The transmission of optical images in water is controlled by a large number of parameters which determine the photon level, contrast, and resolution of the image. The basic parameters describing the optical properties of water are well known and include the volume attenuation, scattering and absorption coefficients as well as the volume scattering function which describes the angular distribution of the scattered light. Conventional instrumentation for measuring these parameters is not entirely adequate for studying image transmission and communications over long water paths. he principal difficulty is associated with the very strong narrow angle scattering of light produced by water. Scattering at angles as small as a hundredth of a degree or less can be important for image propagation and conventional instrumentation does not respond appropriately in this narrow angle region. In addition, measurement accuracy must be exceptionally high. This is particularly true for propagation over long paths since many of the relations describing light transmission in water are exponential in nature. Small errors in the propagation constants become very significant when operation is attempted over many attenuation lengths. For example, a 0.01m-1 measurement error in the volume attenuation coefficient leads to an error of a factor of nearly 3 in transmission loss over a 100 meter path.
There may be some doubt as to what the title Coherent Optics refers to. To me it means that part of optics that depends upon the coherence of the light for its description. Classically, of course, long before the word partially coherent light came into use, coherent systems were known and formed the basis for that portion of the study of light called Physical Optics. Hence interfer-ence and diffraction phenomena are well recognized; interferometry has developed into a discipline all its own with a wide ariety of types of interferometers that confound the neophyte. Many of the various interferometers are named which provides a listing that looks like a scientific "who's - who" --Michelson, Mach-Zehnder, Twyman-Green, Fizeau, Fabry-Perot, Rayleigh, Lummer-Gehrcke, Jamin, Sirks-Pringsheim ........, interferometers. Again we must pity (with a certain amount of smug superiority) the uninitiated who doesn't realize the difference between Fabry-Perot fringes and Fizeau fringes. The literature contains many works on interferometry, the intent reader may well refer to Steel (1967), Tolansky (1955), Candler (1951).
Holographic motion pictures provide a means for recording and observing transient, dynamic, small-scale events occurring at unpredictable times and locations in a given volume of space. Using an argon ion laser to generate repetitive pulses of 50 μs duration at a wavelength of 514.5 nm (5145 Å), holographic movies of living marine plankton organisms were produced by recording a series of in-line holograms at 70 frames/s on 35 mm film. The reconstructed holographic images may be viewed with a standard microscope, photographed with a still camera, or copied with a conventional movie camera for subsequent projection. Image resolution of 10 μm was obtained.
By "optical turbulence" is meant small inhomogeneities in the index of refraction of seawater, their origins, and the effects they have on underwater optical systems. For most conventional underwater photographic and TV imaging systems as normally used, these effects are negligible most of the time-only under exceptional circumstances do they make an appreciable difference. However, they become a more significant factor as more sophisticated imaging systems are constructed that must function over longer ranges with high resolution.
The sea change experienced in a large under-water acoustic energy source, placed on the ocean floor at a 300-fathom depth, is discussed as it is examined from the surface three years later by reactivation of an installed closed-circuit video link. The author recapitulates an earlier paper on this subject that was presented at the SPIE Seminar of February 1968 (published in the Seminar Proceedings, vol. 12, pp. 73-80), updates the background of the initial ocean emplacement, and discusses the sea changes in the submerged structure and instrumentation. He illustrates the various areas of interest by videotape recordings. Many questions have arisen concerning the effects of long-term deep submergence on various parts of the video' apparatus including the camera, camera viewport, the camera pan and tilt unit, the lighting unit, and the long cable. This paper discusses some of these questions.
This paper concerns a simple, underwater camera which in use is operated flooded with water. All of its parts including lens, shutter, and photographic film are exposed to and operate in direct contact with the water in which the camera is immersed. As the paper progresses, I'll first describe the camera, then show some underwater photographs made with it, and finally discuss some problems we had at the beginning of its use and tell how we overcame the problems.
The efficient performance of any task in the hostile underwater environment requires that due care be exercised in the design of the man-machine interface to take full advantage of the enormous potential available in the human mechanism. In particular, it was believed that significant benefits could be realized if the human brain was introduced as an integrally functioning element of an under-water remote controlled vehicle system.
Spherical shell sector windows have been found to have a higher structural efficiency under hydrostatic loading than conical frustums of same thickness to diameter ratio. Although acrylic plastic windows of spherical shell sector shape have been found to be ideal for panoramic windows in continental shelf depths, glass or glass ceramic will have to be utilized for abyssal depths. Some exploratory tests with glass windows of spherical shell sector shape have shown considerable promise for such application.
Historical Sketch. Although the underwater illumination flare is a comparatively recent development in the field of pyrotechnics, the use of pyrotechnic devices such as fireworks and rockets has been known for a long time. Their origin is believed to have been in Asia, possibly not too long after the time of Christ. It has been generally accepted that pyrotechnic mixtures were well known in China and Asia centuries before the Arabs and Greeks brought this knowledge to Europe, and fireworks and rockets are known to have been used as instruments of war by the Arabs as early as the Seventh Century.
For some time, GAF Corporation has produced a D1000 Blue Insensitive Color Film Type 2575 for use in aerial photography over water, where the recording of blue light is undesirable and unnecessary. In fact, it has been the practice in aerial color photography to filter out the blue light reaching the film, even when recording with ordinary tri-pack color films, by means of a yellow filter over the camera lens. In this case, the resulting pictures have a yellow appear-ance due to the formation of the yellow dye in the unexposed blue-sensi-tive layer of the reversal processed film; and the filter factor required in making the exposures seriously reduces the effective speed of the film in a situation where maximum speed may be needed for penetration of water depths. With the blue-insensitive film, no filter is required, and in addition to this, due to the fact that no blue-sensitive layer is present to absorb part of the light reaching the green and red sensitive layers, the effective speed of the film is in-creased by about one stop over that of' the conventional GAF 500 Color Film. (Ref. 1 and 2)
For the past 20 years, Eastman Kodak Company has displayed in New York's Grand Central Terminal the largest color transparency in the world. The Colorama, as it is called, measures 18 ft. high by 60 ft. long and is changed every three weeks.
There has been for the last several years an intermittent dialogue going on between people in optics and those in acoustics. It has centered largely on the possible use of optical technology in underwater sound systems as part of the signal processing and display equipment. In its earlier stages it had to do with making Fourier transforms or doing matched filtering and more recently has contained heavy emphasis on analogies to conventional optical holography.
DURING THE PAST century, the photogram-metric process of recording, reading, and measuring the photograph has developed into a highly sophisticated, elaborate, and efficient procedure. For reasons involving the evolutionary capabilities and requirements of man, the photogrammetric process has been predominately specialized for the acquisition of photographic recordings in an object space of air. Man's probe into outer and inner space has had a significant influence on the recording phase of the photogrammetric process. It is the purpose of this presentation to discuss the physical nature of an object space of water on the photogram metric process and, in particular, on the recording phase.
Although stereo photogrammetry has long been a valuable tool in aerial photography, (1) the application of this technique to underwater situations has not yet come into widespread use. (2) With the present availability of underwater cameras and deep submergence vehicles,, this situation will surely change. For example, the Westinghouse DEEPSTARS 2,000, 4,000, and 20,000 permit mounting of underwater lights and cameras with rigid stereo (i.e. camera to camera) baselines in excess of 10 ft.
When THRESHER sank on April 10, 1963 the NRL group, which joined the search, had never taken a single ocean floor photograph. Seven years and ten deep ocean searches later this same group has taken more bottom photographs than all others added together. During this period tremendous advances have been made. This paper reviews these advances and makes some projections for the future.
Theoretical and model studies have indicated that placing the light source 10 to 30 ft behind a deep sea camera results in a decrease in backscatter and an increase in useable range. Full scale tests of this technique have been conducted using six light sources with energy capacities of 8,700 Joules each. These tests demonstrate a significant increase in the practical range of underwater cameras. This technique coupled with a large format camera provides a more efficient means of searching the deep ocean floor.
Anyone who has worked underwater can give many reasons for taking pichres. The photograph provides the user with a high resolution, permanent record for later study and evaluation. The photographic camera is an essential tool for anyone working underwater who needs to gather and record high resolution visual information.