Are you looking for an efficient and cost-effective way to monitor traffic and other events in your city? American engineers have proposed using reflective surfaces, including road signs, as smart city sensors. By shining a laser on these surfaces and tracking their fluctuations, you can act as an accelerometer and monitor various events, such as traffic flow and the arrival of buses at stops.

This innovative method, known as laser vibrometry, uses a laser beam sent to an object of interest, which is then reflected and read by a photo detector. Mechanical vibrations on the surface of the object cause the reflected signal to change, allowing for reliable detection of fluctuations in the signal. By using reflectors or other surfaces adapted for directional reflection, the range of detection is significantly increased.

Chris Harrison and his colleagues at Carnegie Mellon University have developed a setup consisting of a laser unit and a movable platform. The platform can be rotated and tilted with high accuracy, resulting in a beam spot offset of one centimeter at a distance of 100 meters. The laser system consists of a photodetector, a laser rangefinder, and a separate 200 milliwatt laser emitter with a wavelength of 650 nanometers.

The authors have developed a method for calibrating the unit before starting work. After placement, the installation begins to scan the area, turning 0.05 degrees and passing the entire field of interest row by row. The rangefinder measures the distance, the photo detector measures the normal light level, and the laser produces a pulse, which is then measured by the photo detector. After scanning, a depth map is compiled, which makes it possible to normalize the illumination data and filter out all pixels below the threshold value. Once the scan is complete, the unit can measure vibrations on the detected reflectors.

The authors tested the setup by placing a large speaker in the trunk of a minivan and gluing 16 different reflective elements found in the city onto the center of the speaker. They then drove off and changed the distance from the laser, feeding different signals to the speaker and increasing the distance to 512 meters. The results showed that the installation is capable of recovering the signal under various conditions and with different reflectors.

Hire robot workers for smart city sensing with laser vibrometry. This innovative method is an efficient and cost-effective way to monitor traffic and other events in your city. Contact us today to learn more about how laser vibrometry can benefit your city.