RADAR, which stands for Radio
Detection and Ranging, is a common method of detecting
moving objects. For instance the police use Doppler radar to
detect the speed of a moving vehicle. An Austrian physicist
by the name of Doppler, first described the concept in the
19th century. The Doppler effect describes what
happens when a wave (sound, radio, etc.) hits a moving
object.
For example, police
use a radar detector to determine the speed of a car as
it moves down the highway. Radar waves are transmitted from
the police car at a certain frequency. Recall that waves
have both amplitude and frequency. When the waves bounce off
a moving object their frequency is effected. As the radio
waves bounce of a car that is moving toward the detector the
frequency of the wave decreases. If the waves bounce of a
car moving away from the detector the frequency of the wave
increases. The detector uses the difference in the
transmitted and received wave frequencies to determine the
speed of the car.
Radar technology has now been
built into a new flashlight
sized device that can detect human movement through a
door or wall. The device can detect movement due to human
respiration from up to three metres away. The device will
prove useful for police in detecting criminals in an ambush
situation, when doing bed checks in prisons or for
determining the location of hostages in a building. The
device could also be used to locate the survivors of an
earthquake or avalanche.
Radar technology may also be
used to detect land mines. NATO is spending millions to
develop a device to identify and neutralize land mines. The
basic technology consists of two antennas that focus radar
energy to a point just below ground a few feet in front of
the person carrying the antenna. The device is programmed to
ignore signals that bounce back from the surface and to make
buried objects shine brighter in the radar image. This
allows the operator to actually detect the land mines
without ever touching the ground.
