Noise Sources in Fiber-Optic Distributed Acoustic Sensing VSP Data

This abstract details the three major noise sources affecting DAS VSP data and describes mitigation methods for each. The first noise source is fading, which occurs over spatiotemporally varying regions in the VSP records with extremely large amplitude values. It is caused by destructive interference of the backscattered light that changes with time. Acquiring repeated shot records and applying weighted stacking can mitigate this issue. Common-mode noise is the second noise source; it is caused by sound and vibration in the vicinity of the interrogator simultaneously imprinting on all data channels. This can be mitigated by extracting the signal that is common to all channels and subtracting it from each one. Temperature changes in the deployed fiber-optic cable or in the interrogator resulting in a low-frequency drift of the measured relative strain data is the third source of noise. While it is possible to low-pass filter the relative strain data, an easier approach is to convert the data to strain rate, which is less susceptible to temperature effects. This study shows that excellent quality DAS VSP data can be obtained by using an appropriate acquisition system, as well as by removing the effects of optical noise using simple processing algorithms.