Radar – Radio Detection and Ranging. (Basic for Orals)
Principle: it Works on Echo Principle (Echo ranging by radar) which is based on the time interval between the transmission of an EM pulse into the environment and reception of its echo.
- Instead of a Sound wave, it uses Radio waves.
- Radar transmission causes an electromagnetic vibration which travels through air @300 m/per micro sec. [1,000,000 = 1 Sec]
Types of Radar:
X Band 3cm, 9 GHZ S Band 10 cm, 3 GHZ Can detect SART Better Tar detecting in RAIN & heavy Weather In fair weather target will show better Better for long range detection (radar horizon greater than 9 GHZ For high discrimination, good sensitivity and tracking performance. Good sea clutter response, tgt less likely to be hidden Less affected by target swap Better for and Rain clutter. Can see small target due to high Freq
Errors of Radar:
- Indirect Echo (reflected): Range true but bearing of a vessel in direction of the obstruction. (mast, funnel or containers on a container ship)
- Multiple Echo: Bounce of energy back and forth, entering antenna in each bounce. . . .
- Side Lobes: Leakage in energy
- Radar to radar interference: Transmission of other radar picked up by our radar.
- Second Trace Echoes: A sent no return, B sent – A return
Limitations of Radar:
- Range Discrimination: Same Bearing different range, the ability of the RADAR set to clearly distinguish two small targets on the same bearing at slightly different ranges. The distance between the two targets is equal to or less than ½ PL
- Bearing Discrimination: 2 targets on the same range but different bearing, separated by 2.5° d, the ability of the radar set to clearly extinguish two targets of the same range and slightly different bearings. (Factor affecting bearing discrimination: High Beam Width)
- Minimum Range:
- Blind/Shadow sectors: Ship structure such as Mast or funnel might create a blind sector.
- Radar Range and Bearing Accuracy:
→ Range Within 30m or 1% of the range scale in use (Whichever is greater);
→ Bearing within 1 degree.
- How to check the performance of radar?
→ By “Performance Monitor” instruction in the user manual
- How often?
→ After start-up and once every watch
- Radar Availability:
→ Fully functional within 4 min after switching on.
→ Fully operational within 5 seconds from standby condition.
- What is Radar Stabilized? – When getting Heading input from the gyro.
- What happens if Gyro fails or Gyro input lost? – The radar will go into “HEAD-UP Orientation”
Difference between Ground and Sea Stabilization:
Ground Stabilization Sea Stabilization Speed and Heading input from GPS Input from Gyro and Log Gives course and speed over ground Course and speed through water Used for Navigation – pilotage, coastal Used for Anti-collision Set and Drift into account Do not take set and drift into account True aspect of vessel unknown True aspect of vessel known Stop vl, move along same rate of set & drift Stop vessel appear to be stopped Fixed target appear STATIONARY Fix Target – Vector opp to set and same rate of drift
Radar Setup for Collision Avoidance:
- Relative Motion: Helps is maintaining situational awareness.
- CU / NU – I prefer CU, as the screen and outside of window view remain the same.
- True trail: To get a true aspect of a vessel
- Relative vector: To see a relative line of approach.
- Speed through LOG, Sea stabilization mode.
Radar Startup & Setup:
- Check scanner for any obstruction (Halyard, working aloft, Any notice near radar screen)
- Switch on radar (do setting till its warming up [What happens in warmup and how much time?])
- Select orientation, motion check Heading and speed input (from where heading and speed input)
- Once you see Stand-by on screen, Press “TRANSMIT”
- Select Range, Pulse length.
- Check Heading marker is aligned with fore and aft line of the vessel.
- Adjust (B-G-T-R-S)
Brilliance: Such that clearly visible and do not hurt your eyes.
Gain: Such as you can see fine speckles on screen. (What Gain does?)
Tunning: Such that targets are best seen on screen (What Tunning does?)
Rain: Only use this if it’s raining. (Always use before Sea clutter, but WHY?)
Sea: If required in bad weather.
- Check Radar Performance by “Performance Monitor” (What is it?)
Carriage Requirement: Min Radar/ARPA requirements [SOLAS Ch 5 – Annex 16]
Gross Tonnage 9 GHZ X Band 3 GHZ X Band EPA ATA ARPA 300 - 500 1 - 1 - - > 500 - < 3000 1 - - 1 - 3000 - 10000 1 1* - 1** 1 10000 + 1 1* - 1** 1
* Can be 9 GHz, if administration considers it appropriate.
– MCA requires a reason why 3 GHz Radar cannot be carried.
** Instead of APA it can be 2nd ARPA.
Ship Size < 500 GT 500 < 10000 GT (HSC<10k GT) All Ships 10000 GT & above Min ops display area 180 mm 250 mm 320 mm Min Display area 195mm x 195mm 270 mm x 270 mm 340 mm x 340 mm Auto ACQ of target - - Yes Min ACQ Radar target cap 20 30 *40 Min Activated AIS target cap 20 30 40 Min Sleeping AIS tgt cap 100 150 200 Trial Manoeuvre - - Yes
*SOLAS 126.96.36.199 at least 20 targets can be acquired both manually???
Limitations of ARPA:
- Target Swap: When two target close by, Information is interchanged.
- Required 3 Min to provide details of target
- If co and spd input is wrong then the output is wrong
- ARPA does not give aspect
- ARPA does not give information about all target on the screen at the same time
‘Performance Standards for Ships Over 10,000 GT
- Diameter 340 mm x 340 mm
- Raster Scan display only
- Manually Acquire at least 40 targets.
- True and Relative vector (Vector length operator adjustable)
- NU or CU presentation mode.
Provides following for any tracked target:
- CPA, TCPA
- Range and Bearing
- Full accuracy data after 3 min for a target at 12 miles
- Preliminary data after 1 min.
After 1 min of Tracking: → CPA accuracy within 1.0 Miles
After 3 min of tracking: → CPA accuracy within 0.3 M and → TCPA accuracy within 30 Seconds.
Operator Alarms and alerts to include:
1 – Collision Threat, 2 – Lost Target, 3 – Guard zone or minimum range
Past track history must be available on all tracked targets.
Min activated AIS target capacity – 40
Min Sleeping target capacity – 200
Trials to be available within 2 scans following :
→ The reduction or increase in one range scale
→ The offset and set of the radar picture
→ A change from true to relative trails.