Radar & ARPA

Question 1

What does RADAR stand for?

Answer 1

It stands for Radio Detection and Ranging

Question 2

What does ARPA stand for?

Answer 2

It stands for Automatic Radar Plotting Aid

Question 3

What is the radar used for?

Answer 3

Radars are used to assist the OOW with collision avoidance, position fixing and tracking monitoring. Its main used is to determine whether a close quarters situation is developing in clear or restricted visibility

Question 4

How does the radar work?

Answer 4

The radar works by transmitting a electromagnetic radio wave and if the wave reflects off an object, their range and bearing can be calculated

Question 5

What is the difference between x-band and s-band radars?

Answer 5

An x-band radar has a 3cm wavelength at 9Ghz, it is best used for collision avoidance, detection of targets and SARTS but can pick up lots of interference.

An s-band radar has a 10cm wavelength at 3Ghz, it is best used for when there is much weather interference and long range scanning but does not provide a sharp image as the x-band and does not interact with a SART.

Question 6

What is sea stabilised on a radar?

Answer 6

Sea stabilised is when STW is being used, which enables a target to display its true trails and allows the OOW to see the relative motion of the other vessel. This is used for collision avoidance.

Question 7

What is ground stabilised on a radar?

Answer 7

Ground stabilised is when SOG is being used by the GPS input and it will display the targets motion over the ground. Best used for coastal navigation

Question 8

What are some limitations of the radar?

Answer 8

• Small objects may not be detected by the radar
• Too much rain or sea clutter may result in target not being detected
• Blind/shadow sectors being created by the vessel own structure blocking targets from being detected

Question 9

What is ARPA used for?

Answer 9

ARPA is required on vessels of 10,000gt and over. It is used to manually or automatically select targets and display the relevant information on that target. ARPA can also perform trail manoeuvres.

Question 10

Name some limitations of ARPA?

Answer 10

• Up to 3 minutes before information can be displayed (CPA, TCPA etc)
• If there is an input error there will be an APRA error
• The accuracy of APRA for IMO standards is 0.3nm and 0.5 minutes

Question 11

How would you set up the radar?

Answer 11

1) Check the antenna for any obstructions before switching on
2) Turn all controls to zero
3) Power on and wait for the radar to warm up
4) Transmit and set the controls appropriately
- Brilliance = the screens brightness and whether its day or night mode
- Gain = Increase until you see a light speckle around your own vessel then turn back slightly
- Tune = Adjust until a clear image is achieved
- Rain = Use if rain is being detected
- Sea = Use if sea is being detected

Question 12

What radar errors are there?

Answer 12

There are 5 in total: 
1 - Indirect Echoes
2 - Side Lobe echoes
3 - Multiple echoes
4 - Interference echoes
5 - Second Trace echoes

Question 13

What are indirect echoes on the radar?

Answer 13

Indirect echoes are cause by the radar beam being deflected by an obstruction, such as a vessels funnel, before reaching a target which increases the distance of the beam.

Question 14

What can you do to fix indirect echoes?

Answer 14

You can decrease the gain as appropriate

Question 15

What are multiple echoes on the radar?

Answer 15

Multiple echoes are caused by two reflecting surfaces bouncing off the target signal back and forth before being received by the scanner. It can happen several times and produce a series of echoes on the same bearing but at different ranges.

Question 16

What can you do to fix multiple echoes?

Answer 16

You can decrease the gain as appropriate

Question 17

What are side lobe echoes on a radar?

Answer 17

Side lobe echoes is caused from a leakage of energy from the main beam, which causes a target to appear at the same range but at different bearings.

Question 18

What can you do to fix side lobe echoes?

Answer 18

You can decrease the gain as appropriate

Question 19

What are radar interference echoes?

Answer 19

This is when a ships radar picks up other radars operating on a similar frequency and pulse repetitions, this causes a spiralling pattern on the display.

Question 20

What can you do to fix radar interference echoes?

Answer 20

You can use the interference suppression

Question 21

What are second trace echoes on a radar?

Answer 21

This usually happens during ducting, echoes will return from considerable distances. The first echo will return after the second pulse has been emitted therefore the scanner thinks it is the second echo returning. The echoes will appear on the same bearing but at a much short range

Question 22

What can you do to fix second trace echoes?

Answer 22

You can change the PRF