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Cross-correlation in band-limited ocean ambient noise fields
1Marine Physical Laboratory, Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0238, USA. mbuckingham@ucsd.edu
The Journal of the Acoustical Society of America
|April 17, 2012
Summary
Ocean ambient noise, when filtered, creates sharp correlation pulses revealing acoustic travel times between sensors. Filter characteristics influence a fine oscillatory structure within these pulses, observed in experimental data.
Area of Science:
- Oceanography
- Acoustics
- Signal Processing
Background:
- Ocean ambient noise is often band-limited due to natural spectral properties or system limitations.
- Such band-limited noise can be modeled as filtered white noise.
Purpose of the Study:
- To analyze the two-point cross-correlation function of band-limited ocean ambient noise.
- To investigate the effects of different filter types (high-pass, bandpass) on noise correlation.
Main Methods:
- Mathematical analysis of the cross-correlation function for filtered noise.
- Consideration of isotropic and surface-generated noise models.
- Examination of filter characteristics, particularly low-frequency cut-off and roll-off.
Main Results:
- Band-limited noise filtering produces sharp correlation pulses at delays corresponding to acoustic travel times.
- A fine structure of rapid oscillations appears within these pulses, influenced by filter steepness.
- These effects are most pronounced when sensor separation is large compared to the longest acoustic wavelength.
Conclusions:
- The analysis explains the observed fine structure in experimental cross-correlation functions of ocean ambient noise.
- Filter design significantly impacts the detailed structure of acoustic travel time information derived from noise correlations.
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