Although metal reflects radar beams better than most surfaces, pretty much any material will reflect radar waves to some extent. In fact, on windy days, windblown dust or even tree leaves are often read by radar devices. And sometimes these spurious readings can be attributed to your vehicle.
Windblown rain can also reflect enough energy to give false signals, particularly if the wind is strong enough to blow the rain close to horizontal. The more rain or wind, the more likely an erroneous radar reading will result. Pre-thunderstorm atmospheric electrical charges can also interfere with a radar unit. That’s because electrically charged storm clouds can reflect a bogus signal back to the radar unit even though they are high in the sky. If such a storm cloud is being blown by the wind at sufficient speed, a false radar reading may result.
c. Calibration Problems
Every scientific instrument used for measuring needs to be regularly calibrated to check its accuracy. Radar equipment is no exception. It must be checked for accuracy against an object traveling at a known (not radar‑determined) speed. If the speed on the radar equipment matches the known speed, the unit is properly calibrated. In practice, the best way to do this is to use a tuning fork as the moving object. While this may seem a far cry from a moving car, the use of a tuning fork is scientifically sound; tuning forks, when struck against a hard object, vibrate at a certain frequency which we hear as an audible tone.
It is time-consuming to use a tuning fork as a calibration device. So a second, but far less accurate, method has been developed to check the accuracy of radar units. This consists of flicking on the “calibrate†or “test†switch built into the radar unit itself and seeing if it calibrates properly. The unit reads a signal generated by an internal frequency generating device, called a “crystal.†The resulting number is supposed to correlate with a certain predetermined speed.
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