Holographic Image Acquisition and Remote Underwater Visualization

Currently there are two approaches to large volume data retrieval for underwater holography: optical methods using high resolution emulsions and digital holography. Underwater digital holography has enabled high resolution real-time data to be obtained with depths-of-field otherwise unobtainable by conventional non-holographic optical techniques. However, conventional emulsion methods provide large volume retrieval at a superior resolution. This paper will discuss a twin camera automated image retrieval system for in-line emulsion holographic reconstruction and future alternative real-time reconstruction methods using digital holography. In both techniques image acquisition and data retrieval from reconstructed holograms presents a number of challenges that hinder the ability to readily extract information. The application of holography to store high resolution three-dimensional data for large volumes is well understood, however here also belies a problem for data retrieval and large information storage, the data extraction is time-consuming and requires manual intervention. The automated holographic reconstruction system has been developed to aid the analysis, databasing and identification of objects captured by in-line holography. Whereas, the digital off-axis system presents an alternative real-time visualisation approach for underwater analysis. Digital off-axis real-time reconstruction will be presented using numerical pre-processing of captured holograms for data extraction and visualization using a spatial light modulator (SLM). This method has the advantage of recording surface information and optimizing the recording quality of holograms in-situ without the necessity of numerical post-processing. Preliminary experimental research has demonstrated optical and numerical reconstructions at interactive frame rates. Observed interlacing artifacts caused by the CCD camera used are presented and discussed. Optical and numerical reconstructions are presented using a spatial light modulator. Fourier methods are presented using a Negative Laplacian finite impulse response filter to pre-process holograms for optimizing the numerical and optical reconstructionn.