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How Laser (Lidar) Works
Laser speed detection is actually light
detection and ranging (LIDAR). LIDAR guns
project a beam of invisible infrared light.
The signal is a series of very short infrared-
light energy pulses that 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 is a newer technology whose
use is not as widespread as conventional
radar; therefore, you may not encounter it
on a daily basis. And unlike radar detection,
LIDAR 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
(LIDAR) 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 that
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.
Laser
How Radar Works
Traffic radar, which consists of microwaves,
travels in straight lines and is easily
reflected by objects such as cars, trucks,
and 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 proximity 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.
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 detector
will occasionally receive non-police radar
signals. Since these X-Band transmitters are
usually contained inside of a building, 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
8500ci Plus’s radar detection abilities are
fully operational.
How “POP” Works
POP mode is a relatively new feature for
radar gun manufacturers. It works by
transmitting an extremely short burst,
within the allocated band, to identify
speeding vehicles in traffic. Once the target
is identified, or “POPPED,” the gun is then
turned to its normal operating mode to
provide a vehicle tracking history, (required
by law).
NOTE: According to the operator’s
manual from the radar gun
manufacturer, tickets should not be
issued in POP mode.
Radar Radar/POP