Investigation and Comparison of φ -OTDR and OTDR-Interferometry via Phase Demodulation

We investigate and compare the φ-optical time domain reflectometry (OTDR) and OTDR-interferometry methods, both using phase demodulation, for distributed acoustic sensing. By theoretical analysis and experiments we show that, while both φ-OTDR and OTDR-interferometry give proper instantaneous amplitude, frequency, and phase properties of the acoustic signal, OTDR-interferometry produces larger signals and offers higher sensitivity, better signal-to-noise-ratio, and larger demodulated signal width than φ-OTDR due to the introduction of the interferometer. This work enables the selection of the better method for distributed acoustic sensing for different situations of surface, seabed, and downhole environments.