Fig. 1. (a) Schematic of φ-OTDR system; (b) system prototype

Fig. 2. Schematic of back pulse-cleaned bag filters

Fig. 3. Configuration of simulation platform in laboratory

Fig. 4. (a) Superposition of 20 consecutive Rayleigh traces; (b) adjacent time-domain difference of the superposition; (c) positioning accuracy; (d) spatial resolution

Fig. 5. (a) Frequency spectrum at 100 Hz; (b) contour map of 100 Hz frequency response

Fig. 6. Contrast diagram of the frequency response contour of three bags

Fig. 7. (a) Experimental scene; (b) schematic of on-site optical fiber laying

Fig. 8. Amplitude-frequency characteristics of normal bags (1-500) and broken bags (500-1000). (a)(b) Frequency spectra contract at 1561 m location; (c)(d) frequency spectra contract at 1493 m and 1561 m locations

Fig. 9. (a) Visual model of classification at 1561 m location; (b) visual model of classification at 1493 m and 1561 m locations