Radar

Question 1

Explain why ranges are more accurate than bearings when plotting a ship’s position

Answer 1

Bearings suffer from half-beamwidth error. When the edge of the beam strikes an object 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

Question 2

Define range discrimination

Answer 2

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

Question 3

Define bearing discrimination

Answer 3

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

Question 4

How would you check and correct for heading misalignment?

Answer 4

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).

Question 5

When setting up, what would you check before transmitting with the radar?

Answer 5

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

Question 6

What two inputs would you check when setting up a stabilised radar?

Answer 6

• Heading input
• Speed input

Question 7

Explain how to set up the following controls:

• Brillance
• Gain
• Tuning

Answer 7

• Brilliance - Increase to a level which allows the OOW to see the display clearly
• Gain - Adjust so that a lightly speckled background of clutter can be seen
• Tuning - Adjust for best response from a small target near edge of the display

Question 8

State the wavelength and frequency of the X-band and S-band radars

Answer 8

X-band 3cm 9GHz
S-band 10cm 3GHz

Question 9

List two advantages of X-band over S-band radar

Answer 9

• More definition of land
• More accurate bearings
  Picks up signals from Sart
  Can be used to track squals

Question 10

List two advantages of S-band over X-band radar

Answer 10

• Better range of detection
• Better at seeing in and through precipitation

Question 11

Briefly explain how the rain clutter control affects the display

Answer 11

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.

Question 12

Briefly explain how the sea clutter control affects the display

Answer 12

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.

Question 13

What five features would you consider when determining a good radar conspicuous object?

Answer 13

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

Question 14

Describe with the aid of a sketch the cause of Multiple Echoes and the effect on the radar display

Answer 14

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.

Question 15

Describe with the aid of diagrams the cause of Indirect Echoes and the effect on the radar display

Answer 15

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.

Question 16

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

Answer 16

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

Question 17

Describe with the aid of diagrams the cause of Blind and Shadow Sectors and the effect on the radar
display

Answer 17

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.

Question 18

Use a sketch of a radar display to show how a Parallel Index line can be used to monitor the track of a
vessel

Answer 18

Question 19

What should be checked when parallel indexing and position fixing?

Answer 19

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

Question 20

What is a SART used for and what type of radar would you expect to see its transmissions?

Answer 20

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

Question 21

Describe the use of a True Vector

Answer 21

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

Question 22

Describe the use of a Relative Vector

Answer 22

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

Question 23

List five factors to take into account when setting the CPA/TCPA alarm on the radar

Answer 23

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

Question 24

List, in order, the six pieces of information ARPA is required to give about a target

Answer 24

• Present Range
• Present Bearing
• Predicted CPA
• Predicted TCPA
• Calculated True course
• Calculated True speed

Question 25

After acquiring a target how long should the OOW wait before being given reliable information based
on steady state tracking?

Answer 25

3 minutes

Question 26

Explain what can happen when two acquired targets are moving close to each other on the display and
what action the OOW should take.

Answer 26

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

Question 27

Briefly explain how the rain clutter control affects the display on your radar.

Answer 27

Rain clutter control is a feature on radar systems designed to suppress or minimize the interference caused by rain. When rain clutter control is active, the radar tried to distinguish between rain echoes and actual targets of interest.

Question 28

Describe the effects of Radar interference and how an operator may account for this interference.

Answer 28

Radar interference
1. Clutter ex land masses, object
2. Rain clutter
3. Sea clearer ex waves
4. Electromagnetic interference ex by other radars

How to counter act

1.	Adjusting Settings: for sensitivity, gain, and clutter suppression  based on the prevailing environmental conditions to minimize interference while maintaining target detection capabilities.
2.	Tuning Filters: Some radar systems feature specialized filters designed to suppress specific types of interference, such as sea clutter or rain clutter.
3.	Understanding Environment:
4.	Regular Maintenance:

Question 29

List FIVE factors that may determine the strength of a returned echo of a target on a radar screen.

Answer 29

1. The size and shape of the vessel
2. The distance
3. The surface characteristics, smooth metallic surfaces seem to reflect radar better.
4. Angle of approach
5. Atmospheric conditions

Question 30

During a voyage where can you find information for Parallel Indexing?

Answer 30

1. Charts
2. Passage plan
3. Pilot book and sailing directions
4. Weather forecasts and notices to mariners
5. Radar and Arpa displays

Question 31

Target reflectivity

Answer 31

MASTS
1. Material
2. Aspect
3. Size
4. Texture
5. Shape