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NAV&RADAR MCA > RADAR and ARPA > Flashcards

RADAR and ARPA Flashcards

1
Q
  1. Write the equation a radar would use to calculate range of an echo and state the speed value (5)
A
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2
Q
  1. Explain why ranges are more accurate than bearings when plotting a ship’s position (5)
A

Bearings suffer from half-beamwidth error. When the edge of the beam strikes an obiect it paints an echo on the radar display, but due to the width of the pulse this is not the centre line of the beam which the bearing measurement should be taken from. Ranges are not affected by this error.

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3
Q
  1. Define range discrimination (2)
A

The ability of the radar to discriminate between two targets on the same bearing and closely spaced in range

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4
Q
  1. Define bearing discrimination (2)
A

The ability of the radar to discriminate between two targets at the same range and closely spaced in bearing

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5
Q
  1. How would you check and correct for heading misalignment? (5)
A

Take visual relative bearings of objects at different points of the compass. Compare these with the relative radar bearings. Any difference is the error in heading marker alignment. Apply this correction in the software function for this purpose (a pass code may be required).

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6
Q
  1. When setting up, what would you check before transmitting with the radar? (2)
A

The radar scanner should be clear of personnel and obstructions (safety)

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7
Q
  1. What two inputs would you check when setting up a stabilised radar? (2)
A

Heading input
Speed input

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8
Q
  1. Explain how to set up the following controls:
    Brillance (2)
    Gain (2)
    Tuning (2)
A

Brilliance - Increase to a level which allows the OOW to see the display clearly (2)

Gain - Adiust so that a lightly speckled background of clutter can be seen (2)

Tuning - Adjust for best response from a small target near edge of the display (2)

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9
Q
  1. State the wave length and frequency of the X-band and S-band radars (4)
A

X-band 3cm 9GHz
S-band 9cm 3GHz

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10
Q
  1. List two advantages of X-band over S-band radar (2)
A

More definition of land
More accurate bearings

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11
Q
  1. List two advantages of S-band over X-band radar (2)
A

Better range of detection
Better at seeing in and through precipitation

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12
Q
  1. Briefly explain how the rain clutter control affects the display (3)
A

It acts on the echo by trying to cut off the trailing edge so that just the leading edge is seen. It applies this to the whole of the range of display.

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13
Q
  1. Briefly explain how the sea clutter control affects the display (3)
A

It suppresses gain. It applies this to the area near to the ship and increases the effect as the control is turned up. It never extends to the whole range.

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14
Q
  1. What five features would you consider when determining a good radar conspicuous object? (5)
A

Material of the object
Aspect
Size (Height and breadth above radar horizon)
Texture of the surface
Shape

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15
Q
  1. Describe with the aid of a sketch the cause of Multiple Echoes and the effect on the radar display (4)
A

A radar pulse bounces off a target at close range, with enough power in it to allow it to bounce back and forth several times, painting an echo each time received.

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16
Q
  1. Describe with the aid of diagrams the cause of Indirect Echoes and the effect on the radar display (4)
A

The radar pulse bounces off some obstruction on the ship before hitting a target, with the echo being received by the same route. The radar thinks the target is in the direction of the obstruction, but at the distance of the target

17
Q

Describe with the aid of diagrams the cause of Side Lobes and the effect on the radar display (4)

A

Side lobes are escape of electromagnetic radiation near to the scanner, if they pick up targets in this area, extra echoes will be painted in the direction of the lobes.

18
Q
  1. Describe with the aid of diagrams the cause of Blind and Shadow Sectors and the effect on the radar display (6)
A

Blind sectors are areas where the radar transmissions are completely obscured and no echoes will be found. Shadow sectors are areas of reduced sensitivity where radar may pick up some targets.

19
Q
  1. Use a sketch of a radar display to show how a Parallel Index line can be used to monitor the track of a vessel ~–.– (5)
A
20
Q
  1. Indicate on the display above what would happen as the vessel gets set off track by tide (2)
A
21
Q
  1. Explain how the OOW would regain track and then remain on track (3)
A

Alter course (into the tide) until the vessel regains track with the Pl off the headland.
Adiust heading to make good the required groundtrack.

22
Q
  1. What should be checked when parallel Indexing and position fixing? (4)
A

Heading marker alignment
Gyro error and gyro input
Alignment of radar with gyro input
Positive identification of navigational objects of interest

23
Q
  1. What Is a SART used for and what type of radar would you expect to see its transmissions? (3)
A

A Search and Rescue Transponder is used for locating a casualty.2
It can be seen on a 3cm (X-band) radar 1

24
Q
  1. Describe the use of a True Vector (2)
A

It indicates the direction a target is moving in (heading on a sea stabilised radar)

25
Q
  1. Describe the use of a Relative Vector (2)
A

It gives indication of risk of collision if in the direction of own ship

26
Q
  1. List five factors to take into account when setting the CPA/TCPA alarm on the radar (5)
A

The state of visibility
Traffic density
Manoeuvrability of the vessel
Proximity of navigational hazards
Master’s standing orders

27
Q
  1. How many targets can the OOW expect to be able to track at one time? (3)
A

Between 20 and 40 depending on the size of vessel

28
Q
  1. List, in order, the six pieces of information ARPA is required to give about a target (6)
A

Present Range 1
Present Bearing 1
Predicted CPA 1⁄2
Predicted TCPA 1⁄2
Calculated 1⁄2 True course 1⁄2
Calculated 1⁄2 true speed 1⁄2

29
Q
  1. After acquiring a target how long should the OOW wait before being given reliable information based on steady state tracking? (2)
A

3 Minutes

30
Q
  1. Explain what can happen when two acquired targets are moving close to each other on the display and what action the OOW should take. (5)
A
  • As two targets get close to one another their tracking gates may overlap.
  • The radar may get confused and stop tracking one target with the other one given its vector.
  • One vector should be deleted from this target.
  • The target should be re-acquired
31
Q
  1. The display below shows an acquired target with a 10 min relative vector which indicates that it will pass astern by 0’.2. It is 6’ away.
    If own vessel is on a course of 040 x 12 kn what roughly is the track of the target? (4)
A

Use the rel. vector to plot an OAW triangle
Calculate WO
WO = 12 x 10/60 = 2’ Plot WO
WA is roughly 2’ long WA= 2 x 60/10 = 12
Target track approx. 080, speed 12 kn

32
Q
  1. What would be your action in the above situation if you can visually see the other vessel, give your reasons (4)
A

This is a crossing situation under (1) rule 15 of the ColRegs with risk of collision. Own vessel is stand on. As the stand on vessel under rule 17, keep course and speed. Continue to monitor track of other vessel.

33
Q
  1. Why is it important to use the radar in Sea Stabilised mode for collision avoidance? (3)
A

If there is a current present the sea stabilised mode will more accurately show the heading of targets on the display and therefore aspect. This is important for applying the ColRegs which are mainly based on aspect.

NAV&RADAR MCA (11 decks)

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