Underwater fish volume estimation using closed and open cavity Helmholtz resonators

Abstract Volume is an important parameter in determining the density of aquatic products. However, due to the distended variation in shape and size of these products, it is difficult to precisely estimate their volume in water. In this study, we proposed a technique known as Helmholtz resonance for estimating the volume of fish in water. In order to do this, a closed cavity resonator was designed and utilised as an underwater prototype to demonstrate the potential for fish volume measurement. However, such a closed cavity resonator is thwarted by the need to open, insert the fish samples and close for measurement to be done. As a potentially more viable alternative, an open cavity resonator, which would allow fish to be measured without the need to close or lock the cavity was developed. Furthermore, this has the potential for automatic fish volume estimation where fish can pass through such an opening on the side of the resonator's cavity for measurement. Similar to the closed cavity resonator, as the volume of sampled fish increased, resonance frequency decreased in the open cavity resonator. The damping of the resonance frequency was caused by the viscous fish flesh and the elastic swim bladder in the anterior chamber of the model fish, a teleostean fish. By use of empirical equations, a linear regression model (R-squared) with an accuracy of 0.99 in the open cavity resonator was obtained. An underwater open cavity Helmholtz resonator has the potential for fish volume measurement.