Detection and tracking of objects in water using a novel sonar technique

A constant monitoring of the fish population and floatsam is essential to the correct ­functioning of a hydropower plant. Nonetheless, all the conventional monitoring ­techniques present ­several disad-vantages. Tracking techniques based on optical observations can be ­unfeasible in the case of pertur-bed water. Optical observations in the IR-range lack of ­sufficient contrast, because water animals are cool-blooded. Radio frequency measurements are ­disadvantageous, because they require the implementation of a tag, which increases the costs and administrative efforts due to animal testing permissions.

The invention consists of a method for constantly monitoring moving objects in water around a hy-dropower plant, which overcomes the difficulties of the conventional methods. ­According to the in-vention, active hydrophones are installed at the borders of the basin. The ­tomographic measurement approach is based on detection cycles, each consisting of the following steps:

• Each hydrophone sends in sequence and with high temporal frequency (200-1000 Hz) a sonic wave while all the other sensors act as receivers;
• The data are analyzed by means of the change of the acoustic impedance and frequency;
• The spatial resolution achievable with the array composed by several hydrophones allows for identifying and tracking single individuals (water animals).

The observation and tracking of water animals in the reservoir of a hydropower plant, allows for operationally reacting to the changes in behavior and number of their population. In dependence of these factors, turbine discharge can be reduced, gated weirs can be opened or discharges in the fishways can be increased. This active management avoids cost-expensive permanent protecting measures. This method can also be used to prevent the obstruction of the intakes of the plant by detecting the concentration and accumulation of debris.

The invention has been tested in the frame of several experiments. The first results have confirmed the feasibility of the approach.