One of the unique sources of aerosol found in the coastal environment is the action of the breaking waves near the shore. This paper utilizes the data obtained from a series of experiments from the Electro Qptical propagation Assessment in coastal nvironments program, EOPACE, which has as one of its objectives the determination of the impact of surf produced aerosols in the propagation of IR radiation. These experiments were carried out in both San Diego and Monterey Bay. This paper discusses some of the observed dynamic aerosol production processes as well as longer term effects involved with the breaking surf and the cloud of aerosol it produces. Several techniques used to investigate these include: a) profiles of aerosol size distributions above the surf b) spectral analysis of observed size selected aerosol concentration time series c) transmission paths across the surf and d) simultaneous aerosol measurements from boat and beach.

Aerosol concentrations over the surf were measured during the EOPACE (Electro-Optical Propagation Assessment in Coastal Environment) Surf-i experiment in La Jolla, California. Particle size distributions were measured on the beach (at three levels) and across the surf (one level). Concentrations of droplets smaller than i im in diameter are little affected by the surf, while those with diameters in the 1-10 im range increase by up to two orders of magnitude. Clear vertical gradients were observed, which vary with particle size. No relation could be established between the surf production and wind speed or wave properties. Extinction coefficients at visible and infrared wavelengths calculated from the particle size distributions show that these are enhanced by a factor of 30 to 100, depending on the wavelength. Using the measured concentrations as boundary condition, calculations with a simple dispersion model show the gradual decrease in the concentration with fetch in off-shore winds. In on-shore winds the surf-enhanced aerosol concentration is effective over only a short range, but nevertheless significant transmission losses may occur. Obviously, these conclusions apply only to the surf encountered during this specific experiment. The effects of the surf in other areas and other ambient conditions will be assessed from the analysis of data collected at a different location and in different conditions.

Observations of the size-differentiated composition of aerosol particles obtained during the EOPACE (Electro-Optical Propagation Assessment in Coastal Environments) Air Mass Characterisation Experiment in April 1996 are reported. These measurements were made on board the RV Point Sur along the southern California coast, with special emphasis on the Southern California Bight, and demonstrate the extreme variability ofboth aerosol composition and loadings within this region. A thermal analytical technique, which relies upon the fact that dominant aerosol species volatilise at characteristic temperatures, was utilised to determine aerosol composition and comprised a heater system coupled to a commercial optical particle counter. Accompanying measurements of soot carbon loadings were obtained by means of a commercial aethalometer and clearly demonstrated the impact of urban pollution upon this littoral region. This study formed one element ofthe Air Mass Characterisation Experiment which included the retrieval of aerosol optical depths from NOAA-14 sateffite overpasses ofthe region.

We compare measurements of marine aerosol size distributions and measurements of visible and infrared aerosol extinction coefficient to predictions made with a marine aerosol model. The measurements were made in the North sea near the Dutch coast in 1993 during the MAPTIP trial and in the Mediterranean near Crete in 1996 during the LAPTEX trial. Measurements ofaerosol size distributions were made with aerosol spectrometers and extinction was measured at wavelengths of O.55, 3.8 and 10.6 im with forward scatter sensors. The model calculates vertical profiles of aerosol size distributions and infrared extinction coefficients in the marine boundary layer. The size distributions are represented as the sum of four log-normal distributions having amplitudes that depend on local meteorological conditions. The model uses a set of aerosol types distinguished by different mode radii that are representative of different ocean regions. Results show that the model performs reasonably well compared to the measurements.

The U.S. Navy Aerosol Model (NAM) was developed to compute aerosol extinction coefficients at visual and infrared wavelengths in the marine boundary layer atmosphere. The NAM provides an empirical assessment of the aerosol particle size distribution, which is derived from an input of background meteorological measurements, representative of real-thne atmospheric conditions. The NAM aerosol size distribution can be specified as the superimposition of three distinct aerosol production mechanisms, the first of which is comprised of an air mass driven component that can be parameterized in a variety of ways. The amplitude of the air mass component is the largest of the three aerosol modes and is the most difficult to measure. The other two modes depend upon wind speed to actuate the aerosol yield and are not of primary interest here. Air mass characterization is accomplished by parameterizing the amplitude of the air mass component four methodologies are discussed: (1) measuring the atmospheric radon gas concentration which is used as an air mass tracer, (2) computing air trajectories to determine air mass histories, (3) indexing trajectories to the radon count, and (4) measuring the condensation nuclei (CN) count. Data bases from the Navy EOPACE (Electro Optical Propagation Assessment in Coastal Environments) program will be employed to test and evaluate the potential air mass parameters. The advantages and disadvantages of each approach are discussed. The air mass index scheme using radon and air trajectories is outlined and the full development of the CN air mass parameter technique, including numerical and analytical solutions, is presented.

The origin of an air mass is an important factor in predicting performance of electrooptical systems in coastal environments. The aerosol content varies significantly depending upon whether the air mass is anthropogenic or natural, marine or continental, rural or urban. Measurement of radon concentration is a traditional method used to determine the origin of an air mass, but sensitive radon monitors are not readily available. A method of determining aerosol concentration from more easily obtainable three-wavelength nephelometer measurements can be used in conjunction with the Navy Aerosol Model to determine the air mass characteristic. This paper explores this process, using data collected during an EOPACE (Electrooptical Propagation Assessment in Coastal Environments) experiment in November 1996. Radon and nephelometer data were collected, along with a full complement of meteorological and aerosol data, during a wide range of meteorological conditions.

The optical properties of the atmosphere over the ocean are determined by the presence of anthropogenic, rural and marine aerosols, in a ratio that is changing with the residence time ofthe air mass over the ocean. Continental aerosols are removed by a variety of processes, whereas sea spray aerosol is produced at the surface due to the interaction between wind and waves, new particles are formed and physical and chemical processes result in complex mixtures. A parameterisation of the air mass characteristics in terms of an air mass parameter (amp) has been proposed. The amp is related to the residence time ofthe air mass over the ocean and several routine measurements were proposed to quantify this parameter. In open ocean conditions this approach appears to work well, but in coastal regions significant discrepancies with experimental data have been observed. In EOPACE, an appreciable effort is made to fmd a better indicator for the amp. The April 1996 cruise with the RV 'Point Sur' offthe Californian coast was mainly dedicated to characterisation ofthe air mass, using measurements of aerosol particle size distributions and chemical composition, lidar and radiosonde profiles, and meteorological data, together with satellite images of aerosol optical depth retrieved form AVHRR data.

Reflectivity is a fundamental parameter for sensing the morphology and composition of clouds and precipitation. However, attenuation due to varying amounts of precipitation, clouds, and water vapor along the propagation path corrupts reflectivity estimates. In this paper, an algorithm to correct for these effects at 33 and 95 GHz is proposed. This algorithm is then applied to corrupted reflectivity images collected with the University of Massachusetts Microwave Remote Sensing Laboratory (MIRSL) Cloud Profiling Radar System (CPRS), which is a dual-frequency (33 and 95 GHz) , fully-polarimetric, pulse-Doppler, ground-based radar. The attenuation correction algorithm consists of two steps. First, different sources of attenuation along the propagation path are identified by classifying each image into regions of: air, ice particles, liquid droplets, rain, mixed-phase particles, and insects. This is accomplished with a rule-based classifier that relies on collocated measurements of velocity, linear depolarization ratio, and height to make classification decisions. The second step is correcting attenuation along the propagation path in a region appropriate manner. By starting at the ground with the assumption that the reflectivity estimate is unattenuated, and working away from the radar adding a region-appropriate amount to the reflectivity estimate at each range gate, attenuation effects in the image can be largely removed. However, if a mixed-phase region where the rate of attenuation is unknown is encountered along the propagation path, the correction is suspended and an alternative approach that corrects attenuation from the top of the cloud down is used. The complete algorithm was applied to the CPRS data and significantly improved reflectivity estimates.

Battlespace meteorological and oceanographic (METOC) conditions can be defined and displayed using the Navy's C4ISR architecture for use in strike planning, optimizing weapons performance, and postoperation assessment. Using the Tactical Environmental Support System (TESS), METOC satellite imagery has been exploited to derive estimates of temperature and cloud conditions along Tomahawk flight paths, and integrated with operational geometry to support missile launches conducted during Joint Warrior Interoperability Demonstration (JWID-95). The integrated and fused displays were sent from the Battle Management Interoperability Center (BMIC) at the Naval Air Warfare Center Weapons Division, Point Mugu, and transmitted to fleet units where they were inserted as strike warfare support products on a home page for transmission to other JWID participants. Other support techniques are also being implemented using home page/internet technology. The EMIEO propagation environment is being characterized remotely by application of the "satellite-JR duct technique" which allows duct heights to be displayed over low-cloud regions over subtropical ocean areas. To provide duct height estimates in regions without clouds or in-situ measurements, or predictions of ducting conditions, the "equivalent altitude" and "experduct" techniques are employed to demonstrate additional automated capabilities using synoptic weather considerations.

EOPACE is a five year multi-national effort to improve performance assessment for electrooptical systems operating in coastal environments. Existing propagation codes such as LOWTRAN/MODTRAN incorporate models that were developed for open ocean conditions and work quite well for this scenario. However, there are processes that are unique to near coastal regions which are not adequately accounted for in LOWTRAN/MODTRAN. Coastal environments may differ significantly from open ocean conditions, and need to be fully characterized. The objectives of EOPACE are threefold: (1) to investigate coastal aerosols by studying surfproduction, coastal air mass characterization, and near ocean surface transmission characteristics; (2) to develop mesoscale and data assimilation models; and (3) to evaluate EO systems performance by studying targets and backgrounds, polarization techniques, performance of forward looking infrared (FUR) and infrared search and track (IRST) systems, and tactical decision aids. Six EOPACE Intensive Operational Periods (TOPs) have been conducted during 1996 and 1 997. Two more TOPs are planned along with one Extended Operational Period (EOP). In situ and remote sensing techniques have been used to infer the impact of surf-generated aerosols, air mass parameterization required for propagation codes, near ocean surface infrared transmission properties, and IRST/FLIR systems performance in coastal environments. Initial results concern coastal aerosols. This paper gives an overview of the EOPACE effort and discusses the initial observations relative to: (1) the impact of surf generated aerosols on visual and JR extinction in a coastal environment, (2) establishing the variability of aerosol concentrations and composition for coastal air masses for the development of a Coastal Aerosol Model (CAM), and (3) quantifying JR propagation characteristics for two wavebands (3- 5 and 8-12 microns) for near ocean transmission.

An analysis is presented showing the effects of molecules and aerosols on atmospheric transmission data obtained during the Electro-Optical Propagation Assessment in Coastal Environments (EOPACE) campaign carried out in San Diego during March and April, 1996. Mid wave infrared transmission was measured over San Diego Bay along a 14.9 km path and a 7.0 km path at heights less than 4 meters above the water. Simultaneous meteorological measurements were obtained from two buoys placed at the mid-points of each path. An aerosol spectrometer was used to measure the aerosol size distribution over each transmission path. Data were analyzed with MODTRAN and Mie theory. The conclusion of this and the next two papers is that low altitude infrared transmission is a complex phenomenon whose mean value may be controlled either by molecular absorption, aerosol scattering, or refractive focusing, and whose fluctuating value is controlled by scintillation.

An analysis is presented showing the effects of refraction, aerosol extinction, and molecular extinction on transmission measurements obtained during the EO Propagation Assessment in Coastal Environments (EOPACE) campaign carried out in San Diego during March and April 1996. Infrared transmission measurements were made over both a 7 km path (mid IR) and a 15 km path (mid JR and far IR) at heights below 10 m above sea level. The average difference between all the measured transmissions and aerosol transmittances over the two paths with results obtained using the JR Boundary Layer Effects Model (IRBLEM) were found to be relatively small, even though the difference for individual measurements can be significant. The effect of molecular transmittance, as calculated using MODTRAN, is found to reduce the transmission by about 35% forthe 7 km path, 72% for the mid JR over the 15 km path, and between 70% and 90% for the far JR over the 15 km path.The effect of aerosol transmittance, as calculated using a variation of the Navy Aerosol Model (NAM), is found to reduce the transmission from 10% to 90% for the mid JR over both the 7 and 15 km paths, and from 10% to 60% for the far JR over the 15 km path. The effect of refractance, the focussing and defocussing of radiation due to atmospheric refraction, on the predicted transmissions is found to account for gains and losses up to 20% for the 7 km path, and gains and losses up to 100% for the 15 km path. Consequently, any JR transmission model for the marine boundary layer (MBL) must properly take into account the effects on the transmission due to molecular extinction, aerosol extinction, and refractance.

This paper concerns the effect of scintillation on the detection range of infrared sensors, where frame rate appears to play an important role. During EOPACE scintillation measurements were carried out over the Monterey and San Diego Bay. For this purpose 2 kinds of sources were used, either a source, modulated with 1000 Hz, or a DC searchlight source. The detector was a silicon detector with a narrow bandfilter around 0.85 tim. The results show that scintillation is always present, even when locally the air to sea temperature difference (ASTD) is close to zero. This indicates that large ASTD variations may occur along the measurement path. The magnitude of the scintillation agrees reasonably well with the theory. This means a big advantage for high frame rate sensors in comparison with low frame rate sensors for detection of point targets at low elevation.

The Electro-Optical Tactical Decision Aid (EOTDA) is a strike warfare mission planning tool originally developed by the US Air Force. The US Navy has added navy sensors and targets to the EOTDA and installed it into current fleet mission planning and support systems. Fleet experience with the EOTDA and previous studies have noted the need for improvement, especially for scenarios involving ocean backgrounds. In order to test and improve the water background model in the EOTDA, a modified version has been created that replaces the existing semi-empirical model with the SeaRad model that was developed by Naval Command, Control and Ocean Surveillance Systems (NRaD). The SeaRad model is a more rigorous solution based on the Cox-Munk wave-slope probabilities. During the April 1996 Electrooptical Propagation Assessment in Coastal Environments (EOPACE) trials, data was collected to evaluate the effects of the SeaRad version of the EOTDA. Data was collected using a calibrated airborne infrared imaging system and operational FUR systems against ship targets. A modified version of MODTRAN also containing the SeaRad model is used to correct the data for the influences of the atmosphere. This report uses these data along with the modified EOTDA to evaluate the effects of the SeaRad model on ocean background predictions under clear and clouded skies. Upon using the more accurate water reflection model, the significance of the sky and cloud radiance contributions become more apparent leading to recommendations for further improvements.

This paper investigates the impact of considering vertically-varying turbulence and aerosol extinction on imaging of long range surface targets, compared with assuming invariant properties in the marine surface layer. Models of turbulence and aerosol extinction in the marine surface layer are presented and calculations of aerosol transmittance and of turbulenceinduced blurring and scintillation are performed and discussed under thermally unstable and stable conditions, taking into account air refraction and the Earth curvature.

The range performance of IRST sensors is partly determined by the propagation of the atmosphere. For low altitude targets the boundary layer of the atmosphere introduces a variety of effects due to inhomogeneities, for which model predictions are not yet well validated. For this reason NATO Research Study Group 5 on "Maritime Infrared Target and Background Signatures, Measurement and Characterization" organized the Low Altitude Point Target EXperiment (LAPTEX) in the Mediterranean Sea at the NATO-FORACS site at Crete (Greece) from 8-26 July 1996. In this experiment a wide beam point source was mounted on a small ship, sailing out and in along a straight line to the detecting sensors. The same ship was equipped with a comprehensive set of meteorological instrumentation. By determination of the signal decrease with range, propagation models such as LOWTRAN7 can be validated. This concerns the transmission, assuming that the source radiant intensity is known. Of similar importance is the increase of scintillation with range, predicted by other models. In this paper the setup of the LAPTEX trial is described and the results of some examples of the extinction and scintillation experiments are presented. It is concluded that for the subtropical conditions like at Crete, the LOWTRAN extinction predictions correspond surprisingly well with the measurements. The agreement between the predicted and measured scintillation appears to be less good.

The most recent version (Ver. 6.22) of the marine boundary layer (MBL) profile program, LWWKD, now allows the creation of a single file containing refractivity profiles for a multiple number of horizontal ranges. This file can then be used in the most recent version (Ver. 5.3) ofthe ray-tracing program, REFRACT, so as to simulate the effects of a horizontally non-homogeneous refractivity profile on predictions of maximum intervision range (MIVR) and minimum mirage range (MMR). Using range dependent meteorological measurements obtained from the Hr.Ms. Tydeman during the Marine Aerosol Properties and Thermal Imager Performance (MAPTIP) campaign, this model shows that under certain conditions, a single horizontally homogeneous profile can produce similar MIVR and MMR predictions to those resulting from using the range dependent profile. In general, a single homogeneous profile can give excellent results if it corresponds to the profile at the range for which the light rays are closest to the surface of the water (the observed horizon) and the refractivity gradient is strongest.

Minimum variance wave front estimation techniques are used to improve Deconvolution from Wave front Sensing (DWFS), a method to mitigate the effects of atmospheric turbulence on imaging systems. Both least-squares and minimum variance wave front phase estimation techniques are investigated, using both Gaussian and Zernike polynomial elementary functions. Imaging simulations and established performance metrics are used to evaluate these wave front estimation techniques for a one-meter optical telescope. Results show that the minimum variance estimation technique that employs Zernike polynomial elementary functions provides the best mean and signal-to-noise ratio performance of all the investigated wave front estimation techniques.

The aerosol modulation transfer function (MTF) describes blurring deriving from light scatter caused by aerosols. Little scintillations or image dancing are involved. When overall atmospheric point spread function (PSF) is analyzed for its turbulence component deriving from angle-of-arrival fluctuations or scintillations, a significant portion of the PSF is left over. This is the aerosol component. This overview describes the basic physical mechanisms for aerosol MTF and its wavelength, weather, and time exposure dependences, as well as a comparison to turbulence MiT.

The use of the matched filter to automatically estimate the pose of a Low Earth Orbiting (LEO) satellite from imagery measured with an adaptive optics telescope is explored. The satellite pose estimation problem is studied for a broad range of atmospheric turbulence levels and target visual magnitudes. Several algorithms which use various types of image preprocessing are examined in an effort to determine the performance bounds on the matched filter for this application. Results presented here show that under normal imaging conditions, the matched filter approach proposed can be expected to yield correct pose estimations in over 80% of the trials considered. Additionally, it is shown that a significant portion of errors are between two poses that are very similar in appearance, such as views of the target about an axis of symmetry. When symmetry-based errors are allowed, correct pose estimations are obtained in over 90% of the cases tested.

Atmospheric turbulence strength profile measurements are presented for a number of astronomical observation sites. These results were obtained using the generalised SCIDAR (SCIntillation, Distance And Ranging) technique which allows both the turbulence strength profile and the velocity of the turbulent layers to be determined as a function of height.

In the fall of 1996, we had the opportunity to mneasure the atmospheric coherence length (Fried's r0 parameter) at the STarfire Optical Range using three instruments. Each instrument measured r0 using a different theory and technique. The first instrument, designed and built by Dr. Donald Walters of the Naval Postgraduate School, is based on measuring the MTF of the atmosphere using a stellar image on a one dimensional detector. The second instrument, designed and built by Lockheed Martin engineers at White Sands Missile Range, is based on measuring the differential motion of stellar images. The third technique in this study used short exposure star images taken through the 1.5m telescope and processed by matching the images to shrot exposure theory values of r0. All of the instruments were located at the STarfire Optical Range and data were collected during both day and night hours. This paper presents the results of these measurements and discusses the different techniques in terms of the results obtained.

The theory of short-exposure (SE) imaging and short-term (ST) beam spread is developed based on the Markov approximation for wave propagation in turbulence and Feymnan path-integral formalism. The theory is not restricted by the weak scintillation conditions, and takes into account diffraction and geometric properties ofthe beam and imaging system. We obtain approximations for the ST beam and SE image structure functions, which are free from the drawbacks ofthe classical SE theory. The SE case modulation transfer function (MiT) has a two-scale shape with larger scale extending up to the diffraction cutoff. We show that the imaging system can be optimized to maintain the highest contrast for the given spatial frequency. The initial beam size and its focusing can be optimized in terms ofthe maximum on-axis intensity and minimum beam size. These effects have no analogy for the long-term cases.

The Starfire Optical Range (SOR) has measured scintillatjon at 1 .5microns over a wide range of elevation angles. Comparison of measured results with theoretical expectations revealed widespread agreement. Increasing zenith angle produced increased spatial correlation distances and loss of high spatial frequency content. The magnitude of the increase in correlation distance agreed with accepted theory which predicts dependence on the distance to the turbulence, which is at the tropopause in this case. The bandwidth ofthe collected signal had no discernible effect on correlation distance nor on the amount of scintillation. For the experimental bandwidths used, none were expected. Aperture averaging followed Yura and McKinley's prediction of a diameter to the 716th dependence. Using spatially separated apertures was also shown to be effective at decreasing the amount of scintillation beyond total area effects. Increasing the aperture dimensions had an even larger effect on the number of fades below a given threshold. For optical communication applications, this should be considered closely.

The physical basis of four basic nonlinear stimulated scattering processes in transparent droplets (SRS, SBS, lasing, scattering on droplet surface vibrations) caused by intensive pumping radiation is considered. The vector Maxwell equations, where the nonlinear polarization is the source for nonlinear harmonics origin, are used as a starting point for theoretical analysis of stimulated processes in a droplet. The solution of this system of equations is written in the form of series through droplet resonance eigenmodes. The main attraction is devoted to the energetic thresholds and angular characteristics of nonlinear scattering processes to be considered. The threshold values of the stimulated scattering in droplets are evaluated depending on the droplets radius. The paper presents the results of theoretical investigations of the task on droplet surface deformations and vibrations under the pressure of the ponderomotive forces caused by intensive laser field also. It is pointed out that for small particles (less or compared to laser radiation wavelength) the surface deformations are initated in perpendicular direction to laser beam axis, while large droplets begin to vibrate along the laser beam. This fact is the consequence of the inhomogenouty of internal electromagnetic field distribution in large droplets, that can lead to strong local surface deformations and even droplet destruction. The induced surface deformations cause the intensive nonlinear scattering of pumping electromagnetic field at the Raman frequency. The angular characteristics of this scattering are considered.

Multiple scattering of laser beams in scattering media can be easy expressed through Greens function of the radiative transfer equation. Therefore numerical calculations of Greens functions are more advisable in comparison with calculations of optical signal for some concrete experimental schemes. In this paper, Green's function for snowfalls is calculated with the standard Monte -Carlo code. A simplest model for the phase function of a snowflake is used. The angular and spatial divergence of radiation due to multiple scattering versus optical depths and particle sizes in snowfalls are discussed.

Intensity fluctuations of laser beams propagating through precipitation reveal the regularities that are different from those for the turbulent atmosphere. Specifically, three regimes of fluctuations can be observed. The first one is the weak scintillation regime where the scintillation index increases with the propagation path. The second regime is the fluctuation saturation where the scintillation index approaches a constant. This saturation level can be an arbitrary number unlike the turbulent atmosphere. The further increase of the propagation path leads to damping of intensity fluctuations. This regime has no analogy in the case of the turbulent atmosphere. In the proposed paper, the regime of fluctuation damping in snowfalls is studied both experimentally and theoretically. The experimental setup consists of a narrow laser beam propagating through a 2 km path. A small detector of 0.1 mm of diameter was placed on the optical axis. The dependence of scintillation index on the optical depth of the path and of flowsnake sizes were considered. According to the fluctuation model proposed early by the authors, the scintillation index can be calculated theoretically by means of numerical solution of the radiative transfer equation. The equation is solved by the Monte-Carlo code with some model phase function for a snowflake. The damping factor of scintillations is calculated as a function of the optical depth and of the angular divergence of the laser beam. Comparison of the calculated and experimental data is presented.

The ability to measure atmospheric turbulence characteristics such as Fried's coherence diameter, the outer scale of turbulence, and the turbulence power law are critical for the optimized operation of adaptive optical telescopes. One approach for sensing these turbulence parameters is to use a Hartmann wavefront sensor (H-WFS) array to measure the wavefront slope structure function (SSF) . The SSF is defined as the second moment of the wavefront slope difference between any two subapertures separated in time and/or space. Accurate knowledge of the SSF allows turbulence parameters to be estimated. The H-WFS slope measurements, composed of a true slope signal corrupted by noise, are used to estimate the SSF by computing a mean square difference of slope signals from different subapertures. This computation is typically performed over a large number of H-WFS measurement frames. The quality of the SSF estimate is quantified by the signal-to-noise ratio (SNR) of the estimator. The quality of the SSF estimate then can in turn be related to the quality of the atmospheric turbulence parameter estimates. This research develops a theoretical SNR expression for the SSF estimator. This SNR is a function of H-WFS geometry, the number of temporal measurement frames, the outer scale of turbulence, the turbulence spectrum power law, and the temporal properties of the turbulence. Results are presented for various H-WFS configurations and atmospheric turbulence properties.

Atmospherically-induced wavefront distortions that follow a Kolmogorov power spectral density has a spatial and temporal behaviour best described as a fractional Brownian motion (FBM) process. FBM is persistent and has a considerable degree of predictability, but its slopes are antipersistent and are not easily predicted by conventional means. However, previous measurements have shown that there is a exploitable degree of persistence and predictability in wavefront slopes. In this paper we describe how lowpass-filtered FBM can model the spectral, temporal and predictive properties of distorted wavefronts. Implications for closed-loop adaptive optics systems will be discussed.

Many optical systems work on the basis of the correclion of the incoming wave-front. This correction has to be as complete as possible. In actual experiments, when working in the visible, only a partial compensation is attainable. In this case correction can be quite good at the image center where the light intensity remains almost constant, depending on the degree of correction performed over the wave-front. The aim of this paper is to analyze the intensity statistics of the light in the image center as a function of the number of Zernike polynomials corrected when adaptive optics systems are used.

Anew Fourier Series atmospheric phase screen generator is introduced. A Fourier Series (FS) is used to represent the wavefront phase as a two dimensional periodic function. The period of the function is chosen to be much larger than the outer scale of the turbulence and thus the FS accurately represents the power in the low spatial frequencies of the wavefront. The accuracy of the representation of the high spatial frequencies is determined by the number of terms used in the FS expansion. The FS based screen generator is capable of simulating atmospheric-induced wavefront phase distortions arising from temporal and/or anisoplanatic conditions. Both the spatial and temporal correlations between wavefront phases screens separated by time and/or angle are properly modeled. The conventional approach of simulating temporal evolution by making a large phase screen and then shifting is avoided. The phase screen generator is presented in an extremely compact and simple vector notation that lends itself for almost immediate implementation on modern mathematical analysis software packages.

Image quality metrics that can be obtained optically using coherent optical systems are discussed. Coherent optical processing to measure these image quality metrics includes several steps: (a) transformation ofthe image plane intensity distribution into a phase modulation ofthe coherent wave using a liquid crystal television; (b) diffraction of the phase modulated wave over a specified distance to enhance particular image spatial frequencies; (c) a secondary intensity-phase transformation; and (d) application of an image quality analyzer based on speckle field statistical properties. We present experimental results, along with corresponding numerical simulations, that demonstrate the effectiveness ofthese technique for adaptive correction of phase-distorted extended source images.

Major efforts in astronomical instrumentation are now being made to apply the techniques of adaptive optics to the correction of phase distortions induced by the turbulent atmosphere and by quasi-static aberrations in telescopes themselves. Despite decades of study, the problem of atmospheric turbulence is still only partially understood. We have obtained video-rate (30 Hz) imaging of stellar clusters and of single-star phase distortions over the pupil of the 200" Hale telescope on Palomar Mountain. These data show complex temporal and spatial behavior, with multiple components arising at a number of scale heights in the atmosphere; we hope to quantify this behavior to ensure the feasibility of adaptive optics at the Observatory. We have implemented different wavefront sensing techniques to measure aperture phase in wavefronts from single stars, including the classical Foucault test, which measures the local gradient of phase, and the recently-devised curvature sensing technique, which measures the second derivative of pupil phase and has formed the real-time wavefront sensor for some very productive astronomical adaptive optics. Our data, though not fast enough to capture all details of atmospheric phase fluctuations, provide important information regarding the capabilities that must be met by the adaptive optics system now being built for the 200" telescope by a team at the Jet Propulsion Lab. We describe our data acquisition techniques, initial results from efforts to characterize the properties of the turbulent atmosphere at Palomar Mountain, and future plans to extract additional quantitative parameters of use for adaptive optics performance predictions.

Large and expensive astronomical facilities are now planning operation of their multi-instruments telescopes under queue scheduling mode. The main idea is to boost the efficiency of astronomical observing making a better use of available dark time. The choice of a given observing program would be driven by environmental constraints which have therefore to be reliably and accurately monitored. Atmospheric seeing is one of those and earlier site survey oriented monitors have now to be upgraded towards unattended continuous operation. Differential Image Motion (DIMM) Seeing Monitoring is now a common feature of a growing number of observatories worldwide because of a straightforward theory and of its robustness to instrumental errors. However, basic rules have to be respected in particular to reduce the sensitivity of such systems to site dependent parameters such as short wavefront coherence time and finite outer scale of the turbulence. In the light of several years of automated seeing monitoring at the La Silla Observatory and as part of the development of the VLT Astronomical Site Monitor, the criteria for designing such instruments are reviewed and results are presented.

On 15 September 1996, a high altitude research balloon was launched SW of the Starfire Optical Range (SOR) on Kirtland AFB, NM. The primary purpose of the balloon launch was to test a low power satellite communications package developed under the direction of Dr. Charles Swenson of Utah State University. An equally important objective of this experiment was to collect laser scintillation data from the balloon at the 1 .5-meter telescope located at the SOR. Scintillation data was also obtained from a star near the location (azimuth and elevation) of the balloon for comparison. The balloon payload was illuminated from the ground with a small aperture 810 nm laser diode transmitter and retro-reflected into the 1.5-meter telescope from a 1 inch optical corner cube. The returned light was detected by a photomultiplier tube. This paper examines the statistics of intensity fluctuations from these two sources and compares experimental results with theory.

In some applications of laser propagation in the atmosphere by means of athptive optical technique or nonlinear optical effect, the method of active beacon light is used, in which a probe light is transmitted to the target and the reflective light acts as beacon light. However, the large reflective light spot on the target can't meet the application of focusing laser beam. In this paper, the threshold effect of phase conjugated light on the target is demonstrated by the presence of atmospheric turbulence. We present that through one or several times of conjugation, a large beacon light spot on the target can be reduced to a beacon light point. In our laboratory, the threshold effect is verified in the cases of two sparkles and a large area light spot on the target. In the experiment, the distance between the target and the conjugation system is lOm, and area of conjugated light spot is one-fifteenth ofthat oflarge area light spot on the target.

The middle-infrared wavelength region around 3-5 m corresponds to the best optical laser band for high atmospheric transmittance and eye-safety. Middle-infrared lasers are used in laser range finders, laser radars, and so on. There are only a few reports on the atmospheric laser transmittance of these middle-infrared optical bands. This paper describes, we believe for the first time, middle-infrared atmospheric transmittance characteristics as measured by the second and third harmonics of tunable TEA-CO2 lasers. The experimental results showed that the laser transmittance at 3.4 - 3.6 m correlated well with the results calculated by the HITRAN-PC code, assuming a middle-latitude, summer condition. The measured transmittance at 4.6 - 4.8 ,um exhibited a fine-structure, probably due to the absorption of atmospheric molecules such as NO2 and H20.

Transmission measurements were taken through the atmosphere over surf at Scripps Institute of Oceanography Pier, La Jolla, USA, during January and February 1996, as a part of a trial of the Electro-optic Propagation Assessment in Coastal Environments (EOPACE) campaign. Simultaneous measurements in the 3-5um and 8- l2um infra-red bands were taken using a Mercury-Cadmium-Telluride (MCT) and Indium Antimonide (InSb) sandwiched detector. The transmissometer was designed so that the image of the source at the receiver is many times the detector size. In this way, the effect of beam wander and detector non-uniformity are negligible. Measurements are relative in the sense that there was no attempt to calibrate transmission to a refened-standard source like a black-body or to use transmission codes. Meteorological and aerosol data were also collected over the path. It was found that the coastal environment does significantly influence the transmission of infrared radiation even over a path as short as a few hundred metres.

The influence of diffraction on the object, coherently illuminated and viewed through a random medium from the same point, on the image quality betterment caused by the counter wave correlation is studied experimentally. The measurements were carried out with the use of setup modeling artificial convective turbulence. It is shown that in the case of spatially limited reflector with the Fresnel number of the reflector surface radius r ranging from 3 to 12 the contribution of the counter wave correlation into image intensity distribution is maximal as compared with the point objects (r U.

The double-passage effects of atmospheric turbulence on the imaging quality and resolution of an optical system , illuminated by the incoherent light ,are discussed in terms of the information content and the nUmber Nd of degrees of freedom of an imaging system. The Van Cittent-Zernike theorem and the Karhunen-Loe've expasion of generalized prolate -spheroidal function for the mutual intensity of stochastic waves is used to calaulate the turbulent average mutual intensity f12 for light from an extended incoherent quasi -monochromatic source and double-passage propagation in weak atmospheric turbulence. It is shown that , for incoherent illumination system and the receiving aperture is larger than the radius A of backscattered beam ,the turbulent spread of the beam may lead a positive effect , and there is a potential supperresolution , the resolution beyond the classical diffraction limit.

There are many laser and optical-navigation systems located at the working world spacedromes, among which are laser range finders, optical refractometers, television systems of monitoring of the visible and infrared spectral range, systems of optical navigation and aiming and so on. These instruments are used in the information systems for solving the problems when launching space rockets. For precise operation of such optical systems the efficient information is needed on the effect of the real atmosphere on precise and energy characteristics of the used optical-electron devises.

This paper proposes a class of nonlinear methods, called Set-Theoretic Deconvolution (STD), developed for joint restoration of M(M >1) monochrome distorted 2-dimensional images (snapshots) of an unknown extended object, being viewed through the optical channel with unknown PSF, whose true monochrome brightness profiles look distinct at M(M>!) slightly different wavelengths chosen. The presented method appeals to the generalized Projection Onto Convex Sets (POCS) formalism, so that the proper projective metric is introduced and then minimized. Thus, a number of operators is derived in closed form and cyclically applied to M-dimensional functional vector built up from estimates for combinations of monochrome images. During the projecting of vector onto convex sets one attempts to avoid non-physical inversion and to correctly form a feasible solution (fixed point) consistent with qualitative not quantitative information being assumed to be known in advance. Computer simulation demonstrates that the resulting improved monochrome images reveal fine details which could not easily be discerned in the original distorted images. This technique recovers fairly reliably the total multichromatic 2-D portrait of an arbitrary compact object whose monochrome brightness distributions have discontinuities and are highly nonconvex plus multiply connected ones. Originally developed for the deblurring of passively observed objects, the STD approach can be carried over to scenario with actively irradiated objects (f.e., near-Earth space targets). Under advanced conditions, such as spatio-spectrally diversified laser illumination or coherent Doppler imaging implementation, the synthesized loop deconvolver could be universal tool in object feature extraction by means of occasionally aberrated space-borne telescope or turbulence-affected ground/air-based large aperture optical systems.

Atmospheric turbulence over long horizontal paths perturbs phase and also can cause severe intensity scintillation in the pupil of an optical communications receiver. This limits the bit error rate over which intensity based modulation schemes can operate. To quantifi the extent ofthe problem, we built a high speed and high resolution wavefront sensor capable of measuring both the amplitude and phase over a horizontal turbulent path. We present resulting measurements of the probability distributions ofboth amplitude and phase as well as Zernike polynomial decomposition ofthe temporal power spectra of phase fluctuations. These results are compared to existing turbulence models, and are used to determine requirements for a wavefront correction scheme using adaptive optics.

Thermal infrared propagation data has been collected across the surf influenced marine atmospheric boundary layer as a part of the Electro-Optical Propagation in a Coastal Environment (EOPACE) surf zone experiment. This data was collected at Scripps Pier, La Jolla, California in January-February 1996. Preliminary analysis shows that the changes in transmittance are highly correlated with changes in bulk environmental parameters such as wind speed and direction, humidity, and marine haze. The effect of wave height is unclear from this preliminary analysis. An unexpected result was the up to 30% drop in transmission measured during the transition period when the wind speed drops and the air mass flow changes direction. This change occurs in the evening when the wind changes direction from onshore to offshore and in the morning when the wind changes from offshore to onshore. A similar drop in transmittance was not found under any other conditions. This is possibly due to the topography of the site with the steep hill rising up from the beach. The onshore-offshore flow may be very much influenced by this land form.

Adaptive optics systems could be used to maintain the quality of a communication laser beam propagated near ground over a few kilometers of turbulent atmosphere. Such an adaptive optics system may incorporate a Shack- Hartmann sensor to measure the wavefront of an arriving beacon laser beam before precompensating that of the communication laser beam through a deformable mirror. We present experimental measurements of the wavefront of a laser beam propagated over distances of 0.94 and 2.4 km acquired using a 1200-subaperture Shack-Hartmann sensor. These data were acquired at 1 kllz frame rate during 2 second time intervals over the span of several days. We acquired and analyzed 41 sets of data. Our analysis shows that the atmosphere is not stationary over these 2second intervals, that the statistics of the wavefront may look very different for the same measured value of the atmosphere structure constant (C) and does not always follow the theoretical predictions based on Kolmogorov turbulence, and that the subtraction of the first 11 Zernike polynomials (first-order correction) improves the wavefront significantly unlike the subtraction of next 1 1 polynomials (third-order correction).