Since the early 1980s, airborne laser systems have been used for making remote measurements of ozone, water vapor, and aerosols in studies of many important atmospheric processes. Advanced airborne systems are under development to demonstrate autonomous operations of these laser systems and to expand their measurement capabilities. In the near future, laser systems will be used in space to investigate a wide variety of global atmospheric processes. This paper describes the current measurement capabilities of airborne laser systems, the use of these systems in recent atmospheric investigations, and the development of advanced lidar systems for aircraft and spacecraft.

In the ocean, typical concentrations of suspended particulates are between 10 and 200 mg/liter. Light-scattering nephelometers have been used for over 15 years to infer concentration and particulate perturbations. The nephelometers are sensitive to about particle concentration of 1 to 2 mg/liter. These particle concentrations can also be remotely sensed by ocean penetrating lidar. The particulate concentrations relate to the turbidity of the water, increasing the backscattering and attenuation of incident laser radiation; the attenuation is usually characterized by K, the diffuse attenuation coefficient. By appropriate processing of the lidar return waveforms, we can remotely infer the K, and thus the particulate concentrations - to a few mg/liter.

An innovative, coherent, cw lidar has been developed that allows path resolved measurements of the received intensity from a continuous wave laser beam backscattered from atmospheric aerosols. The use of a cw transmitter allows for a relatively simple and compact system and minimizes problems with frequency stability of the source. In order to achieve path resolved measurements, the cw laser transmitter is optically, di-phase modulated with a pseudo random code. This allows, with proper signal processing, for separation of the signals created by light scattered from different parts of the path. The range resolution that can be achieved is controlled by the basic pulse width of the pseudo random code and can easily be changed. The current system has a 150-meter full width-half maximum range bin size. The maximum range that can be probed depends on the aerosol backscatter coefficient, transmitter power and the size of the transmit/receive optics. The current system can work out to about 800 meters and needs only 100 milliseconds of data. Potential applications include optical remote sensing of winds, turbulence, chemical species (using DIAL) and perhaps temperature and pressure.

A new active radiosounding method is suggested for global satellite monitoring of a Earth's ozone layer. The method is based on millimeter wave transmission along the path between two satellites, one carrying a transmitter, the other one carrying a receiver. In the case of paths passing over 10 km above the Earth's surface, the influence of oxygen and water vapor absorption is absent, therefore signals of ozone absorption for 2 to 3 mm wavelength spectral lines are free from any interference. In comparison with well-known radiometry, the method is distinguished by its particular precision and resolution.

The complement of meteorological sensors on-board the DMSP satellite F11, launched in November 1991, included the first passive microwave atmospheric moisture sounder system. This system, designated SSM/T-2, and which includes the ground processing software, retrieves water vapor amounts at the surface and at each of five prescribed mandatory pressure levels to 300 mb in terms of relative humidity and specific humidity, as well as the total column-mass of water vapor and the column-mass of water vapor between mandatory levels to 300 mb, and above 300 mb. Sounding channels include three symmetrically-placed acquisition channels on the 183.310 GHz water vapor absorption line, combined with channels at 150.000 and 91.655 GHz. These channels are used in conjunction with four channels from the SSM/T-1 temperature sounder to produce the humidity values. Prior to 19 June 1993, when a failure of the 150 GHz channel occurred, several calibration/validation studies were performed by USAF, Phillips Laboratory, and Aerospace Corporation. A confirming study was conducted by Aerojet Electronic Systems, builder of the moisture sounding system. Generally, the sounder performance was found to be good, with the exception of a number of cases of anomalously large disagreement with the RAOB ground truth. Investigations of these cases suggests that the cases of anomalously large disagreement between the SSM/T-2 and the verification RAOBs lies in the locally-prevailing complexity of atmospheric structure, e.g., atmospheric baroclinicity, clouds, frontal structures, or simply irregular moisture distribution, and in the differing spatial resolutions of the two types of instruments. Average performance statistics for the moisture sounder are presented along with results of anomaly analysis. Suggestions for improving the verification procedures and for using validation disagreements to improve forecasts are offered.

On 20 June 1993, an anomaly was noticed in the 150 GHz channel on the DMSP SSM/T-2 water vapor profiler. This anomaly left the moisture sounder software inoperable, but with several options available for restoring it to operability, albeit with degraded performance. The built-in flexibility of the ground processing software to accommodate this type of anomaly reduced both lost data and repair time. Extension and augmentation of the pre- failure calibration/validation study results have produced new average performance statistics which establish that the SSM/T-2 moisture sounder performance is still acceptable to most users under most conditions. In this paper we describe the on-orbit performance of the repaired moisture sounding system compared with pre-failure performance, and with expected performance. The salient facts of the hardware failure and options for ground software fixes are also described.

Routine monitoring of the Earth's horizon radiance in the 14-16 micron band is necessary because the data can be used for the design of more efficient horizon sensors on spacecraft. The seasonal latitudinal and longitudinal changes in the radiance also need to be monitored for understanding atmospheric dynamics. With these objectives and also to characterize the influence of the Sun and Moon on horizon sensors, an Earth Sensor Radiance Monitor (ESRM) was designed, fabricated and integrated with the Indian Remote Sensing Satellite spacecraft for launch from the East coast of India. The ESRM is described in this paper.

In this paper we give the experiments for the measurement of EBI of an image intensifier with the change of temperature gradient of it. At the same time, we give the curves of EBI versus the different temperature gradients. We show the causes for EBI of an image intensifier with the change of temperature gradient. We conclude, from the calculations and experiments, that there is need for the waiting measurement time for us to minimize the measuremental difference of EBI caused by temperature gradient. The paper provides some scientific basis for improving the objective performance of low light level night vision system in the field.

We present a simple statistical model that has no fractal nature, but certain set of measurements of such model might lead to the conclusion, that it is a fratal. We regard plain model and show how usual fractal dimension D of measured trajectory might take any value 1<EQD<EQ2. We regard the system which statistical behavior is described by a set of Hamiltonians (by two Hamiltonians in the simplest case). Similar multi-Hamiltonian models are known, for example. If one uses the simplest assumption on probability P of realization for different Hamiltonians, for example PequalsN^-(alpha ) where N is a number of measurements during fixed time interval T, then it can be shown, that the measured trajectory might be treated as a fractal with dimensions Dequals2^-(alpha ), 0<EQ(alpha) <EQ1 Dequals1, (alpha) >1. Such results permit us to suggest multi-Hamiltonians models to describe the effects of random media (rain, clouds and turbulence) in the Wave Propagation problems.

Radiative transfer in atmosphere with spherical symmetry dependence of indexes of scattering, absorption, etc., in the presence of source of radiation with axial symmetry (intensive beam, sun, etc.) is studied. Thus the problem of radiative transfer as a whole has cylindrical symmetry. Contrary to the plane or spherical problems, there is no known simple approximations for cylindrical symmetry, similar to well known Schwarzschild-Schuster or Eddington's approximations. We suggest approximation of such kind for radiative transfer problem with cylindrical symmetry. It might be used as a second iteration for the plane approximation for the secondary sources. The simplest case with isotropic conservative scattering near the terminator is presented as example.

A procedure for modeling the transfer of polarized radiation in the spherical atmosphere was laid down. Angular and temporal distributions of the Stokes vector parameters, extent and azimuth of scattered radiation polarization at variations of optico- geometrical parameters of the model have been obtained.

The computer-controlled polarimetric system for remote optical sensing of natural environment under sunlight or pulse illumination is described. The control of spectral-temporal parameters and receiving aperture allows the videospectropolarimetric distributions of scattered light to be constructed to serve as a source of overall information on optical and structural characteristics of objects studied.

The planned mid-course space experiment (MSX) observations will include two experiments for remote detection of atmospheric trace constituents above 10 km altitude, based on measurements of limb spectral radiance by the cryogenic IR interferometer and the ultraviolet and visible spectrographic imagers. The timing of the measurements is particularly advantageous since they will likely be the only regular limb observations of trace constituents during the operational lifetime of the MSX satellite. The SPIRIT III interferometer has a maximum spectral resolution of 1 cm^-1 in six spectrally isolated channels whose vertical fields of view are between 4 and 13 km in line-of-sight tangent altitude. The six channels will provide spectra over wavelengths in the 2.6-28 micrometers range for tangent heights up to 180 km. The capabilities of the interferometer for the planned remote-sensing experiments, based on predicted instrument noise and saturation levels, are described in this paper.

From the standpoint of remote sensing, the scattering and radiative transfer properties of model cirrus clouds with hexagonal columns and plates in visible, near-IR, and IR spectra have been investigated by using the improved ray-optics theory and adding/doubling method. The radiative properties for eight types of water clouds are also studied. It is shown that the single scattering and multiple scattering properties of clouds depend strongly on the cloud macro- and micro- physics, and wavelengths. The analysis of brightness temperatures (BT) indicate that measurements of BT at 2.16, 2.7, and 3.1 micrometers from space may be used to distinguish cirrus clouds from water clouds. Furthermore, a technique for detecting clear skies and cirrus clouds is developed by analyzing the BT difference in both IR windows, i.e., 11.2 and 13.34 micrometers .

Realistic inversions of lidar signals for extinction using the Klett technique must take into account both the theoretical limitations of the inversion and the experimental constraints of the hardware. A simple test of the Klett inversion algorithm s19 is performed with and without experimental limitations and uncertainties. The effect of limited accuracy in the digitization of the lidar return and limited dynamic range is presented. A simplified technique for detecting clouds in the presence of low visiblity is developed, and some limitations are presented.

Techniques for obtaining quantitative values of the temperatures and concentrations of remote hot gaseous effluents from their measured passive emission spectra have been examined in laboratory experiments. The high sensitivity of the spectrometer in the vicinity of the 2397 cm^-1 band head region of CO₂ has allowed the gas temperature to be calculated from the relative intensity of the observed rotational lines. The spatial distribution of the CO₂ in a methane flame has been reconstructed tomographically using a matrix inversion technique. The spectrometer has been calibrated against a black body source at different temperatures and a self absorption correction has been applied to the data avoiding the need to measure the transmission directly. Reconstruction artifacts have been reduced by applying a smoothing routine to the inversion matrix.

A 3D multiparameter radar simulation procedure for rainfall studies is described. The procedure begins with the simulated 3D fields based on the 1986 COHMEX experiment and a mesoscale meteorological model of convective storm. Given the 3D rainfall fields, the sampling volume integration process involved in radar measurements is simulated to give radar observables, namely, reflectivity, differential reflectivity and differential phase shift. Numerous effects are accounted for including: antenna beam pattern, horizontal and vertical gradients, atmospheric and rain attenuation. As a final step, the radar observables are corrupted with a random measurement error to account for the radar hardware system noise and other sources of uncertainty. The simulated radar observables are qualitatively assessed. The simulator is a useful tool for engineers and hydrometeorologists who are interested in examining radar measurement errors and their effect on other variables of interest.

Satellite-sensor based microwave brightness temperatures are compared with radar based reflectivities for a three-dimensional mining cloud. The brightness temperatures are computed using a radiative transfer model based on the discrete-ordinates method. The synthetic reflectivities are generated from a three-dimensional physically based radar simulation. Comparisons between the brightness temperature and reflectivity fields at matched resolutions appear to be well correlated and may indicate that reflectivity measurements could be combined with brightness temperature observations in order to estimate rainrates. Results of a simulation examining the relationship between surface rainfall rate, reflectivity, and brightness temperature measurements are reported. The stochastic framework of this study allows the variance of remotely sensed quantities to be described in terms of variations that might occur in realistic precipitation events, and provides a framework for calibrating satellite-based rainfall estimation methods using radar measured refiectivities.

In this paper, we present the first of a two part discussion to improve the specification of atmospheric transmission calculations using a new methodology to reduce the uncertainty in pixel-level temperature profiles derived from meteorological satellite sounder data. Temperature profiles are examined first, since these data are used to derive the moisture content of the atmosphere. Our results show that the uncertainty in the specification of temperature profiles, for pixel level retrievals of meteorological satellite sounder data, can be assessed using knowledge on the accuracy of the initial-guess to a physical relaxation algorithm.

In this paper, a theoretical study on the remote sounding of maritime atmospheric aerosols (MAA) from space is made. First, a simple transfer model of short wave radiation is established, then the criterion of channel selection for a general remote sounding equation is introduced. The channel for sounding an aerosol parameter is selected according to the degree of predominance (DP) of this parameter. After that, the DPs of various aerosol parameters are analyzed. The results show (1) it may be difficult to sound total aerosol number, aerosol size distribution parameters and aerosol complex refractive index simultaneously, (2) selecting channel in 0.60-1.10 micrometers is suitable for the space sounding of MAA's optical depth with the optimal position of channel in about 0.70-0.90 micrometers , (3) the two channels for the determination of MAA's Angstrom coefficient from MAA's optical depth should be selected in 0.65 +/- 0.1 micrometers and > 1.56 micrometers respectively, and (4) introducing more information about the reflectivity of ocean surface and the pressure of atmosphere at ocean surface etc. may be helpful to obtain more aerosol parameters.

A compact four-channel microwave scanning radiometer for tropospheric remote sensing is being developed. A pair of 53.85 and 56.02 GHz and a pair of 23.87 and 31.65 GHz are adopted as temperature and humidity channels' frequencies respectively. For each pair of frequencies it has an offset reflector antenna and a Dicke-switching receiver. The pair of receivers is assembled in an enclosure, which is mounted on the rotating table of an azimuth mounting and the pair of antennas is connected with the rotating table of an azimuth mounting in the opposite side by a pair of elevation arms. Each antenna is composed of a 90 degree off-set paraboloid and a conical corrugated horn. Each antenna patterrn of four channels has nearly same HPBW, low side lobes, and low VSWR. The dual band humidity receiver is a time sharing type with 0.2K sensitivity at 1-sec integration time. The dual band temperature receiver is a band sharing type with 0.2K sensitivity at 10-sec integration time. The radiometer and observation are controlled by a single chip microcomputer to realize the unattended operation.

This paper reflects the progress of the GFO altimeter design, first described by Walker et. al. The GFO altimeter uses a linear FM waveform, pulse repetition frequency, pulse compression technique, and alpha-beta tracker design similar to an earlier GEOSAT radar altimeter. The current design takes advantage of advanced RF and digital signal processing technologies to produce an instrument that is both light-weight and reliable. Analysis of the range, waveheight, and backscattering cross section performance indicates that the GFO altimeter will achieve equivalent GEOSAT performance in all areas.

The ability to derive aerosol properties from satellites is important for climate change studies and atmospheric corrections in studying surface properties. Although aerosols have been measured over land from satellite, it is more feasible to measure them over low surface albedos such as the ocean. One of the uncertainties that must be dealt with is the aerosol phase function, which depends on the aerosol size distribution and the observing wavelength.

It is well known that the directivity patterns of the radio wave scattering by temperature and humidity fluctuations and by the cross correlation of temperature and humidity fluctuations are the same. On the other hand, it has recently been revealed that for a sound wave these directivity patterns as well as the directivity pattern of sound scattering by wind velocity fluctuations are different. This fact allows us to propose new methods for simultaneous measuring the structure parameters for temperature, temperature-humidity, humidity and wind velocity fluctuations. For example, measuring the radio wave backscattering cross section by a clear air radar, and measuring the sound scattering cross section by monostatic and bistatic acoustic sounding at three different scattering angles, we may in principle retrieve these structure parameters. Note that now there is no good remote sensing method for measuring the structure parameters for humidity and temperature-humidity fluctuations in the atmosphere. Some problems of practical realization of the proposed methods are considered.

The capability of Raman lidar techniques to make accurate measurements of the structure properties and species of the atmosphere has been investigated. The LAMP lidar which was developed at PSU during the past several years has focused on the application of Raman vibrational and rotational scattering results. Measurements have been carried out during several campaign periods which demonstrate the performance of Raman lidar techniques compared to standard rawmsonde balloon payload measurements. The investigation has included water vapor and molecular nitrogen profiles determined from the 1st Stokes vibrational Raman transitions from laser wavelengths of 532 nm, 355 nm and 266 nm. The profiles of the N2 vibrational Raman scatter provide true extinction measurements in the lower atmosphere. Water vapor profiles are determined from the ratio of signals measured at the following wavelength pairs: 660/607, 407/387 and 294/283. The fact that the profile is determined from a signal ratio removes most of the factors which would result in errors in the profiles. The temperature structure has been measured using the rotational Raman scattering in the region between 526 and 532 nm. Measurements have been carried out to evaluate the performance and show the capability of Raman lidar to measure the profiles of atmospheric structure properties and water vapor in the lower atmosphere during night conditions and to determine the daytime measurement capability.

This research uses the case study of methane characterization in order to explore more generally the design of remote sensing systems in response to specific environmental questions, and the integration of space based measurements with those of other platforms. In particular, this analysis examines the potential contributions of space based instruments to one of the most important objectives of a methane characterization program: a better understanding of the spatial behavior of sources. Due to its long atmospheric lifetime and relatively homogeneous distribution, any methane signal to be detected through remote sensing is small. The methane attributes of interest are not directly observable, but must be inferred through inversion of the spatially (and perhaps spectrally), integrated signal received by the instrument. This investigation explores the extent to which methane characterization is limited by uncertainty on the temperature profile, the water profile, surface albedo, and instrument noise. The capabilities of anticipated NASA Earth Observing System instruments in the context of various system configurations will be discussed.

A UV fluorescence lidar system for the remote detection of bioaerosols has been built and tested. At the heart of the UV- LIDAR Fluorosensor system are a 200 mJ quadrupled Nd:YAG laser at 266 nm and a 16-inch Cassagrain telescope. Operating on three data collection channels, the UV lidar is capable of real time monitoring of 266 nm elastic backscatter, the total fluorescence between 300 and 400 nm, and the dispersed fluorescence spectrum (using a small spectrograph and gated intensified CCD array). Our goal in this effort was to assess the capabilities of biofluorescence for quantitative detection and discrimination of bioaerosols. To this end, the UV-LIDAR Fluorosensor system was tested against the aerosolized bacterial spore Bacillus subtilus var. niger sp. globiggi (BG) and several likely interferences at several ranges from approximately 600 to 3000 m. Our tests with BG indicate a detection limit of approximately 500 mg/cubic meter at a range of 3000 m.

Combining stratus cloud measurements from a K_alpha-band radar and a microwave radiometer can give profiles of liquid water and droplet distribution. In addition, in drizzle, the radar measurements can be used to estimate drizzle parameters such as number concentration, liquid water, and droplet distribution.

A solution of the inverse problem concerning finding aerosol size distribution for a multifrequency lidar system working on a small number of wavelengths is proposed. The solution involves a best- fit method of finding parameters in a pre-set formula of particle size distribution. A comparison of results calculated with the algorithm from experimental lidar profiles with PMS data collected in Baltic Sea coastal zone is given.

A comparative transmissometer has been developed for evaluating the simultaneous transmission characteristics for near ocean surface transmissions in the 3 to 5 and 8 to 12 micrometers transmission bands. This transmissometer is a special purpose instrument designed for simultaneously measuring the radio of the 3 to 5 and 8 to 12 micrometers transmission bands. The transmissometer has been operated over the bay of San Diego, CA. to determine the propagation characteristics for near ocean propagation paths. Observed propagation characteristics for both the 3 to 5 and 8 to 12 micrometers bands are compared and discussed as a function of existing sea states and meteorological conditions.

A lot of different approaches to the problem of radiation propagation in scattering media is known, but a choice of an appropriate one to solve a specific problem is more art than science. There is no exact analytical solution to the stationary radiation transfer problem up to now. So, numerous approximate approaches should be used, each of them is reliable within its own range of characteristic parameters of the range. When the nonstationary problem is taken into consideration, the mathematical difficulties increase and, hence, a number of reliable approaches decreases.

This paper gives a brief description of a method to calculate the light-engineering criteria of anti-fog headlight performance under different atmospheric aerosol environments featuring by coarse composition of particles. This method uses the modified small-angle diffusion approximation and aspect-invariance principle to treat the highly forward-extended phase functions of aerosols and rather an intricate angular pattern of the light source. Some exemplary results are presented to illustrate the limiting visibility range of road objects illuminated by anti-fog headlights under snow, dust, rain, and fog conditions.

Small carrying aerosol lidar in which is used small copper vapour laser "Malachite" as source of sounding optical pulses is described. The advantages of metal vapour laser and photon counting mode in acquisition system of lidar gave ability to get record results: when lidar has dimensions (1 x .6 x .3 m) and weight ( 65 kg), it provides the sounding of air industrial pollutions at up to 20 km range in scanning sector 90°. Power feed is less than 800 Wt. Lidar can be disposed as stationary so on the car, helicopter, light plane. Results of location of smoke tails and city smog in situ experiments are cited. Showed advantages of work of acquisition system in photon counting mode when dynamic range of a signal is up to six orders.

During the period June to October 1993, a series of measurements were carried out during Project VOCAR to investigate the properties of the coastal atmosphere over the southern California coastal zone, including the offshore Sea Test Range operated by the Naval Air Warfare Center Weapons Division, Point Mugu, California. During summer, this region is frequented by persistent and strong radio/radar ducting conditions, in a refractive environment similar to those which impact Fleet operations in certain weather regimes worldwide. Characterization of the variability of refractive conditions in the lower atmosphere is a key element of the VOCAR study. Measurements at Point Mugu were made with a number of remote and direct sensing techniques, providing an opportunity to examine their respective capabilities to determine atmospheric refraction and related properties for radar/radio performance assessment applications. Some early results are presented from comparisons of refractive profiles from radiosonde data and an atmospheric lidar.

During the fall of 1993, a field experimental study on marine aerosol properties and thermal imager performance was conducted in the Dutch coastal waters. Aerosol and meteorological instruments, as well as thermal imagers and calibrated targets, were used at several platforms and locations: the Dutch Meetpost Noordwijk (a tower 9 km from the Dutch coast), a beach station in Katwijk, the oceanographic research vessel Hr. Ms. Tydeman, a Lynx helicopter, a P3 Orion, the NCCOSC RDT&E Div airborne platform, and buoy systems. This network of instrumentation was used for obtaining a comprehensive data base of aerosol size distribution profiles and relevant meteorological variables throughout the marine atmospheric boundary layer. Thermal imagery has been included to provide ground truth for assessing the low- level propagation effects near the ocean surface. Measurements have been made of atmospheric turbulence and refractivity effects at wavelengths in the IR and visible, to assess the marine boundary layer effects on the degradation of thermal images. Calibrated targets at different altitudes were observed to the maximum observable range under a wide variety of conditions in both the 3 to 5 and 8 to 12 micrometers bands. These data will be used for the development and validation of IRST models and IR ship signature models with the view of determining the effects of marine-generated aerosols, turbulence and meteorological profiles on their performance.

This paper presents the results of lidar-based investigations of aerosol concentrations and their size distributions over the breaker zones. The measurements were carried out under various weather conditions over breaker zones of the Gulf of Gdansk (1992) and from a station on the open Baltic Sea (International Experiment BAEX in 1993).

The propagation of high-intensive laser beams through aerosol atmosphere remains an attractive concept for a number of aviation and military application. A large set of aerosol nonlinear- optical effects accompanies the propagation of radiation in the atmosphere. Some of them, so-called nonlinear thermal effects, predominate, as a rule, in well absorbing aerosol; the other, nonlinear resonant effects take place in low absorbing particles. Some knowledge of the nature and mechanisms of radiation interaction with aerosol particles are necessary for understanding the processes of laser energy transmission through disperse media. Below are basic results of our long-term experimental and theoretical investigations of the process of intensive CO₂-laser radiation propagation along the atmospheric ground paths containing hydrometeors as well, as recent results on laser interaction with stratospheric aerosols and the process of SRS generation in transparent droplets.

The report presents a theoretical and numerical investigation of extinction and absorption coefficients as well as the single scattering albedo for polydispersed ensemble of plate-shaped crystals. We analyze a value of the efficiency factor for optical radiation in large crystals. It is shown that in the IR range only for crystals with the plane faces, inclined to each other at an angle more than 10 to 12 degrees, the efficiency factor can be assumed to be equal to 2. Analytical expressions for the coefficients of optical radiation extinction and absorption for ice plates are derived in the approximation of physical optics. The formula for extinction explains both the neutral spectral behavior of the extinction coefficient in the visible range and its wavelength dependence in IR range. Computed wavelength dependence of extinction coefficient has a fine structure and carries certain indicators of the ice plate size. The presented formula for calculating of the absorption coefficient estimates optical radiation intensity being absorbed by atmospheric crystals of any shapes. It is shown that spectral absorption dependence in the IR range has the same features as the dependence of absorption index for ice and ranges up to values comparable to those typical of scattering coefficients. Single scattering albedo is shown to be equal to unity in the visible range, while in the IR range it varies from 0.5 to 0.8.

In this paper, the expression for the incident strongly focused laser beam is obtained using the complex-source-point spherical wave theory. Based on the scattering theory, the formulas of radiation pressure of Gaussian beam exerted on a homogeneous sphere is obtained. The numerical results of the radiation pressure and their physical interpretations are presented. In our experiment of optical levitation, we find out that particles (one or more) can also be steadily levitated in the beam for a long time without a feedback apparatus.

A new analytical solution for the local optical characteristics (extinction, light pressure, and absorption coefficients, asymmetry parameter of a phase function) of spherical polydispersions with comparatively large particles are derived. The geometrical optics (GO) approximation is used to solve the problem. To improve the accuracy of the GO approximation the edge effects were taken into account. A comparison with the Mie theory data shows a fairly satisfactory accuracy of our analytic formulas.

The Visibility Impact Summer Study held from July to September 1990 was an intense, comprehensive study intended to measure aerosol size and chemical composition and to ascertain their optical effects. Size distributions for particle diameters from 0.01 to 10 (mu) were measured at hourly intervals and particle samplers were used to obtain chemical compositions at daily intervals at Tehachapi Pass and Edwards AFB, California. The extracted aerosol characteristics are discussed and compared to the desert aerosol model in LOWTRAN and the size and estimated composition of aerosols at China Lake reported upon earlier. We obtain relationships between aerosol mass and wind speed, diurnal size changes, and meteorological effects. Secondarily, extinction was calculated and used with LOWTRAN and radiosonde data for examination of aerosol effects on narrow band 3 to 5 and 8 to 12 (mu) imaging radiometer performance.

An effort to predict desert coarse aerosol statistics but not size distribution according to simple weather parameters has been made. A quantitative analysis of the desert particulate size distribution models was also performed. In this research the size distribution parameters measured by optical counters are related to weather parameters. Known statistical and analytical models such as MODTRAN relate the size distribution parameters only to relative humidity for continental atmospheres. Although humidity has a significant role in the prediction of aerosol size statistics, other weather parameters can also strongly influence the size distribution parameters. Comparisons such as the above can be used to predict under which conditions the MODTRAN aerosol models have good or poor accuracy. It is also hoped that they will lead to improvements in MODTRAN, improving the accuracy of the humidity dependence as well as by incorporating other meteorological parameters into the MODTRAN prediction models.

The experimental data of the backscatter coefficient profile and aerosol pollution over the river Volga along the path Moscow to Nizniy/Novgorod to Moscow obtained with the eye-safe backscatter compact lidar during the complex ecological expedition on board the ship `Ilia Repin' 28 June to 7 July 1993 are presented. We detected the visible and invisible aerosols layers and smoke plume over industrial and ship chimneys. The data obtained in similar conditions allowed us to find pollution-free regions. These regions, such as the village Ples, are considered as a base or background for an aerosol pollution degree estimation within industrial centers and over the Plesheevo Lake near the Russian- USA ecological station.

A compact nanoJoule laser radar system capable of detecting invisible aerosol and dust layers within a kilometer range was developed. A new design for an eye-safe portable backscatter Lidar for measurements of atmospheric propagation and aerosol extinction was used. The experimental data of the aerosol/dust detection, cloud height and time variation of the background solar radiation obtained in both the active and passive lidar operation mode are presented.

An overview of adaptive optics systems development is presented with emphasis on its power to compensate for atmospheric turbulence in imaging and laser propagation. A brief history from the conceptual thinking in the 1950s through laboratory implementation in the 1970s to practical reality in the 1990s will be covered. With ongoing research to solve the problem of atmospheric anisoplanatism, the use of artificial guide stars has become as a prominent point of discussion. The understanding of the artificial guide star phenomena and advances in laser technology are bringing systems from the research and technology development mode into systems with scientific utility. Conflicting technical limitations of guide star brightness, laser psoower, and compensation spatial frequency are traded to achieve the most scientific benefit with the least cost. a summary ore recent results from operating adaptive optics systems in observatories around the world will be followed by a brief look at the future promise of adaptive optics in the commercia sector, including requirements of mass market systems for the amateur astronomer.

The appearance of nonlinear and optoelectronic phase correctors with very high resolution requires changes to traditional adaptive system design. New approaches based on the 2D feedback system concept are discussed.

Overview of the works performed in Moscow State University and devoted to phase compensation of thermal defocusing and turbulent blooming of light beams propagating in natural media is given in this paper. General approach to wavefront optimization is illustrated by the example of stationary wind refraction in regular medium. Model control is considered with respect to attainment of objective function extremum with given accuracy. The main concern is with the study of simplex method applicability to problem of wavefront control. Comparison analysis of effectiveness of simplex method and gradient procedure is carried out. The regime of stationary and nonstationary wind refraction, pulsations of wind velosity and large-scale fluctuations of refractive index are considered.

Using the technique of conditional Marcov processes, we obtain the nonlinear algorithm which estimates the fluctuations of a wave propagated through a random medium. We discuss how the posterior statistical characteristics of these fluctuations and properties of a random medium are related to each other.

Distortions of the wave front in the Earth 'a atmosphere is discuued. The approximation of distortions of the wave localized in the thin layer is considered. The model to construct random realizations of the field with the given structure function is suggested. But the lower atmospheric layers give relatively small contribution to the distortion of wavefronts. In the first approximation the role of the thickneBB of the atmosphere may be described by the linear diffraction equation. It gives the estimation of the density of the dislocations of the wave front of the initial plane wave. It is shown that for this case this density is less than 1 dislocation per 100 square meters, at least for the good seeing condition. Recommendations to use flexible mirrors if the optical path in the atmosphere is leas than 10 km. and the segment mirror if the optical path is greater than 50 km. are suggested. The short program to simulate the wave fronts realizations to count dislocations is supplied.

It is shown that the phenomenon of correlation of opposing waves may lead to improvement of image quality of coherently illuminated objects in a turbulent atmosphere in the case of strong intensity fluctuations. The extent of this improvement depends on the relation between sizes of the output and receiving apertures. The betterment of visibility in a turbulent atmosphere becomes maximal in the case of their proximity and vanishes if the sizes of illuminating and receiving apertures are distinguished from each other significantly.

A naturally occurring, conjugate wave phenomenon in monostatic laser imaging applications is caused by reciprocal scattering pas which experience identical phase delays during the double passage of an electromagnetic wave through a random phase screen or turbulent medium. This 'opposition effect' of 'enhanced backscatter' phenomenon is known to be caused by constructive interference between reciprocal multiple scattering paths. Reciprocal path imaging (RPI) is an attempt to exploit this phenomenon for obtaining diffraction-limited images of extended objects obscured by a random phase screen or turbulent atmosphere. We report upon our current effort to investigate RPI with sparse array receivers and its potential as a mechanism for achieving high-resolution imaging through a turbulent atmosphere without the use of adaptive optics for image compensation. Preliminary work is reviewed and several RPI concepts to be evaluated in the laboratory are discussed.

When synthesizing a large aperture with an array of smaller subapertures for high-resolution imaging applications, it is important not only to arrange the subapertures to achieve minimal spatial frequency redundancy, but also to choose the size of the subapertures necessary to achieve the best possible image quality. Spurious, or ghost, images often occur even for nonredundant dilute subaperture arrays. In this paper we show that array configurations producing a uniform modulation transfer function will not exhibit these undesirable ghost images. A method is then presented for constructing both 1D and 2D configurations of dilute subaperture arrays that result in uniform spatial frequency response with arbitrarily high spatial resolution for reciprocal path imaging applications.

Speckle is inherently an interference phenomenon produced when a rough object or turbulent medium introduces some degree of randomness to a reflected or transmitted electromagnetic field. Speckle characteristics are therefore a major concern in many laser imaging or wave propagation applications. For many applications, a detailed description of speckle size as a function of intensity threshold level is desirable. Extensive experimental measurements of average speckle size as a function of intensity threshold level were therefore made for several different targets and illumination conditions. We then compare these measurements with a theoretical model for excursion areas of speckle intensity. Excellent agreement is obtained for intensity threshold levels greater than approximately twice the mean intensity level.

Experimental investigation of atmospheric coherence diameter is presented in order to examine relative effects of turbulence and aerosol forward scattering. The investigation includes measurements through the open atmosphere for path lengths of several kilometers. In addition to turbulence degradation of atmospheric coherence diameter, it is shown here that aerosol forward scattering also causes severe limitations, particularly for short exposure. Two methods, direct (spatial domain) and indirect (spatial frequency domain), for measuring atmospheric coherence diameter are presented. The methods are theoretically and experimentally independent. Results of both methods are in very good agreement, emphasizing measurement reliability. It is shown that, in contradiction to turbulence, aerosols affect light coherence identically for both short and long exposures. Experimental results during rather extreme atmospheric conditions such as fog are presented too. The results here are applicable to cost-effective imaging system design, and to predicting imaging system performance through the atmosphere.

The work is dedicated to study of turbulent distortions of focused laser beams propagating along high-altitude paths when both source and target are located at certain height in the middle atmosphere. The analysis was carried out for the model of refractive index spatial spectrum providing for anisotropy of turbulence, because there are anisotropic inhomogeneities of large sizes in the shape of disks extended along the Earth's surface in the stratosphere. A long exposure mean intensity distribution as well as a random wandering of laser beam are investigated depending on turbulence and geometry of propagation in the middle atmosphere. It is shown that the large anisotropic inhomogeneties of refractive index give the major contribution into vertical random wandering of a beam. As a result a long exposure distribution of mean intensity becomes anisotropic.

A computer code for simulation of high-power beams thermal blooming in the turbulent atmosphere and imaging in a ground- based telescope is described. This code also allows one to simulate the components of adaptive systems, such as the Hartmann-Shack wavefront sensor and various flexible and segmented mirrors. Our software can be used for estimation of beams and images parameters in the atmosphere and for the investigations of adaptive optical system efficiency.

This paper deals with theoretical and experimental studies of optical waves that compare different models of the atmospheric turbulence spectra. For inhomogeneous optical paths in the atmosphere we introduce the term the turbulence spectrum averaged over the path and present an analysis of some models of spectral density of the refractive index fluctuations for the turbulent atmosphere. The models are compared on the basis of calculation and measurements of statistical characteristics of phase fluctuations of optical waves propagating in the turbulent atmosphere.

Nonadaptive changes to the basic equations is applied to the simulation of thermal blooming of focused high laser beams through the atmosphere in the report. The results show that the accuracy and speed of the computation can be improved efficiently. But it is difficult to calculate the field amplitude near the focused plane because of the beam defocus caused by thermal blooming. A modified nonadaptive-change technique is presented which overcomes the defects of the old technique, and has proven more efficient in the improvement of accuracy and speed of computation, and in the reduction of memory.

Optical breakdown is of importance from the viewpoint of determination of maximum energy of high-power lasers which the atmosphere can withstand as a medium of propagation. In this work we generalize the results of our investigations of the development of laser-induced breakdown in the turbulent atmosphere containing background concentration of solid aerosol particles and analyze the accompanying electrophysical and optoacoustic effects.

A computer system designed for forecasting and on-line accounting the atmospheres influence on optical radiation characteristics are described in this paper. Great attention is paid to peculiarities of the system adaptation to IBM PC/AT.

For description of adaptive systems for atmospheric distortions compensation a common assumption is that intensity of radiation is scattered from the target, small enough to affect the propagation of an incident wave. In this paper the mutual effects of the incident and backscattered radiation is considered. This consideration is made for that case when the target is a small mirror. Solutions of the equations of paraxial optics exist in a form of beams which collapse on scatterers for beam power P>=P_(Omicron )3, where P_(Omicron ) is threshold power the beam collapse in absence of a scatterer dimension tends to zero. The problem of physical realization of the self-focusing on the scatterer is discussed. By means of numerical simulation it is shown that for monotonously increasing beam power P the back scattering leads to self-focusing on small scatterers only if P>=P_(Omicron ).

The random focusing in the turbulent atmosphere and its influence on forming and characteristics of short exposure image of extended incoherent light source is considered. The structure of image single realizations on the base of geometrical optics is described. The problem of statistic description of non-Gaussian fields, connected with strong random focusing is considered. The connection between form of bright regions in image plane and multipoint intensity moments is investigated. The regimes of best source observation are discussed.

New small angle equations are derived for polarized wave propagation in media with turbulence and precipitations (i.e. continuous fluctuations and discrete inclusions). These equations generalize the usual scalar parabolic equation and enable one to investigate simultaneously effects due to both discrete and continuous fluctuations.

The procedure of simulating a signal propagating through the turbulent atmosphere with the Kolmogorov spectrum is described. Using this procedure, the analytical results concerning the resolving power and evolution of the diffraction pattern in turbulent media are tested versus the turbulence strength.

The extended Huygens-Fresnel principle is used to analyze the average intensity distribution and signal-to-noise ratio of a self-luminous, incoherent object with a Gaussian pattern in atmospheric turbulence. The effects of turbulent inhomogeneities in the refractive index on the formation of the images as well as the dependence of the degradation of signal-to-noise ratio on the turbulence strength, object size, and lens radius are investigated.

The condition for superresolution in weak turbulence is formulated. Relationships between various parameters, such as wavelength, strength of turbulence, lens size, etc., for the occurrence of superresolution are investigated. Physical implications of superresolution are also discussed.

We have carried out numerical simulations of waves traversing a 3D random medium with Gaussian statistics and a power-law spectrum with inner-scale cutoff. The distributions of irradiance on the final observation screen provide the probability density function (PDF) of irradiance, which includes the first few moments of irradiance and In-irradiance. Analytic calculations to third order by a path-integral technique are in excellent agreement with these moments. Experimental measurements of irradiance variance as a function of turbulence strength and inner scale for both initially plane and initially spherical waves in the strong-fluctuation regime are in excellent agreement with the simulation variances. The simulation PDFs in the strong- fluctuation regime lie between a K-distribution and a lognormal- convolved-with-exponential distribution. We introduce a plot of the PDF of scaled In-irradiance, on which both the exponential and lognormal PDFs are universal curves, and on which the PDF at both large and small irradiance is shown in detail. We have simulated a spherical-wave experiment, including aperture averaging, and find agreement between the simulated and observed PDFs.

A new approach to the statistical analysis of fluctuating, photon-limited signals that permits us to accumulate and process the lidar returns without averaging of the reflected energy fluctuations is developed. This approach requires recording the photocounts for each pulse in a series of pulses and then determining photocount statistics. Based on the semiclassical theory of photodetection and Mandel's formula, a relationship has been obtained between the time-space cross correlation function and the cross spectrum of the lidar returns and corresponding photocount statistics. It is shown that the relative uncertainties of measuring the cross correlation or the cross spectrum of the lidar returns is determined by the general number of photocounts, but not by their mean value. A fast-scanning lidar system, which is based on a new photocounting analysis approach, is described for 3D wind field mapping in the atmosphere at altitudes up to 5 km. A program for the experimental verification of the new approach is presented.

The theory of a new lidar technique which exploits the residual turbulent scintillation (RTS) effect in order to remotely sense the structure parameter C_n² has recently been reported. In this paper, we describe the design considerations for a demonstration experiment. The primary objective of the demonstration is to collect and analyze a set of data which will demonstrate the RTS effect in the real atmosphere and relate it to C_n². The second objective is to obtain detailed performance parameters which will permit us to design future RTS systems for routine C_n² profiling. The demonstration will require a transmitter based on a pulsed visible-light laser with a clean beam profile, and a receiver based on a gated imaging system with a digital readout. The receiver aperture must be large in order to collect as much light as possible. Specific design considerations are developed here for a demonstration based on an existing laser used in conjunction with the 1.5-meter telescope at the Starfire Optical Range in Albuquerque, New Mexico, and its associated optics and data recording equipment.

A new volume-scanning crossed-path lidar technique for studying atmospheric intermittency in the surface and boundary layers is proposed. This technique provides a spatial resolution of 25 m and a temporal resolution of several seconds, and it permits us to study turbulent structures and processes in the atmospheric surface and boundary layers by performing a volumetric mapping of the optical refractive index structure parameter field. Unlike radar and acoustic sounders, this technique is not affected by humidity fluctuations. Lidar performance estimates show that the proposed technique is practical.

Phenomena that originate from the double passage of waves through the same turbulent inhomogeneities are discussed. The physical meaning of these phenomena is qualitatively demonstrated using simple examples of spherical waves scattering from point scatterers. The backscattering from extended bodies, i.e. coherently reflecting bodies and random large-scale rough surfaces, and coherence enhancement by backscattering are considered.

A new method of real-time high resolution imaging through the atmosphere is presented. This technique is based on the knowledge of average atmospheric MTF at the time the image is received. Atmospheric effects are modeled by a noisy spatial frequency filter including an average component described by the average atmospheric modulation transfer function, and a noisy component modeled by the atmospheric point spread function's power spectral density. Analytical results are accompanied by experimental image restoration examples, indicating significant image quality improvement based upon knowledge of average atmospheric MTF. This method can be used to help overcome the jitter characteristics of turbulence, and is capable of yielding real-time image restoration with resolution limited essentially only by the hardware itself.

A new remote sensing technique is described here for monitoring the vertical distribution of the intensity of atmospheric turbulence. The technique has several applications, including improving the performance of adaptive optics systems, prediction of laser beam degradation on long distance propagation paths, and site surveys for astronomy. The physical phenomenon underlying this method is caused by phase fluctuations, and as a result, this method does not saturate with increasing refractive index structure characteristic C_n² or with distance, and it is not affected by variations in the inner scale of turbulence. This method permits us to measure both the vertical profile of C_n² and an anizotropy coefficient of the atmospheric turbulence. Estimates of expected measured quantities are obtained, and they show that the proposed technique could be realized with existing optical systems.

The phenomenon of coherence enhancement after double passage propagation through turbulence has previously been experimentally observed for a system comprising of a mirror illuminated by two point-sources. The degree of coherence enhancement obtained was increased significantly in an experiment which manipulated the polarization states of the illumination and reflected light. The physical nature of this phenomenon consists basically in the appearance of correlation in the backscattered field in regions around the illumination sources. Essentially it is a result of reciprocity--any optical paths through the turbulence which begins at one source and ends on the other has its' corresponding partner which traverses the same paths in the same direction. Accordingly, we can expect from simple physical considerations that the same effect of coherence enhancement may be observed after backscattering from optically rough surfaces. In this report, we present results of experimental investigation of this phenomenon and describe an experimental system that demonstrates the phenomenon of coherence enhancement after backscattering from rough surface through turbulence.

Up to now, most of optical techniques of vertical turbulence profiling were based on the analysis of the scintillation produced at the ground level, preventing from low altitude layer detection. A simple optical combination allows us to explore the atmosphere, wiping out a particular layer while remote layers located beneath or above, are reinforced. A laboratory experiment which involves an optical bench and a simulated turbulent layer is described, and shows the potentialities of the new concept.

The generalization of the Monte Carlo method for calculation complex-valued Feynman path integrals have been performed. Calculation of the Feynman path integrals (in parabolic approximation) have been done. The new modified path integral representation of the Green function moments of stochastic wave equation has been developed. Calculations of the first, second, and fourth moments of the Green function of stochastic wave equation have been performed for random media in the presence and without large-scale inhomogeneities.

In this paper we analyze optically active turbulence variations in the daytime under well-developed convective activity of the ABL. We consider fast variations of the refractive index structure parameter C_n² with quasi periods from some tens of seconds to a few tens of minutes and spatial scales from tens of meters to several some kilometers. Spectral characteristics and probability density distribution of C_n² variations and their height dependence are presented. The strong intermittent structure of C_n² is common with the convective ABL. The distribution of probability of C_n+2) at low heights is not lognormal and has a considerable negative asymmetry. The representative comb structure of spectra of C_n+2) variance are observed. Typical temporal and spatial scales of C_n² variations are estimated. It is shown that, in spite of a rather high mean level of turbulence, there are time intervals with duration of a few minutes when its influence on wave propagation is slight enough to interfere with optical observations.

Air temperature fluctuations were measured by resistance thermometers mounted on a mast at heights of 14.5, 18.5, 19.0, 20.8, and 39.5 meters over a uniform steppe surface under stable and unstable stratifications. The results of measurements were compared with calculations based on the models of 3D spectrum (Phi) (k) for locally isotropy and locally axisymmetric turbulent inhomogeneities.

Based on the measured height distributional data of the turbulent structure constant (C_n²), this article analyses the effect of turbulent outer scale (L_o) on atmospheric transverse coherence length r_o and isoplanatic angle ((theta) _o). The calculation result shows that r_o and (theta) _o will obviously increase when limited L_o is considered. The r_o and (theta) _o are much large for telescope at 2.2 micrometers . The limit of (theta) _o is likely to be several arcminutes and may possibly be even larger.

Propagation of electro-optical signals through the boundary and coolant mixing layers on a hypervelocity vehicle can cause severe `aero-optic' signal degradation. This paper examines the use of approximate turbulence structure functions and various turbulence models in predicting such signal degradation. Approximate and exact solutions are compared. Characteristics of the Strehl ratio for small and large turbulence scale regimes are discussed.

A formulation has been constructed to recover the statistics of the moving average of the scintillation Strehl from a discrete set of measurements. A program of airborne atmospheric propagation measurements was analyzed to find the correlation function of the relative intensity over displaced propagation paths. The variance in continuous moving averages of the relative intensity was then found in terms of the correlation functions. An empirical formulation of the variance of the continuous moving average of the scintillation Strehl has been constructed. The resulting characterization of the variance of the finite time averaged Strehl ratios is being used to assess the performance of an airborne laser system.

The aperture-averaging factor associated with optical scintilations of unbounded plane and spherical waves is calculated for the weak fluctuation regime using a modified spectrum of refractive-index fluctuations that features a high wave number bump. Previous analyses were based on more conventional spectral models and the results were limited to asymptotic regimes depending on the ratio of the first Fresnel zone size (L/k)^1/2 to inner scale l₀. Simple interpolation formulas are developed here for all such ratios, and comparisons of results with numerical integration values and experimental data show excellent agreement.

A general expression is developed for the wave structure function (WSF) of a Gaussian beam wave using a modified spectrum of refractive-index fluctuations that features a high wave number bump. Effective beam parameters that characterize the turbulent spot size and phase front radius of curvature are used to formally extend this expression into the strong turbulence regime. The implied spatial coherence length from this expression for the WSF is less than that predicted by conventional spectral models whenever the Fresnel zone size is much larger than the initial beam radius. In the case of a focused beam, the predicted coherence length is slightly greater than that predicted by conventional spectral models when the Fresnel zone size is much smaller than the initial beam radius. The presence of the spectral bump appears to have little effect on coherence when the Fresnel zone size and initial beam radius are of comparable size.

The 1D nonstationary boundary-value problem (layered medium) of a wave incidence on a layer of inhomogeneous medium is considered. Combining the imbedding method and singularity method the relations between wave amplitude on the pulse front and medium refractive coefficient is determined. These relations allow us to solve the following inverse problems: (1) The space structure reconstruction for refractive coefficient provided time dependence for a wave reflected from a layer is given. (2) The structure reconstruction for refractive coefficient inside a some space provided time dependence for a field in a fixed point is given. This procedure allows us to find an analytical solution in some cases, e.g. for wave fields exponentially depending upon time in a media.

We describe an experimental method, using Michelson Interferometry and fourier transform, to determine wave fronts deformations after double passage through a wavy air-water interface. We consider the statistical aspect by using the averaged fourier spectra over many independent realizations. The spreading of fourier spatial spectra obtained from interferometric images can be used to determine heterodyne efficiency in airborne hydrographic systems using optical coherent detection.

The PROTURB model, developed by the Battlefield Environment Directorate of Army Research Laboratory, calculates an estimate of optical turbulence strength and its effects on visible and IR imaging and laser system performance. The PROTURB model was earlier compared to data obtained from the REBAL 92 field test held in Bushland, Texas, and data supplied by the Army Test and Evaluation Command Ft. Belvoir Meteorological Team. Recent PROTURB updates included modifying the radiative flux portion of the energy balance model. Here we present a new comparison using data from three locations that differ greatly in meteorological conditions, and moderate climatic conditions. There also exists a considerable difference in site characteristics such as ground conditions and vegetation. We discuss the data collection and reduction effort, and show how this data compares with PROTURB predictions.

MODTRAN2' is the most recent version of MODTRAJP, the Moderate Resolution Atmospheric Radiance and Transmittance Model, officially released by the Geophysics Directorate, Phillips Laboratory, in early 1993. It encompasses all the capabilities of LOWTRAN 73, the historic 20 cni' resolution (full width at half maximum, FWHM) radiance code, but incorporates a much more sensitive molecular band model with 2 ciii' resolution. The band model is based directly upon the HITRAN4 spectral parameters, including both temperature and pressure (line shape) dependencies. Because the band model parameters and their applications to transmittance calculations have been independently developed using equivalent width "binning" procedures, validation against full Voigtline-by-line calculations (eg. FASCODEb) is important. Extensive spectral comparisons have shown excellent agreement. In addition, simple timing runs of MODTRAN vs. FASCOD3P (released in 1992) show an improvement of more than a factor of 100 for a typical 500 cm spectral interval and comparable vertical layering. It has been previously established that not only is MODTRAN an excellent band model for "full path" calculations (that is, radiance and/or transmittance from point A to point B), but it replicates layer-specific quantities to a very high degree of accuracy6. Such layer quantities, derived from ratios and differences of longer path MODTRAN calculations from point A to adjacent layer boundaries, can be used to provide inversion algorithm weighting functions or similarly formulated quantities. One of the most exciting new applications is the rapid calculation of reliable IR cooling rates7, including species, altitude, and spectral distinctions, as well as the standard integrated quantities. Comparisons with prior line-by-line cooling rate calculations'9 are excellent, and the techniques can be extended to incorporate global climatoIogies°.

Our numerical simulations use relatively complex models of the atmosphere to investigate both Kolmogorov and non-Kolmogorov models. We find that the measurements of Bester et al. for light passing through the upper atmosphere are within the limits of behavior for Kolmogorov models, but often only if the outer scale of turbulent fluctuations is between 15 to 100 m. The possibility that the measured behavior might be non-Kolmogorov is not excluded. We also examine measurements made along short paths in the surface boundary layer, where some measurements of Bester el al. showed variations in the atmospheric fluctuations with seeing conditions which appeared to be non-Kolmogorov. These variations can perhaps be explained by standard models, but require that seeing improve with increasing wind speed in the surface layer. We discuss some other measurements which lend some support to that idea. However, we cannot exclude non-Kolmogorov behavior. We find that meteorological data is needed concurrent with astronomical observations, to help constrain the models. The size of the outer scale, the wind velocity profile and the turbulence spectrum are important to the ultimate capabilities of interferometers and other systems with adaptive optics.

The current state of knowledge of atmospheric propagation effects on radiowaves which impact system performance are reviewed, with particular emphasis on prediction models and techniques developed from satellite propagation beacon measurements. The availability of satellite beacons, operating at frequencies from below 10 GHz to well above 30 GHz, beginning about two decades ago, has provided researchers with a vast array of data for the development and validation of atmospheric prediction models for the principal atmospheric degradations effecting radiowave systems. These effects include; rain attenuation and depolarization, oxygen and water vapor attenuation, ice particle depolarization, ionospheric scattering and tropospheric scintillation.

Recent results achieved in the simulation of laser speckle in real-time are presented and discussed. Far field speckle has been simulated by a number of researchers using computer generated random phase screens to develop single frame pictures, however, our simulation develops a speckle picture in time, a movie, that we believe adequately illustrates speckle behavior as reflected from rotating and translating surfaces. The simulation was developed on a coarse array parallel supercomputer and the movies are formatted as QuickTime sequences. These sequences may be viewed on personal computers or workstations using easily obtained presentation software. Of interest is our correlation to speckle produced in the laboratory using lasers and translated surfaces and captured as frame sequences using a CCD camera.

Our approach in addressing complex terrain scenarios is to utilize a high resolution wind (HRW) model that will provide a high resolution microscale analysis of the surface layer horizontal wind and temperature fields. The wind model uses Gauss' Principle of Least Constraints for a variational adjustment of an initial estimated wind field in a single surface layer to conform with terrain structure, mass conservation, and buoyancy forces. From meteorological measurements taken at a single location, HRW can calculate wind vectors over a 5 x 5 km area with grid points spaced 100 meters apart. These micrometeorological data as well as canopy information can then be used as inputs to the Rachele-Tunick model to calculate optical turbulence parameters at each grid point within the microscale area. The output will be 2D optical turbulence contours from which integrated line of sight turbulence calculations can be made.

There is continuing interest in the comparative performance of thermal imaging systems operating in the 3 to 5 micrometers and 8 to 12 micrometers bands under maritime conditions. As a contribution to this, the following paper describes atmospheric transmission calculations carried out for both bands using the LOWTRAN 7 code based on weather observations obtained from the U.K. Meteorological Office for 28 maritime weather stations.

Physical aspects of dispersion (dependence of refraction factor value from frequency) emergence in case of radiowave propagation in atmosphere with nonlinear dependence of atmosphere refraction factor value from coordinates have been considered. A dispersion phenomenologic model proved by results of nature measurements in surface millimeter range direct visibility radioline has been put forward.

We present the theoretical and experimental study results of sea and land clutter and explosion scattering obtained in the millimeter wave band and needed for detection and identification analysis of radars operating in frequency band from 10 to 75 GHz. The empirical models for calculation of specific radar cross- section as a function of grazing angle, frequency and wind velocity are elaborated. The models for power spectra calculation of sea and land clutter are obtained. The radar reflection models from explosion are analyzed and it is shown that reflections for a long time are caused by the scattering by turbulent gas products of explosion.

Single IR sensor passive ranging from an observer to a target embedded in the atmosphere exploits the effect of atmospheric attenuation of the signal. By judicious choice of wavebands the range and altitude to a target can be determined passively with a single observer. This result will be shown to be relatively insensitive to assumed atmospheric models or precise source spectral content. A detailed closed-form solution relating range (and altitude) to observed target intensities will be presented. Previous studies of this type have required either detailed knowledge of the source spectra or spectral resolution of individual rotational lines. The single sensor passive ranging methodology requires no such detailed information.

The photos of the setting Moon taken from space with angular resolution about 10 arcsec were processed. The small-scale variations of arrival angles were measured from the shape of the Moon's contours distorted by refraction. Along with noticeable variations of refraction angles the numerous cases of multipath propagation were observed. As a result statistical characteristics of refraction angle variations and multipath propagation were estimated for the height interval 10 to 30 km. The RMS value of relative variations of refraction angles with the scales less than 1 km was about 0.017. The probability of multipath propagation during observations from the height 350 km was estimated about 10%, and the maximum observed spread in arrival angles during multipath propagation was 80 arcsec.

The results of an experimental investigation of optically active turbulence in the atmospheric boundary layer (ABL) over Moscow are given. Both quantitative and qualitative data on the ABL structure are obtained due to remote acoustic sensing. Statistical data are given on daily variations in the mean value of the refractive index structure parameter C_n² (for winter and summer), on the vertical profiles of C_n² for different types of the ABL thermal stratification and also on the seasonal occurrence of the type of stratification. The distinctions in the behavior of optical turbulence over a city and a homogeneous terrain are discussed as well as the deviations of the real profiles of C_n² in the urban ABL from the known model representations.

Results of the field measurement of scintillation for a 7 micrometers band semiconductor laser beam are described. To investigate the contribution of absorption, wavelength of the IR laser was tuned to a H₂O absorption line center. The scintillation for a 0.67 micrometers visible laser was also monitored to compare with the IR's scintillation. This experiment was carried out in the daytime in the winter as well as in the summer of 1993. The power spectral density functions (PSDFs) were calculated from the experimental results of each season. In winter, the level of the PSDFs for the visible light was found about 10 times bigger than that for IR light. The PSDFs agreed with the theory reported by Filho. In summer, the PSDFs levels of the IR light, however, rise up to those of the visible one. The measured PSDFs for the TDL disagreed with the theoretical PSDFs. The scintillation for the IR lights is weaker than that for the visible lights in the theory only based on the temperature fluctuation. However, our experimental results show that the PSDFs for IR light is as strong as that for the visible lights in the condition of the high temperature and humidity.

We propose a technique for measuring the statistical distribution spectrums of scintillation, beam spread, and spot dancing. The intensity of the laser beam is directly converted into the amplitude of photoelectronic pulse and fed to a multichannel analyzer. And by using the beam width (or displacement)-time- amplitude conversion technique, the statistical spectrums are determined rapidly. In the system the spectrums of scintillation, spread, and spot dancing may be simultaneously measured in a sampling rate of 3,000/s. The measurement precisions predicted are of 0.5% to amplitude, of 3 micrometers to width and of 5 micrometers to spot dancing in the laboratory static air. When a laser beam passes through the turbulent atmosphere, several effects induced by the turbulence would be met. They are intensity fluctuation (scintillation), intensity distribution (speckle), beam spread, spot dancing, and phase fluctuation. But in view of the physical measurement, the measurements of the intensity fluctuation and distribution depend on the detection of light intensity and on the position of beam. And beam spread or spot dancing will be determined by a beam cross-section and a displacement respectively. However, the measurement of phase fluctuation is essentially related to the wave propagation time varied along the path in the turbulent atmosphere. Therefore it only needs three physical parameters to be measured, which are amplitude, length, and time.