3,754 research outputs found
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Off-axis transmission holographic system for recording aquatic particles
We describe a holographic system for recording particles suspended in water. The hologram plate is located in air, separated from the test tank by an air/glass/water boundary. The holographic emulsion is therefore unaffected by adverse aquatic conditions within the tank (i.e. surface contamination, non-uniform swelling). The design geometry is intended to minimise the aberrations that arise from recording subjects located in water and replaying their hologram image in air.
Third order aberrations, most crucially spherical aberration and astigmatism, are suppressed to give an experimental resolution of 7 lp/mm using USAF 1951 target in water 600mm from the boundary. Particles (plankton species) in the
sub-millimeter to several millimeters size range are observed at planar sections within the recording volume by visual inspection of the hologram replayed in real image mode
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Holographic mensuration of suspended particles in aquatic systems
The distribution and dynamics of aggregates in the aquatic environment play an important role in the modelling of biogeochemical processes. Previous work on aggregates in the ocean (e.g. sedimentary 'marine snow' particles), which vary in size from tens of microns to several millimetres, has used electronic counting or conventional photography coupled with image analysis. Here we describe a non-destructive in situ approach by use of holographic mensuration, hologrammetry, that affords greater scope and higher accuracy for the enumeration, sizing, and spatial distribution determination of aggregate particles. By means of two complimentary techniques, in-line and offaxis transmission holography, we present the initial experiments conducted in our laboratory and discuss the preliminaiy results from real image analysis
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In situ off-axis holography of marine plankton
We present an off-axis transmission holographic technique for recording marine plankton in situ within a test tank of 36,000 ml with a pulsed laser in a 40 ns interval. The holographic plate is located in air and is therefore unaffected by aquatic conditions that may cause emulsion degradation (e.g. non-uniform swelling and surface contamination). The reference beam
traverses a path in air only, and thus remains unaffected by dense concentrations of plankton. Third order aberrations, notably spherical aberration and astigmatism, are suppressed to yield an experimental resolution of 7 lp/mm (70 micrometres) with a USAF 1951 target located 600 mm in water from the observation window. Plankton particle counts examined by real image reconstruction show a strong correlation with duplicate samples examined under a microscope
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A data extraction system for underwater particle holography
Pulsed laser holography is an extremely powerful technique for the study of particle fields as it allows instantaneous, noninvasive high-resolution recording of substantial volumes. By replaying the real image one can obtain the size, shape,
position and - if multiple exposures are made - velocity of every object in the recorded field. Manual analysis of large volumes containing thousands of particles is, however, an enormous and time-consuming task, with operator fatigue an
unpredictable source of errors. Clearly the value of holographic measurements also depends crucially on the quality of the reconstructed image: not only will poor resolution degrade size and shape measurements, but aberrations such as coma and astigmatism can change the perceived centroid of a particle, affecting position and velocity measurements.
For large-scale applications of particle field holography, specifically the in situ recording of marine plankton with 'HoloCam,' we have developed an automated data extraction system that can be readily switched between the in-line and off-axis geometries and provides optimised reconstruction from holograms recorded underwater. As a videocamera is automatically stepped through the 200 by 200 by 1000mm sample volume, image processing and object tracking routines locate and extract particle images for further classification by a separate software module
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Ambient humidity control for maximising replay intensity and resolution in aberration-compensated off-axis holograms of underwater objects
In hologrammetry it is usually more desirable to reconstruct the real image than the virtual image, since the latter must be viewed at a distance through the window of the holographic plate itself. In applications where the recorded scene was in water but with replay into air it is necessary to correct for the refractive index difference. This can be done by reconstructing the image with shorter wavelength illumination combined with a change in beam angle to satisfy the grating equation, but these changes mean that the Bragg condition may no longer be satisfied during replay, reducing the diffraction efficiency and making the reconstructed images difficult to see. Changing the replay beam angle to better satisfy the Bragg condition makes the images brighter, but also renders them unrecognizable by introducing severe optical aberrations. A possible solution is to alter the Bragg properties of the hologram. In particular, the emulsion thickness can be conveniently controlled by altering the humidity of the atmosphere surrounding the hologram without causing any long-term changes or damage to the holographic plate. The validity of using humidity change to tune the Bragg properties of emulsions during replay has been demonstrated by measuring the brightness and perceived resolution of a reconstructed real image from a hologram over a wide range of humidities. The results have been compared with a simple model based on the Flory-Huggins theory of polymer swelling
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Optimising replay intensity and resolution in aberration-compensated
In hologrammetry it is desirable to reconstruct the real image rather than the virtual image as the latter must be viewed at a distance through the window of the holographic plate itself. When a scene is located in water but the image is replayed in air, it is necessary to correct for the refractive index difference by reconstructing the image with shorter wavelength illumination and changing the beam angle to satisfy the grating equation. However this means that the Bragg condition may no longer be satisfied during replay, reducing the diffraction efficiency and decreasing the signal-to-noise ratio of the reconstructed images. Changing the replay beam angle to satisfy better the Bragg condition makes the images brighter but also renders them unusable by increasing the optical aberrations. Our solution is to alter the Bragg properties of the hologram by altering the humidity of the surrounding atmosphere. This approach has been experimentally demonstrated for Agfa 8E56HD emulsions by measuring the brightness and resolution of a reconstructed real image from an off-axis hologram over a humidity range from 6 to 93 percent. The emulsion swelling and its effect on the Bragg properties of the hologram were modelled using the Flory-Huggins theory of polymer swelling
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The development and sea trials of a subsea holographic camera for large volume in-situ recording of marine organisms
We describe the development, construction and sea testing of an underwater holographic camera (HoloCam) for in situ recording of marine organisms and particles in large volumes of sea water. HoloCam comprises a laser, power supply,
holographic recording optics and plate holders, a water-tight housing and a support frame. Added to this are control electronics such that the entire camera is remotely operable and controllable from ship or dock-side. Uniquely the camera can simultaneously record both in-line and off-axis holograms using a pulsed frequency doubled Nd-YAG laser. In-line holography is capable of producing images of organisms with a resolution of better than 10 Pm (at concentrations up to a few thousand per cubic centimetre at the smallest sizes). Off-axis holograms of aquatic systems of up to 50,000 cm3 volume, have been recorded. Following initial laboratory testing, the holo-camera was evaluated in an observation tank and ultimately was tested in Loch Etive, Scotland. In-line and off-axis holograms were recorded to a depth of 100 m. We will present results on the test dives and evaluation of the camera performance
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HoloCam: A subsea holographic camera for recording marine organisms and particles
The HoloCam system is a major component of a multi-national multi-discipline project known as HoloMar (funded by the European Commission under the MAST III initiative). The project is concerned with the development of pulsed laser holography to analyse and monitor the populations of living organisms and inanimate particles within the world's oceans. We describe here the development, construction and evaluation of a prototype underwater camera, the purpose of which is to record marine organisms and particles, in-situ. Recording using holography provides several advantages over conventional sampling methods in that it allows non-intrusive, non-destructive, high-resolution imaging of large volumes (up to 10^5 cm^3) in three dimensions. The camera incorporates both in-line and off-axis holographic techniques, which allows particles from a few micrometres to tens of centimetres to be captured. In tandem with development of the HoloCam, a dedicated holographic replay system and an automated data extraction and image processing facility are being developed. These will allow, optimisation of the images recorded by the camera, identification of species and particle concentration plotting
Study protocol for a multicentre longitudinal mixed methods study to explore the Outcomes of ChildrEn and fAmilies in the first year after paediatric Intensive Care: the OCEANIC study.
INTRODUCTION: Annually in the UK, 20 000 children become very ill or injured and need specialist care within a paediatric intensive care unit (PICU). Most children survive. However, some children and their families may experience problems after they have left the PICU including physical, functional and/or emotional problems. It is unknown which children and families experience such problems, when these occur or what causes them. The aim of this mixed-method longitudinal cohort study is to understand the physical, functional, emotional and social impact of children surviving PICU (aged: 1 month-17 years), their parents and siblings, during the first year after a PICU admission. METHODS AND ANALYSIS: A quantitative study involving 300 child survivors of PICU; 300 parents; and 150-300 siblings will collect data (using self-completion questionnaires) at baseline, PICU discharge, 1, 3, 6 and 12 months post-PICU discharge. Questionnaires will comprise validated and reliable instruments. Demographic data, PICU admission and treatment data, health-related quality of life, functional status, strengths and difficulties behaviour and post-traumatic stress symptoms will be collected from the child. Parent and sibling data will be collected on the impact of paediatric health conditions on the family's functioning capabilities, levels of anxiety and social impact of the child's PICU admission. Data will be analysed using descriptive and inferential statistics. Concurrently, an embedded qualitative study involving semistructured interviews with 24 enrolled families at 3 months and 9 months post-PICU discharge will be undertaken. Framework analysis will be used to analyse the qualitative data. ETHICS AND DISSEMINATION: The study has received ethical approval from the National Health Services Research Ethics Committee (Ref: 19/WM/0290) and full governance clearance. This will be the first UK study to comprehensively investigate physical, functional, emotional and social consequences of PICU survival in the first-year postdischarge.Clinical Trials Registration Number: ISRCTN28072812 [Pre-results]
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