RADAR Flashcards
What does ARPA stand for?
Automatic Radar Plotting Aid
Which band will pick up a SART distress signal?
X band
Describe the characteristics of an activated SART device on the RADAR…
At a distance the SART will produce a series of 12 blips on the radar screen towards the centre of the radar, as range reduces these blips become arcs. Making it harder to identify the target especially in restricted visibility.
Describe the differences between water track and ground track?
Water track is the ships heading through the water and ground track is the actual track covered over the ground when drift etc. is taken into account.
What information will ARPA provide?
CPA, TCPA, Speed, Heading, Bow Crossing
What settings would you have for collision avoidance?
Relative Motion, North Up, STW, True Trails + Relative Vectors, or Relative Trails + True Vectors.
Describe the horizontal beamwidth…
The horizontal beam width is the angular width of the beam, usually 1 or 2 degrees. Varies with wavelength and inversely antenna size. For example the reduced beam width on an x band radar will give better target discrimination.
Describe the vertical beamwidth…
The vertical beamwidth is normally about 25 degrees allowing for rolling of the vessel. Radar beams reflecting from the water can cause interference.
Describe Side lobes…
Transmissions of radio waves either side of the main beam operating a reduced power.
What will different pulse length settings achieve?
A longer pulse length can detect targets at a further distance whilst a shorter pulse length will provide better resolution.
What is refraction?
Refraction is caused by atmospheric conditions due to differences in atmospheric conditions (temperature, moisture and pressure).
What are the different types of refraction?
Sub-refraction when an abnormal drop in temperature as the beam travels through the atmosphere causes the beam to curve upwards.
Super-refraction when temperature increases with height and moisture sharply decreases causing the beam to curve further over the cooler surface of water.
Ducting is when a radar beam is transmitted along the curvature between two layers at temperature inversions (warm + cold for example), will produce increased beam length that is equal to the curvature of the earth.
What is the difference between STW and SOG speed inputs?
Speed through water is input via gyro and doppler log and is not affected by current, Speed over ground is input via GPS and takes into account the effect of current.
Other than for aspect reasons, why may sea stabilized be inaccurate?
Sea stabilized may be inaccurate due to error in speed log and gyro heading inputs
Where would you find information regarding blind spots/shadow sectors?
The information should be displayed on a diagram near to the RADAR.
