Can they catch you using sound?
Acoustics developed as sneaky speeding deterrent
Just watch for microphones
There's no radiation, radar or other telltale sign that there's a detector there, which might defeat the point of having detectors -- but that's another issue. It's what happens after the sound has been capture that's intriguing.
Captured sound is digitally filtered to remove background noise and then, according to the report, software can calculate the speed of the vehicle by the sound of its engine. It uses knowledge about the type of engine, the angle and type of road at the capture point, and the Doppler shift as the car passed by.
It can measure engine speed by detecting firing pulses and comparing the noise with a library of acoustic signatures. This allows it to estimate the size of engine, we're told. How it'll cope when most vehicles use just a handful of engines -- a point we're rapidly approaching -- isn't known.
It's been tested too, by recording vehicles travelling at known speeds and comparing results. The system measured the correct speed within a few percentage points in 32 out of 33 instances.
Developed with funding from the US Department of Energy, the system has been patented.
Scary or what?
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