In Situ Measurements of Sound Speed and Density of Live Zooplankton

与传统的水泵和渔网取样技术相比，声学技术在海洋生物调查中的应用提供了一种更有效的方法来绘制海洋生物的空间分布、丰度和时间变化。由于声学方法是遥感技术，它们只是间接测量。为了从原始声学数据中正确推断出有用的生物信息，需要可靠、稳健和准确的声学模型。迄今为止，各种声学模型已经开发出来，并在实验室实验和现场应用中取得了很大进展。为了准确地解释声学数据，无论选择何种模型，无论模型是简单的还是复杂的，都需要选择合适的生物散射体声学特性，如声速和密度对比（和）。我们发现，即使使用相同的模型，目标强度或体积散射强度在声速和密度对比变化2%的情况下可以变化多达6 dB或2倍的偏差。由于声速对比和/或密度对比的偏差，目标强度预测的差异可能与选择不同声学模型所造成的差异一样大，甚至更大。此外，和的变化不仅会导致散射水平的不同，而且会导致散射模式随频率和取向角的变化而不同。我们建议开发一种可靠且稳健的方法来进行与声学数据共同登记的声学特性的原位测量，即提供时变的和对应于声学数据收集的动物的实际位置。一个实验室版本的原位测量系统，浮游生物的声学特性（APOP），将开发和评估。所提出的方法包括测量水-浮游动物混合物的后向散射。通过使用宽带后向散射声学设置，来自混合层边界的两个界面的声干扰引起的频率响应与混合层中的有效声速和密度对比（和）直接相关。在提供浮游动物体积分数的电导率测量的辅助下，利用“有效介质”理论，可以推断出浮游动物体内声速和密度的对比（和）。本研究分为两个阶段：(1)测量系统的初步实验室开发和初步系统性能评估；(2)更广泛的实验室测量，使用多种不同的浮游动物物种来测试系统性能的稳健性和一致性，并对系统进行一些改进。第二阶段的工作对于实现从实验室版本到将用于实际现场应用的版本的更平稳过渡非常重要和必要。在整个实验中，误差分析将指导实验。此外，将对基于不同理论考虑的“有效介质”概念进行深入研究。

Applications of acoustic techniques to marine biological surveys provide a more efficient way to map the spatial distribution, abundance and temporal variation of marine organisms in the ocean compared with traditional sampling techniques involving pumps and nets. Since acoustical methods are remote sensing techniques, they are only indirect measurements. In order to correctly infer useful biological information from raw acoustic data, reliable, robust, and accurate acoustic models are required. To date, various acoustical models have been developed and much progress has been made both in laboratory experiments and field applications. To accurately interpret acoustic data, no matter what model is chosen and whether the model is simple or sophisticated, one needs to select appropriate acoustic properties of the biological scatterers, such as sound speed and density contrasts ( and ). We have found that even using the same model, the target strength or volume scattering strength can vary as much as 6 dB or a 2 fold bias for a 2% variation in sound speed and density contrasts. Differences in target strength predictions due to biases of sound speed contrast, , and/or density contrast, , could be as large as or greater than those due to the choices of different acoustic models. In addition, variations in and result in not only different scattering levels, but also different scattering patterns as a function of frequency and orientation angle. We propose to develop a reliable and robust method to conduct in situ measurements of acoustic properties co-registered with the acoustic data, i.e., to provide time varying and corresponding to the actual positions of the animal where the acoustic data are collected. A laboratory version of an in situ measuring system, Acoustic Properties Of Plankton (APOP), will be developed and evaluated. The proposed method involves measurement of the backscattering from a water-zooplankton mixture. By using a broadband backscattering acoustical setup, the frequency response due to the acoustical interferences from two interfaces bounding the mixture layer is directly related to the effective sound speed and density contrasts ( and ) in the mixture. With the assistant of conductivity measurement which provides volume fraction of the zooplankton and the use of the theory of `effective medium`, the sound speed and density contrasts ( and ) in the zooplankton can be inferred. The proposed research is divided into two phases: (1) initial laboratory development of the measuring system and preliminary system performance evaluation, and (2) more extensive laboratory measurements using a variety of different zooplankton species to test the robustness and consistency of the system performance, and some refinement of the system. The effort of phase two is very important and necessary to achieve a much smoother transition from the laboratory version to the one that will be used for the actual field applications. Throughout the proposed experiments, error analysis will be conducted to guide the experiments. In addition, the concept of the `effective medium` based on different theoretical considerations will be examined thoroughly.