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Sawada, K., Takahashi, H., Abe, K., Ichii, T., Watanabe, K., and Takao, Y. 2009. Target-strength, length, and tilt-angle measurements of Pacific saury (Cololabis saira) and Japanese anchovy (Engraulis japonicus) using an acoustic-optical system. – ICES Journal of Marine Science, 66: 1212–1218. Pacific saury and Japanese anchovy generally congregate in dense groups or schools. An acoustic-optical system (the Japanese Quantitative Echosounder and Stereo-video Camera System or J-QUEST) has been developed to measure accurately the target strength (TS) of fish in a dense school. J-QUEST comprises a quantitative, 70 kHz, split-beam echosounder and a stereo-video camera. It was deployed from a research vessel to collect concomitant measures of TS and stereo images of in situ Pacific saury and Japanese anchovy. The stereo-video camera provides estimates of the fish lengths (L) and tilt-angles corrected for J-QUEST motion. In this way, empirical models of TS vs. log(L) were derived for Pacific saury and Japanese anchovy and compared with theory.

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SUMMARYMultidigit multiplication is widely used for various applications in recent years, including numerical calculation, chaos arithmetic, and primality testing. Systems with high performance and low energy consumption are demanded, especially for image processing and communications with cryptography using chaos. Karatsuba algorithm with computational complexity of O(n 1.58 ) has been employed in software for multiplication of hundreds to thousands of bits, where n stands for bit-length of operands. In this paper, hardware design of multidigit integer multiplication based on Karatsuba algorithm is described and its VLSI realization is evaluated in terms of the cost, performance, and energy consumption. We present two design choices of the Karatsuba hardware: RKM (Recursive Karatsuba Multiplier) and IKM (Iterative Karatsuba Multiplier). We found that RKM has less area cost than WTM (Wallace Tree Multiplier) for bit-length larger than 2 9 with area cost of 30 mm 2 . Critical path delay of RKM is always larger than that of WTM. Therefore, we should use WTM as combinational circuits for IKM to have better cost performance. We also found that a version of IKM using 0.18 µm process can perform 1024-bit multiplications 30 times faster than software at the area cost of 10.9 mm 2 . Energy for the computation by the IKM version was found to be nearly 1/600 of that consumed by general-purpose processor which executes the software. The results obtained by this study will help system designers for applications requiring multidigit multiplication to select design alternatives including ASIC realization.

The relationship of target strength (TS), tilt angle and the effect of swimbladder resonance were examined using a theoretical scattering model for Maurolicus japonicus (30.4-46.8 mm standard length (SL)) at 38 kHz and 120 kHz, based on swimbladder measurements. The effect of tilt angle on TS was seen at 120 kHz, but was minimal at 38 kHz. The effect of resonance on TS was clear at 38 kHz, but was minimal at 120 kHz. This was due to the small size (average 11 % of SL) and oval shape with a relatively high aspect ratio (average 0.48) of the swimbladder. Considering the effect of resonance, the TS-SL relationships at 38 kHz were estimated: TS = 10.0 log 10 SL − 61.3 at 200 m depth. Considering the effect of tilt angle, the average TS (TS avg) −SL relationship at 120 kHz was estimated: TS avg = 16.5 log 10 SL − 75.1.