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Clever Penguin
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If they work like I assume they do, by comparing the wavelength emitted with the wavelength reflected back, they might use an interferometer. If so, how does it work?
They don't use intergerometers. Speed radars use the Doppler shift to measure speed.Clever Penguin said:If they work like I assume they do, by comparing the wavelength emitted with the wavelength reflected back, they might use an interferometer. If so, how does it work?
DrClaude said:They don't use intergerometers. Speed radars use the Doppler shift to measure speed.
DrClaude said:I should also add that hand-held lidar speed guns are also quite common. These are based on the timing of light pulses. The thread title mentionned speed cameras, and to the best of my knowledge they still use Doppler radars.
In the UK, where I live, speed cameras that are used for prosecution are required by law to use an additional secondary method to measure speed as well as the primary method that triggers the camera. The two methods must give the same answer (within specified error bars) for a prosecution to succeed. In the case of Doppler radar cameras, the secondary method is photographic, pretty much as you described.anorlunda said:Just use image analysis to measure the time for the car to pass two marks with a known distance between them. The same video images could capture the plate number and a photo of the driver.
DrGreg said:In the UK, where I live, speed cameras that are used for prosecution are required by law to use an additional secondary method to measure speed as well as the primary method that triggers the camera. The two methods must give the same answer (within specified error bars) for a prosecution to succeed. In the case of Doppler radar cameras, the secondary method is photographic, pretty much as you described.
Speed cameras use interferometers to measure the speed of a vehicle by emitting a laser beam and measuring the time it takes for the beam to reflect off the vehicle and return to the camera. By using the principle of interference, the camera can accurately calculate the speed of the vehicle based on the change in frequency of the reflected beam.
No, not all speed cameras use interferometers. Some speed cameras use other methods such as radar or lidar to measure vehicle speed. Interferometers are just one of the technologies that can be used in speed cameras.
Interferometer-based speed cameras are generally considered to be very accurate, with a margin of error of less than 1%. However, the accuracy can be affected by external factors such as weather conditions or the angle of the vehicle in relation to the camera.
Yes, interferometers can be jammed or interfered with by using certain devices or materials that can disrupt the laser beam. However, this is illegal and can result in severe penalties. Speed cameras also have measures in place to detect and prevent any attempts at jamming or interfering with the interferometer.
Yes, there are alternatives to using interferometers in speed cameras, such as radar or lidar. These technologies may have different strengths and weaknesses and may be used in different types of speed cameras. It ultimately depends on the specific needs and regulations of the area where the speed camera is being used.