To detect deformation in civil engineering structures due to earthquakes, heavy rainfall and significant age-related degradation, the RTRI developed U-Doppler, a non-contact-type vibration measuring system applicable to structures (Fig. 1). This system measures structural vibration caused by train passage, impact excitation or microtremor by radiating a laser beam from a point between 1 and 100 m away. It has a function to compensate for the effects of vibration and inclination of the optical sensor unit with a built-in vibration sensor to ensure high-precision measurement even in outdoor environments. Adopting a long-distance remote measurement method with U-Doppler enables improvement of the efficiency and safety of measurement, since it is unneccessary to install sensors at locations high above structures and remove them later.

The U-Doppler is already being used to estimate the natural frequency of viaducts and bridge piers (Fig.2) and to measure the dynamic deflection of bridge girders (Fig.3), and further use is planned.