This PDF file contains the front matter associated with SPIE Proceedings Volume 6747, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

In the framework of a cooperative program between Singapore and Germany, radar propagation measurements over sea were carried out in the tropical area of Singapore Strait. The data have been analyzed and propagation models have been tested using the relevant environmental information. It turned out that the tropical atmospheric conditions were considerably different to those of moderate climate areas, such as the Baltic Sea or the North Sea. The paper describes the experimental approach and discusses results of tropical conditions compared to those of European coastal environments.

A multinational campaign was organized by the NATO SET56 Group to assess transmission and propagation in coastal environments: the VAlidation Measurements of Propagation in IR and RAdar (VAMPIRA) experiment. VAMPIRA was conducted in the Baltic, near Surendorf, Germany, from 27 March to 4 April 2004. During VAMPIRA, transmission was measured in the IR and the visible using a diversity of techniques. Among these, transmission was deduced from point-target tracking using blackbodies on board a boat. In this paper, VAMPIRA transmission measurements in the IR are compared with model predictions. We use MODTRAN for the calculation of gaseous attenuation in conjunction with aerosol extinction models currently available, namely: NAM (as in MODTRAN), WKDAERX (as in IRBLEM), ANAM3 and MEDEX. The various models are presented and put in their historical contexts. We found that under most stable situations encountered at VAMPIRA, the 3-mode models, NAM and WKD, provide better prediction than the 4-mode models ANAM3 and MEDEX.

The performances of Electro-Optical (EO) systems such as visible or infrared cameras, lasers, operating within the Marine Surface Boundary Layer (MSBL), i.e. at heights up to a few tens of meters above the sea surface, are disturbed by various propagation mechanisms: molecular attenuation, aerosol extinction, refraction and turbulence. Refraction is responsible for focusing and defocusing of rays, detection range limitations, mirage formation and angular deviation. These refraction phenomena can be efficiently described using ray-tracing in conjunction with bulk estimations of the refractivity profiles based on the Monin-Obukhov (MO) theory. For stable atmospheric conditions (i.e. air temperature greater than sea temperature), the accuracy of the model predictions has been strongly discussed in the recent years. By using measurements of apparent target elevations recorded during the VAMPIRA trial, this paper aims at clarifying this discussion.

The NATO Panel SET-088 TG-51 has the charter to investigate infrared research topics relating to Littoral Ship Self-Defence. The two main research areas for TG-51 are low-altitude maritime IR propagation phenomenology and ship signature properties. Atmospheric scintillation and refraction prediction models were validated in several trials conducted by different NATO groups. So far most trials were conducted in cold waters. In June 2006, TG 51 performed the SAPPHIRE trial (Ship and Atmospheric Propagation PHenomenon InfraRed Experiment) to collect data in littoral areas under conditions of warm sea temperatures. The location of the trial was the US Naval Research Laboratory's Chesapeake Bay Detachment (CBD) field site on Chesapeake Bay. The objectives of the trial were to validate ship signature models and scintillation/refraction models. In the SAPPHIRE trial, the purpose of FGAN-FOM was to investigate the influence of changing weather conditions on the apparent elevation of a target. Therefore, we set up an IR-camera at CBD overlooking Chesapeake Bay observing a set of lights installed on an Island in 16 km distance. In this paper we discuss and analyse the measured elevations and compare them to the propagation model IRBLEM (IR Boundary Layer Effects Model) by DRDC, Canada.

A multinational field trial (SAPPHIRE) was performed at the Chesapeake Bay, USA, during June 2006 to study infrared ship signature and atmospheric propagation effects close to the sea surface in a warm and humid environment. In this paper infrared camera recordings of both land and ship mounted sources are analyzed. The cameras were positioned about 4 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 earlier field trials performed in Norway during typical North-Atlantic atmospheric conditions (cool air with little water content), and differences between medium wave and long wave infrared are emphasized. The ship mounted source - a calibrated blackbody source - was used to study contrast intensity and intensity fluctuations as a function of distance. The distance to the apparent horizon is also determined. In addition, normalized variance of intensity for land based sources has been calculated for a number of cases and these values can easily be converted to refractive index structure constant C²_n-values. Measurement results are compared to results from the IR Boundary Layer Effects Model (IRBLEM).

Optical refraction tends to occur frequently in the atmospheric boundary layer. Due to a gradient in the temperature as function of height, rays are bending down towards the earth (super-refraction), or up towards to the sky (sub-refraction). As a consequence, images of targets at long range may be distorted and mirages may occur, while the maximum detection range may be affected. In addition the irradiance, received from a point target at a sensor pupil, may increase or decrease due to atmospheric focusing effects. Sub-refraction tends to occur more frequently over sea-paths, as the air is normally cooler than the water. Currently available propagation models, like IRBLEM [1] and EOSTAR [2] adequately describe the mentioned effects for this condition. However sparse data are available for model validation in super-refractive conditions, when the air is warmer than the water. For this reason, the SAPPHIRE trial, (Ship and Atmospheric Propagation Phenomena Infrared Experiment), was organized in the Chesapeake Bay near Washington DC by NATO Task Group TG51 in June 2006. At this location and in this time of the year, the probability for having positive ASTD (Air to Sea Temperature Difference) conditions is high. In the bay a buoy was positioned, on which a set of precision temperature sensors was mounted. They provided as well ASTD values as temperature gradients at a height of 3.7 m. By means of a geodetic theodolite, absolute AOA's (Angle Of Arrival) were measured for a set of lights at various altitudes, located on the other side of the bay at a distance of 16.2 km. The buoy was located at about mid-path position. Positive ASTD conditions did occur on a number of days allowing validation of the values of the AOA, predicted by the models, based upon the meteorological data, simultaneously collected at the buoy. It was found, that the temperature profile, generated by the bulk model for the marine surface layer [3] is incorrect, resulting in deviations in the AOA, compared to the data from the theodolite. A set of empirical temperature profiles has been created, using the ASTD and the gradient in the temperature as function of height as input. One of them provides of predicted AOA values, which fit well with the measurements during the trials period. Errors in the prediction are resulting from the variability of the meteorological conditions, causing inhomogeneities along the path. Furthermore the measurement accuracy was limited due to image blur by atmospheric turbulence in a number of occasions.

Measurements of the spectral radiance of the sky and the sea, taken near Halifax during the September 2001 SIMVEX trial, indicated that the use of user defined atmospheric profiles, i.e. high altitude atmospheric contributions, were necessary in order to obtain agreement between measurements and results from simulations using atmospheric radiance codes. This paper analyzes data obtained under hot and humid conditions during the SAPPHIRE trial at Chesapeake Bay, Maryland, USA, in the summer of 2006. Digital recordings of the sea and sky background were made using cameras sensitive in both the 3 - 5 μm and 8 - 12 μm wavelength range. The center of the field of view of the cameras was pitched from -5 to +15 degrees. In parallel with the imaging experiments, spectrometric data was collected at the same time. In addition, many different types of meteorological data were collected. Measurements of the vertical radiance profile near the horizon will be compared with simulation results from ShipIR using various meteorological input parameters.

We present results from infrared imaging experiments, performed under hot and humid conditions at Chesapeake Bay, Maryland, USA in the summer of 2006. Specifically, the objective was to study the intensity of the exhaust gases from a ship at different distances. In particular there is an interest to quantify the intensity decrease of the plume with distance and correlate this with simulations of atmospheric transmission. For this purpose the ship ran a predetermined course making broad-side passes at predetermined distances from the shore-based IR camera as part of the course. The distances were 1.6, 2.4, 3.2, 4, 6, and 8 km. The cameras are sensitive in the 3 - 5 μm and 8 - 12 μm wavelength ranges. Digital recordings were made during the ship broad-side passes. It is challenging to identify gas cloud pixels against a background because the pixels are not necessarily clustered. We present a statistical method to identify the gas cloud pixels, calculate their average intensity, and determine the contrast between the gas pixels and the background pixels as a function of distance. The contrast versus distance data are then compared with simulations using standard atmospheric transmission software.

The performance of an optical sensor may be affected by small-scale fluctuations of the atmosphere, quantified through the refractive index structure parameter C_n². The values of C_n² along the optical path are modulated by large eddy fluctuations of the atmospheric fields. The resulting variations in the optical propagation have been scarcely documented due to the difficulty in measuring them. In this study, we use a micro-meteorological model to diagnose C_n² in 3D+time in the case of a convective boundary layer. The regions of high C_n² match with the convective plumes that drive the boundary layer dynamics. The variability of C_n² is larger in the bulk boundary layer, where the mean C_n² is low; it decreases in the surface layer and in the inversion, where the mean C_n² is large. The impact of this distribution on horizontal optical propagation is analyzed, based on well-known analytical solutions of wave propagation through turbulence. Despite the optical path averaging, a large variability remains for the wave coherence length and the scintillation rate. Implications in terms of optical applications are given. In conclusion, the challenges in extending our modelling approach to present-day weather prediction are discussed.

An optical plane wave propagating through atmospheric turbulence is affected by irradiance fluctuations known as scintillation. The scintillation index of an optical wave in strong turbulence can be analyzed by extended Rytov theory, which uses filter functions to eliminate the effect of cell turbulence sizes that do not contribute to scintillation, and it already has been calculated by Kolmogorov's power spectral density model. However several experiments showed that Kolmogorov theory is sometimes incomplete to describe atmospheric turbulence properly. In this paper, for a horizontal path, we use extended Rytov theory to carry out plane wave scintillation index analysis in non Kolmogorov strong turbulence. We do it using a non Kolmogorov power spectrum which uses a generalized exponent factor and a generalized amplitude factor. Although our final expressions for the scintillation have been obtained by extended Rytov theory, which is necessary to adopt in strong turbulence conditions, they reduce to the proper results also in weak turbulence.

The characterization of the vertical turbulence distribution on an astronomical site should be based on statistical behaviour, as it is required for other parameters in site testing. We present the statistical results of the optical-turbulence profiles at the Roque de los Muchachos and Teide observatories at the Canary Islands (Spain). The data were obtained using the generalized scintillation detection and ranging technique at the 1m Jacobus Kapteyn Telescope and 1.5m Carlos Sánchez Telescope. Statistical results are based on 68 nights in 2004 and 38 nights in 2005 of measurements at the Roque de los Muchachos observatory (La Palma) and 27 nights of observations at Teide Observatory (23 in 2004 and 4 in 2005). Statistically, most of the turbulence is concentrated close the ground level (2400 m above sea level) with no more than two relative intense turbulent layers at higher altitudes. The temporal evolution of the monthly statistical turbulence profiles indicates that the turbulence is concentrated at low altitude layers in winter.

Within the scope of the investigation of material for camouflage, concealment, and deception (CC&D material) in desert environment, it is necessary to evaluate the impact of turbulence on thermal imagers in the MWIR and in the LWIR. Turbulence decreases the effectiveness of electro-optical systems. It causes a reduction of the spatial resolution of thermal imagers, which is characterized by the turbulence modulation transfer function MTF. Turbulence MTF depends on atmospheric parameters, e.g. the strength of atmospheric turbulence as described by the structure parameter of the refractive index fluctuations, C_n², the atmospheric path length, the cross-wind velocity, and on the sensor parameters, i.e. the wavelength and the aperture diameter of the front optics. The total MTF is the product of turbulence MTF and sensor MTF, which in turn is the product of detector MTF and optics MTF. As a figure of merit for the spatial resolution, we used the area under the total MTF (MTFA). Based on our turbulence measurement that was taken in arid climate in Negev desert, Middle East, we calculated the total MTFA for a dual-band thermal imager (MWIR and LWIR) with two available optics under diverse turbulence conditions and for different path lengths up to 5 km. The selected C_n² values are representative for the diurnal run of C_n² in arid summer or different times of day, respectively. We defined a turbulence degradation factor X to estimate the impact of turbulence on the image quality as a function of time of day and path length. Resulting MTFAs and the corresponding turbulence degradation factors will be discussed in details.

A critical issue to calculate the image transmission through cirrus clouds is to obtain a detailed description of the angular distribution of the scattered radiation in the forward direction. Computation of the scattering phase function on the basis of microphysics description of the cloud thanks to ray-tracing codes, seems to be the best way to fulfill this requirement. However, a comprehensive microphysical model can not be found, because of the great variability of the ice crystals composing natural cirrus. An optimization process has been developed to find the best mixing ratio of four pristine ice crystals shapes that minimizes the error on the forward peak of the scattering phase function. To achieve this goal, a comparison with a reference phase function derived from MODIS database has been led. The bulk scattering properties of the seven size distributions defined in this database have been computed at four wavelengths in the spectral domain from visible to medium infrared, applying the mixing ratio obtained after an optimization at 0.55μm. Used as an input to a propagation model based on a Monte Carlo method, PSF have been computed. They show very good agreement with the PSF calculated with the corresponding reference scattering properties.

Most non-conventional approaches to image restoration of scenes observed over long atmospheric slant paths require multiple frames of short exposure images taken with low noise focal plane arrays. The individual pixels in these arrays often exhibit spatial non-uniformity in their response. In addition base motion jitter in the observing platform introduces a frame-to-frame linear shift that must be compensated for in order for the multi-frame restoration to be successful. In this paper we describe a maximum a-posteriori parameter estimation approach to the simultaneous estimation of the frame-to-frame shifts and the array non-uniformity. This approach can be incorporated into an iterative algorithm and implemented in real time as the image data is being collected. We present a brief derivation of the algorithm as well as its application to actual image data collected from an airborne platform.

Adaptive optics provides a real time compensation for atmospheric turbulence which severely limits the resolution of ground-based observation systems. The correction quality relies on a key component: the wavefront sensor. An adaptive optics system in the mid-IR providing high spatial resolution for ground-to-air applications has been designed at ONERA and is currently integrated. It includes an IR Shack-Hartmann wavefront sensor operating on an extended source. This paper describes and justifies the design of the IR wavefront sensor. First images and tests with the Shack-Hartmann wavefront sensor camera are presented.

Hereby we present the idea of a new passive sensor intended to compensate atmospheric turbulence distortions of object images. It is based on the applications of the already successful concept of adaptive optics. The main application of this sensor will be the compensation of the trajectory jitter of flaring objects in the far distance which will allow quicker identification and better tracking. The system consists of a wavefront sensor and a deformable correcting mirror, both commercially available, keeping the overall costs and size in reasonable limits. The research is divided into two main topics: the first is the characterization of the influence of the atmospheric turbulence on the object image when the observer's line of sight is parallel to the ground. The second is the development of the components and the software to achieve the required performances. First progress have been made on determining the shape of the deformable mirror with good accuracy by means of a modal reconstruction as well as in measuring the wave front distortions of a point-like source due to atmospheric turbulence.

Reconstruction of wind profile based on the turbulent spatio-temporal statistics of reflected spherical wave focused by the receiving telescope is considered. Both the expression for the spatial temporal correlation function and spectrum and the algorithm of wind profiling based on the spatio-temporal spectrum of intensity of a wave scattered off an infinite diffuse target are presented. Computer simulations show wind profiles reconstruction by the developed algorithm.

Two parts of the problem were analyzed. The first one is the adequate description of turbulence. The result is the simulation of the evolution of the refractive index due to turbulence. The second one is the beam focusing on condition that the refractive index is subject to spatial and temporal variations. The turbulence was simulated with the aid of the solution to the Navier-Stokes equations. Three kinds of initial conditions were used: (i) the vortical field was given, the velocity divergence (dilatation) being zero and the temperature being constant; (ii) the velocity divergence was given, the vorticity being zero and the temperature being constant; (iii) there is a temperature distribution, the vorticity and the dilatation being zero. In all cases, the initial values of the density are constant. The problem is set in the infinite space, the initial data being random functions. The solution of the Navier- Stokes equations was reduced to the solution of integral equations of the Volterra type. The iterative procedure was used. The comparison of the subsequent iterations allows to conclude that the convergence takes place. The problem of compensation for turbulent distortions of a laser beam was solved. The resolving function determines the necessary deformation of the mirror. The knowledge of the resolving function indicates the way to the beam focusing in the turbulent atmosphere.

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. A special wave front sensor is applied, which operates using the broad laser beam as a reference wave. The calculations are performed for different models of the vertical variations of the structural parameter of the refractive index of the turbulent atmosphere. The wave front sensor was used, which enables to reconstruct the continuous phase of the reference wave. As the estimates show, the parameters of the formed field are quite close to that plane wave. So 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 for formation of LGS by means of a focused laser beam. 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.

The spatial dynamics of vortex dipole nested in a Gaussian optical beam is analyzed with scalar diffraction theory. It is shown that the generation and annihilation of vortices are accompanied by extreme wave front distortions. Process of nucleation and annihilation of vortex dipole is considered to confirm the vortex aftereffect in the process of transformation of an aberration wave front into a singular one. After the vortex dipole annihilation the absolute values of the average and Gaussian curvatures increase greatly in the local areas of wave front. The phase reconstruction error increases in these areas in the process of wave front sensing. To investigate the features of the vortex aftereffect for simple field the light rays which take part in the combined translational and rotary motion of energy around the field zero-lines are constructed. The phase is computed as a potential of the optical field using the light rays. Integration of the phase gradient along the ray or energy-stream line allows a unique value of the phase to be connected with a point of the ray. Wave front of the beam is constructed from the computed phase. As in the vicinity of the vortex core the energy-stream line takes a spiral shape the phase incursion along the line increases. After the vortex annihilation and vanishing of the spiral shape the incursion remains and creates the vortex aftereffect in the form of the extreme wave front distortions. The revealed effect should be taken into account when constructing the systems of adaptive optics aimed at functioning in strong turbulence conditions.

The sensing of phase front of the vortex laser beam has been carried out with the help of a Hartmann-Shack sensor. The vortex beam is generated in the form of a Laguerre-Gaussian beam (LG₀¹ mode) with the help of the special helicoidal phase plates manufactured by the kinoform technology. The measured shifts of focal spots on the hartmannogram are compared with the calculated shifts. From the measured wave front tilts the reconstruction of singular phase surface has been performed with using the novel reconstruction technique. The removing of phase singularity from an optical vortex is demonstrated in the close-loop adaptive system including the bimorph deformable piezoceramics-based mirror.

The detection and tracking of naval targets, including low RCS objects like inflatable boats requires a thorough knowledge of the propagation properties of the maritime boundary layer. Models are in existence, which allow a prediction of the propagation factor using the parabolic equation algorithm. As a necessary input the refractive index of the atmosphere has to be known. This parameter, however, is strongly influenced by the actual atmospheric conditions, characterized mainly by air-sea temperature difference, humidity and air pressure. An approach was initiated to retrieve the vertical profile of the refractive index from sea clutter data. The method is based on the LS-SVM (Least-Squares Support Vector Machines) theory and has already been validated on simulated data. Here an inversion method to determine propagation factors is presented based upon data measured during the Vampira campaign conducted as a multinational approach over a transmission path across the Baltic Sea. As the propagation factor has been measured on two reference reflectors mounted onboard a naval vessel at different heights, the results can be combined in order to increase the accuracy of the inversion system. The paper discusses results achieved with the inversion method.

The forecasts of the optical turbulence in the marine surface layer are made in different seasons based on the numerical products of the numerical weather prediction model. It is found that the seasonal variation of the surface optical turbulence is not prominent over the oceans between 30°S and 30°N, but much larger over the higher latitude oceans with weaker surface optical turbulence in the summer hemisphere and stronger surface optical turbulence in the winter hemisphere. The surface optical turbulence strength in the height 10m above the sea level is greater than 10^-15m^-2/3 for 10.6μm, but less than 10^-15m^-2/3 for 0.55μm over the most parts of the oceans around the world. The horizontal patterns of the forecasted surface optical turbulence strength are similar to each other based on the same time products respectively from the two different numerical weather prediction models, but the horizontal pattern of the forecasted surface optical turbulence is much sharper with the higher model horizontal resolution.

The determination of turbulent-layers wind speed observed through Generalized SCIDAR technique (G-SCIDAR) requires an efficient and contrasted code. We have developed a fully automated algorithm based on wavelet transforms to derive the velocity magnitude and direction of atmospheric turbulent layers from G-SCIDAR measurements. The algorithm makes use of five cross-correlations of a series of scintillation patterns separated by lapses of Δt, 2Δt, 3Δt, 4Δt and 5Δt. The wavelet analysis of such cross-correlation images provides the position, direction and altitude of the different turbulent layers detected in each image. The comparison and consistency of results in consecutive cross-correlations allows the determination of the turbulence layers velocities and avoids misidentifications associated with noise and/or overlapping layers. The software includes the correction due to the projection effects on the observing direction of the actual velocity vector of turbulence layers. The algorithm has been applied to simulated data with excellent results, as well as to actual G-SCIDAR observations. For the validation of velocities derived for real G-SCIDAR data we have compared them to the velocities provided by balloon measurements. The software has been designed to analyze huge amounts of G-SCIDAR measurements.

In order to characterized the vertical atmospheric structure at the Teide Observatory (Tenerife, Spain), we are using two different remote sensing technics: SODAR (SOund Detection And Ranging) and SCIDAR (SCIncitillation Detection And Ranging) at this astronomical site. We present in this work the preliminar results on the comparison of the simultaneous data from four consecutive nights in March 2007 using both technics. We have analized the SCIDAR C²_N profiles as well as an estimation of the structure constante of temperature function,C²_T, provided by SODAR. Such C²_T were compared to the simultaneous C²_N profiles from SCIDAR, determining a calibration factor between the measurements provided by SCIDAR and SODAR. As it was expected, our preliminary results indicate that this calibration factor is very sensitive to the variations of weather conditions.

We have developed an algorithm to eliminate the dome seeing contribution to turbulence profiles derived from G-SCIDAR data. The algorithm, based on the parity of functions, is completely automated and it takes only a few seconds to process a full night of G-SCIDAR data. Seeing measurements obtained from turbulence profiles derived from G-SCIDAR observations and removing the dome contribution with our algorithm are in good agreement with seeing data obtained using Differential Image Motion Monitors (DIMMs). An important advantage of the proposed procedure is that it permits an automated reduction during the calculation process and it could be implemented to work in real time. The formulation to identify the shape of the dome seeing could be extended to other problems of shape recognition whenever it is even.

In this paper we present a prototype of an adaptive optics system developed for the control of geometrical fluctuations in a laser beam in air and based on the interferometric detection of the beam phase front. We show that this technique is very effective also when high sensitivity and high band-pass are required for correction of small perturbations. The working principle is also very simple and direct. In fact, the laser beam is made to interfere with a reference beam, properly obtained, and the phase difference is read by means of an array of photodiodes. A digital control system acquires the output signal from the array, computes the error signals and generate the correction signal, sent to the deformable mirror. In the paper we discuss some experimental results, the limits of the prototype and future developments and improvements.

We have built a hybrid turbulence profiler measuring simultaneously the atmospheric turbulence structure with a Shack- Hartmann wave front sensor and a G-SCIDAR (scintillation sensor). This is the first instrument combining two different techniques to measure simultaneously the turbulence structure. The hybrid profiler has been installed at the Carlos Sánchez Telescope (TCS) at the Teide Observatory (OT), in Tenerife Spain. The G-SCIDAR arm is already working properly and we are still testing the Shack-Hartmann arm.

A multinational campaign was organized by the NATO SET56 Group to assess transmission in coastal environments: the VAlidation Measurements of Propagation in IR and RAdar (VAMPIRA) experiment. VAMPIRA was conducted in the Baltic Sea, near Surendorf, Germany, from 27 March to 4 April 2004. During VAMPIRA, transmission was measured in the IR and the visible using a diversity of techniques. Transmissometers were installed across Eckernfoerde Bay, while aerosol measurements were made on the pier using Particle Measurement Systems (PMS), and visibilitymeters were deployed onshore and on a boat. Furthermore, VAMPIRA included point-target tracking experiments using blackbodies mounted on a boat. Some VAMPIRA measurements have already been presented at various symposiums. The purpose of this paper is to compare VAMPIRA transmission measurements and make comparisons with transmission estimates that can be deduced from the blackbody tracking sessions.