A new type of noncontact displacement meter has been developed that employs a diffusion laser beam (DLB) . This DLB system was adopted to reduce the influence of weather conditions on measurements and to avoid any harmful effects to the eyes, skin, etc. To achieve these goals, the DLB displacement meter employs a large-diameter light source and has a large diffusion angle. In addition, it displays the measurement value in real time, performs continuous measurements, can be installed at sites inexpensively, and is capable of measuring displacements greater than 30cm.
In order to verify the precision, performance, and utility of this DLB displacement meter, some experiments were conducted in the laboratory and outdoors. The results of the laboratory experiments demonstrated that the DLB displacement meter could measure displacements of 10. 0mm on a 50-m baseline length to a precision of within ± 0. 2mm. This precision is higher than that of a surface extensometer, which is a contact-type meter. The open-air experimental results showed that the DLB displacement meter is influenced less by obstacles between the meter and the measurement point than conventional laser-beam displacement meters. In addition, the DLB displacement meter was capable of measuring with a precision of ± 0. 8mm under a visibility of 10m on a 16-m baseline length, whereas a prism total station was not able to measure to the same level of precision under identical conditions. In particular, comparison testing in the open air revealed that the surface extensometer produced appreciable measurement errors due to poor tracking of the invar wire on expansion or contraction, whereas the DLB displacement meter exhibited good tracking of the displacements in front of and behind the reflective plate.
The DLB displacement meter was applied to landslide monitoring. Its accuracy and applicability were equal to or exceeded those of a surface extensometer in practice.
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