Restive properties and detection of fish

Abstract

This thesis details the development of a new method of fish detection and measurement that is designed for operation across a river channel without the need for a permanent man-made structure.

The method is based on an array of small sensor units that may be extended to monitor an entire river width. An electronic resistance sensor, personal computer interface control and automatic calibration were developed and tested for the detection and measurement of resistive targets. The sensor could detect 306 mm resistive targets at a range of 700 mm with a basic accuracy of 25 ppm.

Stainless steel rod and freshly killed fish targets produced very similar changes in the electrical resistance measured between wide-spaced point electrodes. Subsequent measurements indicated relationships between resistance change signal (RCS) and resistive target length, position, water depth, water conductivity and electrode separation. Mathematical models were developed to describe the relationship between RCS and electrode separation, target length and target range from the plane of the electrodes.

The mathematical models were incorporated into computer simulations of two methods of target range compensation. Both of these methods were shown to reduce the target length estimation error, compared with no target range compensation, by ≥ 62%. A system that used six point electrodes to compensate for target range was shown to length targets with high accuracy compared with existing systems (± 40 mm length error (1.96 σ) at a range of 650 mm).

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