The sharp retroreflective peak that is commonly exhibited in the bidirectional reflectivity distribution function of diffuse
surfaces was investigated for several materials relevant to ladar applications. The accurate prediction of target cross-sections
requires target surface BRDF measurements in the vicinity of this peak. Measurements were made using the
beamsplitter-based scatterometer at the U.S. Army's Advanced Measurements Optical Range (AMOR) at Redstone
Arsenal, Alabama. Co-polarized and cross-polarized BRDF values at 532 nm and 1064 nm were obtained as the bistatic
angle was varied for several degrees about, and including, the monostatic point with a resolution of better than 2 mrad.
Measurements covered a wide range of incidence angles. Materials measured included polyurethane coated nylons
(PCNs), Spectralon, a silica phenolic, and various paints. For the co-polarized case, a retroreflective peak was found to
be nearly ubiquitous for high albedo materials, with relative heights as great as 1.7 times the region surrounding the
peak and half-widths between 0.11° and 1.3°. The shape of the observed peaks very closely matched coherent
backscattering theory, though the phenomena observed could not be positively attributed to coherent backscattering or
shadow hiding alone. Several data features were noted that may be of relevance to modelers of these phenomena,
including the fact that the widths of the peaks were approximately the same for 532 nm as for 1064 nm and an
observation that at large incidence angles, the width of the peak usually broadened in the in-plane bistatic direction.
The Advanced Measurements Optical Range (AMOR) began operations in 1978 with a mission to measure ladar target
signatures of ballistic missiles and to advance the understanding of object features useful for discrimination of reentry
vehicles from decoy objects. Ground breaking ladar technology developments and pioneering ladar target signature
studies were completed in the early years of AMOR operations. More recently, AMOR functions primarily as a user test
facility measuring ladar signatures of a diverse set of objects such as reentry vehicles and decoys, missile bodies, and
satellite materials as well as serving as a ladar sensor test-bed to recreate realistic missile defense engagement scenarios
to exercise and test missile seeker technologies. This paper gives a status report on current AMOR capabilities including
the optical system, target handling system, laser systems, and data measurement types. Plans for future facility
enhancements to provide improved service to ladar data users in the modeling and simulation field and to ladar system
developers with requirements for advanced test requirements are also reported.
Bidirectional reflectivity distribution function (BRDF) measurement results are reported for the monostatic case and for
small bistatic angles for several low-scatter diffuse materials illuminated at the 1.064 &mgr;m and 532 nm wavelengths.
Materials such as ESLI Vel-Black, Edmund Scientific flocked paper, and 2% Spectralon were measured. All materials
were measured using both co-polarized and cross-polarized transmit-receive configurations. The MRDF/BRDF
scatterometer at the Advanced Measurements Optical Range (AMOR) at Redstone Arsenal in Huntsville, Alabama was
used for these measurements and is described here; this beamsplitter-based system can make BRDF measurements with
incidence angles from 0 to 80° and with in-plane and out-of-plane bistatic angles from + 3.5° through -3.5°, including
the monostatic point.
Recent developments in far ultraviolet technology have advanced the state of the art in FUV instrumentation notably in the area of space flight experiments. In this paper, we report on a significant advance in far ultraviolet calibration technology which makes it possible to take full advantage of the improved instrumentation. A new far ultraviolet diffusive source has been developed which is capable of calibrating every pixel of an 8 degree field of view imaging camera to better than 10% absolute accuracy throughout the far ultraviolet wavelength region.
Pure aluminum films have the highest reflectance among all metals in the far-ultraviolet (FUV) wavelength range extending from 120-230 nm. Unfortunately, aluminum is a highly reactive material and is only free of oxidation when deposited in an ultra-high vacuum chamber (p < 10-10 torr). Aluminum films prepared in high-vacuum (conventional) chambers (p approximately equals 10-6 torr) always oxidize regardless of deposition technique, deposition rate, and substrate temperature. Therefore, if a conventional chamber is sued for fabrication of aluminum multilayer devices based on theoretical designs, each aluminum film in the theoretical model should be considered as at least a two-layer structure of aluminum and aluminum oxide film.s Spectral performance optimization of an aluminum mirror is possible if the thickness and optical constant of the oxidized part of the aluminum film are known. Experimental results where XPS depth profiling was used to determine oxide thicknesses are reported.
In certain cases a space-borne optical instrument with a dielectric window requires a transparent conductive coating deposited on the window to remove the electrostatic charge collected due to the bombardment of ionized particles. Semiconductor and metal films are studied for use as transparent conductive coatings for the front window of far ultraviolet camera. Cr is found to be the best coating material. The theoretical search for the semiconductor and metal coating materials and experimental results for ITO and Cr films are reported.
New advances in VUV thin film filter technology have been made using filter designs with multilayers of materials such as Al2O3, BaF2, CaF2, HfO2, LaF3, MgF2, and SiO2. Our immediate application for these filters will be in an imaging system to be flown on a satellite where a 2 X 9 RE orbit will expose the instrument to approximately 275 krads of radiation. In view of the fact that no previous studies have been made on potential radiation damage of these materials on the thin film format, we report on such an assessment here.