Computer-video combo can 'see' vibrations.

• Position: Structural Stability

To the naked eye, buildings and bridges appear fixed in place, unmoved by forces like wind and rain. In fact, though, these large structures do experience imperceptibly small vibrations that, depending on their frequency, may indicate instability or structural damage. Researchers at the Massachusetts Institute of Technology, Cambridge, have developed a technique to "see" vibrations that otherwise would be invisible to the naked eye, combining high-speed video with computer vision techniques.

Normally, high-speed video would not pick up such subtle vibrations from a building. To do this, the researchers employed a computer vision technique called "motion magnification" to break down high-speed frames into certain frequencies, essentially exaggerating tiny, subpixel motions. The vibrations measured by the technique matched those picked up by accelerometers and laser vibrometry--precise but expensive techniques commonly used in infrastructure monitoring.

Today, engineers typically monitor infrastructure using multiple accelerometers--sensors that measure acceleration, which then can be used to calculate velocity and, ultimately motion. Accelerometers are very precise, but cost more than $1,000 each, and a single accelerometer only measures a single point along a structure. Even with an array of sensors, accelerometers "can't achieve high density of spatial measurements," notes...