Vibration detection using low cost optical sensing systems for geological applications

The master thesis deals with Optical Fiber Sensing and aims to improve geological vibrations detections of dangerous events in a mountain landscape. In the system, the sensors are represented by the optical fibers and their polarization state is continuously monitored by a polarimeter. The intensity of a vibration detected on a mountain side is monitored looking at the variation of the angular speed of the state of polarization . Higher will be the speed and bigger will be the event degree of strength. One of the main goals of the work is to sense multiple fibers at the same time and, as the title of the work quotes, to maintain the low cost condition in the system. Therefore, an optical switch has been implemented. The instrument, inserted before the polarimeter, allows to check different measurements almost simultaneously and has the purpose to enhance correct detections of dangerous events and to minimize the probability of false alarm. During the thesis, two working fields have been proposed. The first deals with the measured data in post-processing, therefore it acquires measurements and evaluates outcomes in a second moment. It aims to set correctly simulation parameters and to enhance as much as possible the results. When a strong event has been detected, an alarm should be returned, but it requires that at least two fibers have sensed the same strong vibrations, otherwise a false alarm will be displayed. Then, tests have been performed in real time. This simulation aims to an implementation in a real debris subjected environment. In this way, if an alarm is detected and validated as correct, a warning message is output as fast as possible and allows a rapid time of reaction of the employees that are checking the mountain slide. Moreover, when the alert is detected, the different fibers measurements have been cross-correlated in order to: evaluate the distances in time of the vibrations, to compute the falling speed of the event, and to understand at which position of the mountain side the landslide has started and where it was at the detection time.