Search

Omnidirectional underwater voice communication by means of scattered light at ranges of 1,000 yards or more in clear ocean water appears to be possible with commercially available lamps and phototubes. Longer ranges, up to 1,750 yards, are possible with the same components if they are used in a 20 degree directional system. Still longer ranges are possible with more intense light sources. Technical evidence is presented in support of these possibilities and engineering equations are provided for the design of such optical communication systems. The equations show that scattered light penetrates ocean water much further than does non-scattered light, primarily because the attenuation coefficient for scattered light is (typically) about one-third of the attenuation coefficient for non-scattered light. Experimental data on the long-range propagation of scattered light from underwater sources is interpreted and extrapolated for engineering purposes. Data concerning the long-range transmission of polarized scattered light by natural waters is presented, and the role of polarization as a means for establishing multiple voice communication channels is discussed. (Author), Includes ''Light in the Sea'', Reprinted from Journal of the Optical Society of America, Vol. 53, no. 2, 214-233, February, 1963.

Vertical ground-to-space beam transmittance, path radiance, and contrast transmittance for green light was measured from a ground station on ten occasions during August and September 1962. On each occasion a Reconnaissance Laboratory photographic airplane photographed a pattern of white, grey, and black targets on the ground adjacent to the Visibility Laboratory equipment. The targets were radiometrically monitored by Cornell AUTICAL Laboratory in such a manner that target-to-aircraft beam transmittance, path radiance, and contrast transmittance could be obtained from the aerial photographs. The in tended purpose of this joint experiment is a comparison of the target-to-space data predicted by the ground-based instruments with the ground to-aircraft photographic data. The ground-based data are presented in this report, but comparison with the aerial data must await the completion of data reduction from the aerial photographs by Cornell Aeronautical Laboratory.

An attempt was made to demonstrate the utility of analytic approximations in visual search analyses. This has been accomplished by choosing a simple example in which apparent contrast did not change with observer altitude and vertical downward line of sight was assumed. The use of analytic approximations are in no way restricted to these simple cases. With analytic expressions for visual thresholds, equations can be derived which describe area search rates for any combination of altitude, optical aid magnification, target area, and apparent target contrast. Equations can also be derived which describe the optimum optical aid magnification for a given altitude, target area, and apparent contrast. The analytic determination of optimum magnification makes it possible to define maximum area search rate attainable for a specified target area and apparent contrast. (Author)

The surface of the sea provides the background against which all floating objects are seen by observers aloft. The luminance of this background depends upon the lighting and upon the sea-state. Measurements of the apparent luminance of the sea from aircraft are possible but expensive. A sea surface simulator has been devised which enables the luminance distribution of the sea surface to be measured under any outdoor lighting conditions without the presence of an ocean and without an airborne photometer. (Author), Also available as PB-154 019.

The Fourier transform relationship between the front and rear focal planes of a simple lens has been used extensively in recent years. One important application has been that of attempting to restore degraded imagery by Fourier transforming the degraded imagery by Fourier transforming the degraded image, performing filtering in the Fourier plane, and accomplishing a second Fourier transform to obtain the restored image. These techniques have direct application to the problem of restoring images degraded by atmospheric turbulence and apply equally well to both temporally variant and temporally invariant degradation. The present report shows that the Fourier transform property is an approximation valid only for low spatial frequencies. At high spatial frequencies the Fourier transform achieved by a simple lens has serious phase errors. These phase errors will place severe limitations upon image restoration operations involving imagery with high spatial frequency content. (Author)

The contrast reducing properties of any path of sight inclined downward through the atmosphere can be specified by a single dimensionless number analogous to a reflectance and called the directional reflectance of the path of sight R*. The contrast transmittance of the path depends solely upon the ratio of the directional path reflectance to the inherent directional reflectance of the background. Previously published optical atmospheric data derived from in-flight measurements have been used to produce tables of R* for two clear-weather conditions. A simple nomograph and numerical examples are included.

The irradiance pattern was measured for the propagation of a collimated beam of light underwater. A neodymium-doubled green laser was transmitted horizontally at a six foot depth in Lake Winnipesaukee, N. H. The irradiance was measured at distances from 0 to 100 feet and for off-axis angles from 0 to 58 degrees. The water had an attenuation length of 4.54 ft/ln and an absorption coefficient of 0.0446 ln/ft. The ratio of attenuation coefficient to absorption coefficient was 4.94. The fractional power contained within a cone of various angles was computed. At 20 attenuation lengths only 10% of the total power is contained within a cone of 4 degrees whereas at 4 attenuation lengths this same cone contains 50% of the power. (Author)

A number of investigators have postulated several possible mechanisms to account for the spatial summation which is exhibited by the human visual system. This report describes the results of an investigation to determine the extent to which retinal image quality together with the probability summation due to simultaneous stimulation of many receptors can account for the experimental evidence. It is shown that these two mechanisms are sufficient to produce the degree of spatial summation exhibited by the visual system and that the resulting visual performance is compatible with quantum limitations. (Author)

The design features of a radiance photometer capable of measuring the directional distribution of natural light underwater are described. (Author)

The ability of astronauts or satellite-borne cameras to see land masses, coast lines, or lesser objects on the surface of the earth depends upon the apparent contrast (C sub r) of the object as viewed from orbital altitude. This report describes a method believed to be capable of providing input data for the apparent contrast equation on the basis of optical measurements made from ground stations., Included in the report is Image Transmission by the Troposphere I, pub. in the Jnl. of the Optical Society of America 47:499-506, Jun 57.

A variable-range viewer for use with binocular and terrestrial telescopes was devised to enable small test charts to be vi fed in the laboratory under well-controlled, realistically simulated outdoor conditions. Object distances from 2 to 20 miles are covered by 4eans of a variable magnification optical system. Contrast attenuation by the atmosphere is introduced automaticalloy as the simulated range is changed. Provision was made for presetting any desired meteorological range from 2 to 100 miles. (Author)