Marine radar helps ships see nearby vessels, coastlines, buoys, rain squalls, and other hazards when visibility is poor. It works at night, in fog, and during storms, making it one of the most important navigation tools at sea. A radar set gives the crew a moving map of objects around the ship so they can avoid collisions and stay on course.
For submarines near the surface, radar can also reveal a periscope, mast, or conning tower if enough of it reflects the signal.
Key Facts
- Radar range from echo time is d = ct/2, where c is the speed of light and t is the round-trip travel time.
- Radio waves travel at about c = 3.00 x 10^8 m/s in air.
- Marine radar usually uses microwave radio waves because they reflect well from metal ships, coastlines, and rain droplets.
- Bearing is the direction of a target measured in degrees around the ship, often from 000° to 359°.
- Short pulse widths improve range detail, while longer pulses can improve detection of distant weak targets.
- Relative motion on the radar display shows how targets move compared with your own ship, not always their true motion over Earth.
Vocabulary
- Radar
- Radar is a system that sends out radio waves and uses returning echoes to locate objects.
- Echo
- An echo is the reflected radar signal that returns after bouncing off a target.
- Range
- Range is the distance from the radar antenna to a detected target.
- Bearing
- Bearing is the direction from the ship to a target, usually measured in degrees.
- Radar cross section
- Radar cross section describes how strongly an object reflects radar waves back toward the receiver.
Common Mistakes to Avoid
- Forgetting to divide the round-trip distance by 2 is wrong because the radar pulse travels to the target and back before the time is measured.
- Assuming every bright radar return is a ship is wrong because coastlines, rain clouds, buoys, waves, and sea clutter can also reflect radar.
- Reading relative motion as true motion is wrong because the radar display may show how objects move compared with your own moving ship.
- Ignoring small or weak targets is wrong because objects such as a periscope, small boat, or low buoy may create faint returns that still matter for safety.
Practice Questions
- 1 A radar pulse returns from a nearby ship after 40 microseconds. Using c = 3.00 x 10^8 m/s, calculate the range to the ship in meters.
- 2 A coastline echo appears 12 km away on the radar. How long does the radar pulse take for the round trip from the ship to the coast and back?
- 3 A radar display shows a large bright line to the east and scattered patches to the north during a storm. Explain which return is more likely to be coastline and which is more likely to be rain, and describe one clue a navigator could use to decide.