The responses are mostly monitored by accelerometers, GPS, and image-based monitoring methods.
In the case of accelerometers, very precise measurement of acceleration level of a member or structure
is possible. However, the lateral displacement must be estimated by numerical integration since
displacements cannot be measured directly from an accelerometer [8]. Contrary to the case of
accelerometers, GPS allows direct measurement of the displacement history of a high-rise building [1–4].
However, the accuracy of current GPS poses limitations in measurement of lateral displacements since
the measured displacement may include about 10 mm errors in the x, y, and z coordinates [9]. The
image-based monitoring methods using digital charged coupled device (CCD) cameras have been
applied to measurements of structural responses with a relatively high accuracy in the range of several
millimeters. The image-based structural behavior monitoring techniques require a number of cameras
and installation of a fixed reflective point on target structure. In addition, accurate measurements of the
distances between cameras and a fixed point placed outside a target structure are necessary to ensure the
accuracy in the measurements. In recent years, a new terrestrial radar interferometry technology [10] has
been developed and applied to monitoring of deformations