RADAR stands for Radio Detection And Ranging. It’s a mandatory navigational equipment.
On the basis of wavelength, there are 2 types of Radar i.e. X-Band (3 cm) Radar & S-Band (10 cm) Radar.
S-Band is generally not preferred because nearby object can’t be detected properly as compared to X-Band and for the same HBW (Horizontal Beam Width) as X-Band, the length of scanner would have to be increased.
Working of RADAR
Short burst of radio waves travels in a straight line with the speed of light, transmitted from radar scanner (antenna) and when these pulses (waves) hit a target, they reflects and received by scanner again as echoes. When these echoes are processed by radar, they appear on radar screen or display.
Major components of RADAR are Transmitter, Transmit-Receive Cell, Waveguide, Antenna (Scanner), Receiver, Trigger Generator & Display.
Simply, there is an antenna (scanner) on the top of the radar that rotates continuously and transmits radio waves. Transmitter generates radio waves. Antenna (Scanner) rotates to scan the entire surrounding area. Antenna is used for both transmitting radio waves and receiving echoes. Transmit-Receive Cell isolates transmitting waves during transmission. Waveguide is a metal tube for carrying radio waves. Antenna is used to direct the radio waves towards the objects and receive echoes. It also indicates the target’s bearing. Trigger generator measures the travel time of pulse and echo. Display shows the output or echoes in plan form. It’s also called as Plan Position Indicator (PPI).
For generating good echo, radar pulse should have very high energy, short wavelength and for very short time period.
Characteristics of Radar
VBW (Vertical Beam Width)
HBW (Horizontal Beam Width)
PL (Pulse Length)
PRF (Pulse Repetition Frequency)
Motion and Orientation of Display
There are 3 ways that radar information can be displayed on a screen i.e. North up, Course up, Ship’s head up. The orientation is indicated on the display by the position of the heading marker that corresponds to the fore/aft line of the ship.
There are 2 motions of radar display on ships generally i.e. Relative motion & True motion.
Check radar performance in every 4 hours. When using the radar for position fixing, positively identify all object using range and bearing. Here, range is more accurate than bearing.
Check the gyro error and compare radar heading marker with compass heading of the ship.
Check the accuracy of the variable range marker.
Be aware of blind and shadow sectors.
When radar is used for collision avoidance, the speed input should be from a water-stabilised source and speed given by GPS is ground stabilised.
Noteworthy Points: RADAR may not show on the screen everything you would expect to see visually. It may show on the screen things you can’t see visually because objects are out of visual range but within radar range. The movement of echoes or tracks on the screen may be vastly different to the movement of the ships producing them and this occurs due to the effect of relative motion. Measurement of range by radar is more accurate than the measurement of bearing.