RADAR is a piece of equipment onboard a ship that assists in safe navigation and collision avoidance by indicating other craft, obstructions and hazards, navigation objects, and shorelines.
Marine RADAR consists mainly of four units:
1. The Transmitter
2. The Aerial or Scanner
3. The Receiver
4. The Display Unit
Working Principle of Marine RADAR:-
The transmitter sends short powerful bursts of electromagnetic energy, called pulses, through the scanner at a specific number of times per second, called the Pulse Repetition Frequency (PRF) or Pulse Recurrence Rate (PRR).
These pulses travel at the speed of light (300 meters/microsecond) and when they strike any object (target) in their path, they are reflected in the scanner as echoes.
The receiver processes each echo and causes it to show up visually as a bright spot, called a blip, on the display unit screen. The display unit is a rectangular screen within which a circular area represents on a scale, an actual area around the ship.
The circular area is called the Plan Position Indicator (PPI). The distance represented by the radius of the circle is called the range scale in use.
In the circle on the screen, a bright spot is made to move in a radial path from the center to the circumference. The visible radial line created by the moving spot is called a trace.
One trace is created for every pulse sent out through the scanner. When an echo is received and processed by the receiver, the tracing spot's sudden brightening and fattening occur momentarily.
Though the tracing spot is moving continuously during this time, the blip created by it (paint) remains stationary and visible for some time.
This is how RADAR detects the presence of a target in the vicinity.