In coastal areas, the simplifying assumptions of horizontal homogeneity used in open ocean analysis are not always useable. Various human-generated aerosol sources such as towns and industrial centers can provide a complex portrait of merging plumes of non-natural aerosols which are advected out to the littoral zones. The extensive meteorological and aerosol measurements made during the Marine Aerosol Properties and Thermal Imager Performance (MAPTIP) experiment provided an ideal opportunity to view how these aerosol were advected from their sources to the littoral zone of the North Sea. MAPTIP was conducted along the Dutch coast in October/November 1993. The NCCOSC, RDT&E DIV (NRaD) instrumented Navajo aircraft flew two star pattern flights a day during the experiment at altitudes below 500 feet. During these flights, aerosol size distribution measurements along the flight path were being continuously recorded. These measurements were utilized for making aerosol concentration maps of the various sized aerosol groups. This paper shows the mesoscale effects of aerosol advection making the marine boundary layer in a littoral zone much more complicated than that of an open ocean.

A comparative transmissometer has been developed for evaluating the simultaneous transmission characteristics for near ocean surface transmissions in the 3 - 5 micrometers and 8 - 12 micrometers bands. this transmissometer is a special purpose instrument designed for simultaneously measuring the changes in transmission of the 3 - 5 micrometers and 8 - 12 micrometers transmission bands. the transmissometer has been operated over the San Diego Bay, California, to determine the transmission characteristics for near ocean propagation paths. Observed propagation characteristics for both the 3 - 5 micrometers and 8 - 12 micrometers bands are compared and discussed as a function of existing sea states and meteorological conditions. The observed transmission characteristics for the two wave bands are compared with LOWTRAN calculations. Rapid fluctuation in received signal strength, their power spectra, and correlation coefficients are also discussed.

As previously reported aerosol size and composition and meteorological data were collected at three sites (Tehachapi Pass and Rogers and China Lake dry lake beds) in the western Mojave Desert in the summer of 1990. Aerosol size distributions exhibit the usual accumulation and wind speed dependent dust modes. The dust mode aerosols are illite clay. Their composition is wind speed independent for speeds up to 10 m/s, i.e. there is no silicate mode. Dust mass is wind speed independent up to 7 m/s. Beyond that, dust mass is exponentially related to wind speed by m equals 0.55 exp (0.59 u). Dust mass computed from the measured size distributions also exhibits the 7 m/s threshold. These characteristics are significantly different from the dust model used in LOWTRAN7/MODTRAN (based on Sahara data) which uses a large particle silicate mode in placed of the dust mode. It needs to be determined whether the optical properties of the two dust models are different enough to warrant changing the model in LOWTRAN. Their optical properties (extinction, albedo and asymmetry factor) from 2 to 12 (mu) are compared and used in LOWTRAN 7 for a variety of geometries and wind speeds. Perhaps two desert dust models should be used, one for an old desert such as the Sahara and another one for young deserts.

Knowledge of the aerosol extinction coefficient at infrared wavelengths is necessary for predicting the performance of electro-optical systems such as thermal imagers. Recently, Gerber Scientific Inc. has developed an instrument that makes a local measurement of the aerosol extinction coefficient at a wavelength of 10.6 micrometers . It exploits the strong correlation observed between visible light forward scattered between 0 and 3.6 degree(s) and the infrared extinction coefficient. We report field measurements made with this instrument in advection fog conditions and compare the results with transmissometer measurements of extinction in the 10 - 12 micrometers band.

A ship radiometer is currently being constructed which will make sun, sky and ocean surface multi-wavelength radiance measurements. The measurements will be used to derive aerosol and ocean surface optical properties. This paper describes the basic design of this radiometer.

Light backscattered from turbid media in the crossed-polarized channel shows a symmetrical pattern. It depends on the pathlengths distribution of the multiply scattered photons. The present paper investigates the relation between the cross-polarized backscattered light and the number of collisions experienced by photons in a narrow beam geometry.

The production of top of atmosphere (TOA) radiance estimates, along with an assessment of the quality of these estimates has always been a problem for the vicarious calibration of satellite systems. A new approach using ground based atmospheric data for quality assessment is currently being explored by the Applied Physics group in University College Dublin (UCD), Ireland. Ground based full spectral measurements are used, in conjunction with meteorological data, as inputs to various radiative transfer models. Collectors measure vector and scalar irradiance. direct irradiance (radiance), reflected radiance and sky radiance at particular viewing angles. Solar aureole irradiance is also measured, partly to analyse aerosol scattered radiance at particular viewing angles and partly to act as a component of the model validation effort. A multichannel spectrometer is used to simultaneously monitor these collectors in the visible from 415 nm to 840 nm with a spectral resolution of 5 nm. Redundant collectors are used for comparison with the outputs of the models to validate the models and assess the potential quality of TOA radiance estimates. A technique for extraction of the bidirectional reflectance distribution function is also explored.

The Optical Physics Division of the Phillips Laboratory with support from the DoE Atmospheric Radiation Measurement (ARM) Program is developing a state-of-the-art line-by- line atmospheric radiative transfer model as the successor by FASCODE. The goal of this project is to create a computationally efficient model which contains the most up-to-date physics. The new model, known as FASCODE for the Environment, or `FASE', will combine the best features of FASCODE and LBLRTM, the DoE's standard radiative transfer model. FASE will also contain new features such as new cross-sections for heavy molecules, an improved solar irradiance model, and improvements to the Schumann-Runge bands and continuum. The code will be optimized for vectorized and/or parallel processing, put under configuration control for easy maintenance, and will be structured into separate modules for each function: atmospheric profiles, layer optical properties, radiative transfer, multiple- scattering, etc. This modular structure will allow for increased flexibility and easy customization of the code for specialized applications, such as a forward model for iterative inversion algorithms. Ease-of-use will be enhanced with improved input control structures and documentation to accommodate the needs of novice and advanced users. This paper addresses changes which have been made to FASCODE and LBLRTM to create FASE, and gives an overview of the modular structure and its capabilities.

Two improvements are made in modeling polarimetric scattering by ensembles of particles. (1) We propagate the complex scattering matrix instead of the phase function. This allows us to calculate the phase and polarization properties of an entire cloud of particles. Radiation transfer models deal only with the intensity of the scattered light. The advantage is that the new model can deal with situations in which the light is scattered coherently. (2) Monte Carlo methods require calculation of scattering at all angles for each successive particle. The new model requires the calculation of only one scattering angle. This allows for use of sophisticated electromagnetic scattering models such as the Discrete Dipole Approximation, WKB or Digitized Green Function models. The advantage is that we can treat particles of arbitrary morphology more accurately.

Optical communication must contain clouds as parts of communication channels. Propagation of optical pulses through clouds causes widening in the spatial domain and attenuation of the pulse radiant power. These effects decrease the received signal and increase bit error rate (BER). One way to improve the BER of the communication system is by using adaptive methods to obtain more signal relative to noise power. Based on mathematical models of spatial widening of optical radiation derived by Monte-Carlo simulation, a mathematical model for optimum performance of digital optical communication through clouds is developed. The purpose of the optimum adaptive communication system suggested here is to improve the BER by optimizing according to meteorological conditions the spatial distribution of the detected radiation beam using a detector array where the external amplification of each detector is adaptable. Comparison and analysis of three models of communication systems in fog cloud channels are presented: (1) the optimum adaptive detector array aperture, (2) an ordinary single detector aperture of the same size, and (3) a small detector aperture. Improvement of more than four orders of magnitude in bit error rate under certain conditions is possible with the new adaptive system model.

Overall atmospheric modulation transfer function (MTF) is essentially the product of turbulence and aerosol MTF. Models describing meteorological dependences of both C_n² and coarse aerosol size distribution have been developed previously. Here, they are used to predict turbulence MTF, aerosol MTF, and overall atmospheric MTF according to weather. Comparison of predictions to measurements yields very high correlations and suggests that such prediction models can also be very useful in image restoration based on weather data at the time and general location in which the image was recorded. An interesting aspect of this work is that measurements of aerosol MTF with different imaging instrumentation are very different, as expected from theory developed previously concerning the practical aerosol MTF actually recorded in the image. This is dependent upon instrumentation parameters. This experimental verification supports the model that the `practical' aerosol MTF is very dependent upon instrumentation.

The presence of clouds may delay boost plume detection by an airborne electro-optical sensor until the target is above the cloud layers. This paper assesses the feasibility of monitoring the radiant emittance at the top of the clouds vertically above the target for early detection and discrimination. Spherical wave propagation through clouds is modeled by Monte Carlo scattering calculations and optical transport approximations. Effects of cloud characteristics, such as total water content, particle size distribution, and layer thickness, are evaluated.

The Navy Oceanic Vertical Aerosol Model predicts the vertical distribution of aerosol in the first 6 km above the ocean. Its inclusion in the Atmospheric Transmission/Radiance Computer Code (LOWTRAN) will prove to be a useful tool in predicting atmospheric transmission in the marine atmosphere. One shortcoming in the model's application is the lack of available meteorological profile data necessary for the required input. These parameters vary widely depending on wind direction, season, location, etc. Default meteorological profiles have been developed for use when the required measured meteorological inputs are not available. These profiles have been developed using existing world-wide data bases. The profiles provide default parameters averaged by month for selected Marsden Squares. Measured meteorological data and default profiles are compared.

Airborne measurements of mid and far infrared (IR) sea radiances were obtained using a calibrated dual-wavelength band thermal imaging system (AGEMA 900). The measurements were used to evaluate a sea radiance model which is based on the Cox-Munk wave slope statistics and is incorporated into a modified version of LOWTRAN 6. The measured and modeled IR blackbody sea temperatures for three days (which included low, moderate and high wind speeds) are compared as a function of the observation altitude. For all three data sets, the far IR modeled sea temperatures are less than the measured values by 1 degree(s)C to 3 degree(s)C at all altitudes. There is slightly better agreement (1 degree(s)C to 2 degree(s)C) between the measured and modeled temperatures for the mid IR band. In these instances, however, the modeled temperatures are greater than the measured values, except at altitudes where the sea backgrounds were contaminated by sun glint. Observations are presented which show that the far IR sea radiances are more closely influenced by the actual sea temperature than are those for the mid IR band, and that the strong `close-in' absorptions of carbon dioxide and water vapor control the mid IR radiances.

This paper presents a 2D computer simulation of observed intensity and phase behind a time evolved phase screen. Both spatial and temporal statistics of the observed intensity is compared to theoretical predictions. In particular, the intensity statistics as a function of detector position within the propagated laser beam are investigated. The computer simulation program was written using the C-programming language running on a SUN SPARC-5 workstation.

Several observations of atmospheric turbulence statistics have been reported which do not obey Kolmogorov's power spectral density model. These observations have prompted the study of optical propagation through turbulence described by non-classical power spectra. This paper presents an analysis of optical propagation through turbulence which causes fluctuations in the index of refraction. The index fluctuations are assumed to have spatial power spectra that obey arbitrary power laws. The spherical and plane wave structure functions are derived using Mellin transform techniques. The wave structure function is used to compute the Strehl ratio of a focused plane wave propagating in turbulence as the power law for the spectrum of the index of refraction fluctuations is varied from -3 to -4. The relative contributions of the log amplitude and phase structure functions to the wave structure function are computed. At power laws close to -3, the magnitude of the log amplitude and phase perturbations are determined by the system Fresnel ratio. At power laws approaching -4, phase effects dominate in the form of random tilts.

Modelling refractive index turbulence over paved surfaces is of significant importance to predict limitations on optical remote sensing systems operated over roads, airport runways, or urban areas. Since optical turbulence is generated by the turbulent heat transfer between ground and atmosphere, its magnitude depends on the thermal and dynamical properties of the surface. Compared with typical vegetated and unvegetated surfaces, the pavement has a significantly smaller roughness length, a lower albedo, and a higher heat conductivity and capacity. This results in a turbulent situation which is very different from that found over other areas and therefore needs special investigation. This paper presents a model to calculate the structure function constant C_n² and the inner scale l₀ of the refractive index fluctuations over a paved road. The basic input parameters are air temperature, surface temperature, and wind speed. We limit ourselves to the dry case. The model is verified by measurements taken in summer 1994 over a motorway near Vienna. Both C_n² and l₀ were determined using displaced-beam laser scintillation. The optical data is compared with the model applied to on-site meteorological observations. Good agreement is observed.

During 1994 an experiment took place over the North Sea in order to derive the infrared atmospheric scintillation and beam deformation process. An infrared point source was positioned at a platform in sea, with a height ranging between 1.5 and 7 m above the sea level. Some additional sources, at different height levels, were installed later on in the experiment. The receiver system was placed at 18 km on a pier near the coast of the Netherlands. Recordings took place with the receiver at two heights, 40 and 15 m above the average sea level. A single recording consisted of 10 seconds of measurements at 25 Hz with a 64 X 64 elements Cincinnati IRC-64A camera in the 3 - 5 micrometers band. Examples of these recordings are presented. The data were analyzed for scintillation effects, atmospheric point spread function effects and refraction effects. These data are compared to the atmospheric conditions that were recorded simultaneously, in order to model the infrared scintillation effects with meteorological conditions. Results of these comparisons are shown.

Propagation through irregularly random media is addressed by using advanced models for the medium and the propagation. This problem is of importance in actual propagation scenarios, where small- and large-scale inhomogeneities, inadequate sampling, source and target fluctuations cannot be avoided. The paper reviews briefly the governing equations and the qualitative aspects of propagation. Propagation through burst-like medium, and a medium decomposed into stochastic and coherent structures are developed.

The results of laboratory measurements of the spatial distribution of the four-point coherence function (fourth moment) of a spherical wave are presented. Using a special interferometric system we have illuminated a rough surface through turbulence with a coherent point source and observed the interference pattern in the source plane. Experimental data demonstrate the existence of a region where coherence enhancement after backscattering through turbulence may be observed. The time averaged intensity distribution in this region is described by the fourth moment of a spherical wave propagated through turbulence. This study demonstrates that the measurements of the fourth moment may also be applicable for estimating of the inner scale of the turbulence.

Atmospheric optical turbulence (AOT) degrades seeing conditions over long horizontal paths. Embedded into the typical AOT diurnal cycle are two time periods in which the AOT is at a minimum; these periods are called neutral events (NE). Previously, we stated that the NE generally occurs 60 min after sunrise and 40 min before sunset. We refine this empirical model using a statistical analysis on a March-June 1994 AOT-NE data set sampled over the Tularosa Basin, New Mexico. Reviewing the months successively, a systematic change in the time differential between sunrise (sunset) and NE was observed. This and other March-to-June trends are discussed, as are several factors that cause variations in the NE forecast. We conclude with recommendations for refining the AOT-NE forecasting model.

Optical communications offer high data rate satellite to ground communications in a small, low mass, and low power consumption package. However, turbulence-induced scintillation degrades the link performance as the zenith angle increases. To investigate the effect of atmospheric turbulence on the optical link at high zenith angles, we performed a 570 Mbps optical communications link across a 42 km horizontal path, and have measured the effects of aperture averaging on the irradiance variance. The variance clearly showed a dependence on the aperture size, decreasing with increasing aperture size. These results were used to calculate the log-amplitude variance and the atmospheric structure constant, C_n², across the link. The bit error rates across the link were also measured. The results show that the link performance was dominated by burst errors with error rates that ranged from 10^-6 to 10^-2, increasing with decreasing aperture size.

We introduce a model for the power spectrum of stratospheric turbulence that is based on data from in situ measurements and on results of the theory of saturated internal gravity waves. We then study the effect of that stratospheric turbulence has on the scintillation, the coherence of starlight, and on the degradation of star image. It is shown that because the stratospheric phase structure function is approximately quadratic over distance comparable with the aperture of a large telescope, stratospheric turbulence does not significantly degrade short-exposure images of star but does degrade long-exposure ones. The influence of stratosphere on star image degradation is more important in the IR than in the visible range because of the specific dependence of the stratospheric coherence radius on the light wavelength. Star image motion and blurring are determined by different characteristics of the atmosphere and cannot be explained solely on the basis of Kolmogorov model. The modified astronomical imaging theory predicts greater improvement in resolution due to tilt removal than a conventional theory.

The multi-frame blind deconvolution algorithm is considered for processing astronomical speckle images when only a few frames of data are collected. It has been noted that when the speckle data contains even moderate amounts of shot noise the algorithm often converges to the trivial point solution. The convergence properties of the Knox-Thompson algorithm are well understood, however when only a few frames of data are used, the algorithm often contains false structure referred to as processing artifacts. In this paper we consider penalized blind convolution as a `clean up' for the Knox-Thompson algorithm. The utility of this combination is demonstrated images of the Jovian moon Ganymede taken on a 1.5 meter telescope.

A joint effect of the non-Kolmogorov stratospheric and Kolmogorov tropospheric turbulence on star image motion is studied, and the theoretical predictions are compared with measured data. It is shown that for a large telescope the stratosphere can produce a considerable effect on star image motion. The stratospheric component of a wavefront tilt, similar to the tropospheric one, is wavelength independent, and that permits us to sense the tilt at visible wavelengths for compensation at near infrared wavelengths. The techniques which permit us to single out the contribution of the stratosphere to star image motion, and to exclude the effect of uncontrolled telescope motion on the measured data are described. An analysis of the stratospheric effect on the phase fluctuations power spectrum of a starlight is performed, and it is shown that this effect possibly should be taken into account for interpretation of the interferometric stellar data.

A technique for measuring a full aperture tilt (FAT) with a laser guide star (LGS) is proposed. It is shown that information about a FAT is lost in a conventional LGS scheme because of the reciprocity of propagation paths. As a consequence neither the conventional LGS scheme nor its modifications with the receiver coaxial with the transmitter can be used to sense the FAT. A bistatic scheme that permits us to overcome the above difficulty is considered. This scheme permits us to single out the tilt component corresponding to the transmitting beam which is highly correlated with the FAT for a natural star. The tilt component corresponding to the reflected wave can be averaged out by averaging a LGS image motion over its angular extent. Such an averaging, however, does not affect the tilt component corresponding to the transmitting beam. This tilt conservation effect occurs due to the fact that a random motion of the transmitting beam causes a displacement of the LGS as a whole. The accuracy of measuring a FAT with a LGS is determined and the requirements for the measurement scheme are discussed.

One of the simplest manifestations of multiple scattering is the phenomenon of enhanced backscattering, which arises from the constructive interference of radiation which has traversed reversible paths from the source through the scattering medium and back in the source direction. Closely related effects occur when radiation is back-reflected through weakly scattering random media: a `double passage' geometry commonly encountered in monostatic lidar, radar and sonar systems. In addition to an enhanced signal level, double passage through a random medium can also lead to increased signal fluctuation or fading by comparison with a bistatic configuration, in which scattering on the outward and return paths is uncorrelated. The relative merits of these two modes of operation depends on system geometry and background noise as well as the nature of signal fluctuations. In this paper the effects of enhanced backscattering on system performance are discussed with reference to a range of noise and signal fluctuation models. Quantitative calculations of the performance of a simple detection scheme are used to illustrate the different regimes of operation and make comparisons between monostatic and bistatic configurations and between direct and homodyne detection.

We describe experimental investigations of the confocal microscopy method for imaging optically rough objects through turbulence. We have compared the potential of one- and two- lens illumination/receiving systems for the situations when illumination and viewing proceed through the same and different inhomogeneities of the medium respectively (double and independent passage geometries). Active imaging through independent inhomogeneities (two- lens geometry) gives a maximum factor (root)2 improvement (in comparison with passive imaging system) irrespectively of the turbulence properties.

The results of interferometry experiments utilizing a Ku band synthetic aperture (imaging) radar flying repeat-pass trajectories are described. The radar is equipped with on-board differential GPS, which permits precise control and measurement of flight paths. Additional inertial sensors allow high-bandwidth motion compensation of the SAR images. Interferometric processing of flight data permitted formation of topographic images. However, due to the shallow grazing angles (10 degrees) and propagation through 40 km of atmosphere, phase anomalies were visible which were attributed to atmospheric granularity. This paper examines the phase disturbances visible in repeat-pass interferometric experiments and quantifies the phenomenon in relation to available sources on this subject. The line-of-sight path through the lower atmosphere is significantly longer than in previous satellite interferometric experiments. Data from a series of flights spanning late 1993 and early 1994 are presented, along with topographic radar imagery processed at 4 m resolution.

The present paper is devoted to the application of the phase conjugation method for the thermal blooming compensation. Analysis of the numerical experiment data has shown that the appearance of continuous auto-oscillations in adaptive system is connected with the occurrence of dislocations in the reference beam. The use of the Hartmann sensor with low spatial resolution and modal estimation of the phase results in smoothing the phase estimate and damps the AOS oscillations.

This paper deals with the analysis of optical measurements data on the atmospheric turbulence characteristics. Some conclusions are drawn on the variability of the most large scale component of the turbulent inhomogeneities, spectrum for the atmosphere as a whole and for the boundary atmospheric layer as well.

This paper presents the results of lidar based investigations of wind speed and wind history influence on the residence times of marine aerosols. The measurements were carried out in the breaker zones of the southern Baltic Sea.

We showed that the output of a cross-correlation with gas spectra could be triple-correlated to reduce the effects of Gaussian noise for improved discrimination. Such processing is directly applicable to a correlation spectrometer but could be applied to other designs. In spite of the added processing, triple-correlating the output of a spectrometer allowed us to generally increase the SNR by over a factor of ten. We were able to discriminate between two gases at low SNR values with the triple correlation technique.

Diffracted part of the light scattered by both one particle and a scattering medium is rigorously separated from the total multiple scattered intensity. Simple analytical equations for the diffracted part based on the wave parabolic equation are obtained for both the transillumination scheme and the lidar scheme of measurements. The advantage to use the diffracted part for the inverse problems of retrieval of particle size distributions and particle number density profiles from the multiple scattered intensity is discussed.

Marine aerosol was studied with the excimer-dye laser multifrequency lidar of Institute of Oceanology in several sites on the Southern Baltic Polish coast. The aerosol was sounded from lidar located in a van a few hundred feet from the shore in different meteorological conditions. The soundings were performed at several angles to the horizon, starting from horizontal optical path. The backscattered signal collected at 2 - 4 wavelengths allowed for calculation of total aerosol concentration and estimation of its size-distribution every 20 feet of the optical paths at several heights over the sea surface. This allowed for 2D mapping of aerosol concentration over the wave-breaking zone and the shore. The 2D aerosol concentration maps obtained in the research will be useful for verification of models of mass and energy fluxes in the wave-breaking zone of coastal sea basins.

Since 1987, we have measured the transverse coherence length (Fried's r_o parameter) and the isoplanatic angle, (theta) _o, using optical instruments at the Starfire Optical Range (SOR). Through the end of December 1994, we have accumulated 160, 653 r_o measurements and 185,488 (theta) _o measurements. The transverse coherence length, r_o, was determined by measuring the short exposure modulation transfer function of the atmosphere using a 35.5 cm Celestron transfer observing bright stars. The isoplanatic angle was obtained using a stellar scintillation technique on bright stars with a 10 cm Meade telescope. Prior to 1992, a 20 cm Celestron telescope with an apodized aperture was used. Means and frequency distributions of r_o and (theta) _o have been determined for the period 1987 through December 1994, for each individual year and for each month using measurement from all years. In addition, for the period November 1993 to December 1994, we used Albuquerque National Weather Service rawinsonde wind data and a model of the C_n² profile to estimate the Greenwood frequency f_G. These estimates generally compare well with measured Greenwood frequency data obtained from the high speed wavefront sensor in the 1.5 m adaptive optics system. The summaries presented are a first attempt to characterize the optical turbulence at the SOR and may be used to plan experiments during months of statistically low atmospheric turbulence and Greenwood frequency.

The surface autocorrelation function can be retrieved from the values of the far-field integrated irradiance. The inversion procedure is discussed in the frame of a theory of integrated wavelet transformation. For different types of autocorrelation functions, the capabilities and limitations of the inversion procedure are studied. The influence of experimental noise and the specific choice of the analyzing wavelet are also investigated.

TAISIR, the Temperature and Imaging System InfraRed, is a nominally satellite based platform for remote sensing of the earth. One of its design features is to acquire atmospheric data simultaneous with ground data, resulting in minimal dependence on external atmospheric models for data correlation. One technique we employ to acquire atmospheric data is a true multi-angle data acquisition technique. Previous techniques have used only two angles. Here we demonstrate the advantage of using a large number of viewing angles to overconstrain the inversion problem for critical atmospheric and source parameters. For reasonable data acquisition scenarios, simulations show source temperature errors of less than 1 K should be possible. Tradeoffs between flight geometry, number of look angles, and system signal-to- noise are given for typical parameter ranges.

The effect of correlation of opposing waves (one of them is incident on the viewed object and the other is reflected from it) on short-exposure imaging in turbulence is investigated theoretically. The case of strong optical turbulence is considered. As a result it is shown that the spatial spectrum of the mean of intensity in the image of coherently illuminated in a turbulent atmosphere object is presented in a form of two terms. The first term describes the short-exposure image of an incoherently illuminated object, and the other owes its origin to correlation of the opposing waves. This term contains the spectral components of the high- frequency part of spatial spectrum of the object, filtered by inhomogeneous medium in the absence of counter wave correlation. Both incoherent term of the spatial spectrum of short- exposure image and coherent one cover the more high-frequency range than in the case of long-exposure image. The behavior of quality of short-exposure coherent images as compared to long-exposure ones is estimated.

This paper presents the results of lidar investigations of aerosol concentrations over the breaker zones. These investigations have been carried out in the Institute of Oceanology PAS since 1992. The measurements were carried out under various weather conditions during several cruises aboard the y/s Oceania on the Baltic and during shore experiments from the Polish coast towards the Gulf of Gdansk as well as the open Baltic Sea. Simultaneous measurements with a PMS aerosol spectral probe and impactors were carried out during the experiments. The concentrations and size distribution functions of aerosols as well as vertical and horizontal gradients of aerosol concentration, mass fluxes and residence times were determined from backscattered lidar signals at various altitudes.

The topic of enhanced backscattering (EBS) from random media has generated considerably research interest for the last two decades in Eastern Europe and for the last decade in the West. Two distinct scattering phenomena that are unique to scattering by random media are capable of producing enhanced backscatter: coherent reciprocal path scattering (RPS) and incoherent random focusing events. When coherent RPS is responsible for EBS, the maximum enhancement factor is two. Several theoretical models exist for EBS from random rough surfaces and by atmospheric turbulence individually; however, no theoretical model exists for the EBS due to the combination of rough surface and atmospheric turbulence enhancement. Simple geometrical optics models are presented that illustrate the EBS due to RPS by the combination of saturated atmospheric turbulence and a rough surface target upon a monostatic laser radar system.

The problem of imaging airborne particulate is overcome by the use of a Gated Back- Scattering Imaging Lidar system. Standard video systems are not capable of identifying most particulate or biological elements. By using ultra short pulsed laser signals exclusively tuned for specific atmospheric and aerosol conditions, Lidar systems are capable of identification of specific airborne particulate. A gated Lidar system can be adjusted to return a signal from a specific layer located within a column of the atmosphere. The operator can vary the width of the investigated layer and the relative location of this layer within the atmosphere. Multiple receiver systems are capable of imaging numerous layers simultaneously. One of the major advantages of gated Lidar is that back scatter from layers before and after the region to be searched is reduced to zero. This discrimination in layer searching will increase the signal to noise ratio of the system, substantially increasing the likelihood of target recognition. These systems are used for the detection of biological constituents, atmospheric pollutants and wind shear detection.

We present measurements of the atmospheric refractive index structure parameter C_n² and the inner scale l_o made with a SLS-20 scintillometer manufactured by Scintec GmbH. The measurements are compared to measurements of scintillation made with a simple in-house built scintillometer and to C_n² derived from measurements of C_T² made with differential temperature probes. We found that the combination of l_o and C_n² data provided by the SLS-20 allowed us to calculate the log-amplitude variance of the scintillation measured with the in-house scintillometer with good agreement. Poor agreement was found between the SLS-20 and temperature probe C_n² data primarily because of the limited frequency response of the probes.

The results of experimental study of the mean and variance of intensity of laser beam after double passage in turbulence are presented. The experiments were held in the artificial turbulent medium created with the use of the laboratory convectional generator of turbulence. The pathlength in measurements equaled 2 m, the refractive index structure constant C_n² ranged up to about 5 (DOT) 10^-11 cm^-2/3. As a reflector the plane mirror was used and measurements were carried out at different sizes of mirror both on correlated path (when incident and returned waves pass along the same pathway) and in the case of considerable spacing their pathways. The mean intensity on the correlated path, as compared with uncorrelated one, is shown to increase when the reflector dimensions are multiple of even number of Fresnel zones and to decrease when dimensions are multiple of odd number of zones. Intensity relative variance is maximal if reflector diameter multiples to integer of Fresnel zones m and is minimal for the mirror sizes multiple to (m + 0.5) Fresnel zones.

There is currently no active, single-ended optical technique for remotely sensing the refractive index structure characteristic C_n² in the turbulent atmosphere. A capability to remotely measure C_n² is needed in several areas. In astronomy, the vertical profile C_n²(h) is required in order to understand and improve the performance of adaptive optics systems, and measurements of C_n² in arbitrary directions above fixed points on the ground would be useful in site surveys. Researchers in basic atmospheric physics need an optical technique because it would be sensitive to temperature fluctuations only and not water vapor fluctuations, unlike the radar and acoustic sounders which are currently used. Understanding laser beam degradation, for communications, power beaming, or weapon system development, also requires a knowledge of C_n². An optical remote sensor for C_n² could also be used for horizontal, path-averaged measurements, to infer fluxes of heat and momentum over land or sea surfaces. We have recently proposed three different lidar-type techniques for remote sensing of C_n², based on the following phenomena: enhanced backscattering, residual turbulent scintillation, and image distortion. Each of these techniques is reviewed here in terms of its advantages and disadvantages for various applications, and some considerations for practical systems are also discussed.

The characterization of the water vapor continuum remains an important problem concerning infrared propagation in the atmosphere. Radiometric imaging within the atmosphere in the 8 to 12 micrometers and 3 - 5 micrometers regions, and eye safe lidar in the 2 micrometers and 1.6 micrometers window regions require accurate knowledge of the water vapor continuum. Although the physical nature of the continuum is a complex problem, the observed frequency, pressure and temperature dependence can be represented reasonably well by simple mathematical functions consistent with far wing theories. This approach is the basis for current models used in LOWTRAN/MODTRAN and for the models listed in the SPIE/ERIM EO/IR Systems Handbook (Volume 2 Chapter 1). However, these models are based solely on a limited, but high quality, data set collected by a spectrometer and White cell. Additional information on oxygen broadening and temperature dependence is available from numerous laser measurements of the water vapor continuum. A survey of relevant experimental data is made to determine the best available measurements of the water vapor continuum in various atmospheric window regions. Then the data are fit to an empirical model over the entire window region. A good fit is obtained for typical atmospheric conditions covering the 8 to 12 micrometers and 3 to 5 micrometers regions. No experimental data, covering atmospheric conditions, exist in the 2 micrometers and 1.6 micrometers regions. However, models can be proposed based on far wing extrapolations of the bordering vibrational water vapor bands.

The results of recent measurements of the intensity and phase fluctuations of one micron speckle propagating through a two kilometer (round-trip) turbulent path are presented. The data was collected at BMDO's Innovative Science and Technology Experimentation Facility (ISTEF) at the Kennedy Space Center in Florida using a dual-aperture Nd:YAG coherent array transceiver developed at CREOL. The dual-aperture measurement technique allowed for the discrimination of atmospheric turbulence induced phase perturbations from relative target/platform motion induced phase modulation, since the target motion produces common phase modulation in both receivers. The phase and intensity were found to be Gaussian and K- distributed respectively.

The primary goal of the paper is the use of acoustic measurements to investigate the interaction of intense laser radiation with liquid in the dispersed state. It is well known that the formulation and solution of such problems involve optoacoustics, describing, in this case, acoustic waves generated in the liquid as a result of thermal or striction effects of laser radiation. In this investigation, we use acoustic measurements to determine either the absorption of the substance (optoacoustic spectroscopy) or the spatial radiation structure (optoacoustic tomography). Moreover, the authors have used acoustic measurements to obtain the thresholds of phase transitions in liquid aerosols. The latter result provides important information needed in experimental optical studies of aerosols.

In planned intersatellite optical communication systems, the optical payload on board the geostationary satellite will be periodically pointed towards an Optical Ground Station. When the satellite-ground link is established, the turbulence-induced disturbances must be taken into account. The subject of this paper is to assess the statistics for the power fadings that result from the instantaneous point-spread function distortion. Results predicted by an approximate technique which considers the instantaneous point-spread function as a gaussian intensity distribution displaced from the focus due to the angle-of-arrival tilt are compared against results obtained from wavefront simulations produced by fractal generation techniques. The reduction in the cumulative probability of losses that can be obtained by spatial averaging using a multiaperture receiver is also assessed.