Retroreflection measurements: a review.

The five papers comprising the feature of retroreflection measurement in the 15 April 1980 issue of Applied Optics are introduced and briefly reviewed.

Chromaticity measurements of retroreflective material under nighttime geometry.

Chromaticity measurements of three different types of retroreflective material in six common colors are presented. A computer controlled spectroradiometric retroreflectometer system with sample goniometer was employed for the measurements. Geometry-caused chromaticity changes were as great as 0.05 in x and y. Color differences in both CIELUV and CIELAB computed from a base geometry of alpha = 0.2 and beta = -4 degrees attained values as high as 50 units for some materials. The total color extent of each material is plotted from a 4 x 4 measurement matrix of angles. plotted on the CIE 1931 diagram.

Uniform variable light sources for instrument calibration.

This paper describes light sources that were developed for use in calibrating cameras for space exploration. The design produces a nearly uniform luminance field whose correlated color temperature ranges from 4000 K to 5000 K in the visible. Luminance of the source may be continuously varied by as much as 500:1 without affecting the uniformity of the field. The sources, consisting basically of two integrating cavities with an iris diaphragm interposed, use xenon light. Luminances as high as 25,000 cd m(-2) are possible. Such sources are used for light-transfer calibration, as well as spectral response of camera systems. After a brief theoretical treatment, the design variations are discussed. Measurement data on these sources indicates that the angular luminance distribution approximates a uniform diffuser within a 50-deg cone.

Surveyor v: television pictures.

Surveyor V landed in a small crater, 8.5 meters wide and 12.5 meters long, which was probably formed by drainage of surficial fragmental debris into a subsurface fissure. The lunar surface debris layer is exposed in the walls of this crater. At depths below about 10 centimeters, the debris appears to be composed mainly of shock-compressed aggregates, ranging from a few millimeters up to 3 centimeters in diameter, set in a matrix of less-coherent finer particles. Rocky chips and fragments larger than a millimeter are dispersed as a subordinate constituent of the debris.