Radar & Arpa

Question 1

What is multi-path error? (Radar)

Answer 1

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.

Question 2

What is side lobe error? Radar

Answer 2

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)

Question 3

What does a radar do?

Answer 3

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.

Question 4

What is bearing discrimination?

Answer 4

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

Question 5

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

Answer 5

MASTS

Material
Aspect
Size
Texture
Shape

Question 6

What is Minimum range and what is it affected by?

Answer 6

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

Pulse length
Vertical beam width
Height of scanner

Question 7

What’s subrefraction?

Answer 7

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

Question 8

What’s super refraction?

Answer 8

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

Question 9

What is ducting?

Answer 9

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

Question 10

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

Answer 10

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

Question 11

Characteristics of X band?

Answer 11

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

Question 12

What radar mode to be in for collision avoidance?

Answer 12

Sea stabilised - Relative motion display

Question 13

Explain blind and shadow sector

Answer 13

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

Question 14

How do you setup a radar?

Answer 14

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)

Question 15

What are 8 IMO requirements for ARPA?

Answer 15

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.

Question 16

What are some ARPA alarms? (5)

Answer 16

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

Question 17

What is the order of information from ARPA?

Answer 17

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

Question 18

Name some problems with ARPA (7 factors)

Answer 18

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
8. Glint

Question 19

What checks would you conduct on your radar before departure?

Answer 19

Visual check
Heading marker
EBL (through compass bearing)
VRM (through the rings)
Performance monitor
Trial manoeuvre
Set up radar

Question 20

How would you check your radar?

Answer 20

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

Question 21

How often should you check your radar?

Answer 21

Every watch and before departure

Question 22

Characteristics of S band?

Answer 22

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

Question 23

What is ground stabilised radar?

Answer 23

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

Question 24

What is sea stabilised radar?

Answer 24

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

Question 25

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

Answer 25

Trial manoeuvre function

Question 26

How would you set up your X-Band for SART detection?

Answer 26

Set range scale to 6 or 12 nm
Detune the radar
Increase gain
Sea clutter to minimum

Question 27

What does the tuning on a radar function do?

Answer 27

Optimizes its transmitter and receiver to ensure accurate frequency operation