Design, development and application of an underwater holographic camera for the in-situ recording of marine organisms
This thesis details the investigation, design, implementation and testing of an underwater holographic camera ("HoloCam"). The system has been optimised for the recording of plankton and marine particles located within the upper water column of the sea. The ultimate aim of the system is to provide marine biologists with an effective means of enhancing their knowledge and understanding of these organisms and their environment. The HoloCam utilises both in-line and off-axis holographic techniques and facilitates an overlapping volume between the two geometries. This provides a recording range of a few microns for the in-line to large opaque subjects with the off-axis. The in-line system records a volume of 3000 cm3 whilst the off-axis records 47000 cm3. The HoloCam allows recording to a depth of 100 m. The development and optimisation of both holographic systems is detailed with regard to implementation in the HoloCam assembly and the recording of high resolution images of plankton. Special attention is directed towards optimisation of the off-axis illumination system. A new recording medium is also identified and processing schedules for the material are evaluated. The design of all major aspects of the HoloCam system is detailed and the philosophy behind the design is discussed. Rigorous testing of the system is completed under both laboratory and open water conditions. Laboratory trials using the complete HoloCam system have allowed resolutions of 14.3 1p mm-1 to be reconstructed using the off-axis arrangement and 71 1p mm-1 using the in-line. A large number of holograms have been recorded during the open water trials and laboratory replay has allowed many high-resolution images of aquatic particles to be reconstructed. The maximum resolvable detail on the reconstructed images is of the order of 50 mm for the off-axis and 3 mm for the in-line.