Ladies and Gentlemen: On behalf of Captain Holmquist, Commander of the Naval Missile Center, it is my pleasure to welcome you to the Underwater Photo-Optics seminar. It is a privilege for the Missile Center to co-sponsor this meeting jointly with the Point Mugu Chapter of the Society of Photo-Optical Instrumentation Engineers. Captain Holmquist regrets that he cannot be here to welcome you and to learn from your discussions, but he was not able to alter his travel to the Orient.

A brief review of the optical nature of ocean water provides the basis for a discussion of the distribution of flux diverging from underwater local light sources, the propagation of highly collimated beams of light produced by incoherent sources and by lasers. Image transmission by ocean water from underwater objects irradiated by these light sources is also discussed in terms of the observable optical properties of ocean water with the intent of providing a basis for the engineering of underwater viewing devices, and photographic or television systems.

In order to find out if there are major differences in the behavior of laser light and ordinary incoherent light in an underwater environment, four experiments with an RCA pulsed blue-green laser were conducted by U. S. NOTS personnel at the Lake Winnipesaukee Diamond Island Field Station of the Scripps Institution of Oceanography Visibility Laboratory during the summer of 1965. The experiments included:

A study involving polarization phenonema conducted at Lake Winni-pesaukee, New Hampshire, during the summer of 1965 caused one of the authors to think of the possible application of polarization techniques to underwater visibility range and contrast improvement. As a result, a series of tests was conducted at the U. S. Naval Ordnance Test Station (NOTS) Pasadena Annex Morris Dam facility in April 1966.

Nephelometers for making in situ measurements of light scattering at all depths from the surface to the bottom of the ocean are described. Preliminary results in the Atlantic, Pacific, and Arctic oceans and in the Bering and Caribbean seas are summarized.

Modulation transfer function measurements were carried out in relatively clear fresh water using separated narrow-beam transmitter and receiver and diffuse flectance bar and edge targets. The source was a mercury arc lamp. The detector was a multiplier phototube. The results show useful spatial frequency responses up to angular frequencies of 1000 to 2000 cycles per radian at target ranges up to 4 water attenuation lengths. The measured attenuation length for collimated light was 15 feet. With the narrow-beam apparatus, back-scatter was small and was reduced proportionally to the separation between the transmitter and the receiver. The relative backscatter was also reduced as the transmitter beam width was reduced. It was shown that from an examination of the signal response when a target edge was scanned, it was possible to deduce the relative amounts of unscattered and forward scattered light.

The Naval Ordnance Test Station, Pasadena Annex, in conjunction with the Navy's Deep Submergence Systems Project, has initiated a program designed to improve underwater photo-optical systems. Our program objectives were based on the fact that the scattering characteristics of water form the major barrier limiting visibility. One objective is centered around improving overall system efficiency while the other is concerned with increasing the range of visibility. In other words, the first objective admits a limited visibility condition, but assumes that adequate visibility may be maintained at much lower power levels. The second objective is directly concerned with means to reduce the detrimental effects of scattered light. We've labeled these two main divisions of our effort "State of the Art Optimization" and "Extended Range Feasibility. "

Characteristics of an active laser scanning and imaging system are considered in terms of an underwater viewing application. In this system, output of a blue-green iaser is scanned over the field of view by 'in acoustic deflection technique. Diffuse reflected light from the target is detected with a photodetector and the signal generated is used to intensity modulate a synchronized scanned CRT display. Either a non-scanning photodetector such as a photomultiplier or a synchronized scanning detector employing an image dissector can be used. A system analysis is presented which considers the effects of back scatter, attenuation, and system parameters on viewing range as a function of laser power. The analysis considers the improved performance to be obtained by the rejection of back scatter using a synchronized detector. Experimental test tank results were obtained with a bread-board system incorporating a nonscanning detector for a variety of conditions of water clarity and range. Auxiliary experiment's were conducted which illustrate the effectiveness of back-scatter rejection techniques on range enhancement.

Both scattering and attenuation effects severely limit the distance over which under-water viewing is practicable. Within limits, the attenuation effects can be overcome by increasing light source intensity and receiver sensitivity. Scattering effects cannot be treated in such a direct manner. The following is a discussion of two systems which show promise of overcoming the effects of the backscattered illumination.

Underwater optical range-gating, designed to extend the maximum range of underwater photography, has been demonstrated in a series of experiments conducted at the NOTS Morris Dam Test Range. With black tape on Scotchlite being used as a target. comparison photographs of gated and non-gated exposures showed promising improvement in the clarity of the gated pictures. This was attributable to the elimination of most of the backscattered light. A description of the apparatus and a sample of the data obtained at various target distances are presented and discussed.

A pulsed laser transmitter and a range gated imaging receiver will be used to obtain a substantial increase in the operating range of underwater television systems. As discussed in this paper systems possessing this configuration achieve this enhancement of performance by minimizing the ratio of received backscatter to signal energy. Ultimate use of this system is to perform underwater detection and classification. Based on theoretical analyses the overall system noise figure (NF) and modulation transfer function (MTF) are presented. These analyses, together with detailed system parameters, are used to evaluate the anticipated range-resolution performance capabilities of the system. Functional and physical descriptions of the system are included.

It has been suggested that range-gating technIclues may he used to extend the range of mi(rwater laser surveillance systems. This is a very real possibility when it is considered that the intensity of a plane wave propagating through water can be expressed as

A study of operations in the THRESHER area indicated that an angular coverage of about 120 degrees is required for an opti-mum photographic search of the ocean floor. While this coverage has been obtained using a three-camera array, the time and water needed to process and view the film make it desirable to develop a single camera capable of covering the required angle. In order to obtain this sort of coverage with a single lens, it is necessary to replace the usual plane glass window with a hemispherical shell. The design criterion for mating a wide angle lens to a hemisphere were determined and a model 204 EG&G camera was modified to provide a 114-degree angular coverage. This camera was used successfully in search operations off Palomares, Spain. In the weeks that followed the loss of the submarine, THRESHER, it became apparent that though man had made considerable progress in his studies of the deep ocean, he still lacked the ability to search even a relatively small area of the ocean floor. Optic, acoustic, magnetic, and other sensors, which could be used at great depths, were in existence but it was still necessary to learn how to use them as search tools. In the early days of the search, there was a feeling that the short ranges inherent in underwater optical devices made them ineffective tools for ocean floor search. Later came the realization, that while other longer-ranged sensors were useful in locating bottom anomalies, only optical techniques had sufficient resolution to identify theseanomalies. With this realization, came the necessity of making the best use of the optical range available. At the time of the loss of the THRESHER, multiple exposure camera systems, useable at great depths, were available from a number of commercial sources. These systems had been developed to aid marine scientists in their study of the deep ocean. They were generally used either singly or as stereo pairs, a practice which continued throughout most of the first year of the THRESHER search. On the final trip to the THRESHER area in 1963, U.S. Naval Research Laboratory personnel used two cameras, one tilted to each side in order to obtain wider coverage.

As is well known, no break-through has yet been achieved to improve underwater visibility to the point where very large areas could be seen or photographed in one shot, as common in aerial or space photography. An effective solution to this problem is simply to scan the bottom in parallel adjacent strips, using a specially designed vehicle and high capacity camera system. It will be also shown why precision mosaic photogrammetry is now made possible by the use of new water refraction correcting lenses. The necessity of particle back-scatter control by proper light placement and possible nanosecond light pulses and shutters will be shown as an essential factor in improving close-range visibility specially in turbid water. It will be shown why the camera-carrying vehicle must be designed especially for maximum attitude stability to achieve a straight track, constant altitude and constant speed controlled by a special instrument panel and control subsystems. Typical applications are in the fields of undersea cable, pipeline and fixed installation surveys, stereophotogrammetric mapping of the bottom, photography of large submarines and marine life, archeological surveys, landing beach and approach surveys. A recommendation will be made for replacing the old Secchi disk and transmissometer instruments by a new black target for visibility measurement, 1, THE SCANNING PRINCIPLE: Exactly as a single spot of modulated intensity, light travelling along parallel lines upon a phosphor screen will produce a meaningful picture on the total area of the screen, a large number of small area photographs taken at regular adjacent intervals along parallel lines on the bottom of the sea will yield a precise and detailed photographic mosaic when the individual pictures are assembled together along a proportionally scaled-down pattern. However, certain rules must be followed if the cost in time and money is to be held within reasonable limits. First, it is not acceptable to snap thousands of uncontrolled photos along random curved tracks, the result of using manned or unmanned underwater vehicles or swimmers which have no dynamic stability and travel along random sinusoids. Second, it is not possible to join together as a mosaic, especially for stereophotogrammetric restitution, the strongly pincushion-distorted pictures delivered by the old non-corrected lens with flat glass portholes.

It is indeed unfortunate that photography cannot be used over large areas of the sea-bottom as it is so effectively used over land areas. Aerial photography for example has revolutionized map making, surveying, and exploration of all types over the ground since a camera in an airplane can record large areas from great heights, except when the weather is bad.

Our endeavors to unveil new systems to probe and penetrate the resourceful potential of the sea are being rapidly developed. The users of the photo mechanical process have made many attempts to document these new assignments; the majority are inadequate primarily from the lack of positive information concerned with the cause and effect on light sensitive emulsions.

In the field of psychology, very few studies have been concerned with the underwater human photo-optical system. The present paper is based upon a review of approximately 300 publications related to the psychological and behavioral analysis of the photo-optical systems of marine and land animals. Some of these publications include discussions of human vision under water and on land. Information obtained from this review can be useful in the planning of needed research programs and in the design of future underwater instrumentation. The present paper concerns the capabilities and limitations in hue and intensity discriminations of various marine and land animals, including man. Emphasis is on the methodological problems in experimental measurement. With respect to animals, instrumental, physiological, and photo-chemical methods are discussed; for humans, psychophysical methods (i.e., methods of limits, of adjustments, and of constant stimuli) are discussed. The major finding of the present review is that marine animals use color and motion stimuli as cues almost exclusively in contrast to land animals who use primarily distance, shape,and size stimuli as cues, although marine and land animals have structurally similar eyes. This dif ference is discussed in relation to a comparison of the perceptual capabilities and limitations of humans in underwater and land situations. Psychological research in this area may help in the development of reliable underwater illumination methods and the design of underwater instrumentation.

Over the past five years, numerous experimental developmental programs have been conducted for the purpose of extending the range of underwater visibility using video techniques. Although the primary objective of these studies was to extend the vision range beyond that of the unaided human eye, it was necessary for the conduct of this program to develop instrumentation and prediction techniques for determining visibility in a given water environment. This paper describes the theoretical back-ground and experimental confirmation of this instrumentation technique and describes the instrument itself in some detail.

A description is given of the various tech-niques used by the Naval Ordnance Test Station, Pasadena, to obtain underwater photographs during deep ocean operations. The methods used, and the specialized underwater photographic instrumentation used on ships, vehicles, and test platforms are also discussed. The projects selected for this discussion include: 1. Project Pop-Up 2. SUBROC Static Firing Tests 3. The YFU 53 Support Vessel 4. The Underwater Tripod System 5. The Cable-controlled Underwater Research Vehicle

The severe attenuation and scattering properties of water necessitate the use of artificial illumination in many underwater viewing and photographic situations. This has been of increasing importance in recent years as men descend deeper into the oceans where natural light is nonexistent. These same properties also impose severe limitations on the use of artificial light in water. In addition to these optical properties, constraints are also imposed by the physical properties of water, particularely pressure. There are, however, elements of control that can be exercised in the design and application of underwater light sources, which will permit some degree of optimization. A few principlesof under-water illumination have been evolved which can be applied to optimize artificial illumination for a variety of applications.

Flat disk acrylic windows and conical acrylic windows of 300, 60°, 90°, 120°; and 150° included angles have been tested to destruction under short-term hydrostatic loading. Both the displacements during pressurization and the critical failure pressures have been recorded. The critical pressures of windows used as test specimens in this study have been presented in non-dimensional form and can be used to predict the critical pressures of windows with larger diameters.

A method of producing stereoscopic pictures is described. A digital computer is used to project a line (defined by a series of points whose X, Y and Z coordinates are given) onto a plane from two different eye positions, corresponding to the right and left eyes. By means of an off-line XY plotter which can use either red or green ink, a stereoscopic representation may be obtained of any number of lines, by using suitable filters in front of each eye. This method has been found useful in studying detailed bathymetric and magnetic data from the deep ocean. If the data are sparse, it may be difficult to draw contours from the original data, and this method facilitates the interpretation by making more clear the presence of linear features when the eye position is correctly chosen. "One picture is worth a thousand numbers"