| 摘要 |
<p>Infrasound signals in the band 0.02 to 4 Hz are sensed in the presence of ambient noise generated chiefly by wind as integrated pressure variations, which induce detectable changes in the optical path length, along optic fibers (1), typically extending 100 m to 1000 m and more, arrayed at arbitrary geometries. Two fibers (11-12) connected as a Michelson, Mach-Zehnder or equivalent interferometer where: (i) one fiber (11, 83) is coupled to atmosphere while (ii) the other fiber (12, 82) is not so connected for being hermetically sealed inside a tube (14), permit common mode rejection of noise from (i) temperature changes and (ii) strain, including ground vibration. Because the optic fiber (1) of the infrasound sensor system (1-7) is longer than the distance over which wind-induced pressure changes are coherent, the effects of wind noise on the sensing of infrasound is reduced, and signal-to-noise ratio is increased over a wide bandwidth. To further enhance pressure sensitivity, an atmospherically-exposed fiber (83) may be coupled to and wound around a deformable membrane such as a rubber tube (81) serving as a mandrel. Expansion and contraction of the tube (81) due to infrasound-induced pressure changes strains the fiber (83) one or two orders of magnitude more than atmospheric pressure changes alone.</p> |
