A radar records distance
by measuring the time it takes for a signal to travel from the radar
to an object and back again. There are a number of different ways
to do this with a radar, each using the same basic principle:
A signal with a recognisable pattern is transmitted
at an object. Any echo from the object contains a copy of this pattern.
By comparing the echo pattern with the original transmission, the
time for the echo trip can be measured. The distance is calculated
by multiplying that time by the speed of the radar signal which
is the speed of light (300,000,000 metres per second). The echo
time is tiny: one millionth of a second along a football pitch!