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Conditions for precise measurement of in situ fish target strength (TS) are empirically studied and two indexes are introduced for this purpose. One is the number of fish in the effective reverberation volume which contributes echo tormation at a certain instant and the other is the percentage of the multiple echoes which is derived from a residual of the single echo extraction. With the decrease of both indexes measured target strength approach a certain asymptotic value which is admitted as reliable from the past study. This shows the existence of some threshold values and below these threshold values TS measurement will be successful. The effectiveness of both indexes is confirmed by the data set obtained from one large same fish school in the eastern shelf of Bering sea during the intership calibration between Japanese and U.S. vessels on 15 and 16 August 1991.

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In this paper, we report a simple yet powerful synthetic method for obtaining monodispersed silver nanoparticles by direct thermal decomposition of two materials — one is silver acetate as a source of the metal core and the other is myristic acid as a capping agent. The reaction was performed at 250°C, the boiling point of myristic acid, without additional solvent. The nucleation and growth of the particles were monitored by dynamic light scattering in order to optimize the reaction time. By this simple procedure, we could obtain uniformly sized Ag nanoparticles with the average diameter of 4.8 ± 0.1 nm. Although the particles were synthesized at high temperature, the ligand exchange between myristates and alkanethiolates can be achieved at room temperature. Significant characteristics of Ag nanoparticles attributed to localized surface plasmons were investigated.

This paper reports a laboratory target strength (TS) measurement and theoretical modelling of walleye pollock and Pacific hake. The measurements are performed in a tank as a function of fish tilt an gle, which is controlled in one-degree steps. A precision echo sounder is used and sphere calibrations are conducted before or after the measurement. A specialized soft X-ray imaging system is used to map the fish swimbladder. The X-ray images are digitized to obtain the fish morphological parameters. Based on these parameters, theoretical TS of the fish is calculated using the approximate deformed cylin der model and the general prolate spheroid model. An advantage of using these models lies in their sim plicity and the fact that few parameters are required in the model computation. Calculations indicate a negligible contribution of the fish body to the total scattering in the wide range of tilt angle. The theoret ical TS values are compared with the measured values. Agreement between measured and theoretical TS is reasonably good for near normal incidence, but deteriorates for larger tilt angles. The level of agreement is discussed. Obtained maximum and average TS values are nearly equal to or a little bit smaller than the published data. Using the deformed cylinder model, broad band TS characteristics are generated. Our results highlight the usefulness of the simple method to predict fish TS using the deformed cylinder model associated with X-ray imaging.