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

点击翻译按钮获取中文摘要

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.