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.
A novel integrated optic approach to the design and manufacture of an optical subsystems for a Range-Doppler imaging lidar is described and demonstrated. The approach uses hollow waveguides to guide light between system components which are integrated into a common substrate. The design, manufacture and operation of an eleven element subsystem which is compact, rugged and provides coherent mixing efficiencies in excess of 80% of the theoretical maximum, are discussed. The results of trials of the subsystem at the Army Missile Optical Range, involving measurement of Range-Doppler images of representative targets are described.
A coherent pulse-burst 1.06 (mu) ladar transmitter is described. The output consists of a 1.6 J, 800 microsecond(s) burst of 550 ps pulses occurring at a 50 MHz repetition rate. The burst repetition rate is 10 Hz. The optical frequency stability before coherent processing at the receiver is +/- 100 kHz. The transmitter consists of a CW-pumped mode-locked Nd:YAG oscillator followed by a pulsed double-pass amplifier, and is used as part of a calibrated range-Doppler imaging target signature measurement system