A Comparison between Acoustic Reverberation Structures at 87.5 kHz and Internal Waves
SCRIPPS INSTITUTION OF OCEANOGRAPHY LA JOLLA CA MARINE PHYSICAL LAB
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Reverberation data at 87.5 kHz were obtained with a narrow-beam echo sounder from RP FLIP in January and June 1977 off southern California. Analysis of these data shows that backscattering below the wind-mixed layer was due primarily to discrete point scatterers, which had target strengths ranging from -38 to -73 dB and densities of 0.05 to 50 individuals per 1000 cu m. Based upon these characteristics, the identities of the scatterers are probably swimbladder fish, and possibly squid and siphonophores. Backscattering from smaller organisms has been observed as patches or as a limited number of scattering layers. A visual comparison between scatterer motions and isotherm depth fluctuations showed excellent correlation in terms of both phase and amplitude. Minimum total wave amplitudes as small as three meters were observed. It is suggested that this depth resolution might be improved with better data processing techniques and increased system performance.