EQUIPMENT DEVELOPMENT
Shallow-towed bodies
We are currently developing a number of light-weight tow-bodies for the deployment of echo-sounder transducers from vessels of opportunity, and the reduction of noise from near surface aeration in bad weather. A prototype which carries a Simrad ES 38B 38 kHz split-beam transducer and a custom-built pitch, roll and depth sensor is shown in Figure 1. This towbody can be set up to reach a depth of 50m on 150m of cable at 10 knots, and has sufficient space for the mounting of additional higher frequency transducers. A smaller version (Fig. 2) carries an ES 38-12 split-beam transducer for work in shallower water from smaller vessels.
) |
_large.jpg')) |
Figure 1 |
Figure 2 |
Multi-beam echo-sounder
FRS is collaborating with Marine and Coastal Management, Cape Town, and the Department of Electrical Engineering, University of Cape Town, in the development and testing of a multi-beam high-frequency (420 kHz) echo-sounder for high-resolution imaging of fish schools as an aid to species identification, and for the indirect estimation of target strength in situ by simultaneous echo-counting and echo-integration (64kB), as proposed by Soule and Hampton at the ICES International Symposium on Fisheries Acoustics in 2002. The system (code-named ABACUS: Advanced Beam-former for Acoustic Counting of Underwater Scatterers) is currently undergoing tank and sea trials (see below).
) |
) |