Passive source ranging is a challenging issue of common interest in underwater acoustics. Many passive localization systems in applications, for example, focusing or triangulation location technology rely on the signal delay between widely separated sub-arrays or between hydrophones to estimate the source range. However, their performance is strictly limited by the relative position between the source and the array, the variance of the time delays, and the inhomogeneous and fluctuated environment.

Besides, conventional matched-field processing (MFP) compares the measured field with replica fields computed at all possible source locations using a sound propagation model. There exist extensive replica-field computations. Moreover, it is well known that the mismatch problem usually occurs and the processing performance degrades due to various uncertainties of oceanic environment information, measurement system, computational acoustic model, and complicated background interference.

In this research, a source range estimation approach is established based on the frequency invariability and warping transform without complicated environmental knowledge and extensive computations. The warping transform can be used to compensate for the geometric dispersion effect of reflecting-dominated modes in shallow water waveguides. It can transform nonlinear time-frequency mode signals to linear ones with corresponding stationary quasi-monochromatic components.

The signal autocorrelation function (ACF) always carries similar dispersive characteristics in underwater waveguides and removes the complicated or random phase information of observed signals. The spectrum of the warped signal or its ACF owns a stationary monochromatic output with the invariable frequency features, which are independent of geometry of the source and the receivers.

The formula (see eq. (1))

(1)

representing the approximate relation between characteristic frequency at an unknown source range and the intrinsic frequency extracted by the time warping transform is derived.

So the spectrum of the warped signal ACF is developed to implement the passive source range estimation using a single hydrophone. In this approach, a guided source with known range information is suggested to supply relative invariant scaled frequency features of shallow water waveguide without a priori knowledge of environmental information and extensive computations in MFP.

The experimental data in shallow water with an iso-speed profile and a fluctuated thermocline are used to verify this approach. The relative errors of the source range estimation are basically less than 10%.

This research was supported by the National Natural Science Foundation of China (Grant Nos. 11174312, 10974218 and 11125420).

The research with the title of “Frequency Invariability of Acoustic Field and Passive Source Range Estimation in Shallow Water” has been released in Science China Physics, Mechanics and Astronomy (Vol. 57, No. 2, pp. 225-232, February 2014).

Corresponding author:

ZHOU Shihong

Institute of Acoustics, Chinese Academy of Sciences, Beijing 100190, China

Email: shih_zhou@mail.ioa.ac.cn