We present the experimental demonstration of self-collimation (subdiffractive propagation) of an ultrasonic beam inside a three-dimensional (3D) sonic crystal. The crystal is formed by two crossed steel cylinders structures in a woodpilelike geometry disposed in water. Measurements of the 3D field distribution show that a narrow beam, which diffractively spreads in the absence of the sonic crystal, is strongly collimated in propagation inside the crystal, demonstrating the 3D self-collimation effect.

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Please cite this article as: E. Soliveres, P. Poveda, V.D. Estruch, I. Pérez-Arjona, V. Puig, P. Ordó nez, J. Ramis, V. Espinosa, Monitoring fish weight using pulse-echo waveform metrics, (2017), http://dx.Abstract Fish anatomical vertical dimensions are extracted from a time-of-flight analysis of fish echo shape using narrow-bandwidth echosounding of swimming individuals. These vertical dimensions fit a Gumbel distribution model and are successfully correlated with fish weight. The proposed method can be used to estimate the mean weight of fish in aquaculture cages as an alternative to target strength measurements. Full-waveform acquisition and signal correlation techniques permitted to increase the signal-to-noise ratio and to improve the performance against traditional envelope-based echosounding.

Simultaneous self-collimation of sound beams with different frequencies, corresponding to fundamental wave and to its second harmonic, is proposed theoretically and demonstrated experimentally. The result is obtained when the isofrequency contours for each harmonics, corresponding to different propagation bands, develop flat segments along the same direction. The effect can be utilized for managing (enhancement and control) of nonlinear frequency mixing of narrow sound beams.

Underwater noise has been identified as a relevant pollution affecting marine ecosystems in different ways. Despite the numerous studies performed over the last few decades regarding the adverse effect of underwater noise on marine life, a lack of knowledge and methodological procedures still exists, and results are often tentative or qualitative. A monitoring methodology for the behavioral response of bluefin tuna (Thunnus thynnus) when exposed to ship and wind turbine operational noises was implemented and tested in a fixed commercial tuna feeding cage in the Mediterranean sea. Fish behavior was continuously monitored, combining synchronized echosounder and video recording systems. Automatic information extracted from acoustical echograms was used to describe tuna reaction to noise in terms of average depth and vertical dimensions of the school and the indicators of swimming speed and tilt direction. Video recordings allowed us to detect changes in swimming patterns. Different kinds of stimuli were considered during bluefin tuna cage monitoring, such as noise generated by feeding boats, wind farm operational noise, and other synthetic signals projected in the medium using a broadband underwater projector. The monitoring system design was revealed as a successful methodological approach to record and quantify reactions to noise. The obtained results suggested that the observed reactions presented a strong relationship with insonification pressure level and time. Behavioral changes associated with noise are difficult to observe, especially in semi-free conditions; thus, the presented approach offered the opportunity to link anthropogenic activity with possible effects on a given marine species, suggesting the possibility of achieving a more realistic framework to assess the impacts of underwater noise on marine animals.

Posidonia fields in the "Cabo de Gata" marine natural park, located in the south-east mediterranean spanish coast, have been mapped by means of two different acoustical tools: a vertical single-beam scientific echosounder and a side-scan sonar. The measured transects have been dived and recorded with a video camera in order to validate the predictions from the extracted acoustical data. We compare both the results obtained from the application of commercial software for bottom classification, and the processing with alternative algorithms in the case of the vertical echosounder, with those derived from the analysis of the side-scan sonar data. Acoustics 08 Paris