This PDF file contains the front matter associated with SPIE Proceedings Volume 7108, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Complementary to a measurement campaign of small surface targets in the False Bay, South Africa [1], a set-up could be arranged of atmospheric propagation experiments. This opportunity allowed us to collect another set of transmission data in a coastal area, where the environmental conditions are generally non-homogeneous and rapidly changing. It was found before, that the validity of models, predicting the aerosol size distribution, the vertical temperature profile or the structure constant for the refractive index Cn 2 tends to be questionable in this type of areas [2,3]. Proper knowledge of the relation between the range performance of electro-optical and infrared sensors and in-situ weather parameters is however of key importance for operational use of this type of sensors, so the collection of additional propagation data was very relevant. Refraction data were collected continuously by using a geodetic theodolite with camera system over a 15.7 km path in the False Bay. Transmission- and scintillation data were collected over a 9.6 km path by means of our MSRT (Multi- Spectral Radiometer Transmissometer) and a Celestron telescope (with camera) with a focal length of 1.25 m. Weather parameters were measured at a shore station and on a rock in the bay. The weather was greatly variable with many showers, while the visibility, cloudiness and ASTD (Air-Sea Temperature Difference) conditions were continuously changing. Analysis of the theodolite data delivered absolute AOA (Angle of Arrival) data, which have been compared with predictions from the bulk model for marine boundary layers and from two empirical two-parameter temperature profiles. Transmission data, collected in three spectral bands (around 0.6, 0.9 and 1.5 µm), provided information on the particle size distribution, assumed to be of a Junge type. Knowledge of this information allows the prediction of the atmospheric transmission in other spectral bands, including the IR. The transmission data were compared with the data from a visibility meter on the roof of the IMT building. Both data sets correlated reasonably well. From the high speed MSRT transmission data (integration time 10 ms, sampling rate 30 Hz) the scintillation index (SI) was calculated, which showed a reduction in SI value when it starts to rain, while the SI came back to normal shortly after the shower. The measured SI data were transformed into Cn 2 values (the atmospheric refractive index structure function) and compared with predictions from the bulk model with different type of stability functions for a selected set of measurement periods. The model predictions show deficiences for conditions with small ASTD. The SI data from the MSRT were compared with the scintillation data, collected with the Celestron imaging system, which showed interesting correspondences and differences, which are discussed in the paper. From the Celestron data also the beam wander was determined, providing, similar to the SI, a source of information on Cn 2. It was shown, that the beam wander (blur) also correlates with ASTD.

In order to detect an object, the object has to be distinguished from its background. Often a contrast number is defined, the difference between the signals from the object and its background. Hence, detailed knowledge of both is required. Background measurements made during two measurement campaigns are compared with results from ShipIR modeling efforts. Specifically, background radiance profiles, extracted from infrared camera recordings and spectrometer recordings of the sea and sky, and spectral features are highlighted.

Infrared (IR) detectors can be used as airborne limb-viewing surveillance systems for missile detection. These systems' performances are impacted by the atmospheric inhomogeneous background. In fact, the probability of target detection can be heavily affected. Consequently, the knowledge of these radiance small-scale fluctuations and their statistical properties is required to assess these systems' detection capability. A model of two-dimensional radiance spatial fluctuations autocorrelation function (ACF) is developed. This model is dedicated to airborne limb-viewing conditions in the thermal IR. In the stratosphere and in clear-sky conditions, the structured background is mainly due to internal-gravity-wave-induced temperature and density spatial fluctuations. Moreover, in the particular case of water vapour absorption bands, the mass fraction fluctuations play a non negligible role on the radiative field. Thereby, considering the temperature field and the water vapour field as stochastic processes, the radiance ACF can be expressed as a function of the temperature ACF and the water vapor mass fraction ACF. A local thermodynamic equilibrium model is sufficient for stratospheric conditions and sunlight scattering is neglected in the thermal IR. In addition, determination of the radiance fluctuations ACF requires the knowledge of the absorption coefficient and its first derivatives with respect to the temperature and water vapour mass fraction. Thus, a line-by-line model specific to water vapor absorption bands has been developed. This model is used to precalculate the absorption coefficients and their derivatives. This look-up table method allows circumventing the computational cost of a line-by-line calculation. A detailed description of the radiance fluctuations ACF model is presented and first results are discussed.

It is well known that radar sensors are capable to propagate through smoke and dust with only very little attenuation. The higher the operating frequency, the smaller is the necessary antenna diameter for a required geometrical resolution on the ground. Consequently millimeter waves would be the choice for this type of sensor system. For an optimum system design the question of atmospheric attenuation at different bands within the millimeter wave region due to losses by dust and sand has to be answered. As only little data exist on this topic, respective measurements were done under reproducible laboratory conditions. Different approaches were used to cover a broad range of sand and dust types. The contribution describes the experimental set-ups and gives typical results for calibrated samples of sand and dust, which were derived from the lab measurements. A perspective is given for further investigations upon this topic.

It is considered how the source spectrum influences the measurement accuracy of optical wave arrival angles, as well as the estimation accuracy of the path-averaged structure parameter of the refractive index fluctuations. Two reasons, which can cause the wavelength dependence of the variance of fluctuations of wave arrival angles, are analyzed. The first one is connected with the fact that phases depend on a wavelength in the approximation of smooth perturbations. The second reason is associated with the wavelength dependence of the refractive index and, consequently, its fluctuations. Strict equations are obtained to take into account the influence of the source spectrum on the measurement accuracy of the variance of arrival angle fluctuations and, indirectly, on the estimation accuracy of the path-averaged refractive index structure parameter. It can be stated that for most radiation sources (even nonmonochromatic) the influence of the source spectral composition can be neglected.

The distortion of images due to atmospheric turbulence is one of the major problems in astronomical imaging. To compensate for turbulence induced aberrations in real-time, it is vital to have an accurate model of turbulence strength, C²_N(h), and the average wind velocity, V(h), above a given site. To that end, a bread-board based SCIntillation Detection and Ranging (SCIDAR) system was developed for the Mount John University Observatory (MJUO), located in New Zealand. The system, constructed from commercially available off-the-shelf components, provides the flexibility to capture simultaneous pupil-plane and generalised SCIDAR. This provides a useful tool for the measurement of optical turbulence at sites where the near-ground turbulence is exceptionally strong and masks higher altitude layers. Measurements taken at MJUO, using the purpose-built instrument over the last few years, consistently indicate the presence of very strong near-ground turbulence and at least two high altitude turbulence layers (approximately 6 km and 11km above the site), with an additional layer at 1-3 km when strong ground winds are present. The C²_N(h) trends from several months in 2005 and 2007 and the V(h) trends from two months in 2007 are presented. The coherence length, r₀, for the full profile was consistently 6-7 cm regardless of season or weather conditions in the months used in this trending. The Greenwood frequency, f_G , ranged between 12 and 30 Hz for May and June 2007.

The influence of the strong turbulence regime on the laser beam propagation and focusing has been investigated. Turbulence was modeled on the base of the full Navier-Stokes equations which were transformed into the system of the Volterra type. The influence of a source-like term in the energy equation was analyzed. Statistical properties of turbulence were calculated. Computations were compared with experiments. We investigated the propagation of a laser beam with the aid of parabolic equation method. Focusing for linearly and radially polarized beam was considered. The problem of object-targeting system and the propagation of ultra-short laser pulses were also discussed.

In order to gain insight into the different mechanisms involved in the optical degradation transmitted by infrared (IR) windows at supersonic flight speeds, wave front sensing has been used to quantify aero-optical effects on side-mounted windows of a supersonic fore-body in a series of wind-tunnel experiments. Flow-induced aberrations have been measured at partially duplicated flight conditions at Mach 3.7 and for different mass-density values corresponding to altitudes ranging from 14 up to 22 km. For each altitude condition different lines of sight and window slopes have been considered. Apart from steady shockwave effects, laminar-to-turbulent transition took place on the upstream window and generated intermittency phenomena in the boundary layer whereas on the downstream window, shear layer was completely detached so that full turbulent occurred. To capture these unsteady and turbulent effects the flow-induced optical distortions have been "frozen" by using a 15 ns, 40 Hz pulsed laser at 532 nm. The ability of the Shack-Hartmann wave front sensing technique employed to substract a reference permitted a simple calibration procedure to ensure accurate measurements. Sets of curves of optical phase power spectra and FTMs obtained relating to the various aerodynamic parameters involved will be presented. Their distribution shows a correct behavior according to aerodynamic parameter variations. Isotropic turbulent characteristics could be inferred from the results on the downstream window whereas complete anisotropy prevailed for the upstream window. First comparisons of the results with turbulent aero-optical model will be further discussed at the conference. Further results induced by steady flow components are compared in a companion paper4 in the Conference with CFD steady-state Reynolds-averaged Navier-Stokes simulations.

Optical aberrations induced by turbulent flows are critical issues for the performance of an airborne optical system. In that context experiments were performed on a test-body at Mach 3.7 with several high Reynolds number in the S3MA wind tunnel of ONERA. A Shack-Hartman wave front sensing was performed (see companion paper of R. Deron). The objective of this work was to develop a computational algorithm to model the wave front distortions in temporal averaged field. First the aerodynamical flow field is obtained by RANS computation around the test body and mass-density is interpolated in an optical grid. Then wave front has been calculated using ray tracing from eikonal equations. For this validation two Reynolds numbers were retained and the boundary layer is turbulent on downstream window. A planar optical beam is emitted from the window and passes through the inhomogeneous media from the boundary layer to the shock wave. Various pupil, angle positions and lines of sight are considered. Zernike decomposition and MTF computation allow modal analysis in the near field condition and evaluation of the image quality respectively. Tilt effects appear to be the dominant aberration while higher orders have a limited impact on the image quality, except for large departures from the normal of the window. Discrepancies observed according to the line of sight variation are analysed. Finally simulations results compare favorably with the measurements made with the Shack-Hartmann wave front sensing. So this computational study is conforted and allows to complete the experiment.

In this work a comparison with experimental results of two types of models of density fluctuation for turbulent jets is presented. I also use realization method of the turbulence field in order to calculate beam wander directly.

Recent advances in low-cost high power diode lasers have made available a new type of illuminator source for LADAR remote sensing systems. These sources tend to be smaller more rugged, and have better power conversion efficiency than more conventional pumped crystal solid state lasers. They can be run in short pulse, or long pulse modes with pulse repetitions from DC to 10s of kilohertz. Although they don't have the peak power of a Q-switched laser, they make up for it in higher average power. They also tend to have large optical band widths. These factors make them well suited to direct detection, as opposed to coherent detection, since the lower source coherence reduces detrimental atmospheric effects related to speckle noise and scintillation of the outgoing beam. In this paper we discuss these effects and situations where diode lasers provide an advantage when working through long slant paths.

Lasers offer tremendous advantages over RF communication systems in bandwidth and security, due to their ultrahigh frequency and narrow spatial beamwidth. Unfortunately, atmospheric turbulence causes severe received power variations and significant bit error rates (BERs) in free-space optical communication (FSOC). Airborne optical communication systems require special considerations in size, complexity, power, and weight. We alleviate the deleterious effects of turbulence by integrating multiple techniques into an on/off keying direct detection system. Wave optics simulations show a combination of transmitter diversity, receiver and transmitter trackers, and adaptive thresholding significantly reduces the BER in air-to-air FSOC (up to 13 dB). Two transmitters alone provide a significant BER improvement over one transmitter, especially for the strong turbulence regime with up to a 9 dB improvement. Two beams also provide a reduction in fade length, indicating they will probably provide even greater improvement with interleaving and forward error correction coding.

The image quality is analyzed of an extraterrestrial object formed by astronomical optical system through the turbulent atmosphere. Relative increase the Strehl parameter is calculated under adaptive correction based on the laser guide star technique. The efficiency of adaptive correction of distortions for different type of the guide sources is compared. The calculations are performed for different models of the vertical variations of the structural parameter of the refractive index of the turbulent atmosphere. For a set of guide stars application the higher correction and big increase of the Strehl parameter are obtained, that is indirect evidence of the good correction of the higher mode components, which are badly corrected using the traditional techniques. As comparative calculations for different models of vertical variations of the structural parameter of the refractive index have shown, there are serious differences in the behaviors of the correlation radii for the plane and spherical waves.

We present results of adaptive optics compensation at the receiver of a 3km optical link using a beacon laser operating at 635nm. The laser is transmitted from the roof of a seven-storey building over a near horizontal path towards a 127 mm optical receiver located on the second-floor of the Applied Optics Group at the National University of Ireland, Galway. The wavefront of the scintillated beam is measured using a Shack-Hartmann wavefront sensor (SHWFS) with high-speed CMOS camera capable of frame rates greater than 1kHz. The strength of turbulence is determined from the fluctuations in differential angle-of-arrival in the wavefront sensor measurements and from the degree of scintillation in the pupil plane. Adaptive optics compensation is applied using a tip-tilt mirror and 37 channel membrane mirror and controlled using a single desktop computer. The performance of the adaptive optics system in real turbulence is compared with the performance of the system in a controlled laboratory environment, where turbulence is generated using a liquid crystal spatial light modulator.

The possibility of applying adaptive correction to ground-based solar astronomy is considered. Several experimental systems for image stabilization are described along with the results of their tests. As a result of the installation of the first order adaptive-optics system, the Big Solar Vacuum Telescope (BSVT) acquired the new quality. Different ways of development of an adaptive correction to be used in the BSVT of the Baikal Astrophysical Observatory are discussed. Tests of the modified correlation sensor (MCS) at BSVT have shown that at a proper choice of the filtering function parameters, the MCS reliably measures shifts of the solar granulation image in the telescope first focus under good visibility conditions. The MCS, as a part of the adaptive optical system, was intended for measuring the image shift in the telescope second focus. It turned out that the image quality becomes noticeably worse at image transfer to the second focus. The MCS measures the image shift of solar granulation in the second focus only under extremely good visibility conditions and certain granulation structure. Reduction of the telescope entrance aperture to 170 mm insignificantly affects the image quality and, therefore, the MCS operation.

In the field on blind image deconvolution a new promising algorithm, based on the Principal Component Analysis (PCA), has been recently proposed in the literature. The main advantages of the algorithm are the following: computational complexity is generally lower than other deconvolution techniques (e.g., the widely used Iterative Blind Deconvolution - IBD - method); it is robust to white noise; only the blurring point spread function support is required to perform the single-observation deconvolution (i.e., a single degraded observation of a scene is available), while the multiple-observation one is completely unsupervised (i.e., multiple degraded observations of a scene are available). The effectiveness of the PCA-based restoration algorithm has been only confirmed by visual inspection and, to the best of our knowledge, no objective image quality assessment has been performed. In this paper a generalization of the original algorithm version is proposed; then the previous unexplored issue is considered and the achieved results are compared with that of the IBD method, which is used as benchmark.

Suggestions from the field of image processing to compensate for turbulence effects and restore degraded images include motion-compensated image integration after which the image can be considered as a non-distorted image that has been blurred with a point spread function (PSF) the same size as the pixel motions due to the turbulence. Since this PSF is unknown, a blind deconvolution is still necessary to restore the image. By utilising different blind deconvolution algorithms along with the motion-compensated image integration, several variants of this turbulence compensation method are created. In this paper we discuss the differences of the various blind deconvolution algorithms employed and give a qualitative analysis of the turbulence compensation variants by comparing their respective restoration results. This is done by visual inspection as well as by means of different image quality metrics that analyse the high frequency components.

An analytical signal-to-noise ratio (SNR) expression is derived for unbiased estimates of energy spectra obtained using multi-frame blind deconvolution (MFBD) algorithms. Because an analytical variance expression cannot, in general, be derived, Cramér-Rao lower bounds are used in place of the variances. As a result, the SNR expression provides upper bounds to the achievable SNRs that are independent of the MFBD algorithm implementation. The SNR expression is evaluated for the scenario of ground-based imaging of astronomical objects. It is shown that MFBD energy-spectrum SNRs are usually greater, and often much greater, than their corresponding speckle imaging (SI) energy-spectrum SNRs at all spatial frequencies. One reason for this SNR disparity is that SI energy spectrum SNRs are proportional to the object energy spectrum and the ensemble-averaged atmosphere energy spectrum, while MFBD SNRs are approximately proportional to the square root of these quantities. Another reason for this SNR disparity is that single-frame SI energy-spectrum SNRs are limited above by one, while the MFBD energy-spectrum SNRs are not.

We have previously shown that the Levy fractional Brownian field family accounts for a complete statistical and analytical description of non-Kolmogorov wavefront phase [Opt. Lett. 33(6), 572 (in press, 2008)]. This is a nonstationary process having zero mean and stationary increments; then, replicating the well-known properties of the turbulent phase. Opposite to traditional models relying in the stationary (spectral) approximation of the phase, that ultimately leads to non-physical divergences. Our model avoids these pitfalls and gives exact analytical results to many observable quantities: Strehl ratio, angle-of-arrival variance, seeing and Zernike coefficients, and also, a generalized DIMM theory. Nevertheless, some coefficients are slightly below (~ 5-10%) when compared to other estimates in the occurrence of Kolmogorov turbulence. In the present work we show that this is due to the mono-fractal nature of this model; that is, the absence of inner- and outer-scales. To address this issue we introduce a Gaussian stochastic process whose realizations are multi-fractals: the multi-scale Levy fractional Brownian field.

We present the results of reduction of laser beam geometrical fluctuations that we have experimentally measured using a prototype of Adaptive Optics (AO) system previously designed. The scheme of this prototype provides that the wavefront sensing function is not operated by a Shack Hartmann sensor as usual, but it is based on an interferometric technique which allows to detect the perturbed phase profile using the interference fringes pattern. We show that this technique is of particular interest when high sensitivity and large bandwidth are required for the correction of small perturbations. The architecture of the system is based on a typical Michelson configuration with He-Ne laser source. It is assumed that one arm of the interferometer is passed through by the reference beam while in the other one there is the aberrated wave. The output intensity produces a fringe pattern which is detected by means of a pixellated photodiode. Combining the output of each photodiode, we achieve signals which can be immediately interpreted as aberration coefficients and thus reintroduced into the digital control as error signals in order to calculate the correction commands to be sent to the deformable mirror. The results here presented show that we have obtained 2 decades of noise reduction in the 10 Hz bandwidth, and that the control has been operating 10 dB attenuation up to 200 Hz.