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Nonlinear crosstalk in broadband multi-channel echosounders
Babak Khodabandeloo1, Egil Ona1, Gavin J Macaulay1
1Ecosystem Acoustics Group, Institute of Marine Research, Bergen, Norway.
The Journal of the Acoustical Society of America
|January 30, 2021
Summary
Nonlinear acoustic propagation creates interfering harmonics. Reducing transmit power or adjusting processing windows effectively minimizes this crosstalk interference in echosounder systems.
Area of Science:
- Acoustics
- Oceanography
- Signal Processing
Background:
- Nonlinear acoustic propagation causes signal distortion, generating higher harmonics.
- Harmonics from one echosounder band can interfere with others, causing crosstalk.
- Crosstalk degrades backscattered amplitude frequency response and creates spurious targets.
Purpose of the Study:
- To model nonlinear acoustic propagation in directional beams.
- To assess methods for reducing harmonic interference (crosstalk) in broadband echosounders.
- To compare modeling results with field experiments.
Main Methods:
- Modeling of nonlinear propagation of frequency-modulated acoustic waves.
- Field experiments using seabed echoes and a metallic target sphere.
- Analysis of two crosstalk reduction methods: transmit power reduction and Fourier window length selection.
Main Results:
- Modeling and field experiments showed good agreement.
- Reduced transmit power significantly decreases crosstalk amplitude.
- Proper Fourier window length selection is effective in reducing crosstalk.
- Crosstalk effect was minimal (<0.4 dB) for area backscattering but significant (several dB) for target strength measurements.
Conclusions:
- Nonlinear propagation effects and crosstalk are significant concerns in broadband echosounder systems.
- Reducing transmit power and optimizing processing windows are effective strategies to mitigate crosstalk.
- The impact of crosstalk varies depending on the measurement type (e.g., area backscattering vs. target strength).
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