Acoustic Characterization of the Mesopelagic Boundary Sound Scattering Layer

近海环境中生物声散射层的声学特性尚不清楚，特别是在太平洋的亚热带和热带岛屿附近，这些岛屿的底部坡度可能非常陡峭。声散射层可以代表一个大的声学目标，很容易被错误地认为是一个虚假的底部，并可能干扰声纳系统。夏威夷群岛周围的声波散射层被称为Microronekton的中层海洋边界群落(MBC)，由小鱼、虾和鱿鱼组成。像大多数深层散射层一样，这一层经历了垂直迁移。然而，夏威夷边界的迁移也有一个很大的水平部分，这在一些海岸线是可以预测的。项目组将通过1)在层的不同部分进行多个放牧角度的多频率声波后向散射测量以说明密度和层厚度的差异，2)声学、视频和海洋测量以估计密度和物种以及在背向散射测量的相同位置的海洋条件的关系，3)声学和叶绿素a测量以估计后向散射测量位置的浮游动物和浮游植物丰度和密度，4)岛屿尺度的中海洋边界声散射层在岛屿周围不同位置的空间和时间分布，瓦胡岛是温带和热带太平洋其他岛屿的典范。这项研究将增进我们对中远洋边界群落的环境和特征的了解。中层海洋边界群落是与太平洋和其他底坡陡峭的岛屿有关的沿海生态系统的重要组成部分，增加对其生态的了解对于在这种环境中保护、管理和运作十分重要。这个Microronekton群落也是许多商业上重要物种的重要食物来源，包括比目鱼、金枪鱼和底栖鱼以及旋转海豚。

The acoustic properties of mid-water biologically induced sound scattering layers in coastal environment is poorly understood, especially around sub-tropical and tropical islands in the Pacific, where the bottom slope can very steep. The sound scattering layer can represent a large acoustic target and can easily be mistakenly as a false bottom and can interfere with sonar systems. The sound scattering layer around the Hawaiian Islands is known as the mesopelagic boundary community (MBC) of micronekton comprising of small fishes, shrimps, and squids. This layer, like most deep-scattering layers, undergoes vertical migration. However, the Hawaiian boundary's migration also has a large horizontal component that is predictable along some coastlines. The project team will characterize the acoustic environment of the mesopelagic boundary community by performing 1) multi-frequency acoustic backscatter measurements at multiple grazing angles at different portions of the layer to account for differences in density and layer thickness, 2) acoustic, video and oceanographic measurements to estimate density and species and the relationship of oceanographic conditions at the same locations of the backscatter measurements, 3) acoustic and chlorophyll a measurements to estimate zooplankton and phytoplankton abundance and density at the locations of the backscatter measurements, 4) island scale spatial and temporal distribution of the mesopelagic boundary sound scattering layer at various locations around an island, with Oahu serving as a model for other islands in temperate and tropical Pacific. This research will increase our understanding of the environment and the characteristics of the mesopelagic boundary community. The mesopelagic boundary community is an important part of the coastal ecosystem associated with Pacific and other islands that have steep bottom slopes and increase understanding of its ecology is important for preserving, managing and operating in this environment. This community of micronekton also serves as an important food resource for many commercially important species including billfish, tunas, and bottomfish and also spinner dolphins.