YES! They can. Even if the cop doesn't see you, the radar can, even around corners.
Realize that police officers with radar guns position themselves so you can't see them until it's too late, such as in parking lots or around a bend in the road.
A radar gun is very helpful for police officers; they allow officers to target a specific vehicle, even one that is up to 1,000 feet away, which appears to be going over the speed limit. When the trigger is pulled, the gun emits an infrared light reflects off the vehicle and comes back to the gun counting the number of nanoseconds it took for the light to make that round trip.
As a rule, hand-held police radar guns measure the speed of a vehicle in a field area of approximately 400 feet.
In order to be determined that the vehicle was speeding, a police officer must use three ways: use his/her sight, sound which comes from an audible pitch noise based on the distance the vehicle is from the cruiser, and an actual readout display stating the driver's speed.
As you know, there are many types of radar guns, and all work on a similar principle. A radar gun launches a beam of electromagnetic waves at a moving object. On hitting the object the waves are reflected back toward a detector on the gun, which then calculates the speed of the object by analyzing the nature of the reflected beam.
How Radar Guns Work
History of Radars
Radar is an electronic tool which uses electromagnetic waves called radio waves to detect and locate moving or fixed objects. The word "Radar" is an abbreviation for Radio Detection and Ranging. Today, small and efficient radar units, such as Decatur Speed Trak Police Radar, can be found in almost every police vehicle. It is estimated that 20 million speeding citations are issued annually and that police radars are used in 13 million of these cases. It is imperative that police officers using police radar guns are well-trained and have a good working knowledge of how radar works, because oversimplification of principles behind radar operations can lead to a variety of misunderstandings and errors.
There are Two Types of Radars:
Continuous Wave Radar
a. Doppler Radar
b. Frequency-Modulated Radar
Police Radar utilizes radio waves and the Doppler Effect. Police Laser Radar (Lidar) utilizes light waves and the pulse principle.
Doppler Principle states that the measured frequency of a wave is relative to the motion between the source and the observer. The Doppler Principle can be applied to sound waves, light waves, and radio waves. Doppler Principle is a basis for all modern police radar. In short, Doppler Principle states that when a radar signal hits the object that is moving toward the observer/patrol vehicle, the returning frequency will be higher than the original. When the signal hits that object/vehicle that is moving away from the observer, the returning frequency will be lower than the original one. The frequency change can be used to determine the speed of the target vehicle. Click here for more information on Doppler Principle and Doppler Shift.
How Radar Guns Work
A Radar Gun is used to send out radio waves of specific frequencies in a chosen direction. The traveling waves then bounce off objects, including vehicles, and return to the radar gun 's receiving station. When the waves reflect off a moving vehicle, a measurable frequency shift, called Doppler Shift, occurs. The radar gun computer then uses the frequency shift to calculate the speed of the moving vehicle.
A good analogy for a radar signal is a beam of light from a flashlight. When one shines a flashlight at an object, the object can be seen thanks to the light reflected from the object. Now imagine yourself as the object that at which the light is aimed. The target (the object at which the light is being pointed) can see the light from the flashlight from a much farther distance than the person with the flashlight could ever hope to see the target. That's because the beam loses energy over distance. So while the beam has enough energy to reach the target, the reflected light doesn't have enough energy to travel all the way back to where it started.
Police Radar Guns "see" a vehicle by transmitting a microwave pulse that reaches the target and then comes back to the observer. Then, the Doppler Effect is applied: the frequency of the transmitted pulse is compared to the frequency of the reflection, and speed is calculated by using the difference between the two frequencies.
The idea behind Radar Detectors is the following. The Radar Detector looks for radar "beams" and finds them before they can return a strong enough reflection to "illuminate" you. Radars are essentially microwave radio receivers that make noise or flash lights when they sense an incoming signal on specific frequencies. Superheterodyne reception allows detection of radar around curves or over hills, and it extends detection range straight ahead.