Hi shortchange,
According to the following article: How Speed Measurement "Works" the
only time LIDAR might be not completely accurate is when the operator
has unsteady hands. Then the reading might be off by 10 MPH.
http://www.geocities.com/speeding@sbcglobal.net/SPEEDING7.html
"lidar (li´där), noun. (1) acronym for LIght Detection And Ranging.
(2) a remote sensor that emits electromagnetic waves (infra-red light)
in order to measure reflections for detection purposes (presence,
location, motion, etc.).
Most all of us have seen lasers, too. There's always some idiot
pinhead pointing one at someone during a concert. Well... joy of
joys... now there a bunch of them pointing the very same things at our
vehicles. And the same concept works, with a subtle difference. The
beam is measured for the distance it travels. And it pulses. Very
rapidly. Each pulse is measured for distance, and within about a third
of a second, the distance measured can be divided by that time, and a
speed is the result. Unlike radar, the Lidar IS targeted. So, it is
known exactly what was hit. Well... sort of. We hope. Okay.. maybe
not. But, at least the measurement is more accurate because it's not
prone to radio interference or jamming or such. Unless the Lidar
operator doesn't have hands that are more steady than a neurosurgeon.
Then it could be off just a bit. 10 or so MPH. Just a bit."
===============================================================================
A fair cop! Accurate breath analysis and speed detection
http://www.science.org.au/nova/060/060key.htm
Lidar
"Laser speed guns known as lidar, or ?light detection and ranging?
also use electromagnetic radiation. The term laser stands for ?light
amplification by stimulated emission of radiation?. Lasers are devices
that can control the way energised atoms release photons of light:
these photons form a very narrow beam of light.
The narrowness of this light beam gives rise to the label ?speed gun?,
because it must be aimed at the vehicle by the operator. When the
trigger is pulled, the gun sends an invisible infrared laser light
pulse. It then records the time it takes for the pulse to strike the
target and return to the receiver mounted on the gun. From this time
it is possible to calculate the distance to the object (range) in the
same manner as for radar. The gun sends out hundreds of pulses per
second; if the target is moving in respect to the laser, then the rate
at which the distance to the target is changing is used to derive the
speed of the target from a number of successive range measurements.
The speed of the target is then displayed to the operator.
All laser guns in operation in Australia are tested to ensure that the
laser light being transmitted complies with the appropriate Australian
standard so that it cannot injure a person's eyes if they happen to
look directly into the beam. This is done using an optical power meter
certified by the National Measurement Laboratory with a certificate
issued under the National Measurement Act.
The accuracy of all radar and lidar instruments to measure range and
speed is tested using equipment called a delay generator, which must
also be certified under the National Measurement Act.
The measure of success
In the early years of radar and breath-testing, many people caught
speeding or drink-driving contested the scientific basis of the
evidence. These days, the courts rarely entertain such challenges. The
science, while still evolving, is sufficiently sound to satisfy most
objective judges. And the reliability of the instruments can now be
verified. That?s probably bad news for drink-drivers and speeders but
good news for road safety."
===============================================================================
CopRadar.com - Traffic Radar Handbook - A Comprehensive Guide to Speed
Measuring Systems includes microwave and laser police traffic radar
http://www.copradar.com/index.html
"This document analyzes police traffic microwave and laser radar using
standard electronic countermeasure (ECM) techniques -- the same way
the military analyzes an opponent's (as well as it's own) electronic
systems. Radar operator and factory manuals tell part of the story --
physics, mathematics, operational use, test data, and countermeasure
techniques tell the rest.
All technical information and conclusions quantifiably described using
illustrations, graphs, tables, or mathematical formulas -- based on or
derived from fundamental scientific and engineering principles,
published factory specifications, measured data, or U.S. Government
documents."
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Best regards,
tlspiegel |
