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How Radar Works How Laser Works
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How Radar Works
Traffic radar, which consists of microwaves,
travels in straight lines and is easily reflected
by objects such as cars, trucks, even
guardrails and overpasses. Radar works by
directing its microwave beam down the
road. As your vehicle travels into range, the
microwave beam bounces off your car, and
the radar antenna looks for the reflections.
Using the Doppler Principle, the radar
equipment then calculates your speed by
comparing the frequency of the reflection
of your car to the original frequency of the
beam sent out.
Traffic radar has limitations, the most
significant of these being that it typically can
monitor only one target at a time. If there is
more than one vehicle within range, it is up
to the radar operator to decide which target
is producing the strongest reflection. Since
the strength of the reflection is affected by
both the size of the vehicle and its prox-
imity to the antenna, it is difficult for the
radar operator to determine if the signal is
from a sports car nearby or a semi-truck
several hundred feet away.
How Laser (Lidar) Works
Laser speed detection is actually LIDAR
(Light Detection And Ranging). LIDAR guns
project a beam of invisible infrared light.
The signal is a series of very short infrared
light energy pulses which move in a straight
line, reflecting off your car and returning to
the gun. LIDAR uses these light pulses to
measure the distance to a vehicle. Speed is
then calculated by measuring how quickly
these pulses are reflected given the known
speed of light.
LIDAR (or laser) is a newer technology
and is not as widespread as conventional
radar; therefore, you may not encounter
laser on a daily basis. And unlike radar
detection, laser detection is not prone to
“false” alarms. Because LIDAR transmits a
much narrower beam than does radar, it is
much more accurate in its ability to
distinguish between targets and is also more
difficult to detect. As a result, even the
briefest laser alert should be taken
seriously.
There are limitations to LIDAR
equipment. LIDAR is much more sensitive
to weather conditions than RADAR, and a
LIDAR gun’s range will be decreased by
anything affecting visibility such as rain, fog,
or smoke. A LIDAR gun cannot operate
through glass and it must be stationary in
order to get an accurate reading.
Because LIDAR must have a clear line
of sight and is subject to cosine error (an
inaccuracy which increases as the angle
between the gun and the vehicle increases)
police typically use LIDAR equipment
parallel to the road or from an overpass.
LIDAR can be used day or night.
Radar range also depends on the power
of the radar equipment itself. The strength
of the radar unit's beam diminishes with
distance. The farther the radar has to travel,
the less energy it has for speed detection.
Because intrusion alarms and motion
sensors often operate on the same frequency
as X-Band radar, your Passport will
occasionally receive non-police radar
signals. Since these X-Band transmitters are
usually contained inside of buildings or
aimed toward the ground, they will
generally produce much weaker readings
than will a true radar encounter. As you
become familiar with the sources of these
pseudo alarms in your daily driving, they
will serve as confirmation that your
Passport’s radar detection abilities are fully
operational.