Enhancing the Perfomance of a Submersible Holographic Camera and Automating Analysis for Determining Particle Location and Turbulance in the Ocean

[9909170]这个海洋科学技术发展项目建立在先前工作的基础上，开发和测试一种潜水全息相机系统，使用激光产生全息图，从中可以研究小颗粒的运动和分布。目前，一种用于在海洋中记录原位全息图的潜水式“全息相机”系统利用红宝石激光作为光源，以在线模式运行。它由机载电池供电，并通过两根光纤电缆进行控制，这两根光纤电缆还提供来自其他机载环境传感器的实时数据。该系统旨在最大限度地减少系统对采样水量的影响。目前的工作重点是提高全息相机的性能和继续发展全息图分析程序。全息摄影是一种独特的工具，可以在大样本量上提供微观粒子的瞬时位置，以及每个粒子的形状、大小和方向。一系列全息图也可以用来确定样品体积中液体的完整三维速度场和较大颗粒的相对速度。数据分析过程包括重建记录的全息图，以创建原始样本量的三维冻结图像。通过高倍扫描重建图像，可以在约1000 cm3的样品体积内观察和测量所需的细节，精确到小于10 mm。通过合并和开发软件工具，将进行自动化和提高分析程序的效率的工作，这些工具将执行1)使用各种基于直方图的、非线性和形态滤波器进行图像增强；2)粒子检测，包括使用斑点分析子程序；3)基于粒度和形状的颗粒分类。进一步的增强将提供全息粒子图像测速的能力，通过为全息相机提供一个独立的离轴参考光束，并在样片和胶片之间插入一个空间高通滤波器。测量海洋中三维液体速度分布和选定粒子的相对运动的能力将利用实验室应用的方法得到发展，在实验室应用中，液体流场是通过小颗粒的位移来测量的。将开发原位方法，通过使用粒子在空间中的确切位置精确地确定粒子的轴向位移，从单个全息图中获得所有三个速度分量（粒子跟踪）；通过使用连续性方程可以从其他两个的空间分布中计算轴向分量。提出了解决直线全息和离轴全息重叠问题的方法。现场测试将与海港分部海洋研究所的调查人员一起进行。他们的研究需要浮游生物规模的局部剪切应变（即三维速度分布）数据，以及桡足动物丰度与海洋雪和/或其他资源丰度之间的相关性。这两种都可以由全息相机同时提供。这种传感器可以应用于其他物理和生物海洋学问题，如小尺度湍流、微尺度生物斑块、食物颗粒捕获、描述气泡的大小和运动，包括那些比多频声学技术可以测量的更小的气泡。

9909170KatzThis ocean sciences technology development project builds on previous work to develop and test a submersible holographic camera system using lasers to produce holograms, from which the motion and distribution of small particles can be studied. A submersible "holocamera" system for recording in-situ holograms in the ocean presently operates in an in-line mode utilizing a ruby laser as its light source. It is powered by onboard batteries and is controlled via two fiber optic cables, which also provide real time data from other onboard environmental sensors. The system is designed to minimize the effect the system has on the sampled water volume. The present effort focuses on enhancing the performance of the holocamera and continuing the development of hologram analysis procedures. Holography is a unique tool that can provide the instantaneous location of microscopic particles over a large sample volume as well as the shape, size and orientation of each particle. A series of holograms can also be used to determine the full 3 -D velocity field of the liquid in that sample volume and the relative velocities of larger particles. The data analysis procedure consists of reconstructing a recorded hologram to create a 3 - D frozen image of the original sample volume. By scanning the reconstructed image at high magnification, one can observe and measure desired details down to less than 10 mm within a sample volume of about 1000 cm3. Work will be undertaken to automate and improve the efficiency of the analysis procedures by incorporating and developing software tools that will perform 1) image enhancement using a variety of histogram-based, non-linear and morphological filters; 2) particle detection involving use of blob analysis subroutines; and 3) particle classification based on size and shape. A further enhancement will provide the capability for Holographic Particle Image Velocimetry by providing the holocamera with a separate, off-axis reference beam, and a spatial, high pass filter inserted between the sample volume and the film. The ability to measure the 3-D liquid velocity distribution in the ocean and the relative motion of selected particles will be developed using methods used for laboratory applications where the liquid flow field is measured using the displacement of small particles. In situ methods will be developed to obtain all three velocity components from a single hologram by determining the axial displacement of particles accurately using their exact location in space (particle tracking); and by using the continuity equation that enables computation of the axial component from the spatial distribution of the other two. Methods to address the overlap problem for in-line holography and for off-axis holography are proposed.Field tests will be performed in conjunction with investigators from Harbor Branch Oceanographic Institute. Their research requires data on the local shear strains (i.e. 3 - D velocity distribution) in the scale of planktonic organisms as well as correlation between copepod abundance and marine snow and/or other resource abundance. Both can be simultaneously provided by the holocamera. This sensor could be applied to other physical and biological oceanographic problems such as small scale turbulence, microscale patchiness of organisms, capture of food particles, and describing the size and motion of bubbles including those smaller than multi-frequency acoustical techniques can measure.