A wideband, single-channel acoustical probe for observations of vertical fine structure in zooplankton

Abstract

Single-frequency acoustical estimates of zooplankton biomass are notoriously inaccurate, varying 10–30 dB with variations in sizes of the scatterers. Multifrequency acoustical estimates are much more accurate but require substantial data processing. A compromise system, utilizing wideband acoustical signals (2.5–3.5 MHz) and broadband processing to reduce the sensitivity to scatterer size variations, has been developed. This system offers the advantages of rapid single-channel data rates and high spatial resolution while providing satisfactory accuracy in biomass estimation. System design required development of several novel subsystems: a broadband transducer with an acrylic lens for obtaining reasonable acoustic sample volumes from physically practical elements; a programmable broadband signal generator; and a wideband square-law receiver/detector. [Work supported by ONR Oceanic Biology and NSF Biological Oceanography.]