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The Warsaw Voice » The Polish Science Voice » September 30, 2013
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New Laser Speed Gun for Police
September 30, 2013   
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A group of researchers at the Military University of Technology (WAT) in Warsaw have designed a laser speed gun to help the police catch speeding motorists.

The researchers say the new laser speed gun is more accurate in measuring speed than standard radar devices and more precise: it singles out the vehicle police are targeting without the risk of picking up a reading from a car next to it.

The laser speed gun has been developed at the Military University of Technology’s Institute of Optoelectronics by a team of researchers headed by Jacek Wojtanowski, Ph.D.

An ordinary radar speed gun sends out a radio pulse and waits for the reflection. Then it measures the so-called Doppler shift in the signal and uses the shift to determine the speed. Laser speed guns use a more direct method that relies on the reflection time of light. A laser speed gun measures the round-trip time for light to reach a car and reflect back. It shoots a short burst of infrared laser light and then waits for it to reflect off the vehicle. The gun counts the number of nanoseconds it takes for the round trip, and by dividing this by two it can calculate the distance to the car. By taking hundreds of samples per second it can compare the change in distance between samples and calculate the speed of the car. By taking several hundred samples over the course of a third of a second or so, the level of accuracy can be very high.

Standard radar sets rely on the reflection of electromagnetic microwaves. The main drawback of this method is that the beam of radiation is broad, which means that several vehicles may be caught in the beam at the same time. The divergence of laser beams is 40 times smaller than that of radar beams.

The laser speed gun developed by the Warsaw researchers consists of a laser that works as a transmission system, and a sensor, or a receiving system that detects the light reflected from the vehicle.

The vehicle’s speed is measured by calculating time and path differences. The measurement time is 0.3 seconds and its accuracy is around 1 kilometer per hour. The speeds the device can measure range from 0 to 250 kilometers per hour. The distance from the device to the vehicle can be up to 600 meters.

Nowadays increasingly accurate and reliable speed guns are needed because their readouts are used as evidence in court, the researchers say. They add that readouts from their speed gun cannot be challenged: the device measures the speed of a specific vehicle and there is no way it can mistakenly measure the speed of another vehicle close by at the same time. The device is also resistant to interference from radar and radio stations.

The new laser speed gun is already on the market. An outside company has launched production of it and has already sold the first batch of devices. Meanwhile, the engineers at the Military University of Technology are working to upgrade their invention and additionally equip it with a camera that will record the measurements—take pictures or make a video when measuring vehicle speed.

T. B.
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