This PDF file contains the front matter associated with SPIE Proceedings Volume 8161, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Laser devices are currently in widespread use in particular by armed forces for different tasks. Electro-optical sensors as well as unprotected human eyes are extremely sensitive to laser radiation and can be permanently damaged from direct or reflected beams. Laser damage depends on the interaction between the laser beam and the atmosphere in which it traverses. The atmospheric conditions, including the range, terrain features, turbulence, and atmospheric particulates, may alter the laser's effect on different electro-optical devices and systems. When a laser beam passes through the atmosphere the optical turbulence affects the beam. As a result, temporal intensity fluctuations (scintillations) or spatial variations in intensity within a beam cross-section occur. Atmospheric scintillations pose a safety problem because an observer or sensor can be subjected to the risk of a localized irradiance (local focusing effect) much greater than that which would occur in a non-turbulent medium. In the present work, the influence of the atmospheric channel on laser safety is investigated by use of experimental data of laser beam propagation statistics for different atmospheric conditions. The results can be important in the area of laser remote sensing, wireless optical communications, and active imaging.

Arago spot is a small bright spot that is formed in the shadow of the circular obscurer. The coherent nature of the Arago spot makes it susceptible to the turbulence-induced distortions of the incident wave. We describe the formation of the Arago spot for the using the narrow-angle Fresnel optics diffraction, and develop a simple equation for the field and irradiance distributions in the center of the shadow area behind an obscurer. We calculate the average irradiance distribution, random wander variance and scintillation index of the Arago spot using the Markov approximation for optical propagation in turbulence. Using the same technique we extend the single obscurer results to the Arago spot observed in the image of the annular aperture typical for the Cassegrain-type telescopes. The statistics of the Arago spot distortions can be used for the estimation of the turbulence strength on the propagation path. We suggest an optical design of a build-in sensor that allows monitoring of the turbulent conditions without interfering with the principal function of the optical system.

Several studies on different adaptive optics concepts are presented in the article. Each one of the procedures shows its peculiar advantages when considering different situations where the image distortion, due to atmospheric or artificial turbulence, becomes problematic. A setup is presented based on the usual wavefront reconstruction techniques using a Shack-Hartmann wavefront sensor in a closed loop with a deformable mirror and a computer. The reconstruction method follows the modal approach which has been demonstrated to be more robust and suitable than the zonal one when limited to the correction of the first Zernike components1 . Some results deriving from the studies are reported. A second part in the article describes the measurements and the characteristics of the atmospheric turbulence present in direct tests. Another procedure based on the control of a deformable mirror by mean of a fast iterative procedure is also treated and the relative results about the compensation of laser beams as well as extended images are shown.

In a previous work we quantified the performance improvement resulting from using the bispectrum to reconstruct extended scenes from image sets corrupted by atmospheric seeing over horizontal paths. Here we expand on that work and explore how image reconstruction quality is effected when poor or inaccurate estimates of the point spread function and other free parameters are used for amplitude estimation. We also examine how the number of paths used in the bispectrum phase estimate similarly impacts reconstruction quality. The performance bounds of each of these parameters are explored in terms of the MSE in intensity per pixel of the resulting reconstructions relative to a diffraction-limited reference image. We have found that using more than six distinct phase paths in the bispectrum phase estimate does not result in improvement enough to justify the additional computation time. Similarly, estimates of the turbulence strength used to develop the inverse filter used in may deviate from the optimum by 50% or more while incurring only a 10% reduction in MSE improvement over a range of turbulence values.

We have developed an imaging simulator that accounts for the anisoplanatic effects encountered while imaging extended scenes over horizontal paths. Using an approach that combines geometric and wave optics, an extended scene is divided into discrete point sources. For each point source a ray is traced through discrete Kolmogorovturbulence phase screens toward each pixel in virtual detector. The resulting images express non-uniform tilt and distortion characteristics typical in horizontal surveillance imagery. Using this simulator several large data sets were created based on a known high-resolution source image. By utilizing turbulence corrupted image sets with a known reference image, the performance of image reconstruction techniques can be expressed in terms of common metrics such as Mean Squared Error (MSE). The MSE statistics of a single image corrupted using the simulator over three turbulence conditions are examined relative to a diffraction-limited version of the reference image.

We have developed a technique for extracting atmospheric turbulence induced wavefront error by means of digital holography. The technique enables wavefront error determination as a function of field angle. Closed form expressions for the anisoplanatic wavefront error caused by atmospheric turbulence have been developed for comparison. We show very good agreement between experimental data and the closed form solution. The comparison is made over C_n ² values from approximately 10^-12 to 10-¹⁵ m^-2/3.

The image quality of electro-optical sensors in the (lower-altitude marine) atmosphere is limited by aerosols, which cause contrast reduction due to transmission losses and impact on the thermal signature of objects by scattering solar radiation. The Advanced Navy Aerosol Model (ANAM) aims at providing a quantitative estimate of the aerosol effects on the basis of standard meteorological parameters such as wind speed and relative humidity. For application in coastal regions, the ANAM includes non-marine aerosols that are governed by an ill-defined tuning parameter: the air mass parameter (AMP). The present paper proposes a new parameterization for assessing the effect of these non-marine particles on the propagation. The new parameterization utilizes the Ångström coefficient, which can be experimentally obtained with a sun photometer, and introduces new types of aerosols in ANAM. The new parameterization was tested against experimental validation data acquired at Porquerolles Island at the French Riviera. The limited test data suggested that the new parameterization is only partially efficient in capturing the aerosol signature of the coastal environment. Nevertheless, the new Ångström coefficient algorithm avoids using the ill-defined AMP, and may thus be useful to the ANAM community.

We describe work that will enable the comparison of collected data to beam propagation models. Optical and meteorological data will be collected during an electro-optical field campaign. Turbulence and aerosol extinction play a critical role in the maritime environment of Navy vessels, and observed extinction estimates would serve to determine model fidelity in a shipboard engagement scenario.

The FATMOSE trial (False Bay Atmospheric Experiment) is a continuation of the cooperative work between TNO and IMT on atmospheric propagation and point target detection and identification in a maritime environment (South Africa). The atmospheric transmission, being of major importance for target detection, was measured with the MSRT multiband optical/IR transmissometer over a path of 15.7 km over sea. Simultaneously a set of instruments was installed on a midpath lighthouse for collection of local meteorological data, including turbulence, scintillation, sea surface temperature and visibility. The multiband transmission data allow the retrieval of the size distribution (PSD) of the particles (aerosols) in the transmission path. The retrieved PSD's can be correlated with the weather data such as windspeed, wind direction, relative humidity and visibility. This knowledge will lead to better atmospheric propagation models. The measurement period covered nearly a full year, starting in November 2009 and ending in October 2010. The False Bay site is ideal for studies on propagation effects over sea because of the large variety of weather conditions, including high windspeed, expected from the South East with maritime air masses, as well as Northerly winds, expected to bring warm and dry air from the continent. From an operational point of view the False Bay area is interesting, being representative for the scenery around the African coast with warships in an active protecting role in the battle against piracy. The yearround transmission data are an important input for range performance calculations of electro-optical sensors against maritime targets. The data support the choice of the proper spectral band and contain statistical information about the detection ranges to be expected. In this paper details on the instrumentation will be explained as well as the methods of calibration and PSD retrieval. Data are presented for various weather conditions, showing correlations between different parameters and including statistical behaviour over the year. Examples will be shown of special conditions such as refractive gain, gravity waves and showers.

A commercial long-range scintillometer was deployed over a 2-km path in False Bay, South Africa, for a timeframe of one year. The turbulence data retrieved from the instrument are compared to turbulence parameters inferred from micrometeorological data and models, and the relation between experimental and model-data is explored.

In the perspective of the long range single-photon communications, we study in this work the propagation of a single or twin optical beams in scale length of several tens to a few hundreds kilometres, introducing in the experiment the collection of the whole beam combined to the measure of local irradiance. The experimental models were realized in different localities of Italian Alps as well as between Tenerife and La Palma Islands of the Canary archipelagos. The whole beam at the receiver was acquired and compared to models including the local meteorological conditions.

We report on the development, construction, and use of a Differential Image Motion Monitor (DIMM) for measuring optical atmospheric turbulence over static and dynamic maritime ranges. The optical properties of the DIMM that make it suitable for such measurements will be presented along with a detailed overview of its software systems. Particular emphasis will be given to the numerical methods, image feature recognition, and learning filters implemented in the DIMM software.

We investigate the effects of beam wander on an uncorrected laser system. The goal is to enable an accurate assessment of irradiance at a receiver or target for a shipboard laser system, and in this paper we show that a maritime surface layer turbulence model is important for an accurate vertical profile. The approach is to provide an appropriate and flexible hybrid between high fidelity surface layer similarity theory model and a parametric regression-based model.

Several experiments showed that the classical Kolmogorov power spectral density of the refractive-index sometimes does not properly describe the statistics of the atmosphere. In this paper we show an experimental testbed able to generate non-classical Kolmogorov turbulence by using a liquid crystal spatial light modulator. The testbed is used at Naval Postgraduate School for laboratory investigation of laser beam propagation in maritime environment where a power law different from classical Kolmogorov, 11/ 3, could be present. Applications of this testbed are ship to-ship free space optical communication, imaging and high energy laser weapons.

The performance of terrestrial free-space optical communications systems is severely impaired by atmospheric aerosol particle distributions where the particle size is on the order of the operating wavelength. For optical and near-infrared wavelengths, fog droplets cause multiple-scattering and absorption effects which rapidly degrade received symbol detection performance as the optical depth parameter increases (visibility decreases). Using a custom free-space optical communications system we measured field data in fog within the optical multiple-scattering regime. We investigate the behavior of the estimated channel transfer function using both real field-test data and simulated propagation data based on field-test conditions. We then compare the channel transfer function estimates against the predictions computed using a radiative-transfer theory model-based approach which we also developed previously for the free-space optical atmospheric channel.

The Paulding Mystery Lights are a purportedly unexplained optical phenomenon, occurring nightly, deep in the woods of Michigan's Upper Peninsula. The Michigan Tech Student Chapter of the SPIE initiated a project in 2008 to understand the cause of the Paulding Lights. Previous investigations by skeptics attributed the lights to headlights without explicitly identifying a source location. Our team applied a number of straightforward techniques to identify and then verify the source location of the Paulding Light. Beginning with observation through a telescope, the team moved to using tools such as detailed topographical maps and more common tools such as Google Street View to identify a candidate source location. The candidate source location was then validated by first recreating the light using a vehicle parked in that location. Additional verification was achieved by examining the correlation between the occurrence of the light and the passing of cars at the source location. A spectrometer was also used to compare the visible spectrum of the light to automotive headlamps. Our findings, presented here, indicate that the source of the Paulding light is automobile traffic on a stretch of road about 7 km from the viewing location.