Ocean Environmental Influences of Temperature and Mechanical Stress on Bare Fiber-Optic Sensors of Acoustic Pressures. Part I

摘要

A theoretical analysis is made of the signal-to-noise ratio of a fiber-optic hydrophone based on general forms of power spectra of random environmental noise. The signal is a single-frequency acoustic pressure wave. The noise is a sum of shot noise, laser jitter, environmental temperature fluctuations and environmental mechanical-stress fluctuations. Environmental effects are discussed in terms of autocorrelation functions and power spectra. Explicit formulas are derived for the case of Gaussian autocorrelations. A detailed investigation is undertaken of the effects of temperature fluctuations in the ocean on the phase stability of the signal beam. Both large-scale temperature fluctuations caused by internal waves and small-scale fluctuations caused by velocity turbulence and thermal diffusion are considered. Numerical calculations are made of specific cases of interest. It is concluded that the stability of phase is either strongly affected or moderately affected, depending on the length of the fiber exposed to the medium, the depth in the ocean, the track length of towed sensors, the time of exposure in moored sensors, and the characteristics of built-in instrumental spectral windows. (Author)