This PDF file contains the front matter associated with SPIE Proceedings Volume 8535, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

During the FATMOSE trial, day and night (24/7) scintillation data were collected for point sources at a range of 15.7 km. We used simultaneously our MSRT transmissometer (in scintillation mode) and a high resolution imager for the scintillation measurement. Because of the large source and receiver aperture, corrections were made for the effect of pupil averaging, determined by the transverse coherence length. In the paper examples are shown of scintillation spectra in comparison with Kolmogorov's -5/3 power law and of the log-intensity character of the scintillation. Attention is spent on the saturation effect, occurring in cases of small apertures. By using the multiband scintillation data, we were able to investigate the color dependence of scintillation, of which examples are shown. Measured scintillation data are also compared with predictions from our marine boundary layer based TARMOS model. It appears that the performance of these predictions is hampered by the inhomogeneity of the weather parameters along the path. In the paper several data series out of the large amount of available data are presented, covering a few consecutive days of data with examples of extremely low scintillation levels, probably occurring in cases of near-zero Air-Sea Temperature Difference along the total pathlength.

To predict the performance of coastal and shipborne radars, it is essential to assess the propagation characteristics of electromagnetic waves in the maritime boundary layer. To be independent upon environmental measurements, which are generally not as precise and reliable as they have to be for a proper input to simulation programs, usually based upon parabolic equation models, a method to retrieve the refractive index gradients in the low troposphere is the Refractivity from Clutter (RFC) algorithm. The propagation factor is computed from the received clutter power and is iteratively processed in order to retrieve the refractive index profiles. Under a respective French-German technical agreement a measurement program concerning radar propagation in the maritime boundary layer has been initiated, with contributions from ONERA-CERT, DGA MI / TN, Fraunhofer-FHR and the German Technical Center for Ships and Naval Weapons (WTD 71). The paper gives an overview on the RFC method with examples from the previous campaigns. It describes the experimental set-up and its methodology.

A multinational field trial (SQUIRREL) was performed at the Eckernförder Bucht, in the Baltic Sea, during September 2011 to study infrared ship signature and atmospheric propagation effects close to the sea surface in a cool environment. In this paper mid-wave infrared camera recordings of ship-mounted sources are analyzed. The camera was positioned about 6 m above mean sea level. Several meteorology stations - mounted on land, on a pier and on a buoy - were used to characterize the propagation environment, while sensor heights were logged continuously. Both sub- and superrefractive conditions were studied. Measurements are compared to results from an earlier field trial performed at Chesapeake Bay, in 2006, during warm and humid atmospheric conditions. The ship-mounted sources - two calibrated blackbody sources at 200 °C and 100 °C - were used to study contrast intensity and intensity fluctuations as a function of distance. The distance to the apparent horizon is also determined. Measurement results are compared to results from the IR Boundary Layer Effects Model (IRBLEM), and good agreement is found.

A tunable diode laser absorption spectroscopy (TDLAS) device with narrow band (~300 kHz) diode laser fiber coupled to a pair of 12.5" Ritchey-Chrétien telescopes was used to study atmospheric propagation. The ruggedized system has been field deployed and tested for propagation distances of greater than 1 km. By scanning the diode laser across many free spectral ranges, many rotational absorption features are observed. Absolute laser frequency is monitored with a High Fineese wavemeter to an accuracy of 2 MHz. Phase sensitive detection is employed with absorbance of < 1% observable under field conditions. More than 50 rotational lines in the molecular oxygen A-band X-b (0,0) transition near 760 nm were observed. Temperatures were determined from the Boltzmann rotational distribution to within 1.3% (less than ±2 K). Oxygen concentration was obtained from the integrated spectral area of the absorption features to within 1.6% (less than ± 0.04 x 10¹⁸ molecules / cm³). Pressure was determined independently from the pressure broadened Voigt lineshapes to within 10%. A Fourier Transform Interferometer (FTIR) was also used to observe the absorption spectra at 1 cm^-1 resolution. The TDLAS approach achieves a minimum observable absorbance of 0.2%, whereas the FTIR instrument is almost 20 times less sensitive. Applications include atmospheric characterization for high energy laser propagation and validation of monocular passive raging. The cesium Diode Pumped Alkali Laser (DPAL) operates near 894 nm, in the vicinity of atmospheric water vapor absorption lines. Water vapor concentrations are accurately retrieved from the observed spectra using the HITRAN database.

We have previously introduced the Differential Laser Tracking Motion Meter (DLTMM) [Proc. SPIE 7476, 74760D (2009)] as a robust device to determine many optical parameters related to atmospheric turbulence. It consisted of two thin laser beams—whose separations can be modified—that propagate through convective air, then each random wandering was registered with position detectors, sampled at 800 Hz. The hypothesis that the analysis of differential coordinates is less affected by noise induced by mechanical vibration was tested. Although we detected a trend to the Kolmogorov’s power exponent with the turbulence increasing strength, we were unable to relate it to the Rytov variance. Also, analyzing the behaviour of the multi-fractal degree estimator (calculated by means of multi-fractal detrended fluctuation analysis, MFDFA) at different laser-beam separations for these differential series resulted in the appreciation of characteristic spatial scales; nevertheless, errors induced by the technique forbid an accurate comparison with scales estimated under more standard methods. In the present work we introduce both an improved experimental setup and refined analyses techniques that eliminate many of the uncertainties found in our previous study. A new version of the DLTMM employs cross-polarized laser beams that allows us to inspect more carefully distances in the range of the inner-scale, thus even superimposed beams can be discriminated. Moreover, in this experimental setup the convective turbulence produced by electrical heaters previously used was superseded by a chamber that replicates isotropic atmospheric turbulence—anisotropic turbulence is also reproducible. Therefore, we are able to replicate the same state of the turbulent flow, specified by Rytov variance, for every separation between beams through the course of the experience. In this way, we are able to study the change in our MFDFA quantifiers with different strengths of the turbulence, and their relation with better known optical quantities. The movements of the two laser beams are recorded at 6 kHz; this apparent oversampling is crucial for detecting the turbulence’s characteristics scales under improved MFDFA techniques. The estimated characteristic scales and multi-fractal nature detected by this experiment provides insight into the non-Gaussian nature of propagated light.

Results of long-term measurements of the refractive index structure constant in the boundary layer are introduced. The measurements were made on a 150-meter-high lattice mast equipped by nineteen meteorological sensors and one pressure sensor at the bottom of the mast. The Kolmogorov statistical theory of turbulence was used to calculate the refractive index structure constant C²_n, allowing us to present annual cumulative distribution functions (CDFs) and seasonal quantiles. The quantiles of measured height dependence of the refractive index structure constant are also shown and compared with existing models (Hufnagel/Andrews/Phillips, SLC Day and Gurvich). Parameters of a linear model were calculated to fit the measured median height profile of the refractive index structure constant with the uncertainty of measurements also being addressed.

The geomagnetic storms are turbulence in geomagnetic field when interplanetary magnetic field driven by solar wind move southward and continue for extended period of time. Although these occur less frequently, but may energize ionospheric electrons and particles adversely affecting ground- and space-based electronic systems. Ionosphere at higher latitude is more prone to geomagnetic storms. Over lower latitude region like Indian sub-continent, the effect is less prominent but still can exhibit many distinctive effects like scintillations, equatorial ionization anomaly, fountain effect and equatorial electrojets. The increased numbers of free electrons in ionosphere introduce delays in global positioning system (GPS) satellite signals resulting in errors during GPS positioning. In a dual frequency GPS receiver, the line integral of free electron density along the pathway of signal through the ionosphere (i.e., Total Electron Content, TEC) can be measured. In this present paper, GPS observation data of three low latitude GPS stations in India located at Bangalore, Hyderabad and Mumbai during four severe geomagnetic storms from 2003-2005, are processed to measure ionospheric TEC during the events. The measured TEC at each of the station is compared with quietest days of the months to investigate its abnormal changes in responses to severe geomagnetic storms. The consequences of TEC variation is analyzed and correlated with interplanetary magnetic field (IMF-Bz), geomagnetic Kp and Dst-indices to study its behavioral changes during the storms. Eventually the aim of the study is to estimate the influence of ionospheric condition on GPS positioning to devise suitable method for accurate position measurements in the low latitude Indian region.

It is discussed the reliability problem of time-optimized method for remote optical spectral analysis of gas-polluted ambient air. The method based on differential optical absorption spectroscopy (DOAS) enables fragmentary spectrum registration (FSR) and is suitable for random-spectral-access (RSA) optical spectrometers like acousto-optical (AO) ones. Here, it is proposed the algorithm based on statistical method of independent component analysis (ICA) for estimation of a correctness of absorption spectral lines selection for FSR-method. Implementations of ICA method for RSA-based real-time adaptive systems are considered. Numerical simulations are presented with use of real spectra detected by the trace gas monitoring system GAOS based on AO spectrometer.

The usual numerical approach for accurate, spatially resolved simulation of optical propagation through atmospheric turbulence involves Fresnel diffraction through a series of phase screens. When used to reproduce instantaneous laser beam intensity distribution on a target, this numerical scheme may get quite expensive in terms of CPU and memory resources, due to the many constraints to be fulfilled to ensure the validity of the resulting quantities. In particular, computational requirements grow rapidly with higher-divergence beam, longer propagation distance, stronger turbulence and larger turbulence outer scale. Our team recently developed IMOTEP, a software which demonstrates the benefits of using the computational power of the Graphics Processing Units (GPU) for both accelerating such simulations and increasing the range of accessible simulated conditions. Simulating explicitly the instantaneous effects of turbulence on the backscattered optical wave is even more challenging when the isoplanatic or totally anisoplanatic approximations are not applicable. Two methods accounting for anisoplanatic effects have been implemented in IMOTEP. The first one, dedicated to narrow beams and non-imaging applications, involves exact propagation of spherical waves for an array of isoplanatic sources in the laser spot. The second one, designed for active or passive imaging applications, involves precomputation of the DSP of parameters describing the instantaneous PSF. PSF anisoplanatic statistics are "numerically measured" from numerous simulated realizations. Once the DSP are computed and stored for given conditions (with no intrinsic limitation on turbulence strength), which typically takes 5 to 30 minutes on a recent GPU, output blurred and distorted images are easily and quickly generated. The paper gives an overview of the software with its physical and numerical backgrounds. The approach developed for generating anisoplanatic instantaneous images is emphasized.

This paper discusses a novel type of beam director for effective laser beacon formation in deep turbulence conditions. The concept of the proposed beam director is based on an innovative approach employing a Brillouin enhanced four-wave mixing (BEFWM) mechanism for generating a tight (small spot size) laser beacon on a remote image-resolved target. The BEFWM technique enables both amplification and total (phase and amplitude) conjugation of the beacon-forming beam without the need for wavefront sensors, deformable mirrors or predictive feedback algorithms. Total conjugation is critical for beam control in the presence of strong turbulence, whereas conventional adaptive optics methods do not have this capability. The phase information retrieved from the beacon beam can be used in conjunction with an AO system to propagate laser beams in deep turbulence.

The problem of the evolution of an ensemble of vortex rings in air has been solved. The full system of the Navier -Stokes equations was used. The parametrix method was applied. The calculations were performed for a wide range of the ring parameters (circular and elliptic cross-sections, various diameters of the rings, their different orientation in the space etc.). The initial value problem is as follows. The vorticity has non-zero value only inside the rings at initial instant, the density and the temperature being constant everywhere at t=0. If the density is known, then it is possible to find the refractive index. The solution to the Navier-Stokes equations is an oscillating one. Thus the refractive index is an oscillating function with respect to time. These results enable to model turbulence in an adequate way without using the Taylor frozen turbulence hypothesis. The evolution of the frequency spectrum of the density fluctuations was obtained. These results were compared with Tatarskii's data. The intensity of a laser beam propagating through the ensemble of vortex rings in air was found with the aid of the parabolic equation method. A numerical procedure is set forth which allows to solve the problems of superresolution without using regularization methods. The task is as follows. There is a set of experimental data and an instrument function (with some error). We change the domain in such a manner that the corresponding MTF has nowhere zero values. The procedure enables to solve problems of focusing in the turbulent atmosphere.

By using wave optics numerical simulation, the scintillation of pseudo-partially coherent Gaussian beam propagating in atmospheric turbulence is investigated. The effects of partial coherence on scintillation index are analyzed as a function of the correlation length of beam source. The reduction of the aperture averaging scintillation index, on-axis and off-axis scintillation are shown for a horizontal propagation path. The aperture averaging factor of pseudo-partially coherent beam is compared with that of fully-coherent beam. And how the pseudo-partially coherent Gaussian beam behaves like partially coherent Gaussian Schell-model beam is also discussed. It was found that the on-axis scintillation index and off-axis scintillation index of pseudo-partially coherent beam can be reduced greatly by decreasing the coherence degree of beam source. The results of aperture averaging scintillation index also revealed the advantage of using pseudo-partially coherent beam compared to fully coherent beam. However, the aperture averaging factor of a pseudo-partially coherent beam is smaller than that of the fully coherent beam at the same receiving aperture diameter. This implies that the aperture averaging effect of scintillation index may be weakened by reducing the coherence degree of beam source. This work may provide a basis for the utilization of pseudo-partially coherent beam in free-space optical communications.

Wavefront sensing with a holographically created diffraction grating is a promising new approach in adaptive optics. In this paper the realization of such a holographic wavefront sensor for the detection of defocus is presented. Core of the sensor is a computer-generated hologram displayed on a spatial light modulator. The experimental results of the sensor usage are compared with simulated data to proof its functionality. For the sensor design the detector size could be an important parameter. Hence the influence of this factor on the sensor response is analyzed. Furthermore the effect of scintillation on the sensor output is covered. A preliminary simulation shows that the holographic wavefront sensor is not absolutely independent of scintillation, as assumed due to theoretical consumptions.

For the last few years, Laboratory of Astrophysics of Marseille has been carrying out several R and D activities in Adaptive Optics (AO) instrumentation for Extremely Large Telescopes (ELTs). In the European ELT (D = 40 m) framework, both theoretical and experimental studies are jointly led. A new theoretical approach for AO control command law with large degrees of freedom is being developed: it is based on the use of Local Ensemble Transform Kalman Filter (Local ETKF). In parallel, an experimental multi-purpose AO bench is mounted to allow the validation of new wave-front sensing and correction concepts dedicated to the next generation of ELTs. All the main AO components, with a large number of spatial (up to thousand) and/or temporal (up to 1.5 kHz) frequencies, are available. From different combinations of these AO elements, several correction and sensing (low order and high order frequencies) studies are possible. Our AO bench is combining different corrector mirrors (MEMS deformable mirror from Boston Micromachines and Spatial Light Modulator from Holoeye) which can be used with Shack-Hartmann and Pyramid Wave Front Sensors (respectively, SHWFS and PWFS). For this last type of sensor (PWFS), we will use the world’s fastest and most sensitive camera system OCAM² (developed at LAM), to demonstrate the concept of a fast and hyper-sensitive PWFS (up to 100x100 sub-pupils) dedicated to the first generation instruments for ELTs.

Remote sensing applications are generally concerned with observing objects over long distances. When imaging over long horizontal paths, image resolution is limited by the atmosphere rather than by the design and quality of the optical system being used. Atmospheric turbulence can cause quite severe image degradation, the foremost effects being blurring and image motion. Recently, interest in image processing solutions has been rising, not least of all because of the comparatively low cost of computational power, and also due to an increasing number of imaging applications that require the correction of extended objects rather than point-like sources only. At present, the majority of these image processing methods aim exclusively at the restoration of static scenes. But there is a growing interest in enhancing turbulence mitigation methods to include moving objects as well. However, an unbiased qualitative evaluation of the respective restoration results proves difficult if little or no additional information on the "true image" is available. Therefore, in this paper synthetic ground truth data containing moving vehicles were generated and a first-order atmospheric propagation simulation was implemented in order to test such algorithms. The simulation employs only one phase screen and assumes isoplanatic conditions (only global image motion) while scintillation effects are ignored.

When collecting images through turbulence it is always useful to have an estimate of the turbulence strength during the time of the observations. This is particularly true when post-processing of the collected imagery is considered. For space-based objects, one usually resorts to observing a single star for this purpose. We show how this time-consuming procedure can be avoided by estimating the turbulence strength, and the corresponding transfer function, directly from the target observations. The images were collected with the 3.5 telescope at the Starfire Optical Range USAF facility in Albuquerque, New Mexico.

The ability to image underwater is highly desired for scientific and military applications, including optical communications, situational awareness, diver visibility, and mine detection. However, underwater imaging is severely impaired by scattering and optical turbulence associated with refraction index fluctuations. Naturally, the approaches taken to solve the underwater image restoration problem have their origin in atmospheric turbulence compensation algorithms. There is certain similarity between the atmospheric and underwater image degradations but the difference in the scales of refraction index fluctuations in two media brings out the need for significant modifications of atmospheric techniques to be applicable to underwater imagery. Significantly stronger underwater image distortions resulting in large local shifts and warping of the image features require robust tracking using, for example optical flow estimation, even under relatively benign underwater conditions. Comparative performance of multi-frame nonlinear gain “lucky patch” algorithms with variable degree of optical flow technique sophistication is presented for underwater imagery collected in a laboratory tank and in a field exercise. Reliance of image restoration on accuracy of the optical flow algorithm is revealed and one approach to enhance restored image quality using confidence measures of optical flow estimation is proposed.