This PDF file contains the front matter associated with SPIE Proceedings Volume 10425, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Electro-optical and laser systems are presently deployed in naval operations around the world. The performance of these systems is negatively affected by optical turbulence in the atmosphere, quantified by the parameter C_n². The strength of the integrated optical turbulence C_n² was investigated for several coastal locations in different climatic conditions: False Bay (South Africa), the Baltic Sea (Bay of Eckernförde, Germany), the Mediterranean Sea (Crete, Greece), the Gulf of Mexico (Dauphin Island, Alabama, US), and the Arabian Gulf. The over-water, near-surface turbulence was characterized along paths that typically spanned 1.5 - 8.7 km using large aperture scintillometers. The dependency of C_n² on the air-sea surface temperature difference and wind speed is discussed, and the results for the five geographic regions are compared and discussed in terms of environmental conditions and climate.

The refractive index structure parameter is the most common measure of optical turbulence. It is defined as a statistical quantity for the Kolmogorov spectrum energy cascade of turbulent eddies of different sizes. As such it is formally assumed to be constant in time and space. However, the large scale variation with the diurnal cycle, with altitude or with terrain characteristics is well known. The ensemble average in the definition of the refractive index structure parameter is thus assumed to be applied over a restricted region in space and time. The question of how large volume is needed to determine the refractive index structure parameter and on how short temporal scales it can vary has not received significant attention. To study the temporal variation we have used two independent measurement systems to measure the path-averaged refractive index structure parameter over a 171 m path at 1 m above ground with higher than 1 Hz temporal resolution. One measurement system uses the differential angle-of-arrival of an array of LEDs. The other system measures the scintillation of a single path laser beam using a photon counting system, with time correlation of picosecond pulses for simultaneous measurement of signal and background and with temporal autocorrelation-based variance determination to separate turbulence related scintillations from shot noise. The data shows excellent agreement between the two measurement systems on second level temporal variation, giving confidence in that the measured values show true variation of the refractive index structure parameter. Large scale variation of up to two orders of magnitude can be coupled to solar insolation on this partly cloudy day. High frequency variations that are consistent between the systems used show factor two changes at time scales below one second.

Infrared (IR) propagation through the atmosphere is strongly affected by atmospheric turbulence. To correctly model IR propagation, this turbulence must be well characterized and understood. To that end, this paper presents propagation measurements, including detailed meteorological measurements, which have been made over water along a 16 km propagation path. Variation in meteorological parameters, specifically air temperature, will be studied to determine their effect on measurement parameters. Additionally, C_n² (refractive structure parameter) measurements were taken in the Mid-Wave Infrared (MWIR) band. A preliminary comparison of measured values to modeled results from IRBLEM (IR Boundary Layer Effects Model) will be presented. The goal of these comparisons is to determine optimum measurement practices and determine the variation in C_n² given the measured variation in meteorological parameters along the propagation path. Significant work has been done by others to measure and model turbulence and the effects on IR propagation. This paper will contribute to that work by providing an especially well characterized 16 km propagation path along with MWIR C_n² measurements.

This research article proposes an alternative method to measure the discoloration or the color changes of EBT3 films due to exposure by solar ultraviolet (UV A+B) dose. Common methods to measure the color changes of EBT3 are through imaging technique measured by flatbed scanner and through absorbance spectroscopy measured by visible spectrometer. The research presented in this article measure the color changes of EBT3 through simplified optical system using the combination of light emitting diode (LED) as the light source and photodiode as the detector. In this research, 50 pieces of Gafchromic EBT3 films were prepared with the dimension of 3 cm x 2 cm. Color of the films changed from light green to dark green based on the total accumulated UV dose (mJ/cm²) by each film that depends on the duration of exposure, irradiance level (mW/cm²) and condition of the sky. The exposed films were then taken to the laboratory for its color measurement using absorbance spectroscopy technique and using newly developed simplified optical instrument using LED-photodiode. Results from spectroscopy technique indicate that wavelength within red region exhibit better response in term of linearity and responsivity towards the colors of EBT3 films. Wavelength of 626 nm was then selected as the peak emission wavelength for LED-photodiode absorbance system. UV dose measurement using LEDphotodiode system produced good result with coefficient of determination, R2 of 0.97 and root mean square of error, RMSE of 431.82 mJ/cm² while comparatively, similar wavelength but analyzed from spectroscopy dataset produced R² of 0.988 and RMSE of 268.94 mJ/cm².

We report on propagation measurements performed during the MINOTAUROS (Maritime INvestigations On Targets and Atmosphere Under Reduction of Optical Signatures) experiment on Crete, Greece, in late summer of 2016. The field trial has been organized by NATO STO Task Group SET-211 on Naval Platform Protection in the EO/IR Domain with strong support of the Hellenic Navy. Besides meteorological measurements, the experiment included measurements of turbulence using a boundary layer scintillometer on a slant path (d = 8 km) across the entry of Souda Bay (Crete). These are compared to values obtained by a 3D sonic anemometer, which was deployed at one end of the propagation path. Refraction effects have been measured using a 17.5 km path from Drapanos to Gerani. Two meteorological buoys along the path were used to gather information about the atmospheric conditions. An overview and a first analysis of the results are presented. The refraction measurements are compared to simulations using MORTICIA (Model of Range and Transmission in Coastal Inland Atmospheres), a new software tool currently under development in a collaboration of Fraunhofer IOSB and TNO.

For many years sound has been used as a primary method for underwater communication. However, data transmission rate of acoustic systems is low because typical frequencies associated with underwater acoustics are between tens of hertz and hundreds of kilohertz. A higher bandwidth can be achieved with visible light to transfer data underwater. The first challenge for underwater laser communication is scattering and absorption. In addition, there are disturbances caused by spatial and temporal changes in the water refraction index due to temperature and/or salinity variations. Optical turbulence, which includes the two effects, is the main theme of this paper. We will discuss the joint IOSB-NRL experiment whose goal was to test techniques for characterization of underwater optical turbulence and in particular we will focus on differential motion measurement from an LED array.

Operation and design of electro-optical systems are affected by atmospheric turbulence, quantified by refractive structure function parameter C_n². The long-term VerTurM experiment at a rural site in Northwestern Germany served to collect an extended dataset of vertical profiles of C_n² values up to 64 meters, completed by a characterization of the surface layer meteorology. A micrometeorological model in terms of the Monin-Obukhov similarity theory (MOST) was developed to predict the values of C_n² and its results were compared to the measurements.

Atmospheric turbulence impacts on the propagation of electro-optical radiation. Typical manifestations of optical turbulence are scintillation (intensity fluctuations), beam wander and (for laser systems) reduction of beam quality. For longer propagation channels, it is important to characterize the vertical and horizontal distribution (inhomogeneity) of the optical turbulence. In the framework of the First European South African Transmission ExpeRiment (FESTER) optical turbulence was measured between June 2015 and February 2016 on a 2 km over-water link over False Bay. The link ran from the Institute of Maritime Technology (IMT) in Simons Town to the lighthouse at Roman Rock Island. Three Boundary layer scintillometers (BLS900) allowed assessing the vertical distribution of optical turbulence at three different heights between 5 and 12 m above the water surface. The expected decrease of C_n² with height is not always found. These results are analyzed in terms of the meteorological scenarios, and a comparison is made with a fourth optical link providing optical turbulence data over a 8.7 km path from IMT to Kalk Bay, roughly 36° to the north of the three 2 km paths. The results are related to the inhomogeneous meteorological conditions over the Bay as assessed with the numerical weather prediction tool, the Weather Forecast and Research model WRF.

Monitoring of ionospheric parameters (such as Total Electron Content and scintillation) is of great importance as it affects and contributes to the errors encountered by radio signals. It thus requires constant measurements to avoid disastrous situation for space agencies, parastatals and departments that employ GNSS applications in their daily operations. The research objective is to have a better understanding of the behaviour of ionospheric scintillation at midlatitude as it threatens the performances of satellite communication, navigation systems and military operations. This paper adopts seasonal ionospheric scintillation scenario. The mid-latitude investigation of ionospheric effect of scintillation was conducted during the increasing solar activity from 2011-2015. Ionospheric scintillation data were obtained from four ionospheric monitoring stations located at mid-latitude (i.e Shenzhen North Station, Beijing Changping North Station Branch, Beijing North Station and Beijing Miyun ground Station). The data was collected from January 2011 to December 2015. There were absence of data due to software problem or system failure at some locations. The scintillation phenomenon was computed using Global Ionospheric Scintillation and TEC Monitoring Model. There are four seasons which existed in China namely: Spring, Summer, Autumn and Winter. The relationship between TEC, amplitude and phase scintillation were observed for each of these seasons. The results indicated that the weak amplitude scintillation was observed as against phase scintillation which was high. Phase scintillation was gradually enhanced from 2011 to 2012 and later declined till 2014. TEC was also at peak around 00:00-10:00 UT (08:00-18:00 LT). The seasonal events temporal density characteristics comply with solar cycle prediction as such it ascended from 2011 to 2013 and then scintillation parameters declined significantly afterwards.

The Stereo-SCIDAR (Scintillation Detection and Ranging) atmospheric turbulence profiler, built for ESO by Durham University, observes the scintillation patterns of binary elements with one of the four VLT-Interferometer 1.8m auxiliary telescopes at the ESO Paranal Observatory. The primary products are the vertical profiles of the index of refraction structure coefficient and of the wind velocity which allow to compute the wavefront coherence time and the isoplanatic angle with a vertical resolution of 250m. The several thousands of profiles collected during more than 30 nights of operation are grouped following criteria based on the altitude distribution or on principal component analysis. A set of reference profiles representative of the site is proposed as input for the various simulation models developed by the E-ELT (European Extremely Large Telescope) instruments Consortia.

The image quality of ground-based solar telescopes depends on the amount of turbulence in the Earth’s atmosphere, which is strongest in layers close to the ground during daytime. Local optical turbulence affects the performance of adaptive optical systems and reduces the spatial resolution of solar observations. Increased turbulence which is caused by solar irradiation of the infrastructure close to the telescope and obstructions to a free airflow are major concerns, but difficult to detect and to monitor. We have conducted measurements of optical turbulence at the GREGOR solar telescope (Teide Observatory, Tenerife, Canary Islands) to assess quantitatively the influence of the infrastructure on the image quality. The strength of optical turbulence is determined by the structure function parameter of the refractive index Cn2. We have measured the temporal behavior of the free flow optical turbulence about 30m above ground using a laser scintillometer between the towers of the Vacuum Tower Telescope and of GREOR. Local measurements of Cn2 were taken on the observing platform of GREGOR using three ultrasonic anemometers. Two anemometers are located at the north and south ends of the telescope building, a third one was be placed close to the telescope main mirror cell. Air temperature, pressure, humidity as well as wind speed and direction were measured along with refractive index measurements. An image quality indicator based on an estimate of the Fried parameter r0 was recorded whenever the adaptive optics system GAOS at the GREGOR telescope was operating. Recordings of the net solar radiation were obtained from the GONG experiment which is located a few 100 m from GREGOR. All data were taken between May 2015 and March 2016. We investigate the relation between optical turbulence, solar irradiance and meteorological parameters. Under almost all conditions, optical turbulence nearby the telescope is stronger than free flow turbulence. We note significant dependencies of the strength and the horizontal gradient of Cn2 on wind direction. The moderate influence on image quality indicates that there is only a thin layer with strong turbulence just above the telescope.

In the Special Astrophysical Observatory (SAO) continued pilot studies and research astroclimate coherent turbulence, similar to those given by us to the CAO in October 2012. To this end, under the dome of the Big Telescope Altazimuthal (BTA) has been measured astroclimate parameters. Measurements made throughout the volume of the dome of the specialized facilities BTA using ultrasonic weather station AMC-03 is fastened to the structure of the rotating telescope and dome. Also construction of temperature measurements of the telescope and the dome (and their size) used a thermometer and a laser rangefinder.Along with the state of the atmosphere measurements dome of the telescope is controlled ultrasonic meteosystems Meteo-2, mounted on 20-meter meteorological mast at the telescope site. Meteo-2 was used for the registration of long-term observations of atmospheric turbulence parameters for the expedition in order to clarify the conditions of the emergence of coherent areas of turbulence over the observatory territory.

Since 2010 Onera works on the characterization of the nightglow radiation for night-vision applications in moonless conditions. This radiation is mainly due to the deexcitation of hydroxyl molecules in the upper atmosphere (~87km). It is present in the visible range and reaches its maximum value in the short wavelength infrared bands between 1.4 and 1.8μm (Meinel bands). Although few energy reaches the ground, this radiation is emitted over the whole sky and therefore may be an interesting additional light source for night vision systems in moonless or cloudy sky conditions. Moreover, observation of the nocturnal sky in the short wave infrared band gives access to dynamic processes studies, these processes perturbing emission of radiation. In this paper, we present works carried out at Onera about observation and modelling of nightglow radiation.

“Nightglow” is an illumination phenomenon created by luminance processes in the higher earth atmosphere. It covers the spectral range from the ultraviolet up to the thermal infrared, but its maximum is found in the shortwave infrared (SWIR). Although known for a long time the advent of high sensitive SWIR detectors in the last decade enables today’s use for night vision applications. In 2013 Fraunhofer IOSB started its assessment of SWIR for night vision applications. The approach was twofold. Continuous measurements were started to get an understanding of the highly variable illumination levels created by the nightglow under different environmental conditions. Future goal here is the standardization of the SWIR illumination levels corresponding to the defined visual full moon, quarter moon, starlight and overcast starlight ones. Additionally, performance assessment of SWIR detectors in comparison to the visual image intensifiers respectively low light focal plane array detectors were conducted in the laboratory as well as in the field. The paper gives history and status of IOSBs assessment of SWIR for night vision applications. It explains the ideas behind the illumination characterization, the conducted measurements and the inherent problem of artificial stray light. For sensor assessment it presents recent work on the influence of the spectral coverage (e. g. broadband versus atmospheric window only) on system performance for different environmental conditions.

The ECSEL joint undertaking RobustSENSE1 focuses on technologies and solutions for automated driving in adverse weather conditions. One of the main technology challenges is to improve laser scanner performance in fog where the existing 905 nm lidar reliability degrades below tolerances. This report briefly summarizes the results of experimental fog absorbance measurements, which were conducted in VTT icing wind tunnel located in VTT’s premises. The content of the presentation will focus on spectral absorbance measurements in artificial fog in near infrared band.

This paper compares in-situ and path-averaged measurements of the electro-optical transmission, with emphasis on aerosol effects. The in-situ sensors consisted of optical particle counters (OPC) and a visibility meter, the path-averaged data was provided by a 7-wavelength transmissometer (MSRT) and a scintillometer (BLS). Data was collected at a test site in Northern Germany. A retrieval algorithm was developed to infer characteristics of the aerosol size distribution (Junge approximation) from the MSRT data. A comparison of the various sensors suggests that the optical particle counters are over-optimistic in their estimate of the transmission.

This research investigated the potential of the upper atmosphere layer height changes as precursor of the Padang Earthquake on 30 September 2009. We analyzed the occurrence of atmospheric gravity wave (AGW) in all-sky imager (ASI) images and h’F in ionosonde mounted on Kototabang (0.2°S, 100.3°E, -10.4° magnetic latitude) Indonesia from seven days before and after the earthquake and found that there was an unusual evening in h’F variation on 24 and 29 September 2009. A positive h’F deviation on 24 and 29 September 2009 are with a maximum value of 42 and 31.5. For both these dates, the maximum h’F value reached 234 km and 261 km at 00:30 LT and 20:30 LT with the median value of 192 km and 229.5 km, respectively. The increase in h’F on 24 September 2009 before the midnight was caused by encouragement from AGW observed at a wavelength of OH bands (~86 km) that happened a few minutes earlier. While the increase in h’F on 29 September 2009, suspected to be caused by the emergence of the AGW, though it cannot be proven because ASI does not operate due to rainy weather over Kototabang. For Dst index during the month of September 2009, there is nothing worth under -50 nT, this means a change of altitude h’F six and one days before the earthquake is not caused by the influence of magnetic storm but caused by AGW resulting from the epicenter.

In order to improve the quality of correction and dynamic characteristics of the adaptive optical system, in general, the methods of advanced adaptive correction based on the solution of the problem of predicting the phase distribution at the next instant from the optical measurements obtained by the Shack-Hartmann sensor at the moment are considered. The results of numerical experiments are presented.

Many areas of optical science and technology require fast and accurate measurement of the radiation wavefront shape. Today there are known a lot of wavefront sensor (WFS) techniques, and their number is growing up. The last years have brought a growing interest in several schematics of WFS, employing the holography principles and holographic optical elements (HOE). Some of these devices are just the improved versions of the standard and most popular Shack-Hartman WFS, while other are based on the intrinsic features of HOE. A holographic mode wavefront sensor is proposed, which makes it possible to measure up to several tens of wavefront modes. The increase in the number of measured modes is implemented using the conversion of a light wave entering the sensor into a wide diffuse light beam, which allows one to record a large number of holograms, each intended for measuring one of the modes.

Two experiments of urban scintillometry were performed recently. Their objective was to study the SCINDAR Cn² profiler performance on a composite urbanforest ground. The SCINDAR provides horizontal Cn² profiles with a few hundred meter profile resolution. Several improvements in data processing are reported: the choice of the spatial resolution of the profile and the hyper-parameters adjustment for Cn² regularization. The distributed Cn² values along the optical path are estimated every minute with small error bars. Their non-uniformity is shown to be consistent with the differences of the line of sight to ground and the coverage of the terrain. The SCINDAR data are also in the same order of magnitude with the three scintillometer data that were simultaneously recorded.

These experiments were motivated by the search for an answer to the question about the possibility of effective use of incoherent source as reference one. In the experiments were compared to fluctuations in the image shake for coherent radiation source and for an extended incoherent. Simultaneous measurements of the wave-front aberrations in the urban atmospheric turbulence on the horizontal track length of 104 meters at a height of 10 m above the underlying surface were carried out. In result we suggest a new operational scheme of an adaptive optical system, which does not require a reference source to be specially created or formed. The experimental scheme uses tracing the image of an object, selfluminous or illuminated by external sources. The results show a high correlation between the fluctuations of components of the mode decomposition for coherent radiation, and for the incoherent extended source of radiation. This means that a non-coherent source can be used effectively as a reference in a number of applications.

The investigation was fulfilled on the basis of the Navier-Stokes equations for viscous heat-conducting gas. The Helmholtz decomposition of the velocity field into a potential part and a solenoidal one was used. We considered initial vorticity to be small. So the results refer only to weak turbulence. The solution has been represented in the form of power series over the initial vorticity, the coefficients being multiple integrals. In such a manner the system of the Navier- Stokes equations was reduced to a parabolic system with constant coefficients at high derivatives. The first terms of the series are the main ones that determine the properties of acoustic radiation at small vorticity. We modelled turbulence with the aid of an ensemble of vortical structures (vortical rings). Two problems have been considered : (i) density oscillations (and therefore the oscillations of the refractive index) in the case of a single vortex ring; (ii) oscillations in the case of an ensemble of vortex rings (ten in number). We considered vortex rings with helicity, too. The calculations were fulfilled for a wide range of vortex sizes (radii from 0.1 mm to several cm). As shown, density oscillations arise. High-frequency oscillations are modulated by a low-frequency signal. The value of the high frequency remains constant during the whole process excluding its final stage. The amplitude of the low-frequency oscillations grows with time as compared to the high-frequency ones. The low frequency lies within the spectrum of atmospheric turbulent fluctuations, if the radius of the vortex ring is equal to several cm. The value of the high frequency oscillations corresponds satisfactorily to experimental data. The results of the calculations may be used for the modelling of the Gaussian beam propagation through turbulence (including beam distortion, scintillation, beam wandering). A method is set forth which describes the propagation of non-paraxial beams. The method admits generalization to the case of inhomogeneous medium.

It is well known that atmospheric turbulence severely limits the applications based on the laser propagation though the atmosphere. The most common disturbances occurring due to the atmospheric turbulence are beam spreading, beam wandering, and scintillation. These effects are continuously changing in response to atmospheric conditions. In this study, we create a Non-Kolmogorov turbulence model which is based on the geometrical optics approximation and the property of Gamma function and integrate with in Gaussian beam analytically. This approach helps us to understand the propagation of the laser beam at different wavelengths in the atmospheric turbulence.

Analytical expression of the cross-spectral density matrix of the focused electromagnetic MGSM beams propagation through in non-Kolmogorov anisotropic turbulent atmosphere is obtained. With the help of this formulation, the influences of non-Kolmogorov anisotropic turbulence on the spectral density and the degree of coherence of such beams with turbulence inner scale and outer scale effects considered are discussed. The flat-topped intensity profile of the focused electromagnetic MGSM beams can be prolonged a long distance by suitable choices of the source parameters. Compared with the isotropic non-Kolmogorov atmospheric turbulence, anisotropic non-Kolmogorov turbulence with greater anisotropy coefficient produces less effect on the focused electromagnetic MGSM beams. The degree of coherence increased steeply in the initial increasing phase of propagation distance, it then turned round into the decline regimes after reaching a maximum value and trends to 0 after sufficiently long propagation distance. And the values of anisotropy coefficient, non-Kolmogorov power spectrum index, and turbulence inner scale have significant effects on the propagation distance. Increasing wavelength is a good alternative to improve the performance the focused electromagnetic MGSM beams in non-Kolmogorov anisotropic turbulent atmosphere.