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October 27, 2005

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Law Officer Magazine Tactics, Technology and Training for Today's Law Enforcement Professional
with Law Officer Magazine

Radar vs. Lidar: Which will work best for you?

By Greg Koran

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In 1989, the introduction of lidar as an alternative to radar for speed enforcement hit many traffic divisions with an avalanche of hype, excitement and confusion. Unfortunately, many of the first-generation lidar units were heavy, bulky and expensive, and before officers and the courts could accept lidar units, questions about their accuracy and reliability needed to be 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 seen the 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 exactly stuck in the dark ages. Technological advances have produced new features, some of which remain unseen by the user, such as the conversion from analog to digital signals. Other improvements-same direction, fastest mode, etc.-have changed the way many officers perform their enforcement duties.

So, before you submit a purchase order for the latest and greatest lidar unit and haul all of your radar guns to the curb for your department's annual garage sale, consider the capabilities 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 frequency that reflect off of a moving target vehicle and return to the unit. The difference between the transmitted frequency and the return frequency is called the Doppler frequency or Doppler shift, which is used to determine the target vehicle's speed. The greater the shift received by the unit, the greater the speed. Counting units convert the frequency shift into a speed reading 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 a  nearly instantaneous reading. The radio waves shoot out in a cone-shaped pattern that covers roughly two-thirds of a football field at a range of 1,000 feet. The radar unit will display the strongest return signal it receives, and a Doppler tone helps the officer confirm the reading is coming from the intended target.

Lidar (light detection and ranging), on the other hand, sends out a laser beam. The initial bursts of light allow the lidar unit to determine the distance to the target vehicle by calculating the time it takes the beam to reflect off of the vehicle and return to the unit. As the vehicle gets closer to (or farther from) the unit, this distance changes. Lidar units use this change in distance and time as key components to determine the target vehicle's speed. Mathematical formulas help ensure the calculations are accurate and that the lidar unit displays only valid speed readings.

The laser beam is very narrow (about 4 feet wide at 1,000 feet), which allows the lidar operator to select the target vehicle. The lidar signal only hits one vehicle, so there's little doubt which vehicle's speed the unit displays. As an operator, you can obtain a speed reading 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 target vehicle even when the vehicle does not produce the strongest signal. Generally, a smaller vehicle, 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 unit not only displays the vehicle returning the strongest signal, but also the vehicle traveling the fastest. (In the event the fastest vehicle also returns the strongest signal, the unit displays only that vehicle's speed.)

When using lidar, officers must maintain a direct line of sight and keep the lidar signal on the 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 more easily, use a shoulder stock or tripod to steady the device.) Keeping the lidar signal on the target vehicle should not be a major obstacle, but given situations such as the motorcycle and 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 most significant difference between the two technologies. Currently, lidar cannot operate while moving. No way around this one. If you want to perform speed enforcement while driving around, radar is currently the only game in town other than the traditional (and generally less 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 is approaching or receding from your vehicle, and whether the target vehicle moves in the same or opposite direction as you. Additionally, some locations prove extremely difficult or impractical to use stationary radar or lidar for enforcement. Therefore, moving-mode enforcement 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 going 65 mph, a lidar operator simply aims at the motorcycle. Lidar units don't have or need fastest mode because lidar targets only the vehicle the officer chooses. Many vehicles can simultaneously travel through the wide radar beam, which can bring into question which vehicle 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 is actually the intended target vehicle's speed. Lidar units do not provide a Doppler tone because 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 the vehicle). 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 mapping program, the range mode on a lidar device provides quick, easy and professional documentation of traffic collisions and crime scenes. If your department does not have the budget for expensive (and bulky) surveying equipment, a lidar with mapping capabilities may be just the ticket. Lidar can instantly give an officer an accurate measurement of objects 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 touching or moving evidence.

Making the Buy

There's a lot of information out there about both radar and lidar, and many experienced officers have strong opinions on which device is better. I can sum up all the arguments on which unit to buy quite simply: It depends. First, take a look at the type of enforcement you do and the environment in which you work. Although most locations provide prime conditions for either radar or lidar enforcement, at some locations, or even at different times at the same location, you'll find it beneficial to use radar instead of lidar or vice-versa. Do you need moving-mode capability, or will a stationary lidar suffice?

Second, seek input from surrounding agencies that work speed enforcement on similar roadways. Look at the equipment they use and ask about their experiences both in the field and in court.
Many manufactures will provide radar and lidar units to your department for evaluation. Take advantage and try their products

Train & Maintain

Over the many years of radar-based speed enforcement, several key court decisions have shown that a properly working radar unit in the hands of a well-trained officer can accurately measure vehicle speed.

Many of these court cases have since been cited in lidar cases, resulting in similar decisions on the reliability of a lidar unit's ability to accurately measure speed. I cannot stress enough that these court decisions were based on the operator's training and the maintenance of the equipment. Maintain your skills through continued training and yearly recertification, and keep a log of all formal and informal training you do. And stay up-to-speed on the latest and greatest products in real-world enforcement settings. This will enable you and your department to make intelligent decisions about the type of unit, the manufacturer, makes, models and even the various features you need or prefer.

If you purchase the best unit money can buy, it may turn out to be a costly mistake if the equipment doesn't fit your needs.                   

Sgt. Greg Koran is a California POST-certified radar and lidar instructor. He's currently assigned to evening watch as a patrol supervisor. Koran previously served in the traffic division as a motor officer and as a property crimes detective in the investigations division.

About the author

Law Officer magazine is published to support law enforcement by providing the best tactics, technology and training information to police officers from entry level through middle management. Visit the Law Officer Magazine Website for subscription information.






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