A technique has been developed by which satellite upwelling radiance measurements, MODTRAN, and the NOVAM aerosol model can be used to infer lower tropospheric extinction coefficients as a function of wavelength. This technique utilizes: 1) satellite upwelling radiance measurements for determining the total aerosol optical depth for a specific geographic location and time, 2) MODTRAN to calculate the optical depth associated with tropospheric aerosol scatter, assuming that no aerosols are being entrained into the troposphere from other source,s and 3) NOVAM for modeling the optical depth of the lower troposphere as a function of air mass parameter. By adjusting the air mass NOVAM so that the calculated optical depth matches that required for the lower troposphere, the air mass parameter for the lower troposphere can be inferred from remote satellite radiance measurements. Initial results using the EOPACE, database appear promising for inferring extinction coefficients of the lower troposphere as a function of wavelength from remote satellite radiance measurements. It also shows promise for an initial technique for modeling coastal aerosols.

Measurements of sub-micron aerosol particles in southern California coastal areas during the Electro-Optical Propagation Assessment in Coastal Environments program indicate that not only particle concentrations but also the composition of the aerosol is highly variable due to the range of particular and pre-cursor gaseous sources present in the littoral zone. Frequently, in offshore flow, large quantities of soot carbon resulting from fossil fuel burning are mixed with pervasive sulphate aerosol particles, while in onshore flow, significant numbers of sea spray particles are present. At larger particle sizes, the aerosol spectrum may be dominated by sea spray particles produced by the action of the wind on the ocean surface at moderate and high wind speeds. This situation is further complicated along coasts where breaking surf provides an additional source of sea spray, and where offshore breezes may transport aeolian dusts from the land interior. These measurements demonstrate that land-sea breezes and other local meteorological processes give rise to substantial variations in aerosol characteristics on relatively small temporal and spatial scales and, from this knowledge of particulate composition, aerosol refractive indices and, hence, atmospheric extinctions at visible and IR wavelengths have been derived for various environmental conditions.

The aerosol in the coastal environment consists of a complicated mixture of anthropogenic and rural aerosol generated over land, and sea spray aerosol. Also, particles are generate dover sea by physical and chemical processes and the chemical composition may change due to condensation/evaporation of gaseous materials. The actual composition is a function of air mass history and fetch. At the land-sea transition the continental sources cease to exist, and thus the concentrations of land-based particles and gases will gradually decrease. At the same time, sea spray is generated due to the interaction between wind and waves in a developing wave field. A very intense source for sea spray aerosol is the surf zone. Consequently, the aerosol transported over sea in off-shore winds will abruptly charge at the land-sea transition and then gradually loose its continental character, while also the contribution of the surf-generated aerosol will decrease. The latter will be compensated, at least in part, by the production of sea spray aerosol. A Coastal Aerosol Transport model is being developed describing the evolution of the aerosol size distribution in an air column advected from the coast line over sea in off-shore winds. Both removal and production are taken into account. The result are applied to estimate the effect of the changing size distribution on the extinction coefficients. In this contribution, preliminary results are presented from a study of the effects of the surf-generated aerosol and the surface production.

On the basis of a comprehensive series of measurements on the Irish Atlantic coast, an extension of the Navy Aerosol Model (NAM) for the coastal zone is proposed. As in NAM, the dependence of the aerosol concentration on meteorological parameters is parameterized using empirical coefficients. The effect of continental aerosols present in the coastal zone is modeled as a function of fetch. A reasonable agreement is found between the model and the aerosol size distributions as measured on the island Inisheer.

This paper discusses techniques to describe the aerosol and the electro optical properties of the marine atmosphere from 15 meters down to the tops of the highest wave. Emphasis is placed on the experimental Rotorod technique to measure the concentrations of giant sea salt droplets. Data from these devices are parameterized using a lognormal function that is in turn related statistically to parameters such as wind speed, atmospheric stability and height above the surface. The new lognormal function is combined with the Navy Aerosol Model (NAM) to develop a first version of the Advanced Navy Aerosol Model (ANAM). Thus, ANAM allows the construction of an aerosol size distribution at any level from the wave tops to 15 meters an the assessment of electro optical parameters from this distribution using Mie theory. The first results of the ANAM model are compared to experimental data.

The first results are presented from a quantitative model describing the aerosol production in the surf zone. A comparison is made with aerosol produced in the surf zone as measured during EOPACE experiments in La Jolla and Monterey. The surf aerosol production was derived from aerosol concentration gradients measured downwind from the surf zone, after correction for the background size distribution that was measured upwind from the wave breaking zone. The aerosol production model was originally developed from measurements performed along the Baltic coast. The model predicts the aerosol production from the total energy dissipated in the wave breaking zone, calculated from the coastal bathymetry and deep-water surface wave field. In the present work, the parameterization of the aerosol production in the wave breaking zone is maintained, but the energy dissipation in the wave breaking zone is calculated using a different model that produces more realistic surf zone widths. Wave data were obtained from buoys off the Californian coast, while bathymetry data were supplied by the Scripps Institute of Oceanography. Observed and predicted aerosol production in the surf zone are in good agreement, for both sites. The predicted aerosol flux reproduces the day-to-day variations and even some of the observed variations on a time scale of several hours.

Following scintillation experiments during EOPACE measurement campaigns in the spring of 1996, a new set of experiments was designed in November 1996 and August/September 1997 over San Diego Bay. The main purpose was to further investigate the discrepancy between measured scintillation data and values predicted from turbulence models. One simple way to measure scintillation was the decrease of the signal variations with increasing integration time in the IR transmissometer. In addition near IR and midwave IR imagery was used of static and modulated sources. One of the static sources was mounted on a small boat, sailing out to horizon ranges, as was done earlier in the LAPTEX experiments at Crete. For the detection of the signals of the modulated source a set of receivers was used, providing 2 lines of sight at different altitudes above the water. The results show small differences in scintillation at 2 altitudes. The midwave and near-IR scintillation values show little correlation with C_n² values measured at the midway buoy, confirming the earlier experiments. The impact of atmospheric scintillation of IRST performance is again demonstrated.

During the Electro-Optical Propagation Assessment in a Coastal Environment (EOPACE) experiment of May-June 1998, IR scintillation measurements were obtained along a 7 km path over San Diego Bay. Simultaneous meteorological measurement were obtained from a buoy located at the midpoint of the transmission path. Bulk estimates of the refractive index structure parameter, C_n² were computed from the buoy data and compared with scintillation-derived C_n² values. The bulk C_n² estimates agreed well with the scintillation measurements in unstable conditions. The agreement between the two methods was poor for near-neutral and stable conditions. In particular, when the air-sea temperature difference has small positive values the bulk model predicts the vertical refractive index gradient approaches zero, resulting in rapid decrease in bulk C_n² estimates. These predicted decreases in C_n² were not observed in the path-averaged scintillation measurements.

Results of over 300 far IR and mid IR transmission measurements taken during several EOPACE intensive operational periods over the low-level 15 km transmission path across San Diego bay are presented. A thorough comparison with calculations obtained using simultaneously measured bulk meteorological parameters with the IR Boundary Layer Model, illustrate the effects that refractance, aerosol extinction and molecular extinction can have on the transmission. Discrepancies between the transmission measurements and the model's predictions are identified and investigated by varying various model parameters, and looking at available measured aerosol size distributions and refraction measurements over the path. Comparisons with the measured transmissions are reasonably good and show that the total measurements over the path. Comparison with the measured transmissions are reasonably good and show that the total transmission depends critically on all three effects, with the molecular transmittance depending upon the water vapor density and the characteristics of the IR source and detector, the aerosol transmittance upon the visibly, and the refractive effects on the stability of the marine boundary layer or the virtual potential air-sea temperature difference.

Shipboard optical system are used as passive sensors for threat detection. When a threat is at low altitude part of the optical path from it may lie in the marine surface layer where it is distorted by refractivity gradients caused by large vertical changes in temperature and humidity in the first several meters above the sear surface. In addition, the poorly characterized giant sea salt aerosols in this region not only contribute to scattering but add to atmospheric refractivity by an amount equal to the product of water refractivity and aerosol contribution to atmospheric liquid water content. The added refractivity is about 10 percent of that due to water vapor, depending on relative humidity. These aerosols are created from bubble fragments and jet droplets caused by air bubbles bursting at the sea surface and can be hundreds of micrometers in size. Their size and number depend on wind speed and turbulent diffusivity. Because of the droplets' large size the vertical profile of liquid water content decreases more rapidly than exponential leading to correspondingly larger ray bending. As for scattering the large size of the droplets means that Beer's law of extinction does not apply. Part of this work has been presented previously, but the current work will incorporate more up-to-date size distribution data for near sear surface aerosols, obtained from a literature review in progress, into calculations of forward scattering and vertical refractivity profiles using selected wind speeds, relative humidity and air-sea temperature differences.

This paper reports the propagating property of some wavelength laser through the smoke. The experiments includes the CO₂ laser, Nd:YAG laser, diode laser, He-Ne laser. The results show that the transmission ratios of different wavelength laser are dependent on the humidity. And we find another interesting result: the transmittance of CO₂ laser is lower than that of He-Ne and diode laser with a special condition.

In propagation of high power laser through atmosphere, the affection to thermal blooming by aerosol is a research field.This paper reports the experiment result of thermal blooming effect, which is induced by a group of water particle absorbing energy of CW Ar+) laser propagating. Our system includes an aerosol box, some right-angle- reflectors. By mean of increasing of the absorption of the particle, we observed the thermal blooming phenomenon of laser interacting with aerosol. When the density of droplet in the box increases, the laser beam outputting from the box moves down. And the size at the vertical direction becomes small because of the convection of air heated by the aerosol absorbing laser energy. When the density of particles decrease, the beam will go back to the initial location. The experiment shows that aerosol can induce the thermal blooming of high power laser.

WIN-EOTDA is a Navy strike warfare mission-planning tool based on the original Electrooptical Tactical Decision Aid (EOTDA) developed by the US Air Force in the 1980s. The WIN- EOTDA has been adapted to US Navy applications by adding a MS-Windows graphical user interface, Navy sensors and targets, and an improved ocean background model, atmospheric transmission model and sky radiance mode. Future requirements for the WIN-EOTDA include the addition of scene rendering capability, modeling in the midwave IR band, and scenarios involving near surface sensor heights. This report uses data collected during the Electrooptical Propagation Assessment in Coastal Environments (EOPACE) trials to discuss the current Navy improvements to the original ocean background model as well as improvements needed to meet the future Naval requirements. The current improvements involve replacing the original semi-empirical water background model with a combination of the MODTRAN sky radiance model and the SeaRad ocean radiance model. The SeaRad model is a rigorous geometric capillary wave model based on the Cox and Munk wave-slope statistical model. WHile the SeaRad model is suitable for moderate wind, high altitude, slant-path sensor configurations, it is inadequate for the near-surface scenarios required for the future replacement for the WIN- EOTDA. A near-surface water background model must include wave swell and effects of whitecaps. It must be coupled with an atmospheric model that includes refraction and scintillation effects. This report discusses the current improvements to the WIN-EOTDA and how algorithms used for IR Search and Track development, such as in IRTool, could be adapted to meet future requirements. The eventual replacement for WIN-EOTDA is a software program under development by the US Air Force called Target Acquisition Weather Software. The results of this case study indicate the combined SeaRad and MODTRAN modifications improve ocean background prediction performance for the high-altitude strike warfare view angles. This addition of a clutter model, such as in IRTool, may make the ocean background model suitable for surface warfare and near-horizon scenarios. However, this hypothesis warrants further investigation.

Despite recent technical advances, adverse weather still constitutes an important decision factor in the efficient use of IR sensors. The presence of fog, clouds or precipitation affects both the IR transmission and background properties of the atmosphere. Taking these effects into account requires the knowledge of the optical parameters of fog, clouds or precipitation which, in general, fluctuate too much on a scale of a few kilometers to be predictable with acceptable accuracy. Therefore, systems performance calculations based on modeling alone cannot provide all the necessary information for real time, on-site decision making. A promising alternative is continuous monitoring of atmospheric aerosol properties with a lidar. The method use in this study is the multiple-field- of-view technique which takes advantage of the information contained in the multiple scattering contributions to solve for both the droplet concentration and effective diameter. We can then use these solutions to derive the atmospheric radiance and transmittance, and calculate from there the contrast-to-noise ratio of IR images of small targets. Using actual lidar probings, examples of performance curves of a generic surveillance sensor are obtained for two types of targets. Results show that performance can drastically change over an interval as short as one minute, which emphasizes the need for real time, on site monitoring in adverse weather.

A comparison of isoplanatic angles derived from balloon- borne in-situ measurements of the index of refraction structure constant profiles and remote optical measurements of stellar intensity fluctuations using an isoplanometer is shown. Concurrent data taken over a six day period in the spring of 1986 show reasonably good agreement between the methods considering normal atmospheric variability. Possible reasons for differences between individual measurements are discussed.

We have designed, developed and constructed a CO₂ laser based LIDAR-DIAL field tested with preliminary measurements of concentration of water vapor two. Two years we have developed this preliminary measurements using alternatively the R20 and R18 lines in the branch at 10 micron of two twin CO₂ lasers and we have obtained the density profile on a long path of about 800 m. At present the maximum range of the lidar signal on the absorption line is limited by dynamic range and the NEP of our detector. To extend the range of lidar signals a theoretical work has been done about the use of new laser lines for range resolved measurements of water vapor for distance of 1 km. In fact the absorption coefficient of the on-line 10R20 is very strong and the lidar signal for range up to 1 km is obscured by noise of the detector. The theoretical work already gave a good results and presently we are making the experimental measurements to compare with the theoretical data.

Within the framework of our LIDAR activity devoted to air pollution measurements, we realized the injection of a continuous carbon dioxide laser into a high power TE CO₂ laser, to get the possibility of better analyze return signal response and to realize a Doppler wind velocimeter. Apart from the need of temporally smooth pulse to examine measurements result, in remote sensing it is desirable to use narrow band laser sources. The request of high spectral performances is manly based on the possibility to use heterodyne detection, on one hand, to improve the signal to noise ratio, and, on the other, to observe and analyze Doppler frequency shift in the return signal. We are engaged into implement a TE CO₂ laser source by injection of a cw pulse from a low pressure CO₂. Preliminary results we obtained show a smoothing of the output pulse shape and a consequent reduction in spectral band-width, revealing a single longitudinal mode operation.

An analysis results of Vis and NIR LIDAR limitations and improving possibilities show that specifications for electro-optical instrument parameters should be formed on the basis of stability-against-background clutter analysis of receiving signals' processing algorithms used. It allows to formulate the requirements to a measurements accuracy that often can be determined by a background clutter influence.

Two techniques for mitigation of turbulent degradation effects are presented. Both techniques do not require sensing and compensating for the wavefront aberrations. The first method is based on the fact that the coherence radius of a focused beam in a wide range of turbulent conditions does not depend on the strength of turbulence and coincides with a diffractive diameter of the beam. In this regime the coherence scale of the beam increase with increasing distance and decreasing the aperture size. This permits us to mitigate the coherence degradation of the beam. It is the coherence radius to the effective beam size.THe experimental data, which support the theoretical predictions are presented. The second method relates to the phenomenon called regular change of the mean wavefront curvature caused by turbulence. This method use a systems with a variable image plane, which position is adjusted in accordance with variations of the strength of turbulence. Both methods permit us to increase the Strehl ratio of an imaging system without sensing and compensating for wavefront aberrations. A combination of the two techniques can also be exploited.

Adaptive optics can be used to improve the performance of optical wireless communications links degraded by atmospheric turbulence. Accurate wavefront sensing is necessary for some adaptive optics systems to compensate for the effects of atmospheric turbulence. Although the Shack- Hartmann sensor can provide accurate wavefront sensing under controlled conditions, scintillation can restrict the performance of Shack-Hartmann wavefront sensing by creating large intensity fluctuations. These intensity fluctuations can create errors in the wavefront measurement if the intensity dynamic range of the Shack-Hartmann sensor is exceeded. The result of computer simulations which model the performance of the Shack-Hartmann wavefront sensor are presented. Specifically it is shown that the intensity dynamic range of the Shack-Hartmann wavefront sensor can be increased by operating with saturated pixels without an increase in error in the measured wavefront. Operating conditions that maximize the intensity dynamic range of the Shack-Hartmann senor are presented. Experimental results are presented which support the results of the computer simulation.

Atmospheric turbulence over long horizontal paths perturbs phase in the pupil of an optical communications receiver, and also can cause severe intensity scintillations. We describe a real time wavefront compensation system using PC technology to perform all wavefront control tasks. This system uses a modal correction scheme, and we report the first measurements of residual wavefront taken approximately 1 meter above ground level at 1 km range. The effects of turbulence, scintillations and control bandwidth on the correction are all examined.

The effect of atmospheric phase perturbations on the diffractive and coherent properties of the uplink and downlink paths of an active imaging illumination beam has been studied in some detail. Similarly, the scattering and depolarization induced by water and ice cloud particles in the path of coherent laser illumination is currently an area of much production research. In contrast, the effect of cloud particles on the diffractive properties of a laser illumination beam has not received as much attention due primarily to the daunting mathematics of the physical mode. This paper seeks to address some of the mathematical issues associated with modeling the interaction of a coherent illumination beam with a cloud of ice particles. The simulation constructs a 3D model of a cirrus cloud consisting of randomly oriented hexagonal ice crystals in the shape of plates, columns, and bullet rosettes. The size, shape, and vertical distribution of the crystals are modeled after measured particles concentrations and distributions. An illumination pattern, in the form of grid of rays, is traced through the cloud, and the properties of the exiting wavefronts are analyzed.

Adaptive optics is now an operational reality which provides a real time compensation for turbulence degraded images. The degree of correction of an adaptive optics system is fundamentally limited by the flux density received from the object or from a guide source, and by atmospheric turbulence strength and speed. The ultimate performance which can be expected for ideal systems with an optimization of the key parameters are estimated. Two types of systems are routinely operated to date: a Hartmann-Shack wave-front sensor with a discrete actuator deformable mirror and a curvature wave- front sensor with a bimorph mirror. They are compared from physical and technological standpoints.

The Hartmann sensor is a popular wavefront sensor (WFS) for measuring the wavefront gradient in the pupil of an adaptive optical telescope. Conventional methods for estimating the wavefront slope within each WFS subaperture rely on a centroid computation of the subaperture detector irradiance distribution. The centroid computation is equivalent to a first moment calculation. A maximum a-posteriori (MAP) slope estimator improves on the conventional centroid estimator by taking advantage of priori knowledge of the subaperture wavefront slope statistics and total irradiance falling on the subaperture array. In order to derive a closed form solution for the MAP estimator, several assumptions were made in a previously published paper. These assumptions include: infinitely small pixels on the subaperture detector arrays, no read noise in the detection process, and on irradiance spillover between adjacent subapertures. By implementing the Hartmann WFS and MAP estimator in a detailed computer simulation, the performance of the MAP estimator was evaluated using realizable WFS parameters. The simulation shows that even when the assumptions used to derive the MAP slope estimator are relaxed, the MAP estimator outperforms the conventional subaperture centroid estimator.

We address the optimal processing of astronomical images using the deconvolution from wave-front sensing technique (DWFS). A constrained least-squares (CLS) solution which incorporates ensemble-averaged DWFS data is derived using Lagrange minimization. The new estimator requires DWFS data, noise statistics, optical transfer function statistics, and a constraint. The constraint can be chosen such that the algorithm selects a conventional regularization constant automatically. No ad hoc parameter tuning is necessary. The algorithm uses an iterative Newton-Raphson minimization to determine the optimal Lagrange multiplier. Computer simulation of a 1m telescope imaging through atmospheric turbulence is used to test the estimation scheme. CLS object estimates are compared with the corresponding long exposure images. The CLS algorithm provides images with superior resolution and is computationally inexpensive, converging to a solution in less than 10 iterations.

This paper presents a scalar Wiener filter derived in the transform domain of discrete trigonometric transforms. The implementation of the filter is through symmetric convolution, the underlying form of convolution for discrete trigonometric transforms. The symmetric convolution of two sequences is equivalent to their multiplication in the transform domain of discrete trigonometric transforms. This symmetric convolution-multiplication property and the fact that a type-II discrete cosine transform is asymptotically equivalent to the eigenvectors of the correlation matrix of a Markov-I process allows this scalar Wiener filter to be nearly optimum for Markov-I models. The performance of the filter is analyzed for the case of recovering an object corrupted by a 2D Gaussian filter in the presence of noise.

Multi-frame blind deconvolution (MFBD) has been shown to be useful for overcoming the blurring effects of turbulence- and instrument-induced aberrations in ground-based imaging of satellites. In this scenario, the object has a finite extent that is often entirely contained within the sensor field-of-view. We report on the generalization of MFBD to accommodate objects that extend beyond the field of view, as would be encountered, for example, in solar and planetary astronomy or in down-looking scenarios. We simulate both down-looking and up-looking scenarios, and vary parameters such as the level of scene illumination and the number of data realizations included. In the simulations, MFBD performance is evaluated by comparing results to the true scenes as well as to reconstructions using more established Phase-Diverse Speckle techniques. Using real data, MFBD reconstructions of solar-granulation scenes are validated by comparison with well-accepted PDS results.

When carrying out satellite images by imaging vertically through the atmosphere, distortions and blur arise as a result of turbulence and aerosols. Contrast is reduced by path radiance. The recently developed atmospheric Wiener filter, which corrects for turbulence blur, aerosol blur, and path radiance simultaneously, is implemented in digital restoration of Landsat imagery over seven wavelength bands of the satellite instrumentation. A required input is weather. Restoration is most impressive for high optical depth situations, which cause larger blue. Restoration improves both smallness of size of resolvable detail and contrast. Turbulence modulation transfer function (MTF) is calculated from meteorological data. Aerosol MTF is consistent with optical depth. The product of the two yields atmospheric MTF, which is implemented in the atmospheric Wiener filter. Turbulence blue, aerosol blur, and path radiance contrast loss are all corrected simultaneously, as if there were in intervening atmosphere. The primary source of atmospheric blur is seen to be aerosol forward scatter of light. Restorations are shown for various wavelength bands and are quite apparent even under clear weather conditions.

This paper present a statistical analysis of aerosol phase functions measured under marine conditions with the total atmospheric optical thickness. The result of the analysis is an empirical equation that expresses the aerosol phase function of scattering in the visible region through two tabulated empirical functions and a total aerosol optical thickness at 745 nm. The extrapolation of the atmospheric optical thickness to the visible spectrum is accomplished via an angstrom-type empirical equation that includes the wavelength of light and the aerosol optical thickness at 745 nm.

The proposed approach is based on the theory developed for the marine environment. This approach is tuned to be valid in the whole range of optical properties including an unrealistic case of a totally scattering sea. Because the atmosphere below the ozone layer is totally scattering in the visible range of spectrum, the proposed approach may be applied to the atmosphere are presented. The proposed model allows to calculate spectral albedo of the ocean-atmosphere system as a function of three input parameters: the chlorophyll concentration, the aerosol atmospheric optical thickness at near IR, and the solar zenith angle.

The algorithm presented in this paper is based on the previously published analytic theory by the author. That theory is based on the scalar radiative transfer approach and it generalizes the satellite Tanre-Deschampes algorithm to the aircraft situation. the restoration of the atmospheric optical parameters is based on a new empirical relationship between the scattering phase function by aerosols and the total aerosol optical thickness in the near IR. Examples of processed with the proposed algorithm airborne AVIRIS images of the Gulf of Mexico and North-West Atlantic in different spectral bands are presented.

Lidar investigation of dense atmospheric objects in the planetary boundary layer is of a great interest for both the atmospheric optics and applied meteorology. During recent years ever more attention is paid to the effect of the multiple scattering on the backscattered lidar signals. In experimental aspect two types of lidar systems are developed, namely, (i) on the basis of available polarization lidars by introducing receivers with a variable viewing angle [1,2,3, 1 1] and (ii) specially designed for investigation of the multiple scattering effects [41. The second type of lidars are equipped with high power pulse lasers and multiple-field-ofview receivers ensuring a simultaneous recording of signals at several field-of-views; solid coaxial detectors are used. In the present paper the changes in polarization characteristics of the lidar signals depending on the receiver's viewing angle are experimentally studied in cases offog and St clouds (water-droplet) using a lidar of the first type.

According the wave model on the water surface, the returned laser power expression for the airborne laser bathymetry is derived from. The influence of the wavy water surface, the field of view for the IR received system on returned laser power is discussed.

The Air Force Research Laboratory has developed and operated an airborne CO2 DIAL system for chemical detection of trace gases in the atmosphere'. This system, designated Laser Atmospheric Remote Sensing (LARS), is used for chemical detection of trace gases in the column content, topographical backscatter mode wherein detection of trace chemicals is performed by ratioing the backscattered signal strengths of combinations of transmitted CO2 laser lines absorbed by the trace chemical(s) to the backscattered signal produced by non-absorbed laser lines. Identification and quantification of trace chemical signatures sampled at multiple discrete CO2 laser frequencies is dependent upon isolation of the chemical signature from the absorption spectrum of the multi-kilometer atmospheric slant path over which measurements are made. Ambient atmospheric concentrations of C02, H20, and 03 contribute discrete line absorptions in the 9 im —11 tm spectral region in which the LARS system operates. The detailed form of the atmospheric absorption spectrum depends upon the concentration of each absorber and its variation with altitude along the slant measurement path. In addition to discrete atmospheric line absorption that must be accounted for in the DIAL measurements, a weaker continuum (smooth, slowly wavelength-varying) absorption due to water vapor must also be taken into account.

The Air Force Research Laboratory has developed and tested an airborne CO₂ differential absorption lidar system for the remote detection of chemicals. The Laser Airborne Remote Sensing DIAL system uses topographic backscatter to provide a long-range measurement of the column-content absorption of chemical plumes in the path of the laser beam. A high-power CO₂ laser, capable of operation on multiple isotopes, and a Mersenne telescope constitute the major transceiver components. In addition to the laser, telescope, and transceiver optics, several onboard diagnostic instruments were mounted on the flight bench to monitor and optimize the system performance during airborne operation. The flight bench, electronics racks, and data acquisition and experiment control stations were designed to be integrated onto the AFRL C-135E research aircraft, and to utilize the existing pointing and tracking system on the aircraft.

Tilt compensation performance is generally suboptimal when phase measurements from natural or laser guide stars are used as the conjugate phase in an adaptive optics system. Optimal compensation is obtained when the conjugate phase coefficients are estimated from beacon measurements, given knowledge of the correlation between the on-axis object phase and the beacon measurements. In this work, optimal compensation theory is applied to tilt correction for the case of an off-axis higher-order modes are correlated with the on-axis tilt components, a performance gain can be realized when they tilt estimator includes higher-order measurements. For natural guide star compensation, it is shown that equivalent tilt compensation can be achieved at beacon offsets that are three times larger when higher-order modes through Zernike 15 are used in the tilt estimator. For a laser guide star, while tilt information cannot be measured directly due to beam reciprocity, off-axis higher- order modal measurements can be used to estimate tilt components, leading to a maximum Strehl ratio of approximately 0.3 for D/r₀ equals 4 and L₀/D equals 10.

Laser-satellite communication system are subject to signal fading below a prescribed threshold value owing primarily to optical scintillations associated with the received signal, regardless of pointing in errors. The probability of fade associated with a downlink laser-satellite communication system is calculated here as a function of threshold intensity below the mean intensity of a Gaussian-beam wave incident on a coherent equal-gain (EG) receiver array. Previous theoretical studies and experimental data reveal that the mean carrier-to-noise ratio for an EG array receiver system improves greatly over that of a conventional single aperture monolithic coherent detection system. The present theoretical analysis illustrates there is also a significant decrease in the fractional fade time for an EG optical array receiver system with two or more receivers spatially separated by more than the intensity correlation length of the received optical signal.

Aerosol blur, often referred to as the adjacency effect, is well-established as the primary and perhaps only source of atmospheric blur in remote sensing imaging from satellites. However, much of the propagation community considers turbulence blur only in interpreting experiments, and then notes discrepancies with turbulence theory without considering how broad system engineering approach is called for, which includes aerosols, turbulence, absorption, and many other atmospheric effects. In general, turbulence is most significant at low elevations up to a few meters above earth's surface, and aerosol blur is most significant at higher elevations, especially if optical depth is on the order of unity or more.

Three advanced deformable mirrors were tested as part of the Air Force Research Laboratory's adaptive optics program. Two of these mirrors were purchased by the Air Force Research Laboratory for use at the Starfire Optical Range (SOR). One of these, a 941-channel mirror, made by Xinetics under subcontract to Hughes Danbury Optical Systems, is currently in use in the adaptive optics system of the SOR 3.5m telescope. The other, a 577-channel mirror, was refurbished by ITEK from the Mid-Scale Deformable Mirror. The third mirror, with 349 actuators, was made by Xinetics as a demonstration of a new actuator bonding technology. For each mirror, the uniformity of the actuator gain was measured using phase-modulating interferometry. These measurements were used to flatten the mirrors and to apply known Zernike modes. Results presented will include actuator performance statistics and mirror figure accuracy for various commanded figures.