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.]