Underwater Optics Research Articles

Ocean Optics VI

Although the world's oceans, seas and freshwater lakes play a dominant role in the planet's ecosystem, they are possibly the least understood of our natural habitats. The challenges facing scientists and engineers in the study of this environment are immense and unique. Not only is there a need for the creation of new techniques and for advances in classical techniques, but the associated instruments must withstand the rigours of the sea. High on the list of techniques which can be exploited are those based on optics and light. Many state-of-the-art submersible instruments employ some fundamental optical technique as the method of measurement, while optical communications and fibre systems are also major aspects of contact and control of subsea instruments. Of course, the nature, behaviour and propagation of light through water are fundamental characteristics of the oceans themselves. They are also crucial to the understanding of the marine habitat, and the preservation and utilization of this immense resource. We need to know how light propagates through water, and what affects transmission and absorption, and so on. The use of optical instrumentation in the field is increasing, and is replacing more traditional, slower and destructive techniques. Optical techniques provide rapid, precise, non-destructive, in-situ sensing and high quality measurements with reduced possibility of artefacts. A series of conferences on the general theme of underwater optics have been held under the auspices of the Institute of Physics. The most recent of these, Ocean Optics VI, was held in London on 9 October 2001. Selected papers from that meeting, representing the wide range of work currently being undertaken in underwater optics, are featured in this issue of Journal of Optics A: Pure and Applied Optics. The papers range from a demonstration of the use of optics in the measurement of the flocculation of suspended sediments to such novel techniques as holography for the in-situ measurement of plankton, and from the measurement of fundamental physical characteristics such as absorption, irradiance and sea-surface reflectance to the measurement of the chemical constituents of natural seawater. There is also a paper reflecting the large amount of work taking place in satellite image analysis. All in all, the papers included here, while not all-embracing, do demonstrate the range and depth of current research taking place in the expanding field of underwater optics. John Watson University of Aberdeen, UK Derek Pilgrim University of Plymouth, UK Guest Editors

Underwater Optics III<BR> Report on an Institute of Physics Optical Group meeting held 17–18 March 1998, Brighton Centre, Brighton, UK

Underwater Optics III<BR> Report on an Institute of Physics Optical Group meeting held 17–18 March 1998, Brighton Centre, Brighton, UK

Terrestrial optics in an aquatic eye: The sandlance, Limnichthytes fasciatus (Creediidae, Teleostei)

The sandlance, Limnichthyes fasciatus (Creediidae, Teleostei), behaves like a marine chameleon, with independent movements of its turret-like eyes, highly-effective camouflage and rapid strikes for isolated, mobile prey at close quarters. The optical system has a fixed circular pupil, a deep pit fovea and a flattened lens unlike any other teleost lens so far described. The convex, laminated structure of the cornea is also unparalleled in a teleost which suggests that the cornea may play a refractive role that might compensate for the reduced power of the flattened lens. This suggestion has been supported in the present investigation by four independent sets of observations:- i. Purkinje images formed underwater by the cornea; ii. Measurements of the magnification of intra-corneal iridophores viewed through the corneal lenticle; iii. Measurements of the magnification produced by the dissected corneal lenticle and lens when viewed over a grating; iv. Ray tracing experiments comparing the degree of refraction produced by the lens and by the corneal lenticle. All experimental observations confirm that the cornea of the sandlance has a significant refractive role, with a power of approximately 200 D compared with a power of 550 D for the lens. This is the first report of a significant refractive role played by the cornea in a teleost. The optical system of lens plus cornea, in combination with a deep pit fovea, may be more suitable for the detection and visual localisation of small, moving, underwater prey than the conventional wide-field spherical lens system of other teleosts. The evolutionary convergence of this marine optical system and lifestyle with those of the chameleon is remarkable, given the constraints imposed by underwater optics.

海中における物体の色度に関する研究

The shape and color of an object in the water can look considerably differed than it would on land. In fact, the objects all-over color will appear bluish Conceming underwater optics, there are many researches in the field of the physics. How ever, research information concerning the recognition of an perception of color in the water is very limited. In this study, experiment concerning chromaticity measurement were carried out with varying the water depth and distance from the color board of white, red, green and blue Measurement results were expressed on the CIE 1931 Chromaticity Diagram. Chromaticity characteristics of different colored objects in the water were then discussed.

Design Considerations for Laser Based Underwater Optical Systems

Certain typical design requirements of laser based underwater receiver optical systems are dealt with. Some of their special features which are to be considered while designing these systems are highlighted. Optical schemes, which can be used as underwater receiver optics, are also explained.

The Signal/Noise Ratio Concept in Underwater Optics

Underwater ranging capabilities of light are well known to be several orders of magnitude below those of sound waves. This limitation rules out its use for locating targets. However, the desire on the part of the observer to map out a visible two-dimensional display has spurred the applications of light sources to the problem of target recognition.

Laser applications to underwater optics

Laser applications to underwater optics

The evolution of the instrumental technique in underwater optics

Thanks to the use of the photovoltaic cell significant pioneer work in underwater optics was made in the 1930's. Among the principal instruments designed at that time, the beam transmittance meter and the scatterance meter were introduced in oceanographic studies by Hans Pettersson. The development of a technique with photomultiplier tubes provided a new impetus in optical research particularly in the study of scattering problems. A distinct advantage with photomultiplier tubes is that their high sensitivity makes possible the use of interference filters by which almost monochromatic measurements are obtained and the treacherous “band width error” occurring with broad filters is avoided.An equipment of in situ instruments fit for routine observations is described, namely an irradiance meter, a beam transmittance meter and a scatterance meter which measure the spectral energy distribution, the total attenuation coefficient and the total scattering coefficient respectively. The meters are provided with simple depth sensing units and records are obtained with an x−y recorder.It is emphasized that the optical parameters contribute greatly to the description and characterization of water masses.