1-4
The same answer can be obtained using yards instead of feet. In the following calculation, the 6,080
foot approximation of a nautical mile is converted to 2,027 yards and energy speed is changed from 984
feet to 328 yards per microsecond:
A pulse-type radar set transmits a short burst of electromagnetic energy. 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 (6.18 x 2) 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. The range in nautical miles to an object can be found by measuring the elapsed time
during a round trip of a radar pulse and dividing this quantity by 12.36. In equation form, this is:
For example, if the elapsed time for an echo is 62 microseconds, then the distance is 5 miles, as
shown in the following calculation:
NOTE: Unless otherwise stated all distances will be expressed as nautical miles throughout this
module.
