Tuba II-a compact multi-frequency sonar suited to use in autonomous or towed platforms for the study of upper-ocean zooplankton distribution and abundance

TUBA is a towed undulating bio-acoustic instrument, developed at the Southampton Oceanography Centre, to enable the study of zooplankton using seven frequencies covering the range 175 kHz to 2.4 MHz. In TUBA II a significant advancement is the adoption of the 2-wire I/sup 2/C serial communications protocol to allow configuration and control of the instrument over as much as 1300 m of cable. This allows the control of parameters including receiver filter Q and bandwidth, transmit power, pulse width, transmission centre frequencies, and routing of test signals through the receiver stages to check internal noise levels and filter responses. As well as allowing greater control of the unit during scientific experiments, we have greater control during calibration exercises whether in the laboratory, or at sea. Further improvements include new wideband linear power amplifiers, improved receiver circuitry and filtering, and redesigned transducers using modern composite materials for greater sensitivity at the higher frequencies.