction reciprocal to set and the speed will indicate the rate of drift

28
Q

What can you use in your ARPA to show a potential alteration to course or change in speed?

A

Trial manoeuvre function

OOW Oral Study (34 decks)

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