Radiance measurements conducted during tropospheric operations to detect objects on the Earth's surface from a manned aircraft or from an unmanned airborne vehicle (UAV) will involve long, near-horizontal viewing geometries. The computer code MODTRAN is widely used for the prediction of the propagation of infrared radiation through the lower atmosphere. Consequently, we have undertaken to test the predictions of MODTRAN for the 3 - 5 and 8 - 12 micron spectral regions under mid-Eastern desert conditions.

The Phillips Laboratory Remote Optical Sensors (ROS) program is developing the Laser Airborne Remote Sensing (LARS) system for chemical detection using the differential absorption lidar (DIAL) technique. The system is based upon a high-power CO₂ laser which can use either the standard ¹²C¹⁶O₂ or the ¹³C¹⁶O₂ carbon dioxide isotopes as the lasing medium, and has output energies in excess of 4 J on the stronger laser transitions. The laser, transmitter optics, receiver telescope and optics, and monitoring equipment are mounted on a flight-qualified optical breadboard designed to mount in the Argus C-135E optical testbed aircraft operated by Phillips Laboratory. The LARS system is being prepared for initial flight experiments at Kirtland AFB, NM, in August 1997, and for chemical detection flight experiments at the Idaho National Engineering Laboratory (INEL) in September 1997. This paper briefly describes the system characterization, and presents some results from the pre- flight ground testing.

In the context of modern radio physics approach, it is demonstrated theoretically and experimentally that diffraction properties of the received optical radiation may significantly affect the refraction angle measured with a phase sensitive receiving-recording system. Based on this approach harnessing coherent laser phenomena in plane and spherical waves, we suggest and develop to engineering procedures methods for determining the refraction angles from one-wave optical measurements. These methods are also applicable under conditions of highly inhomogeneous optical paths in the turbulent atmosphere. The LIRA multifunctional precision laser system for measuring regular and random optical refraction has been developed. In contrast with the known multiwave methods for remote refraction measurements, this system harnesses one- wave laser radiation. Its operation is based on instantaneous determination of the refraction angle from measurements of the image energy center of gravity of a remote laser source. Measurements are carried out with sampling frequencies up to 1000 Hz. The horizontal field-of-view angle is 100 sec of arc and the vertical field-of-view angle is up to 2 deg of arc. Average angular refraction is measured in the range 0.2 - 200 sec of arc. The measurement error is 0.2 sec of arc. Relative variance of angular refraction is measured in the range 0.1 - 1.0 sec of arc. Atmospheric path length varies between 0.5 and 30 km. The wavelength of the laser source is 0.63 micrometer. Laser sources generating other wavelengths can also be used in the system.

A possibility to use the own infrared radiation of a gas mixture to detect CO in combustion products by means of nondispersion correlation method has been investigated. Water vapor and carbon dioxide in atmosphere has a little effect on the signal. But atmosphere CO restricts registration distances to about 100 m. Presence of H₂ and CO₂ in a jet causes two-valued property of the calibration curve and may bring indeterminacy in detection of CO in jet. Nevertheless, registration of CO absorption mass over 0.1 atm cm in combustion products using own radiation of combustion products is possible.

The paper continues our previous investigations, based on the backscattering coefficient distribution, of the optical properties of aerosol in a coastal zone. The material presents some results of an elastic-backscattering lidar experiment carried out in the Bulgarian Black Sea coastal area in September 1992. The lidar experimental results are presented as 2-D images of the cross-sections of the variation of the extinction as a function of the height and the distance along the sounded path at different elevations. The value of the volume extinction coefficient is calculated according to Klett's inversion method, based on single elastic scattering of the laser emission. Along with the lidar measurements a conventionally measured meteorological parameters are presented. The experimental data considered in the paper demonstrates the lidar sensitivity to underlying surface influence over the optical characteristics of the aerosol.

A recent paper by Belen'kii proposed an inner scale turbulence MTF theory model to explain one of the many types of aerosol MTF experimental results by Dror, Sadot, and Kopeika. A broad comparison is made here between Belen'kii's inner scale turbulence MTF and our practical instrumentation-based aerosol MTF models and experiments. Belen'kii's model is strongly contradicted by those experimental results themselves, as well as by the many other published results not considered by Belen'kii. The Dror, Sadot, Kopeika experiments all contain comparisons of practical instrumentation-based aerosol MTF modeling which was calculated from aerosol size distributions actually measured during the experiments. These aerosol MTF calculations validated rather accurately the practical aerosol MTF model measurements. A summary of 9 independent different types of measurements and analyses which show we measured aerosol MTF and not any form of turbulence MTF is included, as well as specific contradictions between Belen'kii's model and our actual measurements. These also indicate our measurements of turbulence MTF were indeed correct, and that a broad system engineering approach to atmospheric optics should be encouraged instead of the narrow pure turbulence, pure aerosol, or pure absorbing atmospheric models often used.

In July 1996 FGAN-FfO participated in the LAPTEX (low altitude point target experiment) trial in Crete. Aim of this experiment was to improve the knowledge of environmental factors that impact EO system performance in the marine boundary layer. The atmospheric conditions were subtropic with absolute humidities higher than 15 g/m³. FGAN-FfO used two IR-cameras working in different bands for tracking an IR point source mounted on a ship sailing away from the observation site to the horizon. This paper deals with the analysis of the signal decrease with range under different atmospheric conditions. The measurements are compared with LOWTRAN 7 model predictions. Moreover, we studied the detection range performance under certain refraction conditions and the signal increase due to atmospheric focusing effects near the sea surface.

The Air Force Phillips Laboratory is in the process of demonstrating an advanced space surveillance capability with a heterodyne laser radar system to be used, among other applications, for range-resolved imaging of orbiting satellites. In this paper, we present our first satellite feature reconstruction from field results using reflective tomographic techniques.

In most of the techniques currently proposed to overcome the well known limitation of the laser Guide Star of not providing a useful tip-tilt signal, the size of the isokinetic patch plays a major role. Isokinetic patch size, defined as the distance at which the tilt correlation falls below a given threshold, can be measured, in principle, using a star cluster, as the few available measurements in the literature report. We have used the edge of the moon as a reference for the measurement of the tilt correlation over angles spanning from a few arcsec to several arcminutes. We constructed a seeing monitor using a 20-cm portable telescope coupled, through a pair of commercial objectives, with an anamorphic optical relay and a small commercially available 12-bit CCD. The image of the edge of the moon (relayed using the anamorphic relay) is frame-shifted in groups of six or eight in a fast manner, and it is read out later. In this way there is no need for a fast analog-to-digital converter, and only a minor modification to the original commercially available devices is needed. A three-day run at the Asiago Observatory during January 1997 has been performed. The collected data have been extensively analyzed in order to assure their reliability. A comparison with seeing measurements done simultaneously at the focus of the main observatory is presented, showing good agreement. Dispersion of the edge tilts consistent with Poisson statistics is pointed out. Scaling to the planned run at the Canary Island in order to pursue the Adaptive Optics module for the TNG telescope is briefly discussed together with the implication of the results for the various LGS tilt-recovery techniques.

In this paper, a theoretical comparison is made of the mean carrier-to-noise ratio (CNR) for a coherent (heterodyne detection) equal gain (EG) optical array receiver system with that predicted by a conventional single-aperture monolithic coherent detector system. Our analysis shows that the mean CNR for an EG array receiver system improves significantly over that of a single aperture system. Experimental data taken from a recent outdoor experiment over a range up to 1 km between target and transceiver are also presented and compared with the theory for a particular eight-element EG system developed at the University of Central Florida. Optical signals received by the EG receiver array are launched into eight single mode optical fibers. Phase compensation between the individual receivers is accomplished by wrapping the fiber around PZT cylinders that are controlled by phase compensating electronics.

Results of the experimental study of beam pointing stability of Nd:YAG lamp-pumped lasers are described. Possible ways of beam angular position stabilization are considered.

We discuss some possibilities of introducing the distortions of an optical wave phase, propagating along a vertical atmospheric path, as an integral characteristic describing the turbulence along the path. Several models of the turbulence outer scale profile have been analyzed as well as the structural characteristic of the atmospheric refractive index fluctuations in order to find the value of the efficient outer scale. The error in the Strehl ratio determination was estimated. This ratio was computed using the efficient outer scale and compared to its value computed by the model profile of the outer scale.

The simple effective method for computing the spectral thermal radiation intensity from jets of hydrocarbon fuel combustion products viewing through thick atmosphere layers is proposed. The method is based on (1) similarity of radiation characteristics of optically thin turbulent jets and (2) three-group approximation. The first approach can be used because jet radiation filtered by sufficiently thick atmospheric layer is concentrated mainly at frequencies where radiating volume is optically thin. Within three-group approximation developed for radiation transfer calculation in molecular rotational-vibrational bands the lines in each spectral interval are approximated by several (up to 3) groups of lines with the same lower energy levels. This allows one to account for the contribution of so called 'hot' lines that arise due to transitions between excited states and are weakly absorbed in low temperature atmosphere.

The wandering of laser beam energy center was experimentally investigated on near-land atmosphere range of 980 m length under the weak turbulence. The hypothesis about the independence and normal distribution of horizontal and vertical deviations was checked up by Kolmogorov-Smirnov criterion. In the most cases the experimental histograms don't statistically conform to normal (Gaussian) distribution. It is shown, that the substraction of linear trend from the temporal dependence of angular deviations improves the agreement of experimental data with normal law of distribution.

Atmospheric induced aberrations can seriously degrade laser performance, greatly affecting the beam that finally reaches the target. Lasers propagated over any distance in the atmosphere suffer from a significant decrease in fluence at the target due to these aberrations. This is especially so for propagation over long distances. It is due primarily to fluctuations in the atmosphere over the propagation path, and from platform motion relative to the intended aimpoint. Also, delivery of high fluence to the target typically requires low beam divergence, thus, atmospheric turbulence, platform motion, or both results in a lack of fine aimpoint control to keep the beam directed at the target. To improve both the beam quality and amount of laser energy delivered to the target, Northrop Grumman has developed the Active Tracking System (ATS); a novel linear phase conjugation aberration compensation technique. Utilizing a silicon spatial light modulator (SLM) as a dynamic wavefront reversing element, ATS undoes aberrations induced by the atmosphere, platform motion or both. ATS continually tracks the target as well as compensates for atmospheric and platform motion induced aberrations. This results in a high fidelity, near-diffraction limited beam delivered to the target.

Proposed is the novel method of dynamic nonlinear-optical correction for distortions in wide spectral band. The method is based on combining of the negative optical feedback correction and dynamic holography correction in the system, using optically addressed phase modulators.

Multi-segment liquid crystal spatial light modulators have received much attention recently for use as high-precision wavefront control devices for use in astronomical and non- astronomical applications. They act much like piston only segmented deformable mirrors. In this paper we investigate the use of these devices in conjunction with a Shack-Hartmann wave-front sensor. Previous investigators have considered Zernike modal control algorithms. In this paper we consider a zonal algorithm in order to take advantage of high speed matrix multiply hardware which we have in hand.

Given are the results of experimental study on the quasi real time holographic correction for the lens distortions in the passive observational telescope in the visible range of spectrum, using the liquid crystal optically addressed spatial light modulator.

Logicon RDA and Applied Technology Associates have supported PL/LIMI on various imaging experiments during the past years. We are currently supporting an adaptive optics experiment using a 349 actuator deformable mirror. We discuss the system requirements, the design schedule, the final hardware configuration, simulated and actual system performance and planned enhancements. Keywords: Deformable Mirror, Actuator, Electronic system