RADAR Flashcards
What is RADAR
Radio Detection And Ranging
Principle of operation of radar?
Echo ranging principle ( SPEED x TIME) / 2
X band characteristics
3cm 9-10 GH/z
High resolution picture for precise Navigation
(Better definition of land)
More accurate bearings
S Band characteristics
10cm 3GH/z
Sacrifices High resolution for relative freedom from Sea and Rain clutter
Improved range
What determines the Pulse length
Determined by range scale in use
What determines the Pulse Repetition frequency?
Determined by range scale in use.
Short ranges have a high PFR
Long ranges have a low PFR
Can be fine tuned once at desired range, for need of function.
What is the Sea clutter function?
Suppresses the gain, applies this to the area near to the ship. Never extends the whole range
Only to be used if sea conditions require it
Equations for range of targets on radar
Range = speed x Time/ 2
Range = speed x Time / ( 2 x 1852 )
What two inputs should you check when setting up a stabalised radar?
Heading input (Gyro)
Speed input (STW/SOG)
How do we set up Brilliance, Gain, Tuning
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 on the edge of the display
What is Rain Clutter on a radar and how dows it work
Cuts through range clutter and interference.
Does this by trying to cut off the trailing edge so that just the leading edge is seen.
5 features in determining a good radar conspicuous object
1.Material
2. Aspect
3. Size (height and breadth above horizon)
4. Texture of surface
5. Shape
Radar echo errors:
False Echo
Indirect Echo
Side Lobe Error
Multiple Echoes
RADAR interference
Target Loss and Target Swap
SART
X band 3 cm radar, Used for detection of casualties in SAR situations
Factors to consider when setting CPA/ TCPA alarm on radar
Sate of visibility
Traffic Density
Manoeuvrability of vessel
Proximity of navigational hazards
Masters standing orders
In order, 6 pieces of information ARPA gives about a target
- present range
- present bearing
- Predicted CPA
- predicted TCPA
- Calculated True course
- Calculated True speed
How many targets can an OOW expect to have selected for ARPA?
20-40
How to setup a RADAR
- Check for Obstructions
- Turn on Radar (allow magnetron to warm up)
- Press transmit (turn controls to 0)
- Brilliance
Range
Gain
Tune
Clutter ( rain and sea )
How often should we run the performance monitor function
Once per watch, or when unsure as to the reliability of the RADAR
Record in log
What are blind and shadow sectors?
Blind and shadow sectors are fixed areas that the radar’s view is partially (shadow) or totally obstructed (blind).
Card for sectors should be in Bridge
How can we find our Shadow/Blind Sectors?
In the instillation Manual, in the Yellow booklet provided
By turning up the gain and looking for these sectors when operating the radar.
How do we Tune our radar?
Adjust until we have the best visual picture
NOT AUTO for the sake of the exam
How do you know if it is correctly tuned?
In coastal nav?
At sea?
At sea with no swell?
Tune to a conspicuous object/point of contact
At sea, tune to the sea clutter
If no swell, turn vessel to create wake and tune to the vessels own wake
RADAR pre departure checks:
Obstruction of RADAR
BRGTC
Heading marker aligned to fore and aft centreline of the vessel
EBL against gyro bearing of an object
Check Range rings against objects at a known distance
PM function
Setting up X band Radar for SART detection:
Range: 6-12nm
Tuning: De-tune
Gain: Normal gain for long range detection
Video processing, Rain: Used as normal
Video processing, Sea: Reduced to Minimum
