Radar Flashcards
Characteristics of X BAND radar
-3cm wavelength.
-9 Ghz
-accurate navigation.
-creates more lobes
-more clutter response.
-can detect SARTS. Range approx 8miles.
Characteristics of S BAND radar?
-10cm wavelength.
-3 GHZ
-better for long range detection of targets.
-sea clutter response better (targets less likely to be hidden)
What does a radar actually do?
Measures the time taken for a radio pulse to travel from a transmitter and return after being reflected by an object (target)
Name 4 radar set components.
-transmitter
-antenna
-receiver
-display
What does the transmitter do?
Produce short pulses through and Ariel.
What does the antenna do?
Radiates the pulses, rotates to scan the horizon. Speed 20rpm.
Most common scanner= slotted waveguide.
What does the receiver do?
Amplifies returning echoes and produces pulses that are accepted by the display.
What does the display do?
Takes the mass of information by returning echoes and presents in a form.
-real time display.
-synthetic display.
Name some dangers of using radar equipment.
-do not stand too close to radar scanner during transmissions.
-never work inside transceiver/display unit when on.
-be careful of safe distances of radar equipment for Magnetic compass.
COSWP -has safety procedure.
Radar beam characteristics?
-Horizontal beam
0.5-2.0 degree width.
-vertical beam width
20-30 degree
IMO SPEC
What does the scanner rotate at and what speed?
Scanner rotates 360 at 20-30 rpm.
Why is the beam width so big?
Allows for movement of vessel- ie rolling and pitching etc.
Which has good discrimination and bad discrimination?
Narrow horizontal beam width= good (ie can see two targets)
Wide horizontal beam width= poor ie-can see only one target
What is bearing discrimination?
Ability of radar to differentiate between 2 targets on different bearings at same range.
What are radar bearings inaccurate?
Due to horizontal beam width.
What does a longer pulse give?
More energy transmitted, better chance of detecting a target.
Poor discrimination.
What does a short pulse give?
Should be used when detecting targets close to the vessel.
Good discrimination.
Name some factors that determine practical detection range of radar.
-height of scanner
-height of reflective properties of target
-atmospheric conditions.
Name the 5 factors that affect the reflective properties of targets.
MASTS
Material- good radar reflectors ?
Aspect- the direction of result reflections
Size- the more pulses that strike the target the greater the response. Height good.
Texture-surface roughness (rough will scatter reflections in all directions)
Shape- affects size, aspect and surface roughness that appears to radar pulse.
What is a propagation anomalie?
When the radar beam curves away from warm dry air towards cold wet air. Leads to 3 things
1- subrefraction
2-superrefraction
3-ducting
What’s subrefraction?
Cold polar air over warm sea deflect beam upwards. 40% loss range reduction.
What’s super refraction?
Increase of radar range when warm air is over cold air.
What is Ducting?
Temperature inversion.
Can increase radar range to 400nm if antenna is in duct
What is Minimum range and what is it affected by?
The ability to detect and display echoes in close proximity to the radar.
Pulse length
Vertical beam width and height of aerial.
In true motion (ONLY) you have sea stabilisation and ground stabilisation.
Explain sea stab:
On radar-
Target stopped = stationary on display
Moving target= moves, water track
Land= moves contrary to tide.
Explain ground stabilisation.
On radar
Target stopped= moves with tide
Moving= ground track
Land= stationary on display
