Radar Kilometer / Radar Nautical Mile
Radar timing is usually expressed in microseconds. To relate radar timing to distances traveled by radar energy, you should know that radiated energy from radar set travels at approximately 984 feet per microsecond. With the knowledge that a nautical mile is approximately 6,080 feet, we can figure the approximate time required for radar energy to travel one nautical mile using the following calculation:
A pulse-type radar set transmits a short burst of electromagnetic energy. The target range is determined by measuring elapsed time while the pulse travels to and returns from the target. Because two-way travel is involved, a total time of 12.36 microseconds per nautical mile will elapse between the start of the pulse from the antenna and its return to the antenna from a target.
This 12.36-microsecond time interval is sometimes referred to as a RADAR MILE, RADAR NAUTICAL MILE, or NAUTICAL RADAR MILE.
| 1 Radar Kilometer = | 2 · 1000 m | = 6.66 µs | (1) |
| 3 · 108 m/s |
| 1 Radar Mile = | 2 · 1852 m | = 12.35 µs | (2) |
| 3 · 108 m/s |
The range in kilometers to an object can be found by measuring the elapsed time during a round trip of radar pulse and dividing this quantity by 6.66. The range in nautical miles to an object can be found by measuring the elapsed time during a round trip of radar pulse and dividing this quantity by 12.36.