Nuisance alarm reduction: Using a correlation based algorithm above differential signals in direct detected phase-OTDR systems

Abstract

Significant research efforts have focused on techniques for alleviating the nuisance alarm rate (NAR) in the field of φ-OTDR pattern recognition systems. Unfortunately, ephemeral events were mostly neglected in previous research, and algorithms meant for improving classification accuracy were emphasized at the cost of acquiring a very large number of traces. This problem engendered an additional source of NAR in a specific class of events. The proposed solution uses a novel correlation based wrapper on top of differential signals that aims to filter out the effect of unnecessary phases in direct detected φ-OTDR systems. This technique avoids the use of irrelevant data in these differential signals by exploiting a better use of these unnecessary phases and provides a better intensity translation with fewer acquired traces as compared with contemporary techniques of extracting features.

Segregating the true perturbation position from ghost energy points region in ϕ-OTDR systems

“…The differential signals play a very important role in detecting any perturbation by eliminating the common unwanted signals that normally exist at the respective spatial location of each acquired time data vector [24]. A space data set defines a collection of space data vectors along the time domain for several consecutive spatial locations, which is used in the MF technique [23]. When processing differential signals, each processing window is defined to be a collection of all space data sets within two time data sets (as the differential signals process two time data sets in a single operation).…”

“…An overview of the MF technique is presented here. This algorithm was chosen because of its ability to effectively remove noise effects [23], and hence it can better assist S-scan, T-scan and ST-scan methods. Mathematically, the correlation of adjacent data sets in the space domain for the MF approach is defined as follows:…”

“…The MF technique is used on top of differential signals in any scanning processes. From [23], we know that the adjacent correlation of space data sets in this technique provides a better amplitude translation as compared to any other technique (e.g., level crossing, short-time fast Fourier transform, discrete wavelet transform). With σ ρ, this translation boosts the level at the certain spatial locations within the perturbation region, named as high energy points.…”

“…The effect of noise in the respective elements of each adjacently correlated space data set is not proportional and hence degrades the correlation. It implies the non-perturbation region always shows a degradation in the correlation whereas the perturbation region shows a boost in these values [23]. With the correlation operator, the non-consistent noise effects are filtered out, leaving behind the effect due to the high-consistent elements that change proportionally with the applied perturbation.…”

“…Inspired from the simplicity and ease of the cost of installation of direct detected φ-OTDR systems in very long FUT applications like pipeline or border security [1,6,[20][21][22], our proposed work has been implemented with a direct detected φ-OTDR system. The matched filtering (MF) technique presented in [23] has been exploited within the ST-scan process to alleviate the effect of all possible noise interferences that are the main hurdles in detecting true energy points in the space domain and the impact of the applied perturbation along the time domain.…”