This PDF file contains the front matter associated with SPIE Proceedings Volume 7463, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

Institute of Atmospheric Physics measures atmospheric attenuation on experimental FSO link on 850 and 1550 nm for more than one year. Experimental site is located at meteorological observatory on the isolated mountain with frequent fog, low clouds and strong wind occurrence. Measured attenuation is correlated with the wind turbulence intensity, visibility and LWC. Simple empirical models estimating attenuation on FSO link from meteorological parameters are formulated and verified through the experiment described. The paper shows also basic statistical behavior of the longterm FSO signal level in extreme conditions.

In a previous experiment (Tunick, 2008: Optics Express 16, 14645-14654), values for the refractive index structure constant and the Fried parameter were calculated from measurements of signal intensity and angle-of-arrival statistics based on idealized models. Calculated turbulence parameters were evaluated in comparison to scintillometer-based measurements for several cases. It was found that the idealized models alone were insufficient to accurately describe complex, non-uniform microclimate and turbulence conditions. In addition, the signal intensity and focal spot displacement measurements were quite sensitive to platform and light source jitter. In order to compensate for adverse effects such as platform vibrations, an alternative differential image motion method is explored for optical turbulence parameter characterization. Hence, further experimental research is conducted along a 2.33 km free-space laser path to capture differential image centroid data from which Fried parameter and refractive index structure constant information can be obtained. This research is intended to provide useful information for US Army laser communications, long-range imaging and energy-on-target.

We extend our theory of the on-axis beam scintillations [1] for the case of the propagating on slant turbulent paths where turbulence is concentrated in a relatively thin layer near the transmitter. Theory is based on the parabolic equation for the beam wave propagation and Markov approximation for the calculation of the statistical moments of the beam intensity. Ratio of the turbulence layer thickness to the overall propagation path length adds an extra small parameter to the asymptotic analysis. However we show that this only causes some changes for the boundaries between the asymptotic regions established in [1] while preserving their general arrangement.

High-resolution C_n² profiling is essential for characterizing atmospheric turbulence, especially when correction of the laser beam propagation. This is can be done by using distributed light sources. One way of doing so can be achieved by using the Rayleigh or Mie laser guide star as a light source. In this case the time-resolved characteristics of the backward scattered pulse can be used to characterize turbulence continuously along the measured range. This report discusses the operational principles of the laser guide-star scintillometer (LAGUSS) and analyses the results of experimental data for profiling the C_n² as a function of the range.

When light is transmitted through the atmosphere, it can scatter off turbulent vortex filaments in the air that have different densities and indices of refraction. These filaments, or eddies, are distributed through a turbulent air flow and their scale size represents the boundary between an energy cascade down size scales that ends in viscous energy dissipation. We are measuring with high spatial and temporal precision spatial and temporal correlation functions that reveal the turbulence dynamics and inner scale in conditions of single scattering. In essence, we can "see" the shadows of individual turbulent vortices. These measurements are made over short path lengths in conditions of known Reynold's number and average temperature. By changing the characteristics of the air flow in a volume, different length scales can be associated with different conditions. This creates a "fingerprint" that characterizes the turbulence.

At present, system design usually assumes the Kolmogorov model of refractive index fluctuation spectra in the atmosphere. However, experimental data indicates that in the atmospheric boundary layer and at higher altitudes the turbulence can be different from Kolmogorov's type. In optical communications, analytical models of mean irradiance and scintillation index have been developed for a traditional Kolmogorov spectrum and must be revised for non-Kolmogorov turbulence. The image quality (resolution, MTF, etc.) is essentially dependent on the properties of turbulent media. Turbulence MTF must be generalized to include non-Kolmogorov statistics. The change in fluctuation correlations of the refractive index can lead to a considerable change in both the MTF form and the resolution value. In this work, on the basis of measurements and model calculations, the influence of non-Kolmogorov turbulence on imaging and communications through the atmosphere is estimated for different scenarios of vertical and slant-path propagation. The atmospheric model of an arbitrary (non-Kolmogorov) spectrum is applied to estimate the statistical quantities associated with optical communication links (e.g., scintillation and fading statistics) and imaging system. Implications can be significant for optical communication, imaging through the atmosphere, and remote sensing.

Balloons, similar to those used for meteorological observations, are commonly used to carry a small instrumentation package for measuring optical turbulence in the atmosphere as a function of altitude. Two temperature sensors, one meter apart, measure a single point of the temperature structure function. The raw data is processed to provided the value of C_T², and the results transmitted to a ground receiving site. These data are converted to the index of refraction structure constant, C_n². The validity of these measurements depend on the correctness of a number of assumptions. These include local isotropy of the turbulence and the existence of the Kolmogorov inertial subrange, and that the data is not contaminated by the wake of the ascending balloon. A variety of experiments on other platforms, and in the laboratory, demonstrate that the assumptions upon which these balloon measurements are made are not valid for a large percentage of the above described flights. In order to collect data whose interpretation did not require preconceived assumptions, the balloon ring instrumentation system was developed. The ring is 8.69 meters in diameter, with a cross-sectional diameter of 14 cm. The ring is hung just below the balloon, so that the wake goes through the center of the ring, and the sensors are mounted tangent to the circumference of the ring. The raw data is transmitted to the ground with a bandwidth extending to 1.25 kHz. A sample of the measurements taken during a flight at Vandenberg Air Force Base, Calif. is presented.

A recent measurement campaign at Vandenberg Air Force Base, Calif. involved taking simultaneous observations with a VHF radar and high-data-rate (1-micron diameter) platinum wires to sense optical turbulence (from temperature fluctuations). The radar observations produce profiles of the refractive index structure parameter (C²_n ), the turbulent kinetic energy (σ²_t ), the eddy dissipation rate (ε), the inner scale (l_o ), the outer scale (L_o ) of turbulence, and wind speed and direction to an altitude of 20 km AGL. The fine wire measurements were taken from the surface with several sensors mounted on a balloon-ring platform sampling in excess of 3 kHz to balloon burst altitudes (typically above 25 km AGL). The main objectives of this effort are to compare the two measurement techniques and to obtain observations that can address several fundamental turbulence issues of the real turbulent atmosphere related to laser beam propagation. To date, modeling and simulation of laser beam propagation through atmospheric turbulence have relied upon a traditional theoretical basis that assumes the existence of homogeneous, isotropic, stationary, and Kolmogorov turbulence. Results presented from the radar observations include C²_n, σ²_t, ε, l_o, and the standard deviation of vertical velocity (σ_w). A comparison of the profiles of C²_n obtained from the two measurement techniques is shown and discussed. A time series of temperature data obtained from a fine wire probe traversing one radar range gate is presented and discussed. Future measurement and analysis efforts are presented.

Recent measurements of atmospheric optical turbulence from a novel balloon experiment showed some atmospheric turbulence behaviors that departed significantly from the Kolmogorov theory. In many cases, at various altitudes, the turbulence showed no inertial range scaling, thus assigning a value of C²_N to the turbulence was not possible. The actual distributions of the intensity of the turbulence did not match what would be expected from the typical profiles of C²_N . To assess the optical effects of the measured turbulence, the temperature data measured by the balloon-mounted equipment is converted to refractive index data using standard, published conversion factors. The resulting refractive index structure functions at the various altitudes are then used to compute phase-perturbations structure functions. These are then used to generate phase screens, which are then used in a wave-optics propagation code to compute the point-spread function of a point source located at the highest elevation of the data set propagating to the lowest elevation of the data set. The results are then compared to similar results for a Clear One profile and a Hufnagel-Valley profile applied to Kolmogorov turbulence. The results indicate that the recently measured turbulence environment is relatively optically benign compared to either Clear One or Hufnagel-Valley.

The development of an active optical system operating from a shipboard platform will require marine-specific models to predict the atmospheric channel characteristics. Given the variable nature of maritime operational areas, a second important component of a successful system is the integration of local and timely environmental measurements. We describe work to develop a model for beam propagation on an uplink in a maritime environment. Both extinction and turbulence can be important factors in beam degradation, and the prediction capability will require reliable models based upon local data, including meteorological data. Our focus is the determination of model fidelity for engagement scenarios of practical interest. We also discuss the need for quality-assured data and the possibilities for more direct channel assessments.

An automated video enhancement technique capable of image fusion from a stream of randomly-distorted images of a still scene is presented in this paper. The technique is based on the "lucky-region" fusion (LRF) approach and aims to improve locally the image quality according to the following steps: (1) for each image of the video stream an image quality map (IQM) which characterizes locally the image quality is computed, (2) each IQM is compared to that of the current fused image leading to the selection of best quality regions (the "lucky-regions"), and (3) the selected regions are merged into the fused video stream. While the LRF approach succeeds in producing images with significantly improved image quality compared to the source images, its performance depends on the imaging conditions and requires adjustment of its fusion parameter - the fusion kernel size - in order to adapt to an evolving environment (e.g. a turbulent atmosphere). Parameter selection was so far performed manually using a trial-and-error approach which causes the technique to be impractical for a real world implementation. The automated LRF technique presented is relaxed from this requirement and selects automatically the fusion parameter based on the analysis of the source images making it more suitable for practical systems. The improved LRF technique is applied to imaging through atmospheric turbulence for various imaging conditions and scenes of interest. In each case automatically-fused video streams demonstrate increases in image quality comparable to that obtained with manual selection of the fusion parameter.

The environment is nowadays one of the most limiting factors for reliable detection, clear imagery and thus a successful classification of potential threats by electro-optical (EO) sensors. However, the characterization of the environment and the assessment of its impact on sensor performance remains a difficult issue. Measurements of meteorological parameters are not always easy and cannot always be reliable. It becomes more and more interesting to extract the information the environment by new methods. In this paper, the initial steps and the methodology of an inverse scheme that retrieve valuable information about the EO propagation conditions from infrared (IR) camera images is proposed. The use of the method under subrefractive conditions shows that features of the medium can be derived through a thorough analysis of sensor images. By an original use of EO propagation modeling, it is possible to partially reconstruct sensor images that were deformed by a refractive atmosphere.

The radiation coming from a laser which operates in the coastal zone can be detected not only when a detector is placed in front of the laser beam but also when it is located outside the main beam direction. The reason is that in a real detection scheme the power collected by a detector not only comes from direct radiation but also from other radiation sources, like port scattering, aerosol scattering and background radiation. Their relative contributions depend on many factors, i.e. laser features, collecting optics features, meteorological conditions, etc. An important contributor is aerosol scattering and its intensity depends on the aerosol composition and particle density. It was found that more humid conditions cause a decrease in the direct radiation and an increase in the diffuse component. This effect depends on the contribution of hygroscopic and non-hygroscopic aerosols. In the marine-continental atmosphere, represented by a mixture of sea-salts (SSA), anthropogenic salts (WS) and organic carbon (OC), a change in relative humidity from 80% to 95% can change the result for the predicted irradiance level on the sensor by more than a factor of three. Dust-like (DL) particles produce much stronger scatter irradiance than other aerosol types, independently of the off-axis distance.

Laser beam propagation in a marine environment is of critical importance in the different aspects of Target-in-the-Loop operations. Beam wander and beam spread have been found to be due to turbulence. Wavelet-based phase determination is presented here as a viable approach for analyzing turbulence which is a very significant beam degradation factor. This approach can provide higher beam resolution and significant performance enhancement for laser beam propagation in a marine environment. Wavelet-based phase distribution is particularly appropriate for marine environments which have large vertical gradients in turbulence and are difficult to simulate. First, the distorted beam is put though a shearing interferometer resulting in an interference pattern which is proportional to the gradient of the wavefront. One dimensional signals are taken through the two dimensional interferogram. The Morlet wavelet transform is taken of the one dimensional signal and plotted as a spectrogram. The phase of the signal is equal to the phase of the transform. The phase of the signal carries noise and can identify turbulence in real time. Turbulence is a very significant beam degradation factor which is generated by fluctuations in the index of refraction in a marine environment. Phase can be determined by wavelet-based phase determination, allowing better analysis of beam degradation and improved performance.

The Advanced Navy Aerosol model (ANAM), being a modified version of the Navy Aerosol Model (NAM), is a wellknown engineering tool providing a quick and reasonable estimate of the aerosol extinction in the marine near-surface environment on the basis of simple meteorological input data. The original NAM consists of 3 lognormal distributions, which describe freshly produced marine aerosols, aged marine aerosols (produced elsewhere and advected to the measurement site) and a background concentration of marine aerosols. The ANAM adds a 4th lognormal mode to NAM to account for the largest marine particles. To account for non-marine particles, a special lognormal mode, called "dust mode" was included in NAM. The relative importance of the dust mode versus the marine background concentration is governed by a special input parameter known as the air mass parameter (AMP). Unfortunately, the AMP is ill-defined and the NAM user community has found it difficult to attribute a proper value to the AMP. This inconvenience became even more stressing when NAM was used for assessing aerosol extinction in the coastal zone. To overcome this inconvenience, a new approach is suggested which involves replacement of the AMP by the Ångström coefficient. The advantage is that the latter parameter can be directly measured and has a physical relation to the aerosol size distribution. When the particle size distribution is dominated by small particles, usually associated with pollution, the Ångström coefficients are high; in clear conditions they are usually low. Therefore this parameter is a good tracer of the aerosols originated over land and hence a good replacement for the AMP.

Sandia National Laboratories currently utilizes two laser tracking systems to provide time-space-position-information (TSPI) and high speed digital imaging of test units under flight. These laser trackers have been in operation for decades under the premise of theoretical accuracies based on system design and operator estimates. Advances in optical imaging and atmospheric tracking technology have enabled opportunities to provide more precise six degree of freedom measurements from these trackers. Applying these technologies to the laser trackers requires quantified understanding of their current errors and uncertainty. It was well understood that an assortment of variables contributed to laser tracker uncertainty but the magnitude of these contributions was not quantified and documented. A series of experiments was performed at Sandia National Laboratories large centrifuge complex to quantify TSPI uncertainties of Sandia National Laboratories laser tracker III. The centrifuge was used to provide repeatable and economical test unit trajectories of a test-unit to use for TSPI comparison and uncertainty analysis. On a centrifuge, testunits undergo a known trajectory continuously with a known angular velocity. Each revolution may represent an independent test, which may be repeated many times over for magnitudes of data practical for statistical analysis. Previously these tests were performed at Sandia's rocket sled track facility but were found to be costly with challenges in the measurement ground truth TSPI. The centrifuge along with on-board measurement equipment was used to provide known ground truth position of test units. This paper discusses the experimental design and techniques used to arrive at measures of laser tracker error and uncertainty.