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In 1989, the introduction of lidar as an alternative to radar
for speed enforcement hit manytraffic divisions with an avalanche
of hype, excitement and confusion. Unfortunately, manyof the
first-generation lidar units were heavy, bulky and expensive, and
before officers andthe courts could accept lidar units, questions
about their accuracy and reliability needed tobe answered. Today,
technological advances have removed many of those earlier
obstacles.Numerous traffic officers around the country now utilize
lidar, and the courts have also seenthe light.
How does radar stack up to this new kid on the block? Is radar
ready for retirement?Although radar units have been around for
years and seem unchanged, they aren't exactlystuck in the dark
ages. Technological advances have produced new features, some of
whichremain unseen by the user, such as the conversion from analog
to digital signals. Otherimprovements-same direction, fastest mode,
etc.-have changed the way many officersperform their enforcement
duties.
So, before you submit a purchase order for the latest and
greatest lidar unit and haul all ofyour radar guns to the curb for
your department's annual garage sale, consider thecapabilities of
both technologies and figure out exactly what your department
needs.
Basic Principles
Radar (radio detection and ranging) units transmit radio waves
at a designated frequencythat reflect off of a moving target
vehicle and return to the unit. The difference between
thetransmitted frequency and the return frequency is called the
Doppler frequency or Dopplershift, which is used to determine the
target vehicle's speed. The greater the shift receivedby the unit,
the greater the speed. Counting units convert the frequency shift
into a speedreading displayed by the radar unit in miles per
hour.
Aiming the radar in the general direction of the target vehicle
allows the operator to get anearly instantaneous reading. The radio
waves shoot out in a cone-shaped pattern thatcovers roughly
two-thirds of a football field at a range of 1,000 feet. The radar
unit willdisplay the strongest return signal it receives, and a
Doppler tone helps the officer confirmthe reading is coming from
the intended target.
Lidar (light detection and ranging), on the other hand, sends
out a laser beam. The initialbursts of light allow the lidar unit
to determine the distance to the target vehicle bycalculating the
time it takes the beam to reflect off of the vehicle and return to
the unit. Asthe vehicle gets closer to (or farther from) the unit,
this distance changes. Lidar units usethis change in distance and
time as key components to determine the target vehicle'sspeed.
Mathematical formulas help ensure the calculations are accurate and
that the lidarunit displays only valid speed readings.
The laser beam is very narrow (about 4 feet wide at 1,000 feet),
which allows the lidaroperator to select the target vehicle. The
lidar signal only hits one vehicle, so there's littledoubt which
vehicle's speed the unit displays. As an operator, you can obtain a
speedreading for a specific vehicle as long as you have a direct
line of sight with that vehicle.
Working with Radar
The fastest-mode capability of radar allows you to receive a
speed reading from a targetvehicle even when the vehicle does not
produce the strongest signal. Generally, a smallervehicle, such as
a motorcycle, may not produce a speed reading if a larger, closer
vehicle(SUV) returns a stronger signal to the device. When in
fastest mode, however, a radar unitnot only displays the vehicle
returning the strongest signal, but also the vehicle traveling
thefastest. (In the event the fastest vehicle also returns the
strongest signal, the unit displaysonly that vehicle's speed.)
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When using lidar, officers must maintain a direct line of sight
and keep the lidar signal onthe same area of the vehicle until they
obtain a speed reading. While not extremely difficult,it does take
slightly longer than receiving a reading using radar. (To obtain
readings moreeasily, use a shoulder stock or tripod to steady the
device.) Keeping the lidar signal on thetarget vehicle should not
be a major obstacle, but given situations such as the motorcycleand
SUV noted above, many officers prefer to use radar in fastest mode
to easily obtain the
speed of the motorcycle.In terms of enforcement, the ability of
radar to operate in the moving mode is the mostsignificant
difference between the two technologies. Currently, lidar cannot
operate whilemoving. No way around this one. If you want to perform
speed enforcement while drivingaround, radar is currently the only
game in town other than the traditional (and generallyless
effective) pacing option. A moving-mode radar unit with two
antennas and same-direction capabilities can get speed readings
from target vehicles whether the vehicle isapproaching or receding
from your vehicle, and whether the target vehicle moves in thesame
or opposite direction as you. Additionally, some locations prove
extremely difficult orimpractical to use stationary radar or lidar
for enforcement. Therefore, moving-modeenforcement is an extremely
effective and useful capability.
Working with Lidar
When trying to get a speed reading of the motorcycle going 80
mph passing the SUV going65 mph, a lidar operator simply aims at
the motorcycle. Lidar units don't have or needfastest mode because
lidar targets only the vehicle the officer chooses. Many vehicles
cansimultaneously travel through the wide radar beam, which can
bring into question whichvehicle produced the displayed reading. (A
defendant may bring up this argument in court,but an experienced,
well-trained officer should be able to testify as to their tracking
history,i.e., how they knew the defendant's vehicle was producing
the displayed speed reading and,subsequently, that the ticket is
valid.)
Radar units use a Doppler tone to help the officer confirm the
speed displayed by the unit isactually the intended target
vehicle's speed. Lidar units do not provide a Doppler tonebecause
they display the speed of only the vehicle the officer selects.
Lidar does have a
target-acquisition tone that remains constant regardless of the
speed of the target vehicle(one particular unit simulates a Doppler
tone that does correspond to the speed of thevehicle). The tone
confirms that the officer has, in fact, obtained a valid speed
reading.
Lidar has some unique capabilities as well. For example, when
coupled with a mappingprogram, the range mode on a lidar device
provides quick, easy and professionaldocumentation of traffic
collisions and crime scenes. If your department does not have
thebudget for expensive (and bulky) surveying equipment, a lidar
with mapping capabilitiesmay be just the ticket. Lidar can
instantly give an officer an accurate measurement ofobjects several
thousand feet away. At the scene of a collision, a traffic officer
can quickly(and safely) measure an intersection without leaving the
curb. In the case of a crime scene,indoors or out, a lidar's
mapping software can produce detailed diagrams without touchingor
moving evidence.
Making the Buy
There's a lot of information out there about both radar and
lidar, and many experiencedofficers have strong opinions on which
device is better. I can sum up all the arguments onwhich unit to
buy quite simply: It depends. First, take a look at the type of
enforcement youdo and the environment in which you work. Although
most locations provide primeconditions for either radar or lidar
enforcement, at some locations, or even at different timesat the
same location, you'll find it beneficial to use radar instead of
lidar or vice-versa. Doyou need moving-mode capability, or will a
stationary lidar suffice?
