Multi-frequency acoustic measurement of zooplankton

1.提出了一种利用4个频率和Kristensen模型估计海洋中构成声散射层的小生物大小的方法。在这项研究中，假设散射层由一个主要的大小类组成。然后利用基于最小二乘和等级一致性的方法估计优势大小的等效球面半径。2.将估计的大小与通过净抽样获得的生物体的大小组成进行比较。虽然NET捕获的浮游动物往往小于声学估计的大小，但两者在相对意义上是一致的，即大、小和中等大小。目前的系统只有4个频率，分辨率有限，但适用于浮游动物组成简单、覆盖范围广的快速连续测量。由于目前科考船普遍配备了与我们的系统类似的声学仪器，因此本研究开发的方法具有广泛的适用性。3.利用上面估计的尺寸对体散射强度进行了修正。修正后的体积散射强度与网捕浮游动物的对数总体积之间的关系可用4个频率共有的一次方程表示。这个公式中剩余的常量项，理论上应该是零，是由于测量误差和/或净回避与实际生物量的差异造成的。造成误差的主要原因可能是净抽样的生物体体积估计值和散射模型中给出的参数值，这些都需要进一步检验。

1.A method for size estimation of small organisms composing sound scattering layrs in the sea was developed using 4 frequencies and the Kristensen model. In this study, it was assumed that scattering layrs consist of a dominant size class. Then, equivalent spherical radius of the dominant size was estimated by the procedure based on least squares and rank conformity.2.The size estimate was compared to size composition of organisms taken by net sampling. While zooplankton taken by net tended to be smaller than acoustic size estimate, both were consistent with one another in a relative sense, i.e.large, small, and medium sizes. The current system has a limitation in resolution of size composition because of having only 4 frequencies, but it is useful for rapid and continuous measurement with wide coverage where zooplankton composition is simple. Since, at present, research vessels are generally equipped with acoustic instruments similar to our system, the method developed in this study can be applied widely.3.The volume scattering strength was corrected by size estimated above. The relationship between the corrected volume scattering strength and logarithmic total volume of zooplankton taken by net was expressed by first-order equation which was common for 4 frequencies. The constant term, which is theoretically to be zero, remaining in this equation is due to an error in measurement and/or difference from real biomass by net-avoidance. Main causes for the error are probably biovolume estimation of organisms sampled by net and parameter values given in the scattering model, which are needed to be examined further.