Abstract: An electron - optical - photographic system utilizes the novel qualities of an optical density wedge filter for use with a CRT oscillograph having an optical density along the taper of the wedge equal to the square root of the probability density distribution of a random variable, e.g., "white noise" displayed on one side of the X-axis of the oscillograph. The visual portrayal of the amplitude-time presentation of noise (as on a cathode ray tube) is modified by the filter to produce a uniform gray pattern. Addition of a sinusoidal signal to the noise then results in a clear recognition of the signal even when it is well below the noise level.

Abstract: An apparatus and method for detecting deviations from a normal ocean wave pattern which may be caused by interference with artificially created wave patterns, such as from an underwater moving vehicle. A camera mounted in an aircraft has its optic axis vertically disposed and is provided in its image plane with an opaque plate having an arcuate aperture slit concentric with the vertical optic axis and angularly displaced an amount where the ratio of change in reflectance to the change of incidence angle for a light reflected from a smooth surface is a maximum.