Acoustic Attenuation Due to Fish between 0.3 and 4.5 kHz,
Abstract
The systematic series of amplitude fluctuation experiments carried out at regular intervals during 1967 and 1968 continued in 1969, over an extended frequency range between 312 Hz and 4.44 kHz. The diurnal variation in aggregation and depth of fish caused large changes in signal level near sunrise and sunset. The attenuation patterns were predominantly at the higher frequencies in May and June with a peak at 4.44 kHz or above. The lower frequencies showed an attenuation peak at about 700 Hz in August and September. A subsidiary peak occurred in February centred at 1.44 kHz. The attenuation peaks of 700 Hz, 1.44 and 4.44 kHz correspond, with certain assumptions, to scattering and absorption by fish of mean length 24, 12 and 4 cm respectively. The timing of the level changes depends on season and occurs at about twilight. A timing dependence on frequency, which sometimes occurs, may be due to the effect of vertical migration on the resonance frequency.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 01, 1970
- Accession Number
- AD0721576
Entities
People
- P. A. Ching
Organizations
- Admiralty Research Laboratory