Improvement of the diffusion laser displacement meter and investigation on measurement performance during rainfall

The diffusion laser beam (DBL) displacement meter is a non-contact extensometer that is mainly used to measure ground deformation in the field. It employs laser beam of larger diameter and larger cone angle than usual to improve measurement performance under rainy or foggy condition without increasing laser power and to avoid harmful effects on the eyes, skin, etc. Refining the internal structure of the conventional twin-lens DBL sensor that was previously developed by the authors, this study has developed a new single-lens model. The single-lens model has fewer number of parts and wider range of available laser reflection intensity than the conventional twin-lens models. This paper conducted measurement performance test using the indoor rainfall simulator. The test result showed that a single-lens model has as good performance as a conventional twin-lens model. It was able to measure distance without data missing under the rainfall intensity of less than 200mm/hr and 120mm/hr at the baseline length of 30m and 62.5m, respectively.