The Effects of Pulse Width on Fibre-optic Distributed Vibration Sensing Data

Abstract

Summary Systems for distributed vibration sensing (DVS), also known as distributed acoustic sensing (DAS), use a fibre-optic cable as the sensor, rather than the discrete point sensors used in conventional systems. Theoretically, they measure strain, which is the change in the length of the section of fibre divided by the gauge length. In reality, they measure the change in phase of the backscattered light which is directly proportional to strain. However, the phase is not measured at a single position along the fibre; instead, the value is a result of the application of a Gaussian window. The results included here indicate that the laser pulse width used during DVS acquisition can have a significant effect on the quality of the data acquired. As shown previously, the gauge length must be carefully selected due to its strong frequency response, but due to the Gaussian nature of the pulses, their associated frequency response is more muted. The point at which the effect of the pulse width becomes larger than the gauge length is half the gauge length, allowing considerable scope for it to be increased, and thus the SNR of the data improved.