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The sensing system is based on phase-sensitive optical time domain reflectometry (\u03d5-OTDR) technology for signal acquisition and pattern recognition strategies for threat identification. The proposal incorporates contextual information at the feature level and applies a system combination strategy for pattern classification. The contextual information at the feature level is based on the tandem approach (using feature representations produced by discriminatively-trained multi-layer perceptrons) by employing feature vectors that spread different temporal contexts. The system combination strategy is based on a posterior combination of likelihoods computed from different pattern classification processes. The system operates in two different modes: (1) machine + activity identification, which recognizes the activity being carried out by a certain machine, and (2) threat detection, aimed at detecting threats no matter what the real activity being conducted is. In comparison with a previous system based on the same rigorous experimental setup, the results show that the system combination from the contextual feature information improves the results for each individual class in both operational modes, as well as the overall classification accuracy, with statistically-significant improvements.<\/jats:p>","DOI":"10.3390\/s17020355","type":"journal-article","created":{"date-parts":[[2017,2,15]],"date-time":"2017-02-15T10:09:07Z","timestamp":1487153347000},"page":"355","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":117,"title":["A Novel Fiber Optic Based Surveillance System for Prevention of Pipeline Integrity Threats"],"prefix":"10.3390","volume":"17","author":[{"given":"Javier","family":"Tejedor","sequence":"first","affiliation":[{"name":"FOCUS S.L., 28804 Madrid, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3303-3963","authenticated-orcid":false,"given":"Javier","family":"Macias-Guarasa","sequence":"additional","affiliation":[{"name":"Department of Electronics, University of Alcal\u00e1, 28801 Alcal\u00e1 de Henares, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hugo","family":"Martins","sequence":"additional","affiliation":[{"name":"FOCUS S.L., 28804 Madrid, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Daniel","family":"Piote","sequence":"additional","affiliation":[{"name":"FOCUS S.L., 28804 Madrid, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Juan","family":"Pastor-Graells","sequence":"additional","affiliation":[{"name":"Department of Electronics, University of Alcal\u00e1, 28801 Alcal\u00e1 de Henares, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Sonia","family":"Martin-Lopez","sequence":"additional","affiliation":[{"name":"Department of Electronics, University of Alcal\u00e1, 28801 Alcal\u00e1 de Henares, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Pedro","family":"Corredera","sequence":"additional","affiliation":[{"name":"Instituto de \u00d3ptica, CSIC, 28006 Madrid, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Miguel","family":"Gonzalez-Herraez","sequence":"additional","affiliation":[{"name":"Department of Electronics, University of Alcal\u00e1, 28801 Alcal\u00e1 de Henares, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2017,2,12]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Choi, K.N., Juarez, J.C., and Taylor, H.F. 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