Near-surface environmental limitations to high-frequency sonar performance: a review


  1. Trevorrow, M.V.
Corporate Authors
Defence Research Establishment Atlantic, Dartmouth NS (CAN)
This work reviews relevant environmental constraints on the performance of high-frequency forward-looking obstacle or mine avoidance sonars. These high-resolution, narrow-beam systems typically operate at frequencies 100-500 kHz, focused on detection and classification of near-surface targets up to 500 m range. Relative signal-to-reverberation performance vs. range for a-15 dB surface target is modeled using a generic sonar model approach. Reverberation from and absorption by near-surface micro-bubble layers is shown to create very strong interference. Breaking-wave induced bubbles typically begin to appear above 6-10 knots wind speed, with typical bubble density spectra strongly decreasing from 10 to 400 Mum radius. At high-frequencies these micro-bubble layers exhibit strong volumetric backscatter, with maximum volumetric back-scattering strengths near-10 dB (re 1 m1(-)), and strong extinction losses of order 1 dB-m1(-). Detectability of surface targets is limited to less than 20 m at 100 kHz, but the detection range increases with frequency to roughly 250 m at 400 kHz and above. Another significant performance limitation is acoustic refraction by near-surface sound speed gradients commonly found in coastal regions, especially near river-mouths and estuaries and during summer months. TRUNCATED
Refraction;Zooplankton;Micro-bubbles;High-frequency sonar
Report Number
DREA-TM-2001-002 — Technical Memorandum
Date of publication
01 Jan 2001
Number of Pages
Hardcopy;Document Image stored on Optical Disk

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