Atmospheric infrared radiance fluctuations result from fluctuations in the density of atmospheric species, individual molecular state populations, and kinetic temperatures and pressures along the sensor line of sight (LOS). The SHARC-4 program models the atmospheric background radiance fluctuations. It predicts a two dimensional radiance spatial covariance function from the underlying 3D atmospheric structures. The radiance statistics are non-stationary and are dependent on bandpass, sensor location and field of view (FOV). In the upper atmosphere non-equilibrium effects are important. Fluctuations in kinetic temperature can result in correlated or anti-correlated fluctuations in vibrational state temperatures. The model accounts for these effects and predicts spatial covariance functions for molecular state number densities and vibrational temperatures. SHARC predicts the non-equilibrium dependence of molecular state number density fluctuations on kinetic temperature and density fluctuations, and calculates mean LOS radiances and radiance derivatives. The modeling capabilities are illustrated with sample predictions of MSX like experiments with MSX sensor bandpasses, sensor locations and FOV. The model can be applied for all altitudes and arbitrary sensor FOV including nadir and limb viewing.

The Air Force Phillips Laboratory is testing the feasibility of developing a long-path, CO₂ laser-based DIAL system for remote sensing applications from an airborne platform. The validity of DIAL system performance simulations for long slant-range paths is being established by means of well-characterized field experiments in which the contributions of atmospheric transmission and atmospheric-turbulence-induced beam spreading and scintillation are being independently measured concurrently with DIAL system radiometric performance. Initial measurements were performed with both diffuse and specular targets using a 3.2 km path located at the Phillips Laboratory Starfire Optical Range. Measurements reported herein were performed using a slant-range path of 21.3 km originating at the Phillips Laboratory AMOS facility on Maui, Hawaii. The latter location offers a slant-range propagation path from 3.04 km above sea level (ASL) to near sea level. The DIAL system under test utilized a 4-joule class laser coupled to 61 cm aperture beam director telescope. Measurements were performed with the laser operating on the C¹³ isotope in order to increase the atmospheric transmission with respect to a laser operating at C¹²O₂¹⁶ wavelengths. Concurrent atmospheric optical characterization measurements were performed with an infrared scintillometer operating over the same path and at the same wavelength as the DIAL system. Results of atmospheric propagation characterization measurements are described in this paper and results of DIAL system performance and comparisons to simulations are described in accompanying papers.

A laser long range remote sensing (LRS) program is being conducted by the United States Air Force Phillips Laboratory (AF/PL). As part of this program, AF/PL is testing the feasibility of developing a long path CO₂ laser-based DIAL system for remote sensing. In support of this program, the AF/PL has recently completed an experimental series using a 21 km slant- range path (3.05 km ASL transceiver height to 0.067 km ASL target height) at its Phillips Laboratory Air Force Maui Optical Station (AMOS) facility located on Maui, Hawaii. The dial system uses a 3-joule, ¹³C isotope laser coupled into a 0.6 m diameter telescope. The atmospheric optical characterization incorporates information from an infrared scintillometer co-aligned to the laser path, atmospheric profiles from weather balloons launched from the target site, and meteorological data from ground stations at AMOS and the target site. In this paper, we report a description of the experiment configuration, a summary of the results, a summary of the atmospheric conditions and their implications to the LRS program. The capability of such a system for long-range, low-angle, slant-path remote sensing is discussed. System performance issues relating to both coherent and incoherent detection methods, atmospheric limitations, as well as, the development of advanced models to predict performance of long range scenarios are presented.

The Air Force Phillips Laboratory is conducting a series of measurements at the Air Force Maui Optical Station (AMOS) facility on Maui, Hawaii, to determine system requirements for an airborne long path CO₂ DIAL system. The lidar incorporates a cavity-matched 3-J laser with the 60 cm diameter AMOS laser beam director telescope. The beam propagation path is approximately 21 km, originating at the AMOS facility on Haleakala at an altitude of 3 km ASL, and terminating at a target site near sea level. Both heterodyne and direct detection techniques are being compared with respect to radiometric performance and signal statistics. Radiometric models including system optical characteristics, beam propagation considerations, target reflectivity characteristics, and atmospheric effects have been developed and validated experimentally. Predictions and results are presented, compared, and discussed.

The statistics of the normalized Stokes parameters for a stochastic plane wavefield which is Gaussian distributed is examined. The resulting probability density functions and lower-order moments generalized those obtained by previous investigators. Results of some numerical calculations are discussed. As an application of this analysis, we consider multiple scattering of light by a spatially random medium, composed of uncorrelated spherical pointlike particles, where the description of partially polarized light in terms of normalized Stokes parameters may be useful.

The effects of multiple scattering in the lidar returns from clouds have been shown to be appreciable in ground-based systems, both from experiment and from theoretical simulations. The effects are predicted to be greater for space lidar because of the greatly increased ranges. These effects have been shown from simulations to increase cloud pulse penetration dramatically and to exhibit measurable pulse stretching in the lower boundary layer clouds of high optical depth. The lidar returns from clouds in the recent Lidar Inspace Technology Experiment (LITE) displayed all the characteristics predicted from simulations. First, considerable increases in effective pulse penetrations through high clouds, as well as middle- level and low clouds were observed; second, pulse stretching in low and middle-level water clouds was readily observable; third, the introduction of an annular aperture, that blocked off single-scattered radiation, into the field aperture of the lidar receiver telescope demonstrated unambiguously the presence of multiple-scattered returns from boundary-layer clouds. However, returns from high cirrus clouds were not observable through the annular aperture, presumably due to the lower optical depth and much larger particles in these clouds.

The effect of multiple scattering on received power and its polarization state is examined by considering clouds made of spherical water droplets and non-spherical Chebyshev particles. A Monte Carlo code was used and its capability of dealing with homogeneous and stratified clouds is shown by a series of examples.

The influence of atmospheric vertical structure variations on infrared propagation and imaging has been analyzed based on measurements taken during the VAST92 experiment in the German Alps. A blackbody source at a distance of 2.3 km and an altitude of 1.8 km was detected against various sky backgrounds by a scanning DUWIR camera from GEC and a staring PtSi-camera from Mitsubishi. The propagation media has been characterized in detail using supporting atmospheric parameter measurements from lidars, a transmissometer, a spectral radiometer, aerosol counters and various meteorology stations at different elevations. The analysis of these measurements is presented. Two different weather conditions have been selected for analysis in this report: a dynamic cloud layer between sensor and point source, and a clear and stable situation with blue sky in the background. The recorded image sequences of the point source have been analyzed with respect to spatial and temporal fluctuations. Emphasis has been placed on the comparison of the two wavebands (3 - 5 micrometer and 8 - 12 micrometer) and on comparison of different sensing techniques. The results are currently being used to improve and validate point detection algorithms.

A numerical code is used to examine the features of the effect of atmospheric turbidity on the modulation transfer function of an optical system operating on ground, on an airplane or a satellite. Models of size distributions and optical properties of particulate suspended in the atmosphere are considered. The relevant scattering phase functions are calculated by Mie theory and are later used by a code using both Monte Carlo and geometrical optics procedures to evaluate the contribution of atmospheric turbidity to the augmentation of the point spread function. Comparison of ours with other researchers procedures is shown. The effect of atmospheric turbidity is evaluated as due to the presence of scatterers (the secondary sources) whose defocused images are distributed on the plane of the image of the primary source. The positions of the scatterers are determined by a Monte Carlo procedure, while the contribution of each secondary source to the irradiance on the image plane is evaluated by means of geometrical optics. Cases of different aerosols types, geometry aspects of viewing through the atmosphere and atmospheric absorption effects on the MTF are shown.

The model and experimental data on the propagation of the solar light in artificial optically thick spherical metal vapor and particle clouds in the near Earth space (NES) are presented.

In this paper an attempt is made to investigate how incident light propagating through a linear non-image-forming optical device, or scattered by a linear medium is depolarized using the Mueller matrix formalism. There are multiple definitions of depolarization in the literature which led to a difficulty, i.e. a non-depolarizing optical medium may decrease the degree of polarization of an incident completely polarized light. Because of this confusion, our usage is clarified. By considering incident light in the form of pure states of polarization, we are able to show that a particular Mueller matrix decomposition is advantageous for analysis of the physical mechanisms of depolarization of light propagating through linear media. We illustrate our analysis by examining several physically realizable Mueller matrices reported in the optics literature.

The depth mode of light propagation in a 2D-medium with strong absorption and sharply- anisotropic scattering is studied analytically outside the framework of the small-angle diffusion approximation. We propose and realize a regular procedure for optimum determination of the parameters of a postulated approximate angular spectrum in the depth mode. The dispersion in the depth mode and the depth damping coefficient are found. Our results are in good agreement with the exact solution to the transport equation written in the quasi-diffusion approximation, that has been obtained recently in the particular case of the Henyey-Greenstein phase function.

In this paper functional integral approach is applied to the problem of nonlinear processing to find optimum estimates of wavefront distortion in the presence of colored noise. This method allows us to take into account more physical information known about statistical properties of signal and a medium a priori than other methods.

Temporal characteristics of reflected radiation intensity while nonstationary light beam is incident at grazing angles upon the semi infinite medium with large scale scattering centers are investigated. The problem of small-angle light reflection is solved within the FOKKER - PLANK approximation. The analytical expression for reflected radiation intensity is obtained. Temporal characteristics of reflected radiation are investigated in detail in the most important cases of modulation of incident beam:(epsilon) -puls, the sequence of rectangular pulses of different duty factors and harmonically modulated light signal.

Stellar scintillations provide statistical information about the higher atmosphere (7 - 12 km). Since each realization of scintillation is the Fresnel diffraction off high altitude turbulence, it can be inverted separately. Sensors for adaptive optics integrate the wave front error over all layers of turbulence. They measure scintillation for calibration. But this discarded information yields the high wave fronts. Separate correction for low and/or high turbulence widens the repaired field of view. The method requires that the reference star is bright and small, that the middle turbulence (2 - 7 km) is negligible, and that the sensor has good spatio-temporal resolution. Simulations show that the turbulence can be retrieved, with lowest and highest frequencies lost first.

The extended Huygens-Fresnel principle is used to develop a formulation for the average intensity distribution of a partially coherent source in a turbulent medium. The dependence of the average spot size on the beam parameters, the position of the receiving lens, and the turbulence intensity along the path are investigated. It is shown that moving the receiving lens toward the source results in a reduction of the average spot size.

We report on the results of an experiment to analyze and characterize the optical index of refraction structure of an air jet flow using chaotic measures. A laboratory jet flow was interrogated at several downstream positions using a thin laser beam jitter technique and the resulting time series jitter data were analyzed to determine phase space portraits, correlation dimensions, and Lyapunov exponents. These measures help describe the complexity and dynamics of the flow features. As expected, the results indicate an increase in complexity of the flow structure with downstream position. One interesting feature of the results is a sudden increase in the correlation dimension at a position of 5.5 nozzle diameters downstream of the opening, indicating a dramatic increase in complexity. These measurements and chaotic analyses of the jet-flow transition region have interesting implications for the understanding and modeling of the optics of aircraft boundary layers and wakes, stratified atmospheric layers, and atmospheric turbulence.

The extended Huygens-Fresnel principle is used to develop a formulation for the backscattered intensity enhancement of a quasi-homogeneous source through a weak turbulence. Analytical expressions are presented which show the backscattered intensity enhancement as a function of the separation between the transmitter axis and the receiver. The dependence of the backscattered intensity enhancement on the coherence of the source, wave structure function, and the logamplitude covariance function are also investigated.

Adaptive optics and related techniques are now routinely used in the field of astronomical observations to compensate images for turbulence induced degradations and to retrieve the telescope diffraction limited resolution. However, for ground-to-ground applications, the effects of turbulence on both passive and active systems are more severe. The environmental constraints are also more important. Nevertheless, adaptive optics issues exist. The purpose of this paper is to review the evolutions of turbulence limitations according to the observing scenario. The turbulence anisoplanatism effects are emphasized. Furthermore, potential fields of application of adaptive optics and related techniques are presented.

We present experimental results of active imaging of an optically rough object obscured by turbulence. Our approach is based on an arrangement using a coherent focused beam and multiaperture receiving system. An appreciable improvement of image quality was achieved compared to passive imaging systems.

Adaptive optics has been studied for several years as a method to overcome the effects of atmospheric turbulence on ground based astronomy. It is often assumed that full order correction, with one or more actuators per r0, is necessary to achieve any performance improvement in imaging quality with the AO system. Recently it has been shown, both with theoretical analysis and experimental measurements, that even low order adaptive optics (LOAO) can provide image improvements especially when used in conjunction with some sort of computer post processing. In a previous paper we described simulations and experimental results of a LOAO experiment using 25 actuators across a 1.5 meter telescope. In this paper we present performance simulations for a planned experiment with a 163 actuator deformable mirror placed at the pupil of the 3.5 meter telescope at the Phillips Laboratory Starfire Optical Range at Kirtland Air Force Base.

The utility of a blind deconvolution algorithm used in conjunction with the Knox-Thompson algorithm is demonstrated with day time observations of the MIR space station.

The object of this communication is to compare two inversion algorithms in their application to the blind deconvolution problem. After a brief summary of the previous works in this field, we describe the Richardson-Lucy and the steepest descent algorithms and we introduce these methods in the basic error reduction algorithm of Ayers and Dainty. These algorithms are compared when used for blind deconvolution of simulated binary objects convolved by a point spread function and corrupted by a Gaussian additive noise. We consider the effects of the noise level on the reconstruction error, together with the effects of the algorithmic parameters (inner and outer iteration numbers). Particular effects occurring during the reconstruction process are also shown.

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 and orbital element set determination. It has been shown using theory and computer simulations that superior image quality is obtained by first converting the heterodyne returns into intensity projections before using tomographic techniques to reconstruct an image, as compared to using tomographic techniques on the E- field projections directly. In this paper, data from recent field experiments is used to validate this theory. In addition, the field data is used to determine the closing velocity of an orbiting satellite as a function of time.

The problem of compensation for atmospheric distortions of a wave front has been studied sufficiently long. The first papers on this subject were published in the mid-1960s. At that time, however, the engineering base gave no way for designing efficient devices for compensating for atmospheric distortions. In recent years much progress has been reached in developing wave front distortion meters and correctors and then fitting the optical facilities operating under atmospheric distortions with these devices. In recent years in some countries (USA, France, Germany, England, Australia) the stellar optical interferometers with large measuring bases have been developed and designed. One of the first stellar interferometers, using new technologies, is the Mark II stellar interferometer with the measuring base of 3.1 m. The developed Mark III stellar interferometer is a modern type of the interferometers with a measuring base of 12 m oriented to the north-south. The creation of these stellar optical interferometers has become possible due to the use of new optical technologies, namely, laser systems for supporting the constancy of the optical base of the interferometer as well as for adopting the elements and systems of adaptive optics to remote the noise effects. In parallel with these optical antenna arrays the large aperture telescopes-interferometers are designed. For example, at the Mauna Kea Observatory on Hawaii the Keck II telescope is constructed which operated in pair with the Keck telescope (the diameter of the primary mirror is 10 m) will form the optical interferometer with the base of 85 m. European Southern Observatory is conducting the building operations (in Chile at the Serra Paranal Observatory) for design of the 'very large telescope-interferometer' (VLTI), consisting of four telescopes with the aperture 8.2 m. In this interferometer the maximum distance between the interfering optical beams (maximum base) is 128 m. First of all, it should be noted that these novel optical instruments will make it possible to conduct observations of stellar objects with the angular resolution better than 10^-9. These unique instruments, operating through the atmosphere, will give information of great importance, concerning the structure of the atmosphere of different parts of the world. In turn, these instruments should provide reliable data on the state of the atmosphere.

Optical design of a compact adaptive optics system, to be mounted on the side of a large telescope, presents special problems. In particular the limited space requires fast optics. Signal to noise requirements for the wave-front sensor also require that the optics work over a wide optical band. In this paper we describe the design and layout of such an adaptive optics experiment performed on the SOR 3.5 meter telescope.

Experimental observations of the coherence enhancement phenomenon are presented and described. We have illuminated an optically rough moving target through turbulence using two mutually coherent point sources and observed the interference of the scattered fields in the region close to the sources (the region of coherence enhancement) with the help of a special interferometric system. The experiment was carried out under weak and strong intensity fluctuations on the object. Our study shows that the intensity distribution in the region of coherence enhancement is determined by the four-point correlation function and depends on the inner scale of the turbulence.

We evaluate the time-averaged double-passage image of a coherently illuminated object that is obscured by a random phase screen. In particular, we study the effect of changing the location of the random screen on the average intensity spectrum of the image. We consider two cases, when the random screen is at an arbitrary location between the pupil plane of the imaging system and the object plane and when it is located right next to the object. In both cases we find that the average intensity spectrum of the image is diffraction-limited.

Effects of weak turbulence on images of coherent sources or coherently illuminated objects taken with exposure times much greater than the turbulence's time constant are examined using the extended Fresnel principle. Two cases are considered. One in which the turbulent medium fills the region between the imaging system and the object and the other in which the turbulence occurs as a phase screen directly before the object. Assuming the Kolmogoroff spectrum for the index of refraction fluctuations and specifying a modulated Gaussian form to describe the object, a closed form result is reached which illustrates the effect of the turbulence on the image in a conceptually simple manner. A loss of resolution is found, manifesting itself as an effective reduction of the lens size. A simple relation is derived that relates the effective lens size to the actual lens size and the coherence length (rho) _o, of a spherical wave propagating through the turbulent medium. This relation agrees well with the empirically known fact that increasing the size of the primary lens of a telescope beyond approximately 10 cm does little to improve resolution. Turbulence is also found to cause a coherent object to seem incoherent from the standpoint of the viewer if the resolution spot size of the imaging system is larger than (rho) _o. Approximations upon which these results are based are supported by numerical calculations for particular objects. Finally, the implications of these discoveries are compared with papers that demonstrate superresolution for short- and long-exposure imaging.