Forecasting of Optical Turbulence in Support of Realtime Optical Imaging and Communication Systems
NASA Astrophysics Data System (ADS)
Alliss, R.; Felton, B.
2012-09-01
Optical turbulence (OT) acts to distort light in the atmosphere, degrading imagery from large astronomical and imaging telescopes and possibly reducing data quality of free space optical communication (FSOC) links. Some of the degradation due to optical turbulence can be corrected by adaptive optics. However, the severity of optical turbulence, and thus the amount of correction required, is largely dependent upon the turbulence at the location of interest. In addition, clouds, precipitation, and inhomogeneities in atmospheric temperature and moisture all have the potential to disrupt imaging and communications through the atmosphere. However, there are strategies that can be employed to mitigate the atmospheric impacts. These strategies require an accurate characterization of the atmosphere through which the communications links travel. To date these strategies have been to climatological characterize OT and its properties. Recently efforts have been developed to employ a realtime forecasting system which provides planners useful information for maintaining links and link budgets. The strength of OT is characterized by the refractive index structure function Cn2, which in turn is used to calculate atmospheric seeing parameters. Atmospheric measurements provided by local instrumentation are valuable for link characterization, but provide an incomplete picture of the atmosphere. While attempts have been made to characterize Cn2 using empirical models, Cn2 can be calculated more directly from Numerical Weather Prediction (NWP) simulations using pressure, temperature, thermal stability, vertical wind shear, turbulent Prandtl number, and turbulence kinetic energy (TKE). During realtime FSOC demonstrations, in situ measurements are supplemented with NWP simulations, which provide near realtime characterizations and forecasts of the Cn2, the Fried Coherence Length (ro), and time-varying, three-dimensional characterizations of the atmosphere. The three dimensional Weather
NASA Astrophysics Data System (ADS)
Masciadri, Elena; Lascaux, Franck
2012-07-01
We present very encouraging preliminary results obtained in the context of the MOSE project, an on-going study aiming at investigating the feasibility of the forecast of the optical turbulence and meteorological parameters (in the free atmosphere as well as in the boundary and surface layer) at Cerro Paranal (site of the Very Large Telescope - VLT) and Cerro Armazones (site of the European Extremely Large Telescope - E-ELT), both in Chile. The study employs the Meso-Nh atmospheric mesoscale model and aims at supplying a tool for optical turbulence forecasts to support the scheduling of the scientific programs and the use of AO facilities at the VLT and the E-ELT. In this study we take advantage of the huge amount of measurements performed so far at Paranal and Armazones by ESO and the TMT consortium in the context of the site selection for the E-ELT and the TMT to constraint / validate the model. A detailed analysis of the model performances in reproducing the atmospheric parameters (T, V, p, H, ...) near the ground as well as in the free atmosphere, is critical and fundamental because the optical turbulence depends on most of these parameters. This approach permits us to provide an exhaustive and complete analysis of the model performances and to better define the model operational application. This also helps us to identify the sources of discrepancies with optical turbulence measurements (when they appear) and to discriminate between different origins of the problem: model parameterization, initial conditions, ... Preliminary results indicate a great accuracy of the model in reproducing most of the main meteorological parameters in statistical terms as well as in each individual night in the free atmosphere and in proximity of the surface. The study is co-funded by ESO and INAF-Arcetri (Italy).
NASA Astrophysics Data System (ADS)
BozorgMagham, Amir E.; Ross, Shane D.
2015-05-01
To obtain more realistic approximations of atmospheric Lagrangian coherent structures, the material surfaces which form a template for the Lagrangian transport, two concepts are considered. First, the effect of unresolved turbulent motion due to finite spatiotemporal resolution of velocity field data is studied and the resulting qualitative changes on the FTLE field and LCSs are observed. Stochastic simulations show that these changes depend on the probabilistic distribution of position of released virtual particles after backward or forward time integration. We find that even with diffusion included, the LCSs play a role in structuring and bifurcating the probability distribution. Second, the uncertainty of the forecast FTLE fields is analyzed using ensemble forecasting. Unavoidable errors of the forecast velocity data due to the chaotic dynamics of the atmosphere is the salient reason for errors of the flow maps from which the FTLE fields are determined. The common practice for uncertainty analysis is to apply ensemble forecasting and here this approach is extended to FTLE field calculations. Previous work has shown an association between LCS passage and fluctuations in microbial populations and we find that ensemble FTLE forecasts are sufficient to predict such passages one day ahead of time with an accuracy of about 2 h.
Submerged turbulence detection with optical satellites
NASA Astrophysics Data System (ADS)
Gibson, Carl H.; Keeler, R. Norris; Bondur, Valery G.; Leung, Pak T.; Prandke, H.; Vithanage, D.
2013-01-01
During fall periods in 2002, 2003 and 2004 three major oceanographic expeditions were carried out in Mamala Bay, Hawaii. These were part of the RASP Remote Anthropogenic Sensing Program. Ikonos and Quickbird optical satellite images of sea surface glint revealed !100 m spectral anomalies in km2 averaging patches in regions leading from the Honolulu Sand Island Municipal Outfall diffuser to distances up to 20 km. To determine the mechanisms behind this phenomenon, the RASP expeditions monitored the waters adjacent to the outfall with an array of hydrographic, optical and turbulence microstructure sensors in anomaly and ambient background regions. Drogue tracks and mean turbulence parameters for 2 ! 104 microstructure patches were analyzed to understand complex turbulence, fossil turbulence and zombie turbulence near-vertical internal wave transport processes. The dominant mechanism appears to be generic to stratified natural fluids including planet and star atmospheres and is termed beamed zombie turbulence maser action (BZTMA). Most of the bottom turbulent kinetic energy is converted to ! 100 m fossil turbulence waves. These activate secondary (zombie) turbulence in outfall fossil turbulence patches that transmit heat, mass, chemical species, momentum and information vertically to the sea surface for detection in an efficient maser action. The transport is beamed in intermittent mixing chimneys.
Submerged turbulence detection with optical satellites
NASA Astrophysics Data System (ADS)
Gibson, Carl H.; Keeler, R. Norris; Bondur, Valery G.; Leung, Pak T.; Prandke, H.; Vithanage, D.
2007-09-01
During fall periods in 2002, 2003 and 2004 three major oceanographic expeditions were carried out in Mamala Bay, Hawaii. These were part of the RASP Remote Anthropogenic Sensing Program. Ikonos and Quickbird optical satellite images of sea surface glint revealed ~100 m spectral anomalies in km2 averaging patches in regions leading from the Honolulu Sand Island Municipal Outfall diffuser to distances up to 20 km. To determine the mechanisms behind this phenomenon, the RASP expeditions monitored the waters adjacent to the outfall with an array of hydrographic, optical and turbulence microstructure sensors in anomaly and ambient background regions. Drogue tracks and mean turbulence parameters for 2 × 10 4 microstructure patches were analyzed to understand complex turbulence, fossil turbulence and zombie turbulence near-vertical internal wave transport processes. The dominant mechanism appears to be generic to stratified natural fluids including planet and star atmospheres and is termed beamed zombie turbulence maser action (BZTMA). Most of the bottom turbulent kinetic energy is converted to ~ 100 m fossil turbulence waves. These activate secondary (zombie) turbulence in outfall fossil turbulence patches that transmit heat, mass, chemical species, momentum and information vertically to the sea surface for detection in an efficient maser action. The transport is beamed in intermittent mixing chimneys.
Adaptive optical ghost imaging through atmospheric turbulence.
Shi, Dongfeng; Fan, Chengyu; Zhang, Pengfei; Zhang, Jinghui; Shen, Hong; Qiao, Chunhong; Wang, Yingjian
2012-12-17
We demonstrate for the first time (to our knowledge) that a high-quality image can still be obtained in atmospheric turbulence by applying adaptive optical ghost imaging (AOGI) system even when conventional ghost imaging system fails to produce an image. The performance of AOGI under different strength of atmospheric turbulence is investigated by simulation. The influence of adaptive optics system with different numbers of adaptive mirror elements on obtained image quality is also studied.
Aspects of clear air turbulence severity forecasting and detection
NASA Technical Reports Server (NTRS)
Ehernberger, L. J.
1982-01-01
Factors influencing the accuracy of the forecasts of incidences of clear air turbulence (CAT) are discussed, along with techniques for improved verification. Descriptive ranking terms for the intensity of CAT events, ranging from light to extreme, are developed, and meteorological parameters used for predictions are reviewed, including jetstream core location, vertical and horizontal wind shears, stable layers, tropopause height, trough speed, 500-mb vorticity, surface fronts, pressure centers and cyclogenesis, and wind speeds near mountain ridges. Methods of remote detection of CAT, particularly by using radiometry sensitive to the IR water vapor band, are noted to have had some success in detecting actual CAT events and decreasing false alarms. Statistical aspects of CAT encounter severity are discussed, including the establishment of confidence intervals for thresholds of detection of CATs of varying intensities.
Optical turbulence in fiber lasers.
Wabnitz, Stefan
2014-03-15
We analyze the nonlinear stage of modulation instability in passively mode-locked fiber lasers leading to chaotic or noise-like emission. We present the phase-transition diagram among different regimes of chaotic emission in terms of the key cavity parameters: amplitude or phase turbulence, and spatio-temporal intermittency. PMID:24690788
NASA Astrophysics Data System (ADS)
Xiao, Shu-mei; Mei, Hai-ping; Wang, Qian; Rao, Rui-zhong
2013-08-01
An integrated fiber-optic turbulence sensor based on non-balanced fiber-optic Mach-Zehnder interferometer with a small air gap as light path difference has been designed for detecting air refractive index fluctuation. For avoiding sensing signal fading and perturbations from circumstance during signal transmission, the phase generated carrier is used. The turbulence induced air refractive index fluctuations are demodulated by the algorithm of correlation. Background noise of the sensor is below10-17 . By comparing with the refractive index structure constant measured by fine-wire resistance thermometer, results show good agreement in both their magnitude and tendency. For its outstanding property of corrosion protection, the sensor is especially suitable for maritime atmospheric optical turbulence research, which is verified by one month sea beach investigation. Some results of the maritime optical turbulence intensity are reported in the end.
Impacts of optical turbulence on underwater imaging
NASA Astrophysics Data System (ADS)
Hou, Weilin; Woods, S.; Goode, W.; Jarosz, E.; Weidemann, A.
2011-06-01
Optical signal transmission underwater is of vital interests to both civilian and military applications. The range and signal to noise during the transmission, as a function of system and water optical properties determines the effectiveness of EO technology. These applications include diver visibility, search and rescue, mine detection and identification, and optical communications. The impact of optical turbulence on underwater imaging has been postulated and observed by many researchers. However, no quantative studies have been done until recently, in terms of both the environmental conditions, and impacts on image quality as a function of range and spatial frequencies. Image data collected from field measurements during SOTEX (Skaneateles Optical Turbulence Exercise, July 22-31, 2010) using the Image Measurement Assembly for Subsurface Turbulence (IMAST) are presented. Optical properties of the water column in the field were measured using WETLab's ac-9 and Laser In Situ Scattering and Transmissometer (LISST, Sequoia Scientific), in coordination with physical properties including CTD (Seabird), dissipation rate of kinetic energy and heat, using both the Vector velocimeter and CT combo (Nortek and PME), and shear probe based Vertical Microstructure Profiler (VMP, Rockland). The strong stratification structure in the water column provides great opportunity to observe various dissipation strengths throughout the water column, which corresponds directly with image quality as shown. Initial results demonstrate general agreement between data collected and model prediction, while discrepancies between measurements and model suggest higher spatial and temporal observations are needed in the future.
Optical turbulence above mountains seen in 3D
NASA Astrophysics Data System (ADS)
Els, S. G.; Vogiatzis, K.; Otárola, A.; Riddle, R.; Schöck, M.; Skidmore, W.; Travouillon, T.
2010-07-01
Atmospheric optical turbulence is the main driver of wavefront distortions which affect optical telescope performance. Therefore, many techniques have been developed to measure the optical turbulence strength along the line of sight. Based on data collected with the MASS (Multi Aperture Scintillation Sensor), we show that a large sample of such measurements can be used to assess the average three dimensional turbulence distribution above ground. The use of, and a more sophisticated instrumental setup for, such turbulence tomography will be discussed.
Wall induced turbulence distortions of optical measurements
NASA Astrophysics Data System (ADS)
Gustafsson, Ove K. S.; Henriksson, Markus; Sjöqvist, Lars
2009-09-01
Optical measurements and tests of optical instruments are often performed through an opened window or from the roof of an elevated building. This can also be a common situation for free-space optical (FSO) communication systems. Wind friction in combination with solar heating of the wall and the ground will create increased turbulence in a boundary layer close to the wall. For an outgoing laser beam this thin region of strong turbulence causes beam wander, beam broadening and beam break-up. For imaging and detection systems angle of arrival fluctuations and image blurring may result. In an attempt to estimate the strength of the atmospheric turbulence in the layer at the wall the refractive index structure constant (Cn2) was measured with an ultra sonic anemometer as a function of distance from the wall. The measurements were performed at the lower part of a window that was open just enough to give space for the anemometer. The window was placed 10 m above ground in a 12 m high building, with brick wall below the window and wooden panel above the window. Measurements of the turbulence as a function of distance from the wall were performed during different times of the day to study the influence of sun heating of the wall. The measured average Cn2 shows an exponentially decreasing function of distance from the wall. The exponential decay of Cn2 depends on the time of the day. The highest measured value of Cn2 was approximately 3x10-11 m-2/3 near the wall. The influence of wall turbulence is discussed with respect to its influence on laser beam propagation.
Optical monitor for observing turbulent flow
Albrecht, Georg F.; Moore, Thomas R.
1992-01-01
The present invention provides an apparatus and method for non-invasively monitoring turbulent fluid flows including anisotropic flows. The present invention uses an optical technique to filter out the rays travelling in a straight line, while transmitting rays with turbulence induced fluctuations in time. The output is two dimensional, and can provide data regarding the spectral intensity distribution, or a view of the turbulence in real time. The optical monitor of the present invention comprises a laser that produces a coherent output beam that is directed through a fluid flow, which phase-modulates the beam. The beam is applied to a temporal filter that filters out the rays in the beam that are straight, while substantially transmitting the fluctuating, turbulence-induced rays. The temporal filter includes a lens and a photorefractive crystal such as BaTiO.sub.3 that is positioned in the converging section of the beam near the focal plane. An imaging system is used to observe the filtered beam. The imaging system may take a photograph, or it may include a real time camera that is connected to a computer. The present invention may be used for many purposes including research and design in aeronautics, hydrodynamics, and combustion.
Optical intensity interferometry through atmospheric turbulence
NASA Astrophysics Data System (ADS)
Tan, P. K.; Chan, A. H.; Kurtsiefer, C.
2016-04-01
Conventional ground-based astronomical observations suffer from image distortion due to atmospheric turbulence. This can be minimized by choosing suitable geographic locations or adaptive optical techniques, and avoided altogether by using orbital platforms outside the atmosphere. One of the promises of optical intensity interferometry is its independence from atmospherically induced phase fluctuations. By performing narrow-band spectral filtering on sunlight and conducting temporal intensity interferometry using actively quenched avalanche photodiodes, the Solar g(2)(τ) signature was directly measured. We observe an averaged photon bunching signal of g(2)(τ) = 1.693 ± 0.003 from the Sun, consistently throughout the day despite fluctuating weather conditions, cloud cover and elevation angle. This demonstrates the robustness of the intensity interferometry technique against atmospheric turbulence and opto-mechanical instabilities, and the feasibility to implement measurement schemes with both large baselines and long integration times.
Significance of anisotropy and the outer scale of turbulence for optical and radio seeing.
Coulman, C E; Vernin, J
1991-01-01
The small value found for the outer scale of turbulence (namely, Optical and radio seeing measurements are analyzed in support of a proposed turbulence spectrum which exhibits a spectral gap for scales (and hence interferometer baselines) between approximately 10 and 1500 m but which obeys a 5/3 power law between 1500 and 20,000 m. The implications for forecasting the performance of optical and radio telescopes and interferometers are important.
NASA Astrophysics Data System (ADS)
Alliss, R.
2014-09-01
Optical turbulence (OT) acts to distort light in the atmosphere, degrading imagery from astronomical telescopes and reducing the data quality of optical imaging and communication links. Some of the degradation due to turbulence can be corrected by adaptive optics. However, the severity of optical turbulence, and thus the amount of correction required, is largely dependent upon the turbulence at the location of interest. Therefore, it is vital to understand the climatology of optical turbulence at such locations. In many cases, it is impractical and expensive to setup instrumentation to characterize the climatology of OT, so numerical simulations become a less expensive and convenient alternative. The strength of OT is characterized by the refractive index structure function Cn2, which in turn is used to calculate atmospheric seeing parameters. While attempts have been made to characterize Cn2 using empirical models, Cn2 can be calculated more directly from Numerical Weather Prediction (NWP) simulations using pressure, temperature, thermal stability, vertical wind shear, turbulent Prandtl number, and turbulence kinetic energy (TKE). In this work we use the Weather Research and Forecast (WRF) NWP model to generate Cn2 climatologies in the planetary boundary layer and free atmosphere, allowing for both point-to-point and ground-to-space seeing estimates of the Fried Coherence length (ro) and other seeing parameters. Simulations are performed using a multi-node linux cluster using the Intel chip architecture. The WRF model is configured to run at 1km horizontal resolution and centered on the Mauna Loa Observatory (MLO) of the Big Island. The vertical resolution varies from 25 meters in the boundary layer to 500 meters in the stratosphere. The model top is 20 km. The Mellor-Yamada-Janjic (MYJ) TKE scheme has been modified to diagnose the turbulent Prandtl number as a function of the Richardson number, following observations by Kondo and others. This modification
Forecasting turbulent modes with nonparametric diffusion models: Learning from noisy data
NASA Astrophysics Data System (ADS)
Berry, Tyrus; Harlim, John
2016-04-01
In this paper, we apply a recently developed nonparametric modeling approach, the "diffusion forecast", to predict the time-evolution of Fourier modes of turbulent dynamical systems. While the diffusion forecasting method assumes the availability of a noise-free training data set observing the full state space of the dynamics, in real applications we often have only partial observations which are corrupted by noise. To alleviate these practical issues, following the theory of embedology, the diffusion model is built using the delay-embedding coordinates of the data. We show that this delay embedding biases the geometry of the data in a way which extracts the most stable component of the dynamics and reduces the influence of independent additive observation noise. The resulting diffusion forecast model approximates the semigroup solutions of the generator of the underlying dynamics in the limit of large data and when the observation noise vanishes. As in any standard forecasting problem, the forecasting skill depends crucially on the accuracy of the initial conditions. We introduce a novel Bayesian method for filtering the discrete-time noisy observations which works with the diffusion forecast to determine the forecast initial densities. Numerically, we compare this nonparametric approach with standard stochastic parametric models on a wide-range of well-studied turbulent modes, including the Lorenz-96 model in weakly chaotic to fully turbulent regimes and the barotropic modes of a quasi-geostrophic model with baroclinic instabilities. We show that when the only available data is the low-dimensional set of noisy modes that are being modeled, the diffusion forecast is indeed competitive to the perfect model.
NASA Astrophysics Data System (ADS)
Alliss, R.; Felton, B.
2010-09-01
Optical turbulence (OT) acts to distort light in the atmosphere, degrading imagery from astronomical or other telescopes. In addition, the quality of service of a free space optical communications link may also be impacted. Some of the degradation due to turbulence can be corrected by adaptive optics. However, the severity of optical turbulence, and thus the amount of correction required, is largely dependent upon the turbulence at the location of interest. Therefore, it is vital to understand the climatology of optical turbulence at such locations. In many cases, it is impractical and expensive to setup instrumentation to characterize the climatology of OT, particularly for OCONUS locations, so simulations become a less expensive and convenient alternative. The strength of OT is characterized by the refractive index structure function Cn2, which in turn is used to calculate atmospheric seeing parameters. While attempts have been made to characterize Cn2 using empirical models, Cn2 can be calculated more directly from Numerical Weather Prediction (NWP) simulations using pressure, temperature, thermal stability, vertical wind shear, turbulent Prandtl number, and turbulence kinetic energy (TKE). In this work we use the Weather Research and Forecast (WRF) NWP model to generate Cn2 climatologies in the planetary boundary layer and free atmosphere, allowing for both point-to-point and ground-to-space seeing estimates of the Fried Coherence length (ro) and other seeing parameters. Simulations are performed using the Maui High Performance Computing Centers (MHPCC) Mana cluster. The WRF model is configured to run at 1km horizontal resolution over a domain covering several hundreds of kilometers. The vertical resolution varies from 25 meters in the boundary layer to 500 meters in the stratosphere. The model top is 20 km. We are interested in the variations in Cn2 and the Fried Coherence Length (ro). Nearly two years of simulations have been performed over various regions
Study of strong turbulence effects for optical wireless links
NASA Astrophysics Data System (ADS)
Yuksel, Heba; Meric, Hasim; Kunter, Fulya
2012-10-01
Strong turbulence measurements that are taken using real time optical wireless experimental setups are valuable when studying the effects of turbulence regimes on a propagating optical beam. In any kind of FSO system, for us to know the strength of the turbulence thus the refractive index structure constant, is beneficial for having an optimum bandwidth of communication. Even if the FSO Link is placed very well-high-above the ground just to have weak enough turbulence effects, there can be severe atmospheric conditions that can change the turbulence regime. Having a successful theory that will cover all regimes will give us the chance of directly processing the image in existing or using an additional hardware thus deciding on the optimum bandwidth of the communication line at firsthand. For this purpose, Strong Turbulence data has been collected using an outdoor optical wireless setup placed about 85 centimeters above the ground with an acceptable declination and a path length of about 250 meters inducing strong turbulence to the propagating beam. Variations of turbulence strength estimation methods as well as frame image analysis techniques are then been applied to the experimental data in order to study the effects of different parameters on the result. Such strong turbulence data is compared with existing weak and intermediate turbulence data. Aperture Averaging Factor for different turbulence regimes is also investigated.
Optical turbulence in confined media: part I, the indoor turbulence sensor instrument.
Chabé, Julien; Blary, Flavien; Ziad, Aziz; Borgnino, Julien; Fanteï-Caujolle, Yan; Liotard, Arnaud; Falzon, Frédéric
2016-09-01
Optical system performances can be affected by local optical turbulence created by its surrounding environment (telescope dome, clean room, atmospheric surface layer). We present our new instrument INdoor TurbulENce SEnsor (INTENSE) dedicated to this local optical turbulence characterization. INTENSE consists of using several parallel laser beams separated by non-redundant baselines between 0.05 and 2.5 m and measuring the angle of arrival fluctuations from spot displacements on a CCD. After introducing the theoretical background, we give a description of the instrument including a detailed characterization of instrumental noise and, finally, give the first results for the characterization of the turbulence inside clean rooms for optical systems studies.
Optical turbulence in confined media: part I, the indoor turbulence sensor instrument.
Chabé, Julien; Blary, Flavien; Ziad, Aziz; Borgnino, Julien; Fanteï-Caujolle, Yan; Liotard, Arnaud; Falzon, Frédéric
2016-09-01
Optical system performances can be affected by local optical turbulence created by its surrounding environment (telescope dome, clean room, atmospheric surface layer). We present our new instrument INdoor TurbulENce SEnsor (INTENSE) dedicated to this local optical turbulence characterization. INTENSE consists of using several parallel laser beams separated by non-redundant baselines between 0.05 and 2.5 m and measuring the angle of arrival fluctuations from spot displacements on a CCD. After introducing the theoretical background, we give a description of the instrument including a detailed characterization of instrumental noise and, finally, give the first results for the characterization of the turbulence inside clean rooms for optical systems studies. PMID:27607283
Statistics of optical vortex wander on propagation through atmospheric turbulence.
Gu, Yalong
2013-04-01
The transverse position of an optical vortex on propagation through atmospheric turbulence is studied. The probability density of the optical vortex position on a transverse plane in the atmosphere is formulated in weak turbulence by using the Born approximation. With these formulas, the effect of aperture averaging on topological charge detection is investigated. These results provide quantitative guidelines for the design of an optimal detector of topological charge, which has potential application in optical vortex communication systems.
Localization of angular momentum in optical waves propagating through turbulence.
Sanchez, Darryl J; Oesch, Denis W
2011-12-01
This is the first in a series of papers demonstrating that photons with orbital angular momentum can be created in optical waves propagating through distributed turbulence. The scope of this first paper is much narrower. Here, we demonstrate that atmospheric turbulence can impart non-trivial angular momentum to beams and that this non-trivial angular momentum is highly localized. Furthermore, creation of this angular momentum is a normal part of propagation through atmospheric turbulence. PMID:22273930
Localization of angular momentum in optical waves propagating through turbulence.
Sanchez, Darryl J; Oesch, Denis W
2011-12-01
This is the first in a series of papers demonstrating that photons with orbital angular momentum can be created in optical waves propagating through distributed turbulence. The scope of this first paper is much narrower. Here, we demonstrate that atmospheric turbulence can impart non-trivial angular momentum to beams and that this non-trivial angular momentum is highly localized. Furthermore, creation of this angular momentum is a normal part of propagation through atmospheric turbulence.
Characterizing inertial and convective optical turbulence by detrended fluctuation analysis
NASA Astrophysics Data System (ADS)
Funes, Gustavo; Figueroa, Eduardo; Gulich, Damián.; Zunino, Luciano; Pérez, Darío. G.
2013-10-01
Atmospheric turbulence is usually simulated at the laboratory by generating convective free flows with hot surfaces, or heaters. It is tacitly assumed that propagation experiments in this environment are comparable to those usually found outdoors. Nevertheless, it is unclear under which conditions the analogy between convective and isotropic turbulence is valid; that is, obeying Kolmogorov isotropic models. For instance, near-ground-level turbulence often is driven by shear ratchets deviating from established inertial models. In this case, a value for the structure constant can be obtained but it would be unable to distinguish between both classes of turbulence. We have performed a conceptually simple experiment of laser beam propagation through two types of artificial turbulence: isotropic turbulence generated by a turbulator [Proc. SPIE 8535, 853508 (2012)], and convective turbulence by controlling the temperature of electric heaters. In both cases, a thin laser beam propagates across the turbulent path, and its wandering is registered by a position sensor detector. The strength of the optical turbulence, in terms of the structure constant, is obtained from the wandering variance. It is expressed as a function of the temperature difference between cold and hot sources in each setup. We compare the time series behaviour for each turbulence with increasing turbulence strength by estimating the Hurst exponent, H, through detrended fluctuation analysis (DFA). Refractive index fluctuations are inherently fractal; this characteristic is reflected in their spectra power-law dependence—in the inertial range. This fractal behaviour is inherited by time series of optical quantities, such as the wandering, by the occurrence of long-range correlations. By analyzing the wandering time series with this technique, we are able to correlate the turbulence strength to the value of the Hurt exponent. Ultimately, we characterize both types of turbulence.
Near-Ground optical turbulence measurements at Cerro Las Campanas
NASA Astrophysics Data System (ADS)
Prieto, G.; Berdja, A.; Thomas-Osip, J. E.
2011-11-01
We report preliminary results from Near-Ground optical turbulence measurements carried out at Cerro Las Campanas, the future site of the Giant Magellan Telescope (GMT), using MooSci (Moon Scintillomenter), DIMM (Differential Image Motion Monitor) and MASS (Multiple Aperture Scintillation Sensor), focusing on the effects above the future GMT enclosure. This campaign will continue with future observations of the NGL turbulence in order to better model the adaptive optics performance and aid in the design of the GMT AO instrumentation
Propagation of optical coherence lattices in the turbulent atmosphere.
Liu, Xianlong; Yu, Jiayi; Cai, Yangjian; Ponomarenko, Sergey A
2016-09-15
We explore the propagation of recently introduced optical coherence lattices (OCLs) in the turbulent atmosphere. We show that the lattice intensity profile and the spatial degree of coherence will display periodicity reciprocity over long propagation distances even though the lattices are affected by the turbulence. The lattice periodicity reciprocity has been previously conjectured to be advantageous for free-space information transfer and optical communications. We then show how one can increase the distance over which the lattice periodicity reciprocity is preserved in the turbulent atmosphere by engineering input lattice beam parameters. We also show that the OCLs have scintillation indices lower than those of Gaussian beams. PMID:27628352
Trajectory of an optical vortex in atmospheric turbulence.
Dipankar, A; Marchiano, R; Sagaut, P
2009-10-01
Trajectory of an optical vortex has been identified for its propagation in atmospheric turbulence using numerical simulations. An analytical expression has been found, relating the radial departure of the vortex in plane perpendicular to the direction of propagation, to the refractive index structure function parameter and the inner scale of turbulence. The angular orientation of the vortex in the same transverse plane is found to be related to the anisotropy of the medium. The obtained results provide an alternative way to find turbulent parameters with the help of optical vortices.
Forecast analysis of optical waveguide bus performance
NASA Technical Reports Server (NTRS)
Ledesma, R.; Rourke, M. D.
1979-01-01
Elements to be considered in the design of a data bus include: architecture; data rate; modulation, encoding, detection; power distribution requirements; protocol, work structure; bus reliability, maintainability; interterminal transmission medium; cost; and others specific to application. Fiber- optic data bus considerations for a 32 port transmissive star architecture, are discussed in a tutorial format. General optical-waveguide bus concepts, are reviewed. The electrical and optical performance of a 32 port transmissive star bus, and the effects of temperature on the performance of optical-waveguide buses are examined. A bibliography of pertinent references and the bus receiver test results are included.
NASA Astrophysics Data System (ADS)
Park, Sang-Hun; Kim, Jung-Hoon; Sharman, Robert D.; Klemp, Joseph B.
2016-07-01
On 2 November 2015, unrealistically large areas of light-or-stronger turbulence were predicted by the WRF-RAP (Weather Research and Forecast Rapid Refresh)-based operational turbulence forecast system over the western U.S. mountainous regions, which were not supported by available observations. These areas are reduced by applying additional terrain averaging, which damps out the unphysical components of small-scale (~2Δx) energy aloft induced by unfiltered topography in the initialization of the WRF model. First, a control simulation with the same design of the WRF-RAP model shows that the large-scale atmospheric conditions are well simulated but predict strong turbulence over the western mountainous region. Four experiments with different levels of additional terrain smoothing are applied in the initialization of the model integrations, which significantly reduce spurious mountain-wave-like features, leading to better turbulence forecasts more consistent with the observed data.
Intensity fluctuations of asymmetrical optical beams in anisotropic turbulence.
Baykal, Yahya
2016-09-20
Intensity fluctuations of asymmetrical optical beams are examined when such beams propagate through anisotropic turbulence. Anisotropic turbulence is modeled by non-Kolmogorov von Kármán spectrum. The variations of the scintillation index are observed against the changes in the asymmetry factor of the Gaussian beam, power law exponent of non-Kolmogorov spectrum, anisotropic factors in the transverse direction, and the link length. It is found that for all the conditions, asymmetry in the optical beam is a disadvantage but the anisotropy in the atmosphere is an advantage for reducing the intensity fluctuations in an optical wireless communications link operating in the atmosphere. PMID:27661570
Optical measurements of the outer scale of the atmospheric turbulence.
NASA Astrophysics Data System (ADS)
Lukin, V. P.
The light scattering on the turbulence inhomogeneities of the atmosphere is the one of the main mechanism of distortion of the received optical signal. The random spacetime changes of the atmospheric refractive index lead to distortion of the optical beam structure, the fluctuations of the intensity and phase of the optical wave are manifested, in particular, in blurring, shivering and flickering of the source images, as well as in the turbulent extinction of the mean received power of the signal. Several models are compared with measurements of atmospheric parameters.
A flexible testbed for adaptive optics in strong turbulence
NASA Astrophysics Data System (ADS)
Schmidt, Jason D.; Steinbock, Michael J.; Berg, Eric C.
2011-06-01
In recent years, optical wave propagation through strong atmospheric turbulence and adaptive optics compensation thereof has received much attention in literature and technical meetings. At the Air Force Institute of Technology, recent simulation-based efforts in strong turbulence compensation are expanding into laboratory experiments utilizing a versatile surrogate turbulence simulator and adaptive optics system. The system can switch between using two different wavefront sensors, a Shack-Hartmann and a self-referencing interferometer. Wavefront reconstruction takes place on field programmable gate arrays, operating at kilohertz frame rates. Further, the system is able to perform reconstruction and control in software for testing of advanced algorithms (at frame rates below 10 Hz). The entire package is compact enough for transportation to other laboratories and live test facilities. This paper describes the optical layout, architecture, and initial results of real-time operation.
Cui, Linyan; Xue, Bindang; Zhou, Fugen
2015-11-16
Theoretical and experimental investigations have shown that the atmospheric turbulence exhibits both anisotropic and non-Kolmogorov properties. In this work, two theoretical atmosphere refractive-index fluctuations spectral models are derived for optical waves propagating through anisotropic non-Kolmogorov atmospheric turbulence. They consider simultaneously the finite turbulence inner and outer scales and the asymmetric property of turbulence eddies in the orthogonal xy-plane throughout the path. Two anisotropy factors which parameterize the asymmetry of turbulence eddies in both horizontal and vertical directions are introduced in the orthogonal xy-plane, so that the circular symmetry assumption of turbulence eddies in the xy-plane is no longer required. Deviations from the classic 11/3 power law behavior in the spectrum model are also allowed by assuming power law value variations between 3 and 4. Based on the derived anisotropic spectral model and the Rytov approximation theory, expressions for the variance of angle of arrival (AOA) fluctuations are derived for optical plane and spherical waves propagating through weak anisotropic non-Kolmogorov turbulence. Calculations are performed to analyze the derived spectral models and the variance of AOA fluctuations.
The Durham/ESO SLODAR optical turbulence profiler
NASA Astrophysics Data System (ADS)
Wilson, R. W.; Butterley, T.; Sarazin, M.
2009-11-01
An instrument for monitoring of the vertical profile of atmospheric optical turbulence strength, employing the Slope Detection and Ranging (SLODAR) double star technique applied to a small telescope, has been developed by Durham University and the European South Observatory. The system has been deployed at the Cerro Paranal observatory in Chile for statistical characterization of the site. The instrument is configured to sample the turbulence at altitudes below 1.5 km with a vertical resolution of approximately 170 m. The system also functions as a general-purpose seeing monitor, measuring the integrated optical turbulence strength for the whole atmosphere, and hence the seeing width. We give technical details of the prototype and present data to characterize its performance. Comparisons with contemporaneous measurements from a differential image motion monitor (DIMM) and a multi-aperture scintillation sensor (MASS) are discussed. Statistical results for the optical turbulence profile at the Paranal site are presented. We find that, in the median case, 49 per cent of the total optical turbulence strength is associated with the surface layer (below 100 m), 35 per cent with the `free atmosphere' (above 1500 m) and 16 per cent with the intermediate altitudes (100-1500 m).
Characterisation of the Optical Turbulence at Siding Spring
NASA Astrophysics Data System (ADS)
Goodwin, Michael; Jenkins, Charles; Lambert, Andrew
2013-01-01
Measurements of the optical turbulence profile above Siding Spring Observatory were conducted during 2005 and 2006. This effort was largely motivated by the need to predict the statistical performance of adaptive optics at Siding Spring. The data were collected using a purpose-built instrument based on the slope detection and ranging (SLODAR) method where observations of a bright double star are imaged by Shack-Hartmann taken with the Australian National University 24-inch and 40-inch telescopes. The analysis of the data yielded a model consisting of a handful of statistically prominent thin layers that are statistically separated into the ground layer (37.5, 250 m) and the free atmosphere (1, 3, 6, 9, 13.5 km) for good (25%), typical (50%), and bad (25%) observing conditions. We found that ground-layer turbulence dominates the turbulence profile with up to 80% of the integrated turbulence below 500 m. The turbulence tends to be non-Kolmogorov, especially for the ground layer with a power-law index of β ~ 10/3. The mirror/dome seeing can be a significant fraction of the ground-layer turbulence. The median atmospheric seeing is around 1.2 arcsec, in agreement with observational reports.
O`Hern, T.J.; Torczynski, J.R.; Shagam, R.N.; Blanchat, T.K.; Chu, T.Y.; Tassin-Leger, A.L.; Henderson, J.A.
1997-01-01
This report summarizes the work performed under the Sandia Laboratory Directed Research and Development (LDRD) project ``Optical Diagnostics for Turbulent and Multiphase Flows.`` Advanced optical diagnostics have been investigated and developed for flow field measurements, including capabilities for measurement in turbulent, multiphase, and heated flows. Particle Image Velocimetry (PIV) includes several techniques for measurement of instantaneous flow field velocities and associated turbulence quantities. Nonlinear photorefractive optical materials have been investigated for the possibility of measuring turbulence quantities (turbulent spectrum) more directly. The two-dimensional PIV techniques developed under this LDRD were shown to work well, and were compared with more traditional laser Doppler velocimetry (LDV). Three-dimensional PIV techniques were developed and tested, but due to several experimental difficulties were not as successful. The photorefractive techniques were tested, and both potential capabilities and possible problem areas were elucidated.
NASA Astrophysics Data System (ADS)
Wang, Qian; Mei, Haiping; Rao, Ruizhong
2015-04-01
In this article, a high quality fiber optical turbulence sensing array contains several sensors is proposed to obtain time series of air refractive index fluctuations. A fixed sensor is supposed to be set as the origin and others to be arranged in Cartesian coordinates respectively. Under the spatial configurations above, two-point correlation algorithm is used to give two order structure parameters and multipoint correlation algorithm for more structure information about scalar turbulence. For each direction, two-point spatial correlation coefficients varying with distance are provided. Meanwhile spatial power spectrum and outer-scales according to the data are introduced. Multipoint correlations can give more structure information such as the interactions between scales and the spatial structure of relevant fluctuations. In the one-dimension circumstance for instance the x-axis, spatial correlation coefficient tends to take oscillation. After a short-time averaging, it tends to decrease with the increase of spatial displacement, and then tends to zero after outer scale. Further study show that within the limit of outer scale, diurnal variation of the spatial correlation coefficient and intensity reveal a higher similarity, the relevancy is about 60% and keeps stable; once the distance goes across the outer scale, they are uncorrelated. In short, utilizing the fiber optical turbulence sensing array is a new method for measuring spatial correlation of optical turbulence. It can overcome some problems from single-point measurement, especially when using Taylor's frozen-turbulence hypothesis. Some structural information of optical turbulence not only makes the theory of scalar field more abundant, but also in favor of some problems about optical propagation.
Characterising atmospheric optical turbulence using stereo-SCIDAR
NASA Astrophysics Data System (ADS)
Osborn, James; Butterley, Tim; Föhring, Dora; Wilson, Richard
2015-04-01
Stereo-SCIDAR (SCIntillation Detection and Ranging) is a development to the well known SCIDAR method for characterisation of the Earth's atmospheric optical turbulence. Here we present some interesting capabilities, comparisons and results from a recent campaign on the 2.5 m Isaac Newton Telescope on La Palma.
Measurements of optical underwater turbulence under controlled conditions
NASA Astrophysics Data System (ADS)
Kanaev, A. V.; Gladysz, S.; Almeida de Sá Barros, R.; Matt, S.; Nootz, G. A.; Josset, D. B.; Hou, W.
2016-05-01
Laser beam propagation underwater is becoming an important research topic because of high demand for its potential applications. Namely, ability to image underwater at long distances is highly desired for scientific and military purposes, including submarine awareness, diver visibility, and mine detection. Optical communication in the ocean can provide covert data transmission with much higher rates than that available with acoustic techniques, and it is now desired for certain military and scientific applications that involve sending large quantities of data. Unfortunately underwater environment presents serious challenges for propagation of laser beams. Even in clean ocean water, the extinction due to absorption and scattering theoretically limit the useful range to few attenuation lengths. However, extending the laser light propagation range to the theoretical limit leads to significant beam distortions due to optical underwater turbulence. Experiments show that the magnitude of the distortions that are caused by water temperature and salinity fluctuations can significantly exceed the magnitude of the beam distortions due to atmospheric turbulence even for relatively short propagation distances. We are presenting direct measurements of optical underwater turbulence in controlled conditions of laboratory water tank using two separate techniques involving wavefront sensor and LED array. These independent approaches will enable development of underwater turbulence power spectrum model based directly on the spatial domain measurements and will lead to accurate predictions of underwater beam propagation.
Atmospheric turbulence optical model (ATOM) based on fractal theory
NASA Astrophysics Data System (ADS)
Jaenisch, Holger M.; Handley, James W.; Scoggins, Jim; Carroll, Marvin P.
1994-06-01
An Atmospheric Turbulence Optical Model (ATOM) is presented that used cellular automata (CA) rules as the basis for modeling synthetic phase sheets. This method allows image fracture, scintillation and blur to be correctly models using the principle of convolution with a complex kernel derived from CA rules interaction. The model takes into account the changing distribution of turbules from micro-turbule domination at low altitudes to macro-domination at high altitudes. The wavelength of propagating images (such as a coherent laser beam) and the range are taken into account. The ATOM model is written in standard FORTRAN 77 and enables high-speed in-line calculation of atmospheric effects to be performed without resorting to computationally intensive solutions of Navier Stokes equations or Cn2 profiles.
Orbital angular momentum in optical waves propagating through distributed turbulence.
Sanchez, Darryl J; Oesch, Denis W
2011-11-21
This is the second of two papers demonstrating that photons with orbital angular momentum can be created in optical waves propagating through distributed turbulence. In the companion paper, it is shown that propagation through atmospheric turbulence can create non-trivial angular momentum. Here, we extend the result and demonstrate that this momentum is, at least in part, orbital angular momentum. Specifically, we demonstrate that branch points (in the language of the adaptive optic community) indicate the presence of photons with non-zero OAM. Furthermore, the conditions required to create photons with non-zero orbital angular momentum are ubiquitous. The repercussions of this statement are wide ranging and these are cursorily enumerated. PMID:22109489
Orbital angular momentum in optical waves propagating through distributed turbulence.
Sanchez, Darryl J; Oesch, Denis W
2011-11-21
This is the second of two papers demonstrating that photons with orbital angular momentum can be created in optical waves propagating through distributed turbulence. In the companion paper, it is shown that propagation through atmospheric turbulence can create non-trivial angular momentum. Here, we extend the result and demonstrate that this momentum is, at least in part, orbital angular momentum. Specifically, we demonstrate that branch points (in the language of the adaptive optic community) indicate the presence of photons with non-zero OAM. Furthermore, the conditions required to create photons with non-zero orbital angular momentum are ubiquitous. The repercussions of this statement are wide ranging and these are cursorily enumerated.
Optical tomography system for laboratory turbulence measurements
NASA Astrophysics Data System (ADS)
McMackin, Lenore J.; Pierson, Robert E.; Hugo, Ronald J.; Truman, C. Randall
1998-10-01
We describe the design and operation of a high speed optical tomography system for measuring 2D images of a dynamic phase object at a rate of 5 kHz. Data from a set of eight Hartmann wavefront sensors is back-projected to produce phase images showing the details of the inner structure of a heated air flow. Series of reconstructions at different downstream locations illustrate the development of flow structure and the effect of acoustic flow forcing.
Cheng, Mingjian; Guo, Lixin; Li, Jiangting; Huang, Qingqing
2016-08-01
Rytov theory was employed to establish the transmission model for the optical vortices carried by Bessel-Gaussian (BG) beams in weak anisotropic turbulence based on the generalized anisotropic von Karman spectrum. The influences of asymmetry anisotropic turbulence eddies and source parameters on the signal orbital angular momentum (OAM) mode detection probability of partially coherent BG beams in anisotropic turbulence were discussed. Anisotropic characteristics of the turbulence could enhance the OAM mode transmission performance. The spatial partially coherence of the beam source would increase turbulent aberration's effect on the optical vortices. BG beams could dampen the influences of the turbulence because of their nondiffraction and self-healing characteristics.
Cheng, Mingjian; Guo, Lixin; Li, Jiangting; Huang, Qingqing
2016-08-01
Rytov theory was employed to establish the transmission model for the optical vortices carried by Bessel-Gaussian (BG) beams in weak anisotropic turbulence based on the generalized anisotropic von Karman spectrum. The influences of asymmetry anisotropic turbulence eddies and source parameters on the signal orbital angular momentum (OAM) mode detection probability of partially coherent BG beams in anisotropic turbulence were discussed. Anisotropic characteristics of the turbulence could enhance the OAM mode transmission performance. The spatial partially coherence of the beam source would increase turbulent aberration's effect on the optical vortices. BG beams could dampen the influences of the turbulence because of their nondiffraction and self-healing characteristics. PMID:27505641
First results from optical turbulence measurements at Cerro Las Campanas in 2010
NASA Astrophysics Data System (ADS)
Berdja, A.; Prieto, G.; Thomas-Osip, J. E.
2011-09-01
We report preliminary results from optical turbulence measurements carried out in 2010 at Cerro Las Campanas, the future site for the Giant Magellan Telescope (GMT). The instruments involved are MooSci, a lunar scintillometer for the near-ground optical turbulence profile, Differential Image Motion Monitor (DIMM) for the whole atmosphere total seeing, and MASS Multiple Aperture Scintillation Sensor (MASS) for high-altitude optical turbulence estimation. The main purpose of these measurements is to anticipate the optical turbulence strength above the future GMT enclosure, and to provide a means to model the future adaptive optics performance. We also discuss the significance of such a combination of instruments and some hypothetical limitations.
Weak Langmuir optical turbulence in a fiber cavity
NASA Astrophysics Data System (ADS)
Xu, G.; Garnier, J.; Mussot, A.; Trillo, S.; Churkin, D.; Tarasov, N.; Turitsyn, S.; Picozzi, A.
2016-07-01
We study theoretically and numerically the dynamics of a passive optical fiber ring cavity pumped by a highly incoherent wave: an incoherently injected fiber laser. The theoretical analysis reveals that the turbulent dynamics of the cavity is dominated by the Raman effect. The forced-dissipative nature of the fiber cavity is responsible for a large diversity of turbulent behaviors: Aside from nonequilibrium statistical stationary states, we report the formation of a periodic pattern of spectral incoherent solitons, or the formation of different types of spectral singularities, e.g., dispersive shock waves and incoherent spectral collapse behaviors. We derive a mean-field kinetic equation that describes in detail the different turbulent regimes of the cavity and whose structure is formally analogous to the weak Langmuir turbulence kinetic equation in the presence of forcing and damping. A quantitative agreement is obtained between the simulations of the nonlinear Schrödinger equation with cavity boundary conditions and those of the mean-field kinetic equation and the corresponding singular integrodifferential reduction, without using adjustable parameters. We discuss the possible realization of a fiber cavity experimental setup in which the theoretical predictions can be observed and studied.
Characterization of Fibre Channel over Highly Turbulent Optical Wireless Links
Johnson, G W; Henderer, B D; Wilburn, J W; Ruggiero, A J
2003-07-28
We report on the performance characterization and issues associated with using Fibre Channel (FC) over a highly turbulent free-space optical (FSO) link. Fibre Channel is a storage area network standard that provides high throughput with low overhead. Extending FC to FSO links would simplify data transfer from existing high-bandwidth sensors such as synthetic aperture radars and hyperspectral imagers. We measured the behavior of FC protocol at 1 Gbps in the presence of synthetic link dropouts that are typical of turbulent FSO links. Results show that an average bit error rate of less than 2 x 10{sup -8} is mandatory for adequate throughput. More importantly, 10 ns dropouts at a 2 Hz rate were sufficient to cause long (25 s) timeouts in the data transfer. Although no data was lost, this behavior is likely to be objectionable for most applications. Prospects for improvements in hardware and software will be discussed.
NASA Astrophysics Data System (ADS)
Kim, C. K.; Betterton, E. A.; Leuthold, M.; Holmgren, W.; Cronin, A.
2014-12-01
Accurate forecasts of solar irradiance are required for electric utilities to economically integrate substantial amounts of solar power into their power generation portfolios. A common failing of numerical weather models is the prediction of shallow cumulus clouds which are generally difficult to be resolved due to complicated processes in the planetary boundary layer. The present study carried out the sensitivity test of turbulence parameterization for better predicting solar irradiance during the shallow cumulus events near the state of Arizona by using the Weather Research and Forecasting model. The results from the simulations show that increasing the exchange coefficient leads to enhanced vertical mixing and a deeper mixed layer. At the top of mixed layer, an adiabatically ascending air parcel achieved the water vapour saturation and finally shallow cumulus is generated. A detailed analysis will be discussed in the upcoming conference.
NASA Astrophysics Data System (ADS)
Audrey, Crespin; Christine, Lebot; Yves, Bouteloup; Francois, Bouyssel
2011-12-01
A study on Clear-Air Turbulence (abbreviated by CAT) forecast in a Numerical Weather Model is presented in this paper. The main objective of this study is to evaluate ARPEGE Meteofrance-NWP model's ability to reproduce CAT, by calculating various CAT indices at the regional scale (over Europe) in this model. The list of indices used here is inspired from that proposed by R. Sharman & Wolff (2006). Calculated indices are then compared with AMDARs (Aircraft Meteorological DAta Relay) turbulence measurements during winter, early in 2010. This work was performed within DELICAT european project (*DEmonstration of LIdar based Clear-Air Turbulence detection), in the Seventh Research Framework program of the European Union [FP7], in Meteofrance national weather agency.
Optically relevant turbulence parameters in the Marine boundary layer
NASA Technical Reports Server (NTRS)
Davidson, K. L.; Houlihan, T. M.
1976-01-01
Shipboard measurements of temperature and velocity fluctuations were performed to determine optical propagation properties of the marine boundary layer. Empirical expressions describing the temperature structure parameter in terms of the Richardson Number overland were used to analyze data obtained for open ocean conditions. Likewise, profiles of mean wind and velocity fluctuation spectra derived from shipboard observations were utilized to calculate associated boundary layer turbulence parameters. In general, there are considerable differences between the open-ocean results of this study and previously determined overland results.
Optical turbulence and spectral condensate in long fibre lasers
Turitsyna, E. G.; Falkovich, Gregory; El-Taher, Atalla; Shu, Xuewen; Harper, Paul; Turitsyn, Sergei K.
2012-01-01
We study numerically optical turbulence using the particular example of a recently created, ultra-long fibre laser. For normal fibre dispersion, we observed an intermediate state with an extremely narrow spectrum (condensate), which experiences instability and a sharp transition to a fluctuating regime with a wider spectrum. We demonstrate that the number of modes has an impact on the condensate's lifetime. The smaller the number of modes, the more resistant is the condensate to perturbations. Experimental results show a good agreement with numerical simulations. PMID:22870062
Robust optical wireless links over turbulent media using diversity solutions
NASA Astrophysics Data System (ADS)
Moradi, Hassan
Free-space optic (FSO) technology, i.e., optical wireless communication (OWC), is widely recognized as superior to radio frequency (RF) in many aspects. Visible and invisible optical wireless links solve first/last mile connectivity problems and provide secure, jam-free communication. FSO is license-free and delivers high-speed data rates in the order of Gigabits. Its advantages have fostered significant research efforts aimed at utilizing optical wireless communication, e.g. visible light communication (VLC), for high-speed, secure, indoor communication under the IEEE 802.15.7 standard. However, conventional optical wireless links demand precise optical alignment and suffer from atmospheric turbulence. When compared with RF, they suffer a low degree of reliability and lack robustness. Pointing errors cause optical transceiver misalignment, adversely affecting system reliability. Furthermore, atmospheric turbulence causes irradiance fluctuations and beam broadening of transmitted light. Innovative solutions to overcome limitations on the exploitation of high-speed optical wireless links are greatly needed. Spatial diversity is known to improve RF wireless communication systems. Similar diversity approaches can be adapted for FSO systems to improve its reliability and robustness; however, careful diversity design is needed since FSO apertures typically remain unbalanced as a result of FSO system sensitivity to misalignment. Conventional diversity combining schemes require persistent aperture monitoring and repetitive switching, thus increasing FSO implementation complexities. Furthermore, current RF diversity combining schemes may not be optimized to address the issue of unbalanced FSO receiving apertures. This dissertation investigates two efficient diversity combining schemes for multi-receiving FSO systems: switched diversity combining and generalized selection combining. Both can be exploited to reduce complexity and improve combining efficiency. Unlike maximum
Analysis of optical waves propagating through moderate-to-strong non-Kolmogorov turbulence.
Cui, Linyan; Xue, Bindang; Cao, Xiaoguang
2013-09-01
The turbulence effect models derived with the Rytov theory method cannot be applied in the analysis of moderate-to-strong non-Kolmogorov turbulence. In this work, new expressions of the temporal power spectra of irradiance fluctuations are derived theoretically for optical waves propagating through moderate-to-strong non-Kolmogorov turbulence. They are developed under Andrews' assumption that small-scale irradiance fluctuations are modulated by large-scale irradiance fluctuations of the optical wave. A wide range of turbulence strength is considered instead of a limited range for weak non-Kolmogorov turbulence. These expressions have general spectral power law values in the range 3 to 4 instead of the standard power law value of 11/3 for Kolmogorov turbulence. Calculations are performed to analyze turbulence strength and turbulence spectral power law's variations on the final expressions.
OHP02 gravity wave campaign in relation to optical turbulence
NASA Astrophysics Data System (ADS)
Vernin, J.; Trinquet, H.; Jumper, G.; Murphy, E.; Ratkowski, A.
2007-09-01
Herein we present a campaign dedicated to the detection and the characterization of Gravity Waves (GW) in the Earth's atmosphere in relation to the generation of Optical Turbulence (OT). The observations took place in France from 17 to 24 July 2002 at the Haute Provence Observatory (OHP) and simultaneously at the Sirene Observatory, some 20 km apart. From both sites, several balloons were launched that measured the classical PTU-Wind profiles and additionally the structure constant of the temperature field C_T^2 vertical profiles. A Generalized Scidar (GS) technique was implemented at the 1.93 m-diameter OHP telescope, providing C_N^2(h) profiles every minute. From our observations, a significant amount of GW activity was observed at both sites, but without clear evidence of correlation between the two sites. It seems from our observations that a wide spectrum of GW is present at a given altitude and that this could result in a lack of correlation between observat! ions made from two sites 20 km apart. Most GW are non-stationary with long horizontal wavelengths (λ ˜ 100-200 km), kilometric vertical wavelengths (λ ~ 0.5-2 km) and long intrinsic period (T ~ 2-15 h). They belong in the category of "hydrostatic rotating or non-rotating waves". Layers of optical turbulence detected by balloons and the Scidar technique correlate well with regions of GW activity.
Buffer requirements of an optical communication system in atmospheric turbulence
NASA Astrophysics Data System (ADS)
Leclerc, Troy T.; Phillips, Ronald L.; Andrews, Larry C.; Crabbs, Robert
2013-05-01
Expressions related to the buffer requirements of an optical communication system in atmospheric turbulence are developed from the channel signal fade time statistics. Laser irradiance data were recorded over the course of one day by a receiving aperture of variable diameter at the Townes Institute Science and Technology Experimentation Facility (TISTEF) 1km laser range located within the Kennedy Space Center at Cape Canaveral, FL. Fade statistics of collected data and scintillometer measurements were compared to the derived model gamma-gamma fade model. Parallel to the laser instrumentation was a commercial scintillometer unit which reported the refractive index structure coefficient, Cn2 and the inner-scale of atmospheric turbulence, l0. The atmospheric parameters inferred from the collected laser data and the commercial instruments were compared. Mean and variance of the fade times were found to agree well with theory for smaller apertures where effects of aperture averaging are not present and in cases where scintillation is weak to moderate. It is suggested that a more appropriate PDF, with a heavier focus on aperture averaging, may be applied in future studies of free space optical communication system fade statistics.
Comparative measurements of the level of turbulence atmosphere by optical and acoustic devices
NASA Astrophysics Data System (ADS)
Lukin, V. P.; Botugina, N. N.; Gladkih, V. A.; Emaleev, O. N.; Konyaev, P. A.; Odintsov, S. L.; Torgaev, A. V.
2014-11-01
The complex measurements of level of atmospheric turbulence are conducted by the differential measurement device of turbulence (DMT), wave-front sensor (WFS), and also by ultrasonic weather-stations. Daytime measurements of structure parameters of refractive index of atmospheric turbulence carried out on horizontal optical paths on the Base Experimental Complex (BEC) of V.E. Zuev Institute of Atmospheric Optics SB RAS (IOA). A comparative analysis over of the got results is brought.
Cui, Linyan; Xue, Bindang
2015-09-01
Theoretical and experimental investigations have shown that the atmospheric turbulence exhibits both anisotropic and non-Kolmogorov properties. Very recent analyses of angle of arrival (AOA) fluctuations of an optical wave in anisotropic non-Kolmogorov turbulence have adopted the assumption that the propagation path was in the z-direction with circular symmetry of turbulence cells maintained in the orthogonal xy-plane throughout the path, and one single anisotropy factor was adopted in the orthogonal xy-plane to parameterize the asymmetry of turbulence cells or eddies in both horizontal and vertical directions. In this work, the circular symmetry assumption of turbulence cells or eddies in the orthogonal xy-plane is no longer required, and two anisotropy parameters are introduced in the orthogonal xy-plane to investigate the AOA fluctuations. In addition, deviations from the classic 11/3 spectral power law behavior for Kolmogorov turbulence are allowed by assuming spectral power law value variations between 3 and 4. With the Rytov approximation theory, new theoretical models for the variance of AOA fluctuations are developed for optical plane and spherical waves propagating through weak anisotropic non-Kolmogorov atmospheric turbulence. When the two anisotropic parameters are equal to each other, they reduce correctly to the recently published results (the circular symmetry assumption of turbulence cells or eddies in the orthogonal xy-plane was adopted). Furthermore, when these two anisotropic parameters equal one, they reduce correctly to the previously published analytic expressions for the cases of optical wave propagation through weak isotropic non-Kolmogorov turbulence.
New route to optical turbulence in detuned lasers with a compound cavity
Otsuka, K.; Kawaguchi, H.
1984-09-01
A successive subharmonic modulation cascade of self-sustained relaxation oscillations in an inverse order leading to optical turbulence in detuned lasers with compound-cavity configurations is predicted. A brief experimental result which supports the predicted subharmonic modulation phenomenon is shown. The suppression effect of optical turbulence by external light injection, which is important for practical applications, is demonstrated theoretically.
Application of a photodiode-array optical turbulence sensor to wind studies in complex terrain
Porch, W.M.; Green, T.J.
1980-04-01
A digital photodiode-array optical turbulence sensor was used to gather data simultaneously with analog optical anemometer measurements during the July 1979 ASCOT experiment. This system provided useful information regarding the uniformity of optical turbulence used by the optical anemometer to derive cross-path wind speeds. Wind speeds derived from digital analysis of the photodiode-array intensities also provided an independent measure of the cross-path wind speed. Close agreement was found between these two measures of the wind.
Influence of atmospheric turbulence on optical measurement: a case report and review of literature
NASA Astrophysics Data System (ADS)
Yao, Linshen; Shang, Yang; Fu, Dan
2016-01-01
When videogammetry (optical measurement) was carried outdoor or under cruel indoor circumstance, the results would be inevitably affected by the atmosphere turbulence. As a result, the precision of surveying was destroyed. The field of air turbulence's impact on optical measurement was neglected by scholars for a long time, the achievements massed about laser optics and optical communications. The mostly adapted method was noise filtration when the pixel wandering could not be rejected in engineering application, which got little improvement on usual conditions. The principle of influence under atmospheric turbulence on optical measurement is presented in this paper. And experiments data and applications are carried out to announce the impact of atmospheric turbulence. Combining with relevant researches, some essential issues and expectations of the atmospheric turbulence research are proposed.
NASA Astrophysics Data System (ADS)
Weiss-Wrana, Karin R.
2005-08-01
The refractive-index structure parameter Cn2 is the parameter most commonly used to describe the optically active turbulence. In the past, FGAN-FOM carried out long-term experiments in moderate climate (Central Europe, Germany), arid (summer), and semiarid (winter) climate (Middle East, Israel). Since Cn2 usually changes as a function of time of day and of season its influence on electro-optical systems should be expressed in a statistical way. We composed a statistical data base of Cn2 values. The cumulative frequency of occurrence was calculated for a time interval of two hours around noon (time of strongest turbulence), at night, and around sunrise (time of weakest turbulence) for an arbitrarily selected period of one month in summer and in winter. In October 2004 we extended our long-term turbulence experiments to subarctic climate (North Europe, Norway). First results of our turbulence measurement over snow-covered terrain indicate Cn2 values which are similar or even higher than measured values in Central European winter. The statistical data base was used to calculate the expected turbulence-induced aperture-averaged scintillation index for free-space optical systems (FSO system) in different climates. The calculations were performed for commercially available FSO systems with wavelength of 785 nm and 1.55 µm respectively and with aperture diameters of the receiver of 60 mm and 150 mm for horizontal path at two heights, 2.3 m and 10 m above ground.
Cui, Linyan
2014-09-01
Current theoretical temporal power spectra models of an optical wave have been developed for terrestrial environments. The interactions between humidity and temperature fluctuations in the marine atmospheric environments make the marine atmospheric turbulence particularly challenging, and the optical waves' propagation through marine turbulence exhibits a different behavior with respect to terrestrial propagation. In this paper, the temporal power spectra of irradiance scintillation under weak marine atmospheric turbulence, which is one of the key temporal statistics to describe the correlation of irradiance fluctuations at different time instances, is investigated in detail both analytically and numerically. Closed-form expressions for the temporal power spectra of irradiance scintillation are derived for infrared plane and spherical waves under weak marine atmospheric turbulence, and they consider physically the influences of finite turbulence inner and outer scales. The final results indicate that the marine atmospheric turbulence brings more effects on the irradiance scintillation than the terrestrial atmospheric turbulence.
Optical turbulence characterization at the SAAO Sutherland site
NASA Astrophysics Data System (ADS)
Catala, L.; Crawford, S. M.; Buckley, D. A. H.; Pickering, T. E.; Wilson, R. W.; Butterley, T.; Shepherd, H. W.; Marang, F.; Matshaya, P.; Fourie, C.
2013-11-01
We present results from the first year of a campaign to characterize and monitor the optical turbulence profile at the South African Astronomical Observatory's Sutherland observing station in South Africa. A Multi Aperture Scintillation Sensor Differential Image Motion Monitor (MASS-DIMM) was commissioned in 2010 March to provide continuous monitoring of the seeing conditions. Over the first month of the campaign, a Slope Detection And Ranging (SLODAR) from Durham University was also installed, allowing an independent verification of the performance of the MASS-DIMM device. After the first year of data collection, the overall median seeing value is found to be 1.32 arcsec as measured at ground level. The ground layer which includes all layers below 1 km accounts for 84 per cent of the turbulence, while the free atmosphere above 1 km accounts for 16 per cent with a median value of 0.41 arcsec. The median isoplanatic angle value is 1.92 arcsec, which is similar to other major astronomical sites. The median coherence time, calculated from corrected MASS measurements, is 2.85 ms. The seeing conditions at the site do show a strong correlation with wind direction, with bad seeing conditions being associated with winds from the south-east.
Characterization of gigabit ethernet over highly turbulent optical wireless links
NASA Astrophysics Data System (ADS)
Johnson, Gary W.; Cornish, John P.; Wilburn, Jeffrey W.; Young, Richard A.; Ruggiero, Anthony J.
2002-12-01
We report on the performance characterization and issues associated with using Gigabit Ethernet (GigE) over a highly turbulent 1.3 km air-optic lasercom links. Commercial GigE hardware is a cost-effective and scalable physical layer standard that can be applied to air-optic communications. We demonstrate a simple GigE hardware interface to a single-mode fiber-coupled, 1550 nm, WDM air-optic transceiver. TCP/IP serves as a robust and universal foundation protocol that has some tolerance of data loss due to atmospheric fading. Challenges include establishing and maintaining a connection with acceptable throughput under poor propagation conditions. The most useful link performance diagnostic is shown to be scintillation index, where a value of 0.2 is the maximum permissible for adequate GigE throughput. Maximum GigE throughput observed was 49.7% of that obtained with a fiber jumper when scintillation index is 0.1. Shortcomings in conventional measurements such as bit error rate are apparent. Prospects for forward error correction and other link enhancements will be discussed.
Characterization of Gigabit Ethernet Over Highly Turbulent Optical Wireless Links
Johnson, G W; Cornish, J P; Wilburn, J W; Young, R A; Ruggiero, A J
2002-07-01
We report on the performance characterization and issues associated with using Gigabit Ethernet (GigE) over a highly turbulent (C{sub n}{sup 2} > 10{sup -12}) 1.3 km air-optic lasercom links. Commercial GigE hardware is a cost-effective and scalable physical layer standard that can be applied to air-optic communications. We demonstrate a simple GigE hardware interface to a singlemode fiber-coupled, 1550 nm, WDM air-optic transceiver. TCPAP serves as a robust and universal foundation protocol that has some tolerance of data loss due to atmospheric fading. Challenges include establishing and maintaining a connection with acceptable throughput under poor propagation conditions. The most useful link performance diagnostic is shown to be scintillation index, where a value of 0.2 is the maximum permissible for adequate GigE throughput. Maximum GigE throughput observed was 49.7% of that obtained with a fiber jumper when scintillation index is 0.1. Shortcomings in conventional measurements such as bit error rate are apparent. Prospects for forward mor correction and other link enhancements will be discussed.
Forecasting the ocean optical environment in support of Navy mine warfare operations
NASA Astrophysics Data System (ADS)
Ladner, S. D.; Arnone, R.; Jolliff, J.; Casey, B.; Matulewski, K.
2012-06-01
A 3D ocean optical forecast system called TODS (Tactical Ocean Data System) has been developed to determine the performance of underwater LIDAR detection/identification systems. TODS fuses optical measurements from gliders, surface satellite optical properties, and 3D ocean forecast circulation models to extend the 2-dimensional surface satellite optics into a 3-dimensional optical volume including subsurface optical layers of beam attenuation coefficient (c) and diver visibility. Optical 3D nowcast and forecasts are combined with electro-optical identification (EOID) models to determine the underwater LIDAR imaging performance field used to identify subsurface mine threats in rapidly changing coastal regions. TODS was validated during a recent mine warfare exercise with Helicopter Mine Countermeasures Squadron (HM-14). Results include the uncertainties in the optical forecast and lidar performance and sensor tow height predictions that are based on visual detection and identification metrics using actual mine target images from the EOID system. TODS is a new capability of coupling the 3D optical environment and EOID system performance and is proving important for the MIW community as both a tactical decision aid and for use in operational planning, improving timeliness and efficiency in clearance operations.
Velocity fields and optical turbulence near the boundary in a strongly convective laboratory flow
NASA Astrophysics Data System (ADS)
Matt, Silvia; Hou, Weilin; Goode, Wesley; Hellman, Samuel
2016-05-01
Boundary layers around moving underwater vehicles or other platforms can be a limiting factor for optical communication. Turbulence in the boundary layer of a body moving through a stratified medium can lead to small variations in the index of refraction, which impede optical signals. As a first step towards investigating this boundary layer effect on underwater optics, we study the flow near the boundary in the Rayleigh-Bénard laboratory tank at the Naval Research Laboratory Stennis Space Center. The tank is set up to generate temperature-driven, i.e., convective turbulence, and allows control of the turbulence intensity. This controlled turbulence environment is complemented by computational fluid dynamics simulations to visualize and quantify multi-scale flow patterns. The boundary layer dynamics in the laboratory tank are quantified using a state-of-the-art Particle Image Velocimetry (PIV) system to examine the boundary layer velocities and turbulence parameters. The velocity fields and flow dynamics from the PIV are compared to the numerical model and show the model to accurately reproduce the velocity range and flow dynamics. The temperature variations and thus optical turbulence effects can then be inferred from the model temperature data. Optical turbulence is also visible in the raw data from the PIV system. The newly collected data are consistent with previously reported measurements from high-resolution Acoustic Doppler Velocimeter profilers (Nortek Vectrino), as well as fast thermistor probes and novel next-generation fiber-optics temperature sensors. This multi-level approach to studying optical turbulence near a boundary, combining in-situ measurements, optical techniques, and numerical simulations, can provide new insight and aid in mitigating turbulence impacts on underwater optical signal transmission.
Temporal averaging of atmospheric turbulence-induced optical scintillation.
Yura, H T; Beck, S M
2015-08-24
Based on the Rytov approximation we have developed for weak scintillation conditions a general expression for the temporal averaged variance of irradiance. The present analysis provides, for what we believe is the first time, a firm theoretical basis for the often-observed reduction of irradiance fluctuations of an optical beam due to atmospheric turbulence. Accurate elementary analytic approximations are presented here for plane, spherical and beam waves for predicting the averaging times required to obtain an arbitrary value of the ratio of the standard deviation to the mean of an optical beam propagating through an arbitrary path in the atmosphere. In particular, a novel application of differential absorption measurement for the purpose of measuring column-integrated concentrations of various so-called greenhouse gas (GHG) atmospheric components is considered where the results of our analysis indicates that relatively short averaging times, on the order of a few seconds, are required to reduce the irradiance fluctuations to a value precise enough for GHG measurements of value to climate related studies.
Nonlinear random optical waves: Integrable turbulence, rogue waves and intermittency
NASA Astrophysics Data System (ADS)
Randoux, Stéphane; Walczak, Pierre; Onorato, Miguel; Suret, Pierre
2016-10-01
We examine the general question of statistical changes experienced by ensembles of nonlinear random waves propagating in systems ruled by integrable equations. In our study that enters within the framework of integrable turbulence, we specifically focus on optical fiber systems accurately described by the integrable one-dimensional nonlinear Schrödinger equation. We consider random complex fields having a Gaussian statistics and an infinite extension at initial stage. We use numerical simulations with periodic boundary conditions and optical fiber experiments to investigate spectral and statistical changes experienced by nonlinear waves in focusing and in defocusing propagation regimes. As a result of nonlinear propagation, the power spectrum of the random wave broadens and takes exponential wings both in focusing and in defocusing regimes. Heavy-tailed deviations from Gaussian statistics are observed in focusing regime while low-tailed deviations from Gaussian statistics are observed in defocusing regime. After some transient evolution, the wave system is found to exhibit a statistically stationary state in which neither the probability density function of the wave field nor the spectrum changes with the evolution variable. Separating fluctuations of small scale from fluctuations of large scale both in focusing and defocusing regimes, we reveal the phenomenon of intermittency; i.e., small scales are characterized by large heavy-tailed deviations from Gaussian statistics, while the large ones are almost Gaussian.
Qin, Zhiyuan; Tao, Rumao; Zhou, Pu; Xu, Xiaojun; Liu, Zejin
2013-11-20
Based on partially coherent Bessel-Gaussian beams (BGBs), the coherence evolution of the partially coherent beams carrying optical vortices in non-Kolmogorov turbulence is investigated in detail. The analytical formulas for the spatial coherence length of partially coherent BGBs with optical vortices in non-Kolmogorov turbulence have been derived by using the combination of a coherence superposition approximation of decentered Gaussian beams and the extended Huygens-Fresnel principle. The influences of beam and turbulence parameters on spatial coherence are investigated by numerical examples. Numerical results reveal that the coherence of the partially coherent laser beam with vortices is independent of the optical vortices, and the spatial correlation length of the beams does not decrease monotonically during propagation in non-Kolmogorov turbulence. Within a certain propagation distance, the coherence of the partially coherent beam will improve, and the improvement of the coherence of the partially coherent beams is closely related to the beam and turbulence parameters.
Incoherent shock waves in long-range optical turbulence
NASA Astrophysics Data System (ADS)
Xu, G.; Garnier, J.; Faccio, D.; Trillo, S.; Picozzi, A.
2016-10-01
Considering the nonlinear Schrödinger (NLS) equation as a representative model, we report a unified presentation of different forms of incoherent shock waves that emerge in the long-range interaction regime of a turbulent optical wave system. These incoherent singularities can develop either in the temporal domain through a highly noninstantaneous nonlinear response, or in the spatial domain through a highly nonlocal nonlinearity. In the temporal domain, genuine dispersive shock waves (DSW) develop in the spectral dynamics of the random waves, despite the fact that the causality condition inherent to the response function breaks the Hamiltonian structure of the NLS equation. Such spectral incoherent DSWs are described in detail by a family of singular integro-differential kinetic equations, e.g. Benjamin-Ono equation, which are derived from a nonequilibrium kinetic formulation based on the weak Langmuir turbulence equation. In the spatial domain, the system is shown to exhibit a large scale global collective behavior, so that it is the fluctuating field as a whole that develops a singularity, which is inherently an incoherent object made of random waves. Despite the Hamiltonian structure of the NLS equation, the regularization of such a collective incoherent shock does not require the formation of a DSW - the regularization is shown to occur by means of a different process of coherence degradation at the shock point. We show that the collective incoherent shock is responsible for an original mechanism of spontaneous nucleation of a phase-space hole in the spectrogram dynamics. The robustness of such a phase-space hole is interpreted in the light of incoherent dark soliton states, whose different exact solutions are derived in the framework of the long-range Vlasov formalism.
Li, Su-Wen; Liu, Wen-Qing; Xie, Pin-Hua; Wang, Feng-Sui; Yang, Yi-Jun
2009-11-01
For real-time and on-line monitoring DOAS (differential optical absorption spectroscopy) system, a model based on an improved Elman network for monitoring pollutant concentrations was proposed. In order to reduce the systematical complexity, the forecasting factors have been obtained based on the step-wise regression method. The forecasting factors were current concentrations, temperature and relative humidity, and wind speed and wind direction. The dynamic back propagation (BP) algorithm was used for creating training set. The experiment results show that the predicted value follows the real well. So the modified Elman network can meet the demand of DOAS system's real time forecasting.
Li, Su-Wen; Liu, Wen-Qing; Xie, Pin-Hua; Wang, Feng-Sui; Yang, Yi-Jun
2009-11-01
For real-time and on-line monitoring DOAS (differential optical absorption spectroscopy) system, a model based on an improved Elman network for monitoring pollutant concentrations was proposed. In order to reduce the systematical complexity, the forecasting factors have been obtained based on the step-wise regression method. The forecasting factors were current concentrations, temperature and relative humidity, and wind speed and wind direction. The dynamic back propagation (BP) algorithm was used for creating training set. The experiment results show that the predicted value follows the real well. So the modified Elman network can meet the demand of DOAS system's real time forecasting. PMID:20101985
Multi-instrument characterization of optical turbulence at the Ali observatory
NASA Astrophysics Data System (ADS)
Liu, L.-Y.; Yao, Y.-Q.; Vernin, J.; Wang, H.-S.; Yin, J.; Qian, X.
2015-04-01
In order to characterize the atmospheric optical turbulence at Ali observatory, we have deployed multi-instruments, which are able to continuously monitor the optical turbulence for site evaluation. These instruments include the DIMM, MASS, Single Star SCIDAR and Polaris seeing monitor, and we also plan to install SNODAR and Micro-thermal sensors for the turbulence on surface layer by the end of this year. This configuration allows us to collect a substantial database and make cross-comparison of the results. We have successfully obtained the profiles of optical turbulence and wind speed with Single Star SCIDAR, as well as the key parameters for adaptive optics application, such as seeing, coherence time, and isoplanatic angle. The DIMM seeing measurements are also carried out simultaneously. The median seeing measured by the DIMM and SSS in 2013 is 0.69 and 0.79 arcsec, respectively.
NASA Astrophysics Data System (ADS)
Woolsey, L. N.; Cranmer, S. R.
2013-12-01
The study of solar wind acceleration has made several important advances recently due to improvements in modeling techniques. Existing code and simulations test the competing theories for coronal heating, which include reconnection/loop-opening (RLO) models and wave/turbulence-driven (WTD) models. In order to compare and contrast the validity of these theories, we need flexible tools that predict the emergent solar wind properties from a wide range of coronal magnetic field structures such as coronal holes, pseudostreamers, and helmet streamers. ZEPHYR (Cranmer et al. 2007) is a one-dimensional magnetohydrodynamics code that includes Alfven wave generation and reflection and the resulting turbulent heating to accelerate solar wind in open flux tubes. We present the ZEPHYR output for a wide range of magnetic field geometries to show the effect of the magnetic field profiles on wind properties. We also investigate the competing acceleration mechanisms found in ZEPHYR to determine the relative importance of increased gas pressure from turbulent heating and the separate pressure source from the Alfven waves. To do so, we developed a code that will become publicly available for solar wind prediction. This code, TEMPEST, provides an outflow solution based on only one input: the magnetic field strength as a function of height above the photosphere. It uses correlations found in ZEPHYR between the magnetic field strength at the source surface and the temperature profile of the outflow solution to compute the wind speed profile based on the increased gas pressure from turbulent heating. With this initial solution, TEMPEST then adds in the Alfven wave pressure term to the modified Parker equation and iterates to find a stable solution for the wind speed. This code, therefore, can make predictions of the wind speeds that will be observed at 1 AU based on extrapolations from magnetogram data, providing a useful tool for empirical forecasting of the sol! ar wind.
Controlled simulation of optical turbulence in a temperature gradient air chamber
NASA Astrophysics Data System (ADS)
Toselli, Italo; Wang, Fei; Korotkova, Olga
2016-05-01
Atmospheric turbulence simulator is built and characterized for in-lab optical wave propagation with controlled strength of the refractive-index fluctuations. The temperature gradients are generated by a sequence of heat guns with controlled individual strengths. The temperature structure functions are measured in two directions transverse to propagation path with the help of a thermocouple array and used for evaluation of the corresponding refractive-index structure functions of optical turbulence.
Cheng, Mingjian; Zhang, Yixin; Gao, Jie; Wang, Fei; Zhao, Fengsheng
2014-06-20
We model the average channel capacity of optical wireless communication systems for cases of weak to strong turbulence channels, using the exponentiation Weibull distribution model. The joint effects of the beam wander and spread, pointing errors, atmospheric attenuation, and the spectral index of non-Kolmogorov turbulence on system performance are included. Our results show that the average capacity decreases steeply as the propagation length L changes from 0 to 200 m and decreases slowly down or tends to a stable value as the propagation length L is greater than 200 m. In the weak turbulence region, by increasing the detection aperture, we can improve the average channel capacity and the atmospheric visibility as an important issue affecting the average channel capacity. In the strong turbulence region, the increase of the radius of the detection aperture cannot reduce the effects of the atmospheric turbulence on the average channel capacity, and the effect of atmospheric visibility on the channel information capacity can be ignored. The effect of the spectral power exponent on the average channel capacity in the strong turbulence region is higher than weak turbulence region. Irrespective of the details determining the turbulent channel, we can say that pointing errors have a significant effect on the average channel capacity of optical wireless communication systems in turbulence channels.
Lazarian, A.; Pogosyan, D.
2008-10-10
We continue our work on developing techniques for studying turbulence with spectroscopic data. We show that Doppler-broadened absorption spectral lines, in particular, saturated absorption lines, can be used within the framework of the previously introduced technique termed the velocity coordinate spectrum (VCS). The VCS relates the statistics of fluctuations along the velocity coordinate to the statistics of turbulence; thus, it does not require spatial coverage by sampling directions in the plane of the sky. We consider lines with different degree of absorption and show that for lines of optical depth less than one, our earlier treatment of the VCS developed for spectral emission lines is applicable, if the optical depth is used instead of intensity. This amounts to correlating the logarithms of absorbed intensities. For larger optical depths and saturated absorption lines, we show that only wings of the line are available for the analysis. In terms of the VCS formalism, this results in introducing an additional window, whose size decreases with the increase of the optical depth. As a result, strongly saturated absorption lines only carry the information about the small-scale turbulence. Nevertheless, the contrast of the fluctuations corresponding to the small-scale turbulence increases with the increase of the optical depth, which provides advantages for studying turbulence by combining lines with different optical depths. By combining different absorption lines one can develop a tomography of the turbulence in the interstellar gas in all its complexity.
NASA Astrophysics Data System (ADS)
He, Ping; Nunalee, Christopher G.; Basu, Sukanta; Vorontsov, Mikhail A.; Fiorino, Steven T.
2014-10-01
In this study, we present a brief review on the existing approaches for optical turbulence estimation in various layers of the Earth's atmosphere. The advantages and disadvantages of these approaches are also discussed. An alternative approach, based on mesoscale modeling with parameterized turbulence, is proposed and tested for the simulation of refractive index structure parameter (C2n ) in the atmospheric boundary layer. The impacts of a few atmospheric flow phenomena (e.g., low-level jets, island wake vortices, gravity waves) on optical turbulence are discussed. Consideration of diverse geographic settings (e.g., flat terrain, coastal region, ocean islands) makes this study distinct.
NASA Astrophysics Data System (ADS)
García-Lorenzo, B.; Fuensalida, J. J.
2011-01-01
The characterization of the optical turbulence structure at an astronomical site requires a proper data base of the refractive-index structure constant, ?. Our team has been obtaining generalized SCIntillation Detection and Ranging (SCIDAR) observations to monitor ? from 2002 November-2009 January at Teide Observatory (Tenerife, Canary Islands, Spain). The Teide ? data base includes useful data from 153 nights of generalized SCIDAR measurements obtained at the 1.5-m Calos Sánchez Telescope. The overestimation of the turbulence strength as a consequence of generalized SCIDAR data processing has been analysed for all double stars and analysis-plane combinations used in our observations. If this overestimation of the turbulence is not taken into account, the median total seeing and isoplanatic angle derived from the turbulence profiles in the data base are 0.70 and 2.47 arcsec, respectively. We have recalibrated all the derived ?, correcting for this overestimation. The statistical optical turbulence structure above Teide Observatory is derived by combining the 93 662 individual ? that constitute the data base at this site. More than 85 per cent of the total optical turbulence is concentrated in low-altitude layers (<5 km above sea level). The optical turbulence structure presents an evolution of the layers in both strength and altitude. Only the turbulence concentration at the observatory level shows a similar turbulence strength over a standard year. The median values of total seeing and isoplanatic angle of ɛ0= 0.64 arcsec and θ0= 2.83 arcsec demonstrate the excellent quality of the Teide Observatory astronomical site for the implementation of adaptive optics systems.
Laser beam propagation through turbulence and adaptive optics for beam delivery improvement
NASA Astrophysics Data System (ADS)
Nicolas, Stephane
2015-10-01
We report results from numerical simulations of laser beam propagation through atmospheric turbulence. In particular, we study the statistical variations of the fractional beam energy hitting inside an optical aperture placed at several kilometer distance. The simulations are performed for different turbulence conditions and engagement ranges, with and without the use of turbulence mitigation. Turbulence mitigation is simulated with phase conjugation. The energy fluctuations are deduced from time sequence realizations. It is shown that turbulence mitigation leads to an increase of the mean energy inside the aperture and decrease of the fluctuations even in strong turbulence conditions and long distance engagement. As an example, the results are applied to a high energy laser countermeasure system, where we determine the probability that a single laser pulse, or one of the pulses in a sequence, will provide a lethal energy inside the target aperture. Again, turbulence mitigation contributes to increase the performance of the system at long-distance and for strong turbulence conditions in terms of kill probability. We also discuss a specific case where turbulence contributes to increase the pulse energy within the target aperture. The present analysis can be used to evaluate the performance of a variety of systems, such as directed countermeasures, laser communication, and laser weapons.
Two-dimensional simulation of optical wave propagation through atmospheric turbulence.
Hyde, Milo W; Basu, Santasri; Schmidt, Jason D
2015-01-15
A methodology for the two-dimensional simulation of optical wave propagation through atmospheric turbulence is presented. The derivations of common statistical field moments in two dimensions, required for performing and validating simulations, are presented and compared with their traditional three-dimensional counterparts. Wave optics simulations are performed to validate the two-dimensional moments and to demonstrate the utility of performing two-dimensional wave optics simulations so that the results may be scaled to those of computationally prohibitive 3D scenarios. Discussions of the benefits and limitations of two-dimensional atmospheric turbulence simulations are provided throughout.
Turbulence-driven coronal heating and improvements to empirical forecasting of the solar wind
Woolsey, Lauren N.; Cranmer, Steven R.
2014-06-01
Forecasting models of the solar wind often rely on simple parameterizations of the magnetic field that ignore the effects of the full magnetic field geometry. In this paper, we present the results of two solar wind prediction models that consider the full magnetic field profile and include the effects of Alfvén waves on coronal heating and wind acceleration. The one-dimensional magnetohydrodynamic code ZEPHYR self-consistently finds solar wind solutions without the need for empirical heating functions. Another one-dimensional code, introduced in this paper (The Efficient Modified-Parker-Equation-Solving Tool, TEMPEST), can act as a smaller, stand-alone code for use in forecasting pipelines. TEMPEST is written in Python and will become a publicly available library of functions that is easy to adapt and expand. We discuss important relations between the magnetic field profile and properties of the solar wind that can be used to independently validate prediction models. ZEPHYR provides the foundation and calibration for TEMPEST, and ultimately we will use these models to predict observations and explain space weather created by the bulk solar wind. We are able to reproduce with both models the general anticorrelation seen in comparisons of observed wind speed at 1 AU and the flux tube expansion factor. There is significantly less spread than comparing the results of the two models than between ZEPHYR and a traditional flux tube expansion relation. We suggest that the new code, TEMPEST, will become a valuable tool in the forecasting of space weather.
Turbulence-driven Coronal Heating and Improvements to Empirical Forecasting of the Solar Wind
NASA Astrophysics Data System (ADS)
Woolsey, Lauren N.; Cranmer, Steven R.
2014-06-01
Forecasting models of the solar wind often rely on simple parameterizations of the magnetic field that ignore the effects of the full magnetic field geometry. In this paper, we present the results of two solar wind prediction models that consider the full magnetic field profile and include the effects of Alfvén waves on coronal heating and wind acceleration. The one-dimensional magnetohydrodynamic code ZEPHYR self-consistently finds solar wind solutions without the need for empirical heating functions. Another one-dimensional code, introduced in this paper (The Efficient Modified-Parker-Equation-Solving Tool, TEMPEST), can act as a smaller, stand-alone code for use in forecasting pipelines. TEMPEST is written in Python and will become a publicly available library of functions that is easy to adapt and expand. We discuss important relations between the magnetic field profile and properties of the solar wind that can be used to independently validate prediction models. ZEPHYR provides the foundation and calibration for TEMPEST, and ultimately we will use these models to predict observations and explain space weather created by the bulk solar wind. We are able to reproduce with both models the general anticorrelation seen in comparisons of observed wind speed at 1 AU and the flux tube expansion factor. There is significantly less spread than comparing the results of the two models than between ZEPHYR and a traditional flux tube expansion relation. We suggest that the new code, TEMPEST, will become a valuable tool in the forecasting of space weather.
Cui, Linyan
2015-06-01
Analytic expressions for the temporal power spectra of irradiance fluctuations and angle of arrival (AOA) fluctuations are derived for optical waves propagating through weak anisotropic non-Kolmogorov atmospheric turbulence. In the derivation, the anisotropic non-Kolmogorov spectrum is adopted, which adopts the assumption of circular symmetry in the orthogonal plane throughout the path and the same degree of anisotropy along the propagation direction for all the turbulence cells. The final expressions consider simultaneously the anisotropic factor and general spectral power law values. When the anisotropic factor equals one (corresponding to the isotropic turbulence), the derived temporal power spectral models have good consistency with the known results for the isotropic turbulence. Numerical calculations show that the increased anisotropic factor alleviates the atmospheric turbulence's influence on the final expressions.
Ren, Yongxiong; Xie, Guodong; Huang, Hao; Bao, Changjing; Yan, Yan; Ahmed, Nisar; Lavery, Martin P J; Erkmen, Baris I; Dolinar, Samuel; Tur, Moshe; Neifeld, Mark A; Padgett, Miles J; Boyd, Robert W; Shapiro, Jeffrey H; Willner, Alan E
2014-05-15
We propose an adaptive optics compensation scheme to simultaneously compensate multiple orbital angular momentum (OAM) beams propagating through atmospheric turbulence. A Gaussian beam on one polarization is used to probe the turbulence-induced wavefront distortions and derive the correction pattern for compensating the OAM beams on the orthogonal polarization. By using this scheme, we experimentally demonstrate simultaneous compensation of multiple OAM beams, each carrying a 100 Gbit/s data channel through emulated atmospheric turbulence. The experimental results indicate that the correction pattern obtained from the Gaussian probe beam could be used to simultaneously compensate multiple turbulence-distorted OAM beams with different orders. It is found that the turbulence-induced crosstalk effects on neighboring modes are efficiently reduced by 12.5 dB, and the system power penalty is improved by 11 dB after compensation.
Characterizing Optical Turbulence at the GMT Site with MooSci and MASS-DIMM
NASA Astrophysics Data System (ADS)
Thomas-Osip, J. E.; Prieto, G.; Berdja, A.; Cook, K. W.; Villanueva, S.; DePoy, D. L.; Marshall, J. L.; Rheault, J. P.; Allen, R. D.; Carona, D. W.
2012-01-01
In order to guide the adaptive optics design and aid in performance predictions, optical turbulence at the site of the future Giant Magellan Telescope (GMT) is characterized using MooSci, a lunar scintillometer, and MASS-DIMM, a combination differential image motion monitor and multiaperture scintillation sensor. As a new instrument, MooSci, is verified as a reliable ground-layer turbulence profiler. The GMT can expect an improvement of approximately 0.1'' over the site testing results as measured with a DIMM. Turbulence below 30 m is horizontally nonhomogeneous, dependent on wind speed and direction, and on average accounts for 60% of the full ground-layer (up to 500 m) turbulence.
A Microthermal Device for Measuring the Spatial Power Spectrum of Atmospheric Optical Turbulence
NASA Astrophysics Data System (ADS)
Turner, Jonathan; McGraw, J.; Zimmer, P.; Williams, T.; Claver, C.; Krabbendam, V.; Wiecha, O.; Andrew, J.; Warner, M.
2010-01-01
The Measurement Astrophysics group at UNM designed and built a novel microthermal device for characterizing atmospheric optical turbulence at astronomical observatories. This instrument is based on a Wheatstone bridge circuit and uses fine tungsten filaments as resistance temperature detectors. The device makes differential temperature measurements which are directly related to the index of refraction structure constant, Cn2, which quantifies the strength of optical turbulence. The device is designed to work in two modes. In horizontal mode temperature differentials are measured between adjacent sensors. Measurements are combined to recover the differences over all pairwise sensor baselines. These measurements result in a spatial spectrum of turbulence. Measured turbulent spectra are then fit to standard turbulence models which yield estimates of the outer scale of turbulence and the slope of the power spectra. In vertical mode the device operates with pairs of microthermal sensors distributed vertically, each pair being separated horizontally by approximately one meter. Sensor pairs are suspended at multiple heights above the ground allowing measurement of atmospheric turbulence power as a function of altitude. This device was used to monitor optical turbulence during a site testing campaign at the future LSST site on Cerro Pachón. We present preliminary results from operation in both vertical and horizontal modes from October 2008 to December 2009. The microthermal array remains in operation on Cerro Pachón, and continues to produce valuable atmospheric measurements. Our results support the conclusion that Cerro Pachón is an excellent observatory site. The vertical turbulence profile decreases monotonically with height as expected, and the surface layer does not contribute a significant amount to the overall seeing measured at the site. This work was supported by Air Force Grant No. FA9451-04-2-0355. Instrumentation and travel support was provided in part by
Four Years of Optical Turbulence Monitoring at the Cerro Tololo Inter-American Observatory (CTIO)
NASA Astrophysics Data System (ADS)
Els, S. G.; Schöck, M.; Bustos, E.; Seguel, J.; Vasquez, J.; Walker, D.; Riddle, R.; Skidmore, W.; Travouillon, T.; Vogiatzis, K.
2009-08-01
The optical turbulence conditions as measured between 2004 through the end of 2008 above Cerro Tololo, their seasonal as well as nocturnal behavior, are presented. A comparison with the MASS-DIMM system of the Thirty Meter Telescope site testing was conducted and identifies an artificially increased seeing component in the data collected by the CTIO-DIMM system under northerly winds. Evidence is shown that this increased turbulence is caused by the telescope dome. A correction for this effect is attempted and applied to the CTIO-DIMM data. The MASS data of this comparison campaign allow constraints to be set on the general assumption of uniform turbulent layers above a site.
Free-space optical channel simulator for weak-turbulence conditions.
Bykhovsky, Dima
2015-11-01
Free-space optical (FSO) communication may be severely influenced by the inevitable turbulence effect that results in channel gain fluctuations and fading. The objective of this paper is to provide a simple and effective simulator of the weak-turbulence FSO channel that emulates the influence of the temporal covariance effect. Specifically, the proposed model is based on lognormal distributed samples with a corresponding correlation time. The simulator is based on the solution of the first-order stochastic differential equation (SDE). The results of the provided SDE analysis reveal its efficacy for turbulent channel modeling.
500 Gb/s free-space optical transmission over strong atmospheric turbulence channels.
Qu, Zhen; Djordjevic, Ivan B
2016-07-15
We experimentally demonstrate a high-spectral-efficiency, large-capacity, featured free-space-optical (FSO) transmission system by using low-density, parity-check (LDPC) coded quadrature phase shift keying (QPSK) combined with orbital angular momentum (OAM) multiplexing. The strong atmospheric turbulence channel is emulated by two spatial light modulators on which four randomly generated azimuthal phase patterns yielding the Andrews spectrum are recorded. The validity of such an approach is verified by reproducing the intensity distribution and irradiance correlation function (ICF) from the full-scale simulator. Excellent agreement of experimental, numerical, and analytical results is found. To reduce the phase distortion induced by the turbulence emulator, the inexpensive wavefront sensorless adaptive optics (AO) is used. To deal with remaining channel impairments, a large-girth LDPC code is used. To further improve the aggregate data rate, the OAM multiplexing is combined with WDM, and 500 Gb/s optical transmission over the strong atmospheric turbulence channels is demonstrated.
Comparison and analysis of atmospheric optical turbulence in coast and over sea
NASA Astrophysics Data System (ADS)
Cai, Jun; Wu, Xiaoqing; Yang, Yiping
2016-01-01
Observation of meteorological parameters in coast and over sea surface layer will be conducive to understand the interaction between ocean and atmosphere, as well as the mechanism that ocean impacts on climate. Compared with the coast, it is more difficult to measure the atmospheric optical turbulence over sea, which includes measurement error caused by the instability of observation platform, instrument damage caused by poor environment and accuracy of measurement caused by the known and unknown factors, and so on. Conventional meteorological parameters and atmospheric optical turbulence in coast and over sea were observed by instruments equipped on the Marine Meteorological Science Experiment Base at Bohe and characteristics of atmospheric optical turbulence in this region were analyzed. By using temperature, humidity and wind speed, the atmospheric refractive-index structure constant in coast were estimated, and then compared with measured values, which verified the feasibility of this method.
NASA Astrophysics Data System (ADS)
Frisch, Uriel
1996-01-01
Written five centuries after the first studies of Leonardo da Vinci and half a century after A.N. Kolmogorov's first attempt to predict the properties of flow, this textbook presents a modern account of turbulence, one of the greatest challenges in physics. "Fully developed turbulence" is ubiquitous in both cosmic and natural environments, in engineering applications and in everyday life. Elementary presentations of dynamical systems ideas, probabilistic methods (including the theory of large deviations) and fractal geometry make this a self-contained textbook. This is the first book on turbulence to use modern ideas from chaos and symmetry breaking. The book will appeal to first-year graduate students in mathematics, physics, astrophysics, geosciences and engineering, as well as professional scientists and engineers.
NASA Technical Reports Server (NTRS)
Nerheim, N.
1989-01-01
Blind pointing of the Deep Space Network (DSN) 70-meter antennas can be improved if distortions of the antenna structure caused by unpredictable environmental loads can be measured in real-time, and the resulting boresight shifts evaluated and incorporated into the pointing control loops. The measurement configuration of a proposed pointing compensation system includes an optical range sensor that measures distances to selected points on the antenna surface. The effect of atmospheric turbulence on the accuracy of optical distance measurements and a method to make in-situ determinations of turbulence-induced measurement errors are discussed.
SLODAR turbulence monitors for real-time support of astronomical adaptive optics
NASA Astrophysics Data System (ADS)
Wilson, Richard; Butterley, Timothy; Sarazin, Marc; Lombardi, Gianluca; Chun, Mark; Benigni, Samuel; Weir, Donald; Avila, Remy; Aviles, Jose-Luis
2008-07-01
We describe the current status of the SLODAR optical turbulence monitors, developed at Durham University, for support of adaptive optics for astronomy. SLODAR systems have been installed and operated at the Cerro Paranal and Mauna Kea observatories, and a third will be deployed at the South African Astronomical Observatory in 2008. The instruments provide real-time measurements of the atmospheric turbulence strength, altitude and velocity. We summarize the capabilities of the systems and describe recent enhancements. Comparisons of contemporaneous data obtained with SLODAR, MASS and DIMM monitors at the ESO Paranal site are presented.
Turbulent single-photon propagation in the Canary optical link
Capraro, Ivan; Tomaello, Andrea; Dall'Arche, Alberto; Gerlin, Francesca; Vallone, Giuseppe; Villoresi, Paolo; Herbst, Thomas; Ursin, Rupert
2014-12-04
The role of turbulence for Quantum Communications (QC) has been investigated in a 143 km-long link. The analysis of the received signal temporal domain indicate how to exploit constructively its effects in the case of QC along very long free-space links as well satellite links. Novel applications with relevant background noise may be envisaged.
Cui, Linyan; Xue, Bindang; Cao, Xiaoguang; Zhou, Fugen
2014-04-01
Based on the generalized von Kármán spectrum and the extended Rytov theory, new analytic expressions for the variance of angle of arrival (AOA) fluctuations are derived for optical plane and spherical waves propagating through moderate-to-strong non-Kolmogorov turbulence with horizontal path. They consider finite turbulence outer scale and general spectral power law value, and cover a wide range of non-Kolmogorov turbulence strength. When the turbulence outer scale is set to infinite, the new expressions can reduce correctly to previously published analytic expressions [J. Opt. Soc. Am. A, 302188 (2013]. The final results show that the increased turbulence outer scale value enlarges the variance of AOA fluctuations greatly under moderate-to-strong (or strong) non-Kolmogorov turbulence.
Wave optics simulation of atmospheric turbulence and reflective speckle effects in CO{sub 2} lidar
Nelson, Douglas H.; MacKerrow, Edward P.
2000-04-20
Laser speckle can influence lidar measurements from a diffuse hard target. Atmospheric optical turbulence will also affect the lidar return signal. We present a numerical simulation that models the propagation of a lidar beam and accounts for both reflective speckle and atmospheric turbulence effects. Our simulation is based on implementing a Huygens-Fresnel approximation to laser propagation. A series of phase screens, with the appropriate atmospheric statistical characteristics, are used to simulate the effect of atmospheric turbulence. A single random phase screen is used to simulate scattering of the entire beam from a rough surface. We compare the output of our numerical model with separate CO{sub 2} lidar measurements of atmospheric turbulence and reflective speckle. We also compare the output of our model with separate analytical predictions for atmospheric turbulence and reflective speckle. Good agreement was found between the model and the experimental data. Good agreement was also found with analytical predictions. Finally, we present results of a simulation of the combined effects on a finite-aperture lidar system that are qualitatively consistent with previous experimental observations of increasing rms noise with increasing turbulence level. (c) 2000 Optical Society of America.
The effect of thin turbulent shear layers on the optical quality of imaging systems
NASA Technical Reports Server (NTRS)
Steinmetz, W. J.
1975-01-01
A modified C141 transport was outfitted with a 91.5-cm reflector telescope designed to view objects radiating outside the visible window in the infrared range from 1 micron to 1000 microns. The telescope is situated in a cavity which is operated open port. Spoilers were designed which reduce turbulence-induced excitation of the cavity. The aircraft was designed to operate at altitudes up to 15 km to significantly reduce the effect of the H2O and CO2. Furthermore, the optically degrading influence of the large-scale atmospheric turbulence on land-based telescopes is replaced by the effect of the turbulent shear layer resulting from the spoiler upstream of the cavity. A mathematical model was established to describe the effect of turbulent shear layers on imaging systems and to examine the parameters of interest relevant to potential wind-tunnel experimentation.
Zhu, Kaicheng; Li, Shaoxin; Tang, Ying; Yu, Yan; Tang, Huiqin
2012-03-01
Based on the integral representation of Bessel function and the extended Huygens-Fresnel principle, an integral expression of the Wigner distribution function (WDF) for partially coherent Bessel-Gaussian beams (PBGBs) propagating through turbulent atmosphere has been obtained. Also, the analytical formulas of the M2-factor for PBGB propagation in such a medium have been derived, which can be applied to cases of different spatial power spectra of the refractive index fluctuations. The performed numerical results reveal that the M2-factor of a PBGB in turbulent atmosphere depends on the beam parameters of the initial input beam, the structure constants of the turbulent atmosphere, and the propagation distance. These results may be useful in long-distance optical communications in free space or in turbulent atmosphere.
Chen, Mo; Liu, Chao; Xian, Hao
2015-10-10
High-speed free-space optical communication systems using fiber-optic components can greatly improve the stability of the system and simplify the structure. However, propagation through atmospheric turbulence degrades the spatial coherence of the signal beam and limits the single-mode fiber (SMF) coupling efficiency. In this paper, we analyze the influence of the atmospheric turbulence on the SMF coupling efficiency over various turbulences. The results show that the SMF coupling efficiency drops from 81% without phase distortion to 10% when phase root mean square value equals 0.3λ. The simulations of SMF coupling with adaptive optics (AO) indicate that it is inevitable to compensate the high-order aberrations for SMF coupling over relatively strong turbulence. The SMF coupling efficiency experiments, using an AO system with a 137-element deformable mirror and a Hartmann-Shack wavefront sensor, obtain average coupling efficiency increasing from 1.3% in open loop to 46.1% in closed loop under a relatively strong turbulence, D/r_{0}=15.1.
Resilience of hybrid optical angular momentum qubits to turbulence.
Farías, Osvaldo Jiménez; D'Ambrosio, Vincenzo; Taballione, Caterina; Bisesto, Fabrizio; Slussarenko, Sergei; Aolita, Leandro; Marrucci, Lorenzo; Walborn, Stephen P; Sciarrino, Fabio
2015-02-12
Recent schemes to encode quantum information into the total angular momentum of light, defining rotation-invariant hybrid qubits composed of the polarization and orbital angular momentum degrees of freedom, present interesting applications for quantum information technology. However, there remains the question as to how detrimental effects such as random spatial perturbations affect these encodings. Here, we demonstrate that alignment-free quantum communication through a turbulent channel based on hybrid qubits can be achieved with unit transmission fidelity. In our experiment, alignment-free qubits are produced with q-plates and sent through a homemade turbulence chamber. The decoding procedure, also realized with q-plates, relies on both degrees of freedom and renders an intrinsic error-filtering mechanism that maps errors into losses.
Resilience of hybrid optical angular momentum qubits to turbulence
Farías, Osvaldo Jiménez; D'Ambrosio, Vincenzo; Taballione, Caterina; Bisesto, Fabrizio; Slussarenko, Sergei; Aolita, Leandro; Marrucci, Lorenzo; Walborn, Stephen P.; Sciarrino, Fabio
2015-01-01
Recent schemes to encode quantum information into the total angular momentum of light, defining rotation-invariant hybrid qubits composed of the polarization and orbital angular momentum degrees of freedom, present interesting applications for quantum information technology. However, there remains the question as to how detrimental effects such as random spatial perturbations affect these encodings. Here, we demonstrate that alignment-free quantum communication through a turbulent channel based on hybrid qubits can be achieved with unit transmission fidelity. In our experiment, alignment-free qubits are produced with q-plates and sent through a homemade turbulence chamber. The decoding procedure, also realized with q-plates, relies on both degrees of freedom and renders an intrinsic error-filtering mechanism that maps errors into losses. PMID:25672667
Coherent Optical Receiver for PPM Signals under Atmospheric Turbulence
NASA Technical Reports Server (NTRS)
Munoz Fernandez, Michela; Vilnrotter, Victor A.
2005-01-01
Adaptive combining of experimentally obtained heterodyned pulse position modulated (PPM) signals with pulse-to-pulse coherence in the presence of simulated spatial distortions resembling atmospheric turbulence is demonstrated. The adaptively combined PPM signals are phased up via an LMS algorithm suitably optimized to operate with PPM in the presence of additive shot-noise. A convergence analysis of the algorithm is presented, and results with both, computer simulated and experimentally obtained PPM signals are analyzed.
Cheng, Mingjian; Guo, Lixin; Li, Jiangting; Huang, Qingqing; Cheng, Qi; Zhang, Dan
2016-06-10
The analytical formulas for the orbital angular momentum (OAM) mode probability density, signal OAM mode detection probability, and spiral spectrum of partially coherent Laguerre-Gaussian (LG) beams with optical vortices propagation in weak horizontal oceanic turbulent channels were developed, based on the Rytov approximation theory. The effect of oceanic turbulence and beam source parameters on the propagation behavior of the optical vortices carried by partially coherent LG beams was investigated in detail. Our results indicated that optical turbulence in an ocean environment produced a much stronger effect on the optical vortex than that in an atmosphere environment; the effective range of the signal OAM mode of LG beams with a smaller ratio of the mode crosstalk was limited to only several tens of meters in turbulent ocean. The existence of oceanic turbulence evidently induced OAM mode crosstalk and spiral spectrum spread. The effects of oceanic turbulence on the OAM mode detection probability increased with the increase of radial and azimuthal mode orders, oceanic turbulent equivalent temperature structure parameter, and temperature-salinity balance parameter. The spatial partial coherence of the beam source would enhance the effect of turbulent aberrations on the signal OAM mode detection probability, and fully coherent vortex beams provided better performance than partially coherent ones. Increasing wavelength of the vortex beams would help improve the performance of this quantum optical communication system. These results might be of interest for the potential application of optical vortices in practical underwater quantum optical communication among divers, submarines, and sensors in the ocean environment. PMID:27409021
Correlation of optical phase distortion with turbulent structure in a homogeneous shear flow
NASA Technical Reports Server (NTRS)
Truman, C. Randall; Lee, Moon J.
1989-01-01
The relative importance of small-scale and large-scale turbulent structure to phase distortion in propagation through the homogeneous shear flow is the focus of this study. The importance of large-scale vortical structure and the associated scalar distribution to optical distortion induced by propagation through a turbulent shear flow has been established (Truman and Lee 1989). Phase errors induced in a coherent optical beam by these turbulent fluctuations are computed. This scalar field shows elongated regions of intense fluctuations which have an inclination with respect to the mean flow similar to that of the characteristic hairpin eddies. Long-term plans include an examination of the effects of inhomogeneity through consideration of direct numerical simulations of the channel flow, boundary layer or mixing layer.
Characterization of the horizontal optical turbulence (C{/n 2}) data measured at Kongju and Cheonan
NASA Astrophysics Data System (ADS)
Yeong Kim, Bo; Lee, Jun Ho; Soo Choi, Young
2015-06-01
When light from an object or an astronomical star propagates in the earth's atmosphere, atmospheric turbulence can distort and move the image in various ways. A quantitative measure of the intensity of optical turbulence with a refractive index structure parameter, C {/n 2}, is widely used in the statistical characterization of the random refractive index fluctuations generally referred to as optical turbulence. I this study, we investigated the horizontal optical turbulence in the near infrared region (850nm) at two sites in South Korea (Kongju and Cheonan) by using a scintillometer. The scintillometer measured the refractive index structure parameter C {/n 2} over 2.1- and 0.4-km paths, respectively, in Kongju and Cheonan. The first path was over an urban area characterized by a complicated land-use mix (residential houses, a river, bare ground, etc.) whereas the second path was a building-to-building path at a 15-m height on a university campus. In addition to the scintillometer, an independent weather station recorded meteorological conditions such as wind speed, relative humidity, and temperature. Study results indicate the general patterns of the optical turbulence at both sites agree with previous-reported diurnal patterns; they have two dips in C2n, one at around sunrise and the other at sunset, but the night profiles varied strongly depending on the atmospheric conditions. The average values of C {/n 2} for the measurement period were × 10-15 and 2.90 × 10-14 m-2/3 in Kongju and Cheonan, espectively, thus confirming that the optical field is clearer in the former. In addition, the average values of the Fried parameter, r0, were accordingly estimated to be 8.0 and 2.5 cm over a 2-km optical distance at Kongju and Cheonan, respectively.
NASA Astrophysics Data System (ADS)
Saxton-Fox, Theresa; McKeon, Beverley; Smith, Adam; Gordeyev, Stanislav
2014-11-01
This study examines the relationship between turbulent structures and the aero-optical distortion of a laser beam passing through a turbulent boundary layer. Previous studies by Smith et al. (AIAA, 2014--2491) have found a bulk convection velocity of 0 . 8U∞ for aero-optical distortion in turbulent boundary layers, motivating a comparison of the distortion with the outer boundary layer. In this study, a turbulent boundary layer is developed over a flat plate with a moderately-heated section of length 25 δ . Density variation in the thermal boundary layer leads to aero-optical distortion, which is measured with a Malley probe (Smith et al., AIAA, 2013--3133). Simultaneously, 2D PIV measurements are recorded in a wall-normal, streamwise plane centered on the Malley probe location. Experiments are run at Reθ = 2100 and at a Mach number of 0.03, with the heated wall 10 to 20°C above the free stream temperature. Correlations and conditional averages are carried out between Malley probe distortion angles and flow features in the PIV vector fields. Aero-optical distortion in this study will be compared to distortion in higher Mach number flows studied by Gordeyev et al. (J. Fluid Mech., 2014), with the aim of extending conclusions into compressible flows. This research is made possible by the Department of Defense through the National Defense & Engineering Graduate Fellowship (NDSEG) Program and by the Air Force Office of Scientific Research Grant # FA9550-12-1-0060.
On atmospheric turbulence structure constant measurement by a passive optical method
NASA Astrophysics Data System (ADS)
Konyaev, Petr A.; Botygina, Nina N.; Antoshkin, Leonid V.; Emaleev, Oleg N.; Lukin, Vladimir P.
2015-11-01
Development of a passive optical method for measuring the strength of atmospheric turbulence (atmospheric air refractive index structure constant Cn2) from image jitter is discussed. A high-rate digital camera and computer processing, including fast parallel 2D image correlation tracking algorithms, are shown to allow for real-time Cn2 measurements. The results obtained by passive and active optical methods together with meteorological station support of the experiment are compared.
Ren, Yongxiong; Huang, Hao; Xie, Guodong; Ahmed, Nisar; Yan, Yan; Erkmen, Baris I; Chandrasekaran, Nivedita; Lavery, Martin P J; Steinhoff, Nicholas K; Tur, Moshe; Dolinar, Samuel; Neifeld, Mark; Padgett, Miles J; Boyd, Robert W; Shapiro, Jeffrey H; Willner, Alan E
2013-10-15
We experimentally investigate the performance of an orbital angular momentum (OAM) multiplexed free space optical (FSO) communication link through emulated atmospheric turbulence. The turbulence effects on the crosstalk and system power penalty of the FSO link are characterized. The experimental results show that the power of the transmitted OAM mode will tend to spread uniformly onto the neighboring mode in medium-to-strong turbulence, resulting in severe crosstalk at the receiver. The power penalty is found to exceed 10 dB in a weak-to-medium turbulence condition due to the turbulence-induced crosstalk and power fluctuation of the received signal.
NASA Astrophysics Data System (ADS)
Carapezza, Edward M.; Lombardi, Gabrial; Butman, Jerry; Babb, Ivar
2009-09-01
This paper describes an innovative miniature optical sensor for predicting dissolved oxygen concentrations and measuring turbulence in river and littoral water columns. The dissolved oxygen and turbulence sensor consists of a single-frequency laser transmitter and a photodetector on which the scattered light from the turbulent water at the base of a dam or spillway is coherently mixed with a sample of the transmitted beam. This miniature sensor could be used both upstream and downsteam of dams and weirs to predict the amount of dissolved oxygen and turbulence in these waters. It could also be used on mobile platforms, such as unmanned underwater vehicles (UUV's), to monitor the edges of biological or chemical plumes or for wake follow platforms, schools of fish or marine mammals or on stationary unattended underwater sensors to monitor natural aeration and turbulence in littoral and riverine waters. Arrays of fixed unattended sensors could be used to detect the wake of transiting submerged vehicles, scuba divers, marine mammals or large schools of fish. A mobile platform equipped with a miniature sensor could to be cued to the general location and depth of an underwater target and then the platform could use this small aperture sensor to acquire and follow the wake. This dissolved oxygen and turbulence sensor system could be miniaturized and packaged into a very small volume; approximately the size of a wristwatch.
NASA Astrophysics Data System (ADS)
Carapezza, Edward M.; Lombardi, Gabrial; Butman, Jerry; Babb, Ivar
2007-10-01
This paper describes an innovative miniature optical sensor for measuring the turbulence in water columns. The turbulence sensor consists of a single-frequency laser transmitter and a photodetector on which the scattered light from the turbulent water is coherently mixed with a sample of the transmitted beam. This miniature sensor could be used on mobile platforms, such as unmanned underwater vehicles (UUV's), to wake follow platforms, schools of fish or marine mammals or on stationary unattended underwater sensors to monitor natural turbulence in littoral waters. Arrays of fixed unattended sensors could be used to detect the wake of transiting submerged vehicles, scuba divers, marine mammals or large schools of fish. A mobile platform equipped with a miniature turbulence sensor could to be cued to the general location and depth of an underwater target and then the platform could use this small aperture sensor to acquire and follow the wake. This turbulence sensor system could be miniaturized and packaged into a very small volume; approximately the size of a wristwatch.
Temporal broadening of optical pulses propagating through non-Kolmogorov turbulence.
Chen, Chunyi; Yang, Huamin; Lou, Yan; Tong, Shoufeng; Liu, Rencheng
2012-03-26
General formulations of the temporal averaged pulse intensity for optical pulses propagating through either non-Kolmogorov or Kolmogorov turbulence are deduced under the strong fluctuation conditions and the narrow-band assumption. Based on these formulations, an analytical formula for the turbulence-induced temporal half-width of spherical-wave Gaussian (SWG) pulses is derived, and the single-point, two-frequency mutual coherence function (MCF) of collimated Gaussian-beam waves in atmospheric turbulence is formulated analytically, by which the temporal averaged pulse intensity of collimated space-time Gaussian (CSTG) pulses can be calculated numerically. Calculation results show that the temporal broadening of both SWG and CSTG pulses in atmospheric turbulence depends heavily on the general spectral index of the spatial power spectrum of refractive-index fluctuations, and the temporal broadening of SWG pulses can be used to approximate that of CSTG pulses on the axis with the same turbulence parameters and propagation distances. It is also illustrated by numerical calculations that the variation in the turbulence-induced temporal half-width of CSTG pulses with the radial distance is really tiny.
Wave optics simulation of atmospheric turbulence and reflective speckle effects in CO2 lidar.
Nelson, D H; Walters, D L; Mackerrow, E P; Schmitt, M J; Quick, C R; Porch, W M; Petrin, R R
2000-04-20
Laser speckle can influence lidar measurements from a diffuse hard target. Atmospheric optical turbulence will also affect the lidar return signal. We present a numerical simulation that models the propagation of a lidar beam and accounts for both reflective speckle and atmospheric turbulence effects. Our simulation is based on implementing a Huygens-Fresnel approximation to laser propagation. A series of phase screens, with the appropriate atmospheric statistical characteristics, are used to simulate the effect of atmospheric turbulence. A single random phase screen is used to simulate scattering of the entire beam from a rough surface. We compare the output of our numerical model with separate CO(2) lidar measurements of atmospheric turbulence and reflective speckle. We also compare the output of our model with separate analytical predictions for atmospheric turbulence and reflective speckle. Good agreement was found between the model and the experimental data. Good agreement was also found with analytical predictions. Finally, we present results of a simulation of the combined effects on a finite-aperture lidar system that are qualitatively consistent with previous experimental observations of increasing rms noise with increasing turbulence level. PMID:18345082
Ren, Yongxiong; Dang, Anhong; Liu, Ling; Guo, Hong
2012-10-20
The heterodyne efficiency of a coherent free-space optical (FSO) communication model under the effects of atmospheric turbulence and misalignment is studied in this paper. To be more general, both the transmitted beam and local oscillator beam are assumed to be partially coherent based on the Gaussian Schell model (GSM). By using the derived analytical form of the cross-spectral function of a GSM beam propagating through atmospheric turbulence, a closed-form expression of heterodyne efficiency is derived, assuming that the propagation directions for the transmitted and local oscillator beams are slightly different. Then the impacts of atmospheric turbulence, configuration of the two beams (namely, beam radius and spatial coherence width), detector radius, and misalignment angle over heterodyne efficiency are examined. Numerical results suggest that the beam radius of the two overlapping beams can be optimized to achieve a maximum heterodyne efficiency according to the turbulence conditions and the detector radius. It is also found that atmospheric turbulence conditions will significantly degrade the efficiency of heterodyne detection, and compared to fully coherent beams, partially coherent beams are less sensitive to the changes in turbulence conditions and more robust against misalignment at the receiver.
Wave optics simulation of atmospheric turbulence and reflective speckle effects in CO2 lidar.
Nelson, D H; Walters, D L; Mackerrow, E P; Schmitt, M J; Quick, C R; Porch, W M; Petrin, R R
2000-04-20
Laser speckle can influence lidar measurements from a diffuse hard target. Atmospheric optical turbulence will also affect the lidar return signal. We present a numerical simulation that models the propagation of a lidar beam and accounts for both reflective speckle and atmospheric turbulence effects. Our simulation is based on implementing a Huygens-Fresnel approximation to laser propagation. A series of phase screens, with the appropriate atmospheric statistical characteristics, are used to simulate the effect of atmospheric turbulence. A single random phase screen is used to simulate scattering of the entire beam from a rough surface. We compare the output of our numerical model with separate CO(2) lidar measurements of atmospheric turbulence and reflective speckle. We also compare the output of our model with separate analytical predictions for atmospheric turbulence and reflective speckle. Good agreement was found between the model and the experimental data. Good agreement was also found with analytical predictions. Finally, we present results of a simulation of the combined effects on a finite-aperture lidar system that are qualitatively consistent with previous experimental observations of increasing rms noise with increasing turbulence level.
NASA Astrophysics Data System (ADS)
Udina, Mireia; Sun, Jielun; Kosović, Branko; Soler, Maria Rosa
2016-11-01
Following Sun et al. (J Atmos Sci 69(1):338-351, 2012), vertical variations of turbulent mixing in stably stratified and neutral environments as functions of wind speed are investigated using the large-eddy simulation capability in the Weather Research and Forecasting model. The simulations with a surface cooling rate for the stable boundary layer (SBL) and a range of geostrophic winds for both stable and neutral boundary layers are compared with observations from the Cooperative Atmosphere-Surface Exchange Study 1999 (CASES-99). To avoid the uncertainty of the subgrid scheme, the investigation focuses on the vertical domain when the ratio between the subgrid and the resolved turbulence is small. The results qualitatively capture the observed dependence of turbulence intensity on wind speed under neutral conditions; however, its vertical variation is affected by the damping layer used in absorbing undesirable numerical waves at the top of the domain as a result of relatively large neutral turbulent eddies. The simulated SBL fails to capture the observed temperature variance with wind speed and the observed transition from the SBL to the near-neutral atmosphere with increasing wind speed, although the vertical temperature profile of the simulated SBL resembles the observed profile. The study suggests that molecular thermal conduction responsible for the thermal coupling between the surface and atmosphere cannot be parameterized through the Monin-Obukhov bulk relation for turbulent heat transfer by applying the surface radiation temperature, as is common practice when modelling air-surface interactions.
NASA Astrophysics Data System (ADS)
Udina, Mireia; Sun, Jielun; Kosović, Branko; Soler, Maria Rosa
2016-07-01
Following Sun et al. (J Atmos Sci 69(1):338-351, 2012), vertical variations of turbulent mixing in stably stratified and neutral environments as functions of wind speed are investigated using the large-eddy simulation capability in the Weather Research and Forecasting model. The simulations with a surface cooling rate for the stable boundary layer (SBL) and a range of geostrophic winds for both stable and neutral boundary layers are compared with observations from the Cooperative Atmosphere-Surface Exchange Study 1999 (CASES-99). To avoid the uncertainty of the subgrid scheme, the investigation focuses on the vertical domain when the ratio between the subgrid and the resolved turbulence is small. The results qualitatively capture the observed dependence of turbulence intensity on wind speed under neutral conditions; however, its vertical variation is affected by the damping layer used in absorbing undesirable numerical waves at the top of the domain as a result of relatively large neutral turbulent eddies. The simulated SBL fails to capture the observed temperature variance with wind speed and the observed transition from the SBL to the near-neutral atmosphere with increasing wind speed, although the vertical temperature profile of the simulated SBL resembles the observed profile. The study suggests that molecular thermal conduction responsible for the thermal coupling between the surface and atmosphere cannot be parameterized through the Monin-Obukhov bulk relation for turbulent heat transfer by applying the surface radiation temperature, as is common practice when modelling air-surface interactions.
Statistical analysis of cloud-cover mitigation of optical turbulence in the boundary layer.
Curley, Michael J; Peterson, Burl H; Wang, J C; Sarkisov, Sergey S; Sarkisov Ii, Sergey S; Edlin, George R; Snow, Ronald A; Rushing, John F
2006-10-01
One atmospheric phenomenon that adversely affects laser propagation is optical turbulence. From ten months of observation, the refractive index structure constant in the atmospheric boundary layer was found to be significantly reduced under widespread cloudy conditions. The refractive index structure constant (C(n) (2)) depends upon the turbulent flux of momentum, sensible and latent heat. The intensity of a propagating laser beam will not be degraded nearly as much as would be expected under clear or lightly scattered cloud conditions. New experimental data are presented that support this hypothesis. The refractive index structure constant was measured for various cloud-cover conditions.
Zhang, Jiankun; Ding, Shengli; Zhai, Huili; Dang, Anhong
2014-12-29
In wireless optical communications (WOC), polarization multiplexing systems and coherent polarization systems have excellent performance and wide applications, while its state of polarization affected by atmospheric turbulence is not clearly understood. This paper focuses on the polarization fluctuations caused by atmospheric turbulence in a WOC link. Firstly, the relationship between the polarization fluctuations and the index of refraction structure parameter is introduced and the distribution of received polarization angle is obtained through theoretical derivations. Then, turbulent conditions are adjusted and measured elaborately in a wide range of scintillation indexes (SI). As a result, the root-mean-square (RMS) variation and probability distribution function (PDF) of polarization angle conforms closely to that of theoretical model.
Yi, Xiang; Li, Zan; Liu, Zengji
2015-02-20
In clean ocean water, the performance of a underwater optical communication system is limited mainly by oceanic turbulence, which is defined as the fluctuations in the index of refraction resulting from temperature and salinity fluctuations. In this paper, using the refractive index spectrum of oceanic turbulence under weak turbulence conditions, we carry out, for a horizontally propagating plane wave and spherical wave, analysis of the aperture-averaged scintillation index, the associated probability of fade, mean signal-to-noise ratio, and mean bit error rate. Our theoretical results show that for various values of the rate of dissipation of mean squared temperature and the temperature-salinity balance parameter, the large-aperture receiver leads to a remarkable decrease of scintillation and consequently a significant improvement on the system performance. Such an effect is more noticeable in the plane wave case than in the spherical wave case.
Yi, Xiang; Li, Zan; Liu, Zengji
2015-02-20
In clean ocean water, the performance of a underwater optical communication system is limited mainly by oceanic turbulence, which is defined as the fluctuations in the index of refraction resulting from temperature and salinity fluctuations. In this paper, using the refractive index spectrum of oceanic turbulence under weak turbulence conditions, we carry out, for a horizontally propagating plane wave and spherical wave, analysis of the aperture-averaged scintillation index, the associated probability of fade, mean signal-to-noise ratio, and mean bit error rate. Our theoretical results show that for various values of the rate of dissipation of mean squared temperature and the temperature-salinity balance parameter, the large-aperture receiver leads to a remarkable decrease of scintillation and consequently a significant improvement on the system performance. Such an effect is more noticeable in the plane wave case than in the spherical wave case. PMID:25968187
Zhou, Guoquan; Cai, Yangjian; Chu, Xiuxiang
2012-04-23
The propagation of a partially coherent hollow vortex Gaussian beam through a paraxial ABCD optical system in turbulent atmosphere has been investigated. The analytical expressions for the average intensity and the degree of the polarization of a partially coherent hollow vortex Gaussian beam through a paraxial ABCD optical system are derived in turbulent atmosphere, respectively. The average intensity distribution and the degree of the polarization of a partially coherent hollow vortex Gaussian beam in turbulent atmosphere are numerically demonstrated. The influences of the beam parameters, the topological charge, the transverse coherent lengths, and the structure constant of the atmospheric turbulence on the propagation of a partially coherent hollow vortex Gaussian beam in turbulent atmosphere are also examined in detail. This research is beneficial to the practical applications in free-space optical communications and the remote sensing of the dark hollow beams.
Neo, Richard; Goodwin, Michael; Zheng, Jessica; Lawrence, Jon; Leon-Saval, Sergio; Bland-Hawthorn, Joss; Molina-Terriza, Gabriel
2016-02-01
In recent years, there have been a series of proposals to exploit the orbital angular momentum (OAM) of light for astronomical applications. The OAM of light potentially represents a new way in which to probe the universe. The study of this property of light entails the development of new instrumentation and problems which must be addressed. One of the key issues is whether we can overcome the loss of the information carried by OAM due to atmospheric turbulence. We experimentally analyze the effect of atmospheric turbulence on the OAM content of a signal over a range of realistic turbulence strengths typical for astronomical observations. With an adaptive optics system we are able to recover up to 89% power in an initial non-zero OAM mode (ℓ = 1) at low turbulence strengths (0.30" FWHM seeing). However, for poorer seeing conditions (1.1" FWHM seeing), the amount of power recovered is significantly lower (5%), showing that for the terrestrial detection of astronomical OAM, a careful design of the adaptive optics system is needed.
NASA Astrophysics Data System (ADS)
Del Moro, Dario; Piazzesi, Roberto; Stangalini, Marco; Giovannelli, Luca; Berrilli, Francesco
2015-01-01
The FORS (closed loop forecasting system) control algorithm has been already successfully applied to improve the efficiency of a simulated adaptive optics (AO) system. To test its performance in real conditions, we implemented this algorithm in a hardware AO demonstrator, introducing controlled aberrations into the system. We present here the results of introducing into the system both a simple periodic defocus aberration and a real open loop defocus time sequence acquired at the vacuum tower telescope solar telescope. In both cases, FORS yields a significant performance increase, improving the stability of the system in closed-loop conditions and decreasing the amplitude of the residual uncorrected wavefront aberrations.
NASA Astrophysics Data System (ADS)
Yang, Wenxia; Cai, Chao; Ding, Mingyue; Zhou, Chengping; Guo, Xiaoxing
2007-11-01
The goal of this paper is to numerically simulate and analyze the aero-optic effects caused by the hyper-speed turbulence fields surrounding the aircraft under different flight conditions, and to characterize them with the associated optical transfer functions. First, analysis and computation of the aero-optic effects under different flight conditions have been addressed, where the parameters characterizing the hyper-speed turbulence field were obtained by solving its N-S equations via CFD methods. The infrared ray trajectories passing through the flow field with a non-homogeneous distribution of the refraction indices were acquired using the gradient index ray-tracing method, and the transfer function to represent the aero-optic effects was derived considering the principles of Fourier optics. The simulation results showed that the aero-optic transfer function is characterized as a low-pass filter of nonlinearly varying phases, which results the blurring and shifting of the objects in the acquired images.
NASA Astrophysics Data System (ADS)
Liu, Yang; Zhang, Guo-an
2014-09-01
In order to mitigate atmospheric turbulence, the free space optical (FSO) system model with spatial diversity is analyzed based on intensity detection pulse position modulation (PPM) in the weak turbulence atmosphere. The slot error rate (SER) calculating formula of the system without diversity is derived under pulse position modulation firstly. Then as a benchmark, independent of identical distribution, the average slot error rates of the three linear combining technologies, which are the maximal ratio combining (MRC), equal gain combining (EGC) and selection combining (SelC), are compared. Simulation results show that the performance of system is the best improved by MRC, followed by EGC, and is poor by SelC, but SelC is simpler and more convenient. Spatial diversity is efficient to improve the performance and has strong ability on resistance to atmospheric channel decline. The above scheme is more suitable for optical wireless communication systems.
Fluctuations of energy density of short-pulse optical radiation in the turbulent atmosphere.
Banakh, V A; Smalikho, I N
2014-09-22
Fluctuations of energy density of short-pulse optical radiation in the turbulent atmosphere have been studied based on numerical solution of the parabolic wave equation for the complex spectral amplitude of the wave field by the split-step method. It has been shown that under conditions of strong optical turbulence, the relative variance of energy density fluctuations of pulsed radiation of femtosecond duration becomes much less than the relative variance of intensity fluctuations of continuous-wave radiation. The spatial structure of fluctuations of the energy density with a decrease of the pulse duration becomes more large-scale and homogeneous. For shorter pulses the maximal value of the probability density distribution of energy density fluctuations tends to the mean value of the energy density.
NASA Technical Reports Server (NTRS)
Harger, R. O.
1974-01-01
Abstracts are reported relating to the techniques used in the research concerning optical transmission of information. Communication through the turbulent atmosphere, quantum mechanics, and quantum communication theory are discussed along with the results.
Use of Remotely Sensed Aerosol Optical Depth in Particulate Matter Forecasting for Urban Areas
NASA Astrophysics Data System (ADS)
Grant, S. L.; Crist, K.
2011-12-01
Cincinnati, a large metropolitan area in southwestern Ohio, has been listed as a non-attainment area based on the EPA 1997 PM2.5 (particulate matter with aerodynamic diameter < 2.5μm) standard with a number of unhealthy days reported annually for sensitive groups. AirNow provides air quality index for the city, but its accuracy largely depends on the air quality forecast models used and ground-based monitoring network measurements. These networks are inherently limited by their sparse distribution; nonetheless, they form an integral part of many decision-making structure and epidemiological studies. Remote sensing instruments such as MODIS provide daily aerosol optical depth (AOD) products with almost global spatial coverage, which are available on a near-real-time (NRT) basis. This work aims to show that the NRT AOD product obtained from MODIS can improve the air quality forecast in the Cincinnati area. To achieve this, an evaluation of the correlation of AOD retrievals with ground-based PM2.5 observations is carried out. Further to which, the MODIS AOD data is included as a variable in a statistical model to bolster current PM2.5 forecasting capabilities. Other key input parameters to the multiple linear regression model includes surface and vertical weather patterns, mixing height, local wind patterns, relative humidity and temperature.
NASA Astrophysics Data System (ADS)
Ziad, Aziz; Borgnino, Julien; Martin, François; Maire, Jérôme; Bondoux, Erick; Douet, Richard; Fanteï-Caujolle, Yan; Robini, Alex; Daban, Jean-Baptiste
2011-09-01
The futures large telescopes will be certainly equipped with Multi-Conjugate Adaptive Optics systems. The optimization of the performances of these techniques requires a precise specification of the different components of these systems. Major of these technical specifications are related to the atmospheric turbulence particularly the structure constante of the refractive index Cn2 and the outer scale L0. New techniques for the monitoring of the Cn2 and L0 profiles with high vertical resolution will be presented.
Measurements of passive-scalar spectra for grid turbulence using a nonlinear optical technique
O'Hern, T.J.; Torczynski, J.R.; Neal, D.R.; Shagam, R.N. ); Robey, H.F. )
1991-01-01
A nonlinear optical technique has been applied to grid turbulence measurements. A laser beam passing through a turbulent region acquires phase perturbations related to the density perturbations it encounters. If the laser beam is then passed through a crystal of barium titanate (BaTiO{sub 3}), a photorefractive nonlinear optical material, the small-amplitude perturbations to the beam are passed but the large-amplitude unperturbed portion of the beam is deflected away from the beam path. An optical Fourier transform of the perturbations performed by a lens yields the two-dimensional density-perturbation (passive-scalar) spectrum at the lens focal plane or, alternatively, a photorefractive schlieren photograph at the lens image plane. As a test application for this technique, a system was assembled to study the downstream evolution of the density-perturbation spectrum in grid turbulence produced by an electrically heated screen spanning the test section of a wind tunnel. Near the screen, the spectrum is found to consist primarily of large-amplitude peaks at the fundamental and the first few harmonics of the screen-wake spatial frequency. As expected, these amplitudes are observed to decay rapidly in the downstream direction. 8 refs., 12 figs.
500 Gb/s free-space optical transmission over strong atmospheric turbulence channels.
Qu, Zhen; Djordjevic, Ivan B
2016-07-15
We experimentally demonstrate a high-spectral-efficiency, large-capacity, featured free-space-optical (FSO) transmission system by using low-density, parity-check (LDPC) coded quadrature phase shift keying (QPSK) combined with orbital angular momentum (OAM) multiplexing. The strong atmospheric turbulence channel is emulated by two spatial light modulators on which four randomly generated azimuthal phase patterns yielding the Andrews spectrum are recorded. The validity of such an approach is verified by reproducing the intensity distribution and irradiance correlation function (ICF) from the full-scale simulator. Excellent agreement of experimental, numerical, and analytical results is found. To reduce the phase distortion induced by the turbulence emulator, the inexpensive wavefront sensorless adaptive optics (AO) is used. To deal with remaining channel impairments, a large-girth LDPC code is used. To further improve the aggregate data rate, the OAM multiplexing is combined with WDM, and 500 Gb/s optical transmission over the strong atmospheric turbulence channels is demonstrated. PMID:27420516
Optical requirements with turbulence correction for long-range biometrics
NASA Astrophysics Data System (ADS)
Choi, Junoh; Soehnel, Grant H.; Bagwell, Brett E.; Dixon, Kevin R.; Wick, David V.
2009-05-01
Iris recognition utilizes distinct patterns found in the human iris to perform identification. Image acquisition is a critical first step towards successful operation of iris recognition systems. However, the quality of iris images required by standard iris recognition algorithms puts hard constraints on the imaging optical systems which have resulted in demonstrated systems to date requiring a relatively short subject stand-off distance. In this paper, we study long-range iris recognition at distances as large as 200 meters, and determine conditions the imaging system must satisfy for identification at longer stand-off distances.
NASA Astrophysics Data System (ADS)
Bernotas, Marius P.; Nelson, Charles
2016-05-01
The Weibull and Exponentiated Weibull probability density functions have been examined for the free space regime using heuristically derived shape and scale parameters. This paper extends current literature to the underwater channel and explores use of experimentally derived parameters. Data gathered in a short range underwater channel emulator was analyzed using a nonlinear curve fitting methodology to optimize the scale and shape parameters of the PDFs. This method provides insight into the scaled effects of underwater optical turbulence on a long range link, and may yield a general set of equations for determining the PDF for an underwater optical link.
NASA Astrophysics Data System (ADS)
Jumper, E. J.; Hugo, R. J.
1992-07-01
This paper discusses the small-aperture beam technique, a relatively new way of experimentally quantifying optically-active, turbulent-fluid-flow-induced optical degradation. The paper lays out the theoretical basis for the technique, and the relationship of the measured jitter of the beam to optical path difference. A numerical simulation of a two-dimensional heated jet is used to explore the validity of beam jitter to obtain optical path difference in a flow region where eddy production constitutes the major character of the 'turbulent' flow field.
NASA Astrophysics Data System (ADS)
Louthain, James A.; Welsh, Byron M.
1998-09-01
A new atmospheric screen generator is developed for use in performance calculations of adaptive optics and imaging systems. The generator is valid over a wide range of atmospheric turbulence parameters and incorporates both phase and amplitude effects. The new screen generator accounts for diffraction effects caused by turbulence and incorporates the phase, amplitude, and cross statistics of a weak turbulence model. The second order statistics of the phase and amplitude perturbations are based on the auto- correlation functions developed by Lee and Harp and the cross-correlation of the phase and amplitude perturbations derived in this paper. The correlations are derived by modeling the turbulence as a number of layers of randomly varying refractivity perpendicular to the propagation path. As the field propagates through the medium, diffraction occurs at each of the layers. A Fourier series expansion of the wavefront phase and amplitude is used. The screen generator uses the power and cross spectral densities of the phase and amplitude perturbations. The mean square value and the structure functions of the wavefront phase and amplitude are calculated in a Monte Carlo experiment and shown to be within 1% of the theoretical value.
Study of turbulence effects for a free-space optical link over water
NASA Astrophysics Data System (ADS)
Mackey, Ruth; Chen, Mingzhou; Lambert, Andrew; Mackey, David; Goncharov, Alexander
2010-10-01
In this paper we report on measurements of atmospheric turbulence effects arising from water air interaction. The aim of this study is to aid in the design of a free-space optical relay system to facilitate longer line-of-sight distances between relay buoys in a large expanse of water. Analysis of turbulence statistics will provide the basis for adaptive optics solutions to improve the relay signal strength affected by scintillation and beam wander. We report on experiments determining the isokinetic angle using an array of broadband incoherent sources of variable angular separation on the order of 0.1 mrad to 2.8 mrad. The experimental setup consists of a 5 inch telescope with high speed CMOS camera observing over a distance of 300 m close at a height of 1.5 m above the water surface. As part of the turbulence characterisation we experimentally estimate the relative image motion of angle-ofarrival fluctuations and perform other time series analysis. Analysis of the image motion requires new techniques due to the extended nature of the source. We explore different centroiding algorithms and surface fitting techniques.
Temporal frequency spread of optical wave propagation through anisotropic non-Kolmogorov turbulence
NASA Astrophysics Data System (ADS)
Kotiang, Stephen; Choi, Jaeho
2015-12-01
In this paper, we derive new analytic expressions for the atmospheric-induced frequency spread of optical plane and spherical waves propagating in a horizontal path and experiencing anisotropic non-Kolmogorov turbulence. The anisotropic spectrum model is based on the assumption that circular symmetry is maintained in the orthogonal xy-plane throughout the path and that it includes the same degree of anisotropy along the direction of propagation for all the turbulence cell sizes. These expressions are developed in the weak fluctuation region using the Rytov approximation method and are independent of the knowledge of the temporal mutual coherence function for the optical waves. We perform our analysis based on a generalized von Karman power spectrum of the index of refraction. The spectrum considers the effect of finite inner and outer scales of turbulence, together with a non-Kolmogorov spectral power exponent α that varies between 3-4. The simulation results show that the anisotropic parameter impacts on the frequency spread by a factor {\\zeta }2-α . Moreover the frequency spread is most significant for α values around 3.1.
Adaptive-optics compensation by distributed beacons for non-kolmogorov turbulence.
Rao, C; Jiang, W; Ling, N
2001-07-20
In optical propagation through atmospheric turbulence, the performance of compensation with adaptive optics depends on a beacon's spatial distribution. With distributed beacons, the inefficiency of the modal correction, which is defined as the ratio of the anisoplanatic error of the jth mode and the Zernike-coefficient variance, is derived by use of the wave-front expansion on the Zernike polynomials for non-Kolmogorov turbulence. Numerical results are presented for laser beam propagation through constant turbulence with an offset point beacon and an on-axis uniform circular beacon. The results show that compensation for an on-axis uniform circular beacon is much more effective than that for an offset point beacon. The low-order modes are much more correlated than the higher-order modes. The larger the power-law exponent of the refractive-index power spectrum beta, the smaller the propagation path length L and the larger the diameter D of the telescope aperture, the more effective the compensation is. For a specific extended degree of beacon for which there are a maximum number of modes N(max) to be corrected, only low-order-correction systems are useful.
LOLAS-2: Redesign of an Optical Turbulence Profiler with High Altitude-resolution
NASA Astrophysics Data System (ADS)
Avila, R.; Zúñiga, C. A.; Tapia-Rodríguez, J. J.; Sánchez, L. J.; Cruz-González, I.; Avilés, J. L.; Valdés-Hernández, O.; Carrasco, E.
2016-10-01
We present the development, tests, and first results of the second-generation LOLAS-2. This instrument constitutes a strongly improved version of the prototype LOLAS, which is aimed at the measurement of optical turbulence profiles close to the ground, with high altitude-resolution. The method is based on the generalized Scidar principle that consists of taking double-star scintillation images on a defocused pupil plane and calculating in real time the autocovariance of the scintillation. The main components are an open-truss 40-cm Ritchey-Chrétien telescope, a German-type equatorial mount, an electron-multiplying CCD camera, and a dedicated acquisition and real-time data-processing software. The new optical design of LOLAS-2 is significantly simplified compared to the prototype. The experiments carried out to test the permanence of the image within the useful zone of the detector and the stability of the telescope focus show that LOLAS-2 can function without the use of the autoguiding and autofocus algorithms that were developed for the prototype version. Optical turbulence profiles obtained with the new LOLAS have the best altitude-resolution ever achieved with Scidar-like techniques (6.3 m). The simplification of the optical layout and the improved mechanical properties of the telescope and mount make of LOLAS-2 a more robust instrument.
NASA Astrophysics Data System (ADS)
Prabu, K.; Kumar, D. Sriram
2015-05-01
An optical wireless communication system is an alternative to radio frequency communication, but atmospheric turbulence induced fading and misalignment fading are the main impairments affecting an optical signal when propagating through the turbulence channel. The resultant of misalignment fading is the pointing errors, it degrades the bit error rate (BER) performance of the free space optics (FSO) system. In this paper, we study the BER performance of the multiple-input multiple-output (MIMO) FSO system employing coherent binary polarization shift keying (BPOLSK) in gamma-gamma (G-G) channel with pointing errors. The BER performance of the BPOLSK based MIMO FSO system is compared with the single-input single-output (SISO) system. Also, the average BER performance of the systems is analyzed and compared with and without pointing errors. A novel closed form expressions of BER are derived for MIMO FSO system with maximal ratio combining (MRC) and equal gain combining (EGC) diversity techniques. The analytical results show that the pointing errors can severely degrade the performance of the system.
Characterization of dual-polarization LTE radio over a free-space optical turbulence channel.
Bohata, J; Zvanovec, S; Korinek, T; Mansour Abadi, M; Ghassemlooy, Z
2015-08-10
A dual polarization (DP) radio over a free-space optical (FSO) communication link using a long-term evolution (LTE) radio signal is proposed and analyzed under different turbulence channel conditions. Radio signal transmission over the DP FSO channel is experimentally verified by means of error vector magnitude (EVM) statistics. We demonstrate that such a system, employing a 64 quadrature amplitude modulation at the frequency bands of 800 MHz and 2.6 GHz, evinces reliability with <8% of EVM in a turbulent channel. Based on the results, we show that transmitting the LTE signal over the FSO channel is a potential solution for last-mile access or backbone networks, when using multiple-input multiple-output based DP signals.
NASA Astrophysics Data System (ADS)
Anguita, Jaime A.; Neifeld, Mark A.; Vasic, Bane V.
2008-05-01
A multichannel free-space optical (FSO) communication system based on orbital angular momentum (OAM)-carrying beams is studied. We numerically analyze the effects of atmospheric turbulence on the system and find that turbulence induces attenuation and crosstalk among channels. Based on a model in which the constituent channels are binary symmetric and crosstalk is a Gaussian noise source, we find optimal sets of OAM states at each turbulence condition studied and determine the aggregate capacity of the multichannel system at those conditions. OAM-multiplexed FSO systems that operate in the weak turbulence regime are found to offer good performance. We verify that the aggregate capacity decreases as the turbulence increases. A per-channel bit-error rate evaluation is presented to show the uneven effects of crosstalk on the constituent channels.
LSPV+7, a branch-point-tolerant reconstructor for strong turbulence adaptive optics.
Steinbock, Michael J; Hyde, Milo W; Schmidt, Jason D
2014-06-20
Optical wave propagation through long paths of extended turbulence presents unique challenges to adaptive optics (AO) systems. As scintillation and branch points develop in the beacon phase, challenges arise in accurately unwrapping the received wavefront and optimizing the reconstructed phase with respect to branch cut placement on a continuous facesheet deformable mirror. Several applications are currently restricted by these capability limits: laser communication, laser weapons, remote sensing, and ground-based astronomy. This paper presents a set of temporally evolving AO simulations comparing traditional least-squares reconstruction techniques to a complex-exponential reconstructor and several other reconstructors derived from the postprocessing congruence operation. The reconstructors' behavior in closed-loop operation is compared and discussed, providing several insights into the fundamental strengths and limitations of each reconstructor type. This research utilizes a self-referencing interferometer (SRI) as the high-order wavefront sensor, driving a traditional linear control law in conjunction with a cooperative point source beacon. The SRI model includes practical optical considerations and frame-by-frame fiber coupling effects to allow for realistic noise modeling. The "LSPV+7" reconstructor is shown to offer the best performance in terms of Strehl ratio and correction stability-outperforming the traditional least-squares reconstructed system by an average of 120% in the studied scenarios. Utilizing a continuous facesheet deformable mirror, these reconstructors offer significant AO performance improvements in strong turbulence applications without the need for segmented deformable mirrors. PMID:24979411
LSPV+7, a branch-point-tolerant reconstructor for strong turbulence adaptive optics.
Steinbock, Michael J; Hyde, Milo W; Schmidt, Jason D
2014-06-20
Optical wave propagation through long paths of extended turbulence presents unique challenges to adaptive optics (AO) systems. As scintillation and branch points develop in the beacon phase, challenges arise in accurately unwrapping the received wavefront and optimizing the reconstructed phase with respect to branch cut placement on a continuous facesheet deformable mirror. Several applications are currently restricted by these capability limits: laser communication, laser weapons, remote sensing, and ground-based astronomy. This paper presents a set of temporally evolving AO simulations comparing traditional least-squares reconstruction techniques to a complex-exponential reconstructor and several other reconstructors derived from the postprocessing congruence operation. The reconstructors' behavior in closed-loop operation is compared and discussed, providing several insights into the fundamental strengths and limitations of each reconstructor type. This research utilizes a self-referencing interferometer (SRI) as the high-order wavefront sensor, driving a traditional linear control law in conjunction with a cooperative point source beacon. The SRI model includes practical optical considerations and frame-by-frame fiber coupling effects to allow for realistic noise modeling. The "LSPV+7" reconstructor is shown to offer the best performance in terms of Strehl ratio and correction stability-outperforming the traditional least-squares reconstructed system by an average of 120% in the studied scenarios. Utilizing a continuous facesheet deformable mirror, these reconstructors offer significant AO performance improvements in strong turbulence applications without the need for segmented deformable mirrors.
Implications of the homogeneous turbulence assumption on the aero-optic linking equation
NASA Astrophysics Data System (ADS)
Hugo, Ronald J.; Jumper, Eric J.
1995-09-01
This paper investigates the validity of applying the simplified (under the assumptions of isotropic and homogeneous turbulence) aero-optic linking equation to a flowfield that is known to consist of anisotropic and nonhomogeneous turbulence. The investigation is performed in the near nozzle-region of a heated two-dimensional jet, and the study makes use of a conditional sampling experiment to acquire a spatio-temporal temperature field data base for the heated jet flowfield. After compensating for the bandwidth limitations of constant-current-wire temperature measurements, the temperature field data base is applied to the computation of optical degradation through both direct methods and indirect methods relying on the aero-optic linking equation. The simplified version of the linking equation was found to provide very good agreement with direct calculations provided that the length scale of the density fluctuations was interpreted as being the integral scale, with the limits of the integration being the two first zero crossings of the covariance coefficient function.
The performance of space shift keying for free-space optical communications over turbulent channels
NASA Astrophysics Data System (ADS)
Abaza, Mohamed; Mesleh, Raed; Mansour, Ali; Aggoune, El-Hadi M.
2015-01-01
This paper evaluates the performance of space shift keying (SSK) free-space optical communication (FSO) over moderate and strong turbulent channels. It has been shown previously that repetition codes (RCs) using intensity modulation with direct detection techniques are superior to SSK system for a spectral efficiency of 1 bit/s/Hz. It is shown in this study that SSK outperforms RCs using M-ary pulse amplitude modulation for spectral efficiencies of 3 bits/s/Hz or larger. Analytical expressions for the bit error rate for the SSK system under study are derived and extensive simulation results corroborate the correctness of the conducted analysis.
NASA Astrophysics Data System (ADS)
Prabu, K.; Sriram Kumar, D.
2016-01-01
This paper investigates the outage performance of polarization shift keying (PolSK) based multihop parallel relay assisted free space optics (FSO) system over a strong atmospheric turbulence channel with misalignment fading. An exact closed form expression is derived for the end-to-end outage probability of the system. The results are compared with the direct transmission and on-off keying (OOK) based FSO systems. The results indicate that the performance of the PolSK based relay-assisted FSO system is much better than the direct transmission and OOK systems. The outage performance is enhanced by increasing the number of relay path between the transmitter and receiver.
NASA Astrophysics Data System (ADS)
Ziad, Aziz; Borgnino, Julien; Martin, François; Maire, Jérôme; Wassila, Dali-Ali; Berdja, Amokrane; Daban, Jean-Baptiste; Fanteï-Caujolle, Yan; Sarazin, Marc; Tokovinin, Andreï
2010-07-01
The futures large telescopes will be certainly equipped with Multi-Conjugate Adaptive Optics systems. The optimization of the performances of these techniques requires a precise specification of the different components of these systems. Major of these technical specifications are related to the atmospheric turbulence particularly the structure constante of the refractive index C2n(h) and the outer scale L0(h). New techniques based on the moon limb observation for the monitoring of the C2n(h) and L0(h) profiles with high vertical resolution will be presented.
KC-135 aero-optical turbulent boundary layer/shear layer experiment revisited
NASA Technical Reports Server (NTRS)
Craig, J.; Allen, C.
1987-01-01
The aero-optical effects associated with propagating a laser beam through both an aircraft turbulent boundary layer and artificially generated shear layers are examined. The data present comparisons from observed optical performance with those inferred from aerodynamic measurements of unsteady density and correlation lengths within the same random flow fields. Using optical instrumentation with tens of microsecond temporal resolution through a finite aperture, optical performance degradation was determined and contrasted with the infinite aperture time averaged aerodynamic measurement. In addition, the optical data were artificially clipped to compare to theoretical scaling calculations. Optical instrumentation consisted of a custom Q switched Nd:Yag double pulsed laser, and a holographic camera which recorded the random flow field in a double pass, double pulse mode. Aerodynamic parameters were measured using hot film anemometer probes and a five hole pressure probe. Each technique is described with its associated theoretical basis for comparison. The effects of finite aperture and spatial and temporal frequencies of the random flow are considered.
Turbulent phase noise on asymmetric two-way ground-satellite coherent optical links
NASA Astrophysics Data System (ADS)
Robert, Clélia; Conan, Jean-Marc; Wolf, Peter
2015-10-01
Bidirectional ground-satellite laser links suffer from turbulence-induced scintillation and phase distortion. We study how turbulence impacts on coherent detection capacity and on the associated phase noise that restricts clock transfer precision. We evaluate the capacity to obtain a two-way cancellation of atmospheric effects despite the asymmetry between up and down link that limits the link reciprocity. For ground-satellite links, the asymmetry is induced by point-ahead angle and possibly the use, for the ground terminal, of different transceiver diameters, in reception and emission. The quantitative analysis is obtained thanks to refined end-to-end simulations under realistic turbulence and wind conditions as well as satellite cinematic. Simulations make use of the reciprocity principle to estimate both down and up link performance from wave-optics propagation of descending plane waves. These temporally resolved simulations allow characterising the coherent detection in terms of time series of heterodyne efficiency for different system parameters. We show Tip/Tilt correction on ground is mandatory at reception for the down link and as a pre-compensation of the up link. Good correlation between up and down phase noise is obtained even with asymmetric apertures of the ground transceiver and in spite of pointing ahead angle. The reduction to less than 1 rad2 of the two-way differential phase noise is very promising for clock transfer.
Investigation of Hill's optical turbulence model by means of direct numerical simulation.
Muschinski, Andreas; de Bruyn Kops, Stephen M
2015-12-01
For almost four decades, Hill's "Model 4" [J. Fluid Mech. 88, 541 (1978) has played a central role in research and technology of optical turbulence. Based on Batchelor's generalized Obukhov-Corrsin theory of scalar turbulence, Hill's model predicts the dimensionless function h(κl(0), Pr) that appears in Tatarskii's well-known equation for the 3D refractive-index spectrum in the case of homogeneous and isotropic turbulence, Φn(κ)=0.033C2(n)κ(-11/3) h(κl(0), Pr). Here we investigate Hill's model by comparing numerical solutions of Hill's differential equation with scalar spectra estimated from direct numerical simulation (DNS) output data. Our DNS solves the Navier-Stokes equation for the 3D velocity field and the transport equation for the scalar field on a numerical grid containing 4096(3) grid points. Two independent DNS runs are analyzed: one with the Prandtl number Pr=0.7 and a second run with Pr=1.0 . We find very good agreement between h(κl(0), Pr) estimated from the DNS output data and h(κl(0), Pr) predicted by the Hill model. We find that the height of the Hill bump is 1.79 Pr(1/3), implying that there is no bump if Pr<0.17 . Both the DNS and the Hill model predict that the viscous-diffusive "tail" of h(κl(0), Pr) is exponential, not Gaussian.
Investigation of Hill's optical turbulence model by means of direct numerical simulation.
Muschinski, Andreas; de Bruyn Kops, Stephen M
2015-12-01
For almost four decades, Hill's "Model 4" [J. Fluid Mech. 88, 541 (1978) has played a central role in research and technology of optical turbulence. Based on Batchelor's generalized Obukhov-Corrsin theory of scalar turbulence, Hill's model predicts the dimensionless function h(κl(0), Pr) that appears in Tatarskii's well-known equation for the 3D refractive-index spectrum in the case of homogeneous and isotropic turbulence, Φn(κ)=0.033C2(n)κ(-11/3) h(κl(0), Pr). Here we investigate Hill's model by comparing numerical solutions of Hill's differential equation with scalar spectra estimated from direct numerical simulation (DNS) output data. Our DNS solves the Navier-Stokes equation for the 3D velocity field and the transport equation for the scalar field on a numerical grid containing 4096(3) grid points. Two independent DNS runs are analyzed: one with the Prandtl number Pr=0.7 and a second run with Pr=1.0 . We find very good agreement between h(κl(0), Pr) estimated from the DNS output data and h(κl(0), Pr) predicted by the Hill model. We find that the height of the Hill bump is 1.79 Pr(1/3), implying that there is no bump if Pr<0.17 . Both the DNS and the Hill model predict that the viscous-diffusive "tail" of h(κl(0), Pr) is exponential, not Gaussian. PMID:26831396
Propagation of a cosh-Gaussian beam through an optical system in turbulent atmosphere.
Chu, Xiuxiang
2007-12-24
The propagation of a cosh-Gaussian beam through an arbitrary ABCD optical system in turbulent atmosphere has been investigated. The analytical expressions for the average intensity at any receiver plane are obtained. As an elementary example, the average intensity and its radius at the image plane of a cosh-Gaussian beam through a thin lens are studied. To show the effects of a lens on the average intensity and the intensity radius of the laser beam in turbulent atmosphere, the properties of a collimated cosh-Gaussian beam and a focused cosh-Gaussian beam for direct propagation in turbulent atmosphere are studied and numerically calculated. The average intensity profiles of a cosh-Gaussian beam through a lens can have a shape similar to that of the initial beam for a longer propagation distance than that of a collimated cosh-Gaussian beam for direct propagation. With the increment in the propagation distance, the average intensity radius at the image plane of a cosh-Gaussian beam through a thin lens will be smaller than that at the focal plane of a focused cosh-Gaussian beam for direct propagation. Meanwhile, the intensity distributions at the image plane of a cosh-Gaussian beam through a lens with different w(0) and Omega(0) are also studied.
Gamo, H; Majumdar, A K
1978-12-01
A turbulence chamber (0.78 x 0.23 x 2.59 m(3)) consisting of ten small electric heater/blowers with an aluminum foil screen and three screens of 2-mm aluminum wire meshes can generate the nearly homogeneous isotropic turbulence within the 0.5 x 0.05 x 2-m(3) region at the 0.11-m height of optical measurements. The temperature structure constant squared C(2)(T) = 52.9 K(2) m(-?) was obtained from the temperature structure function measurements measured by using a differential microthermocouple system. The refractive-index structure constant squared C(2)n_{at the 632.8-nm wavelength was calculated from C(2)(T):C(2)(n) = 3.00 x 10(-11)m(-?). The average wind velocity and temperature were 0.41 m/sec and 53 degrees C, respectively. From the power spectrum of temperature fluctuations, the inner and outer scales of turbulence are determined: l(o) = 5.0 mm and L(0) = 6.5 cm. The measured temperature structure function and power spectrum of temperature fluctuations satisfy the ? and -5/3 power similarity laws in the inertial subrange, respectively.}
Control of turbulent flow over an articulating turret for reduction of adverse aero-optic effects
NASA Astrophysics Data System (ADS)
Wallace, Ryan
2011-12-01
Force Research Laboratory wind tunnel at Wright-Patterson Air Force Base. Direct measurements of the aero-optic effects were taken via a Malley probe at a fixed pitch angle with and without suction control at a Mach number 0.3, and a corresponding Reynolds number of 2,000,000. Reduction of the aero-optic effects in this test demonstrated that suction control is a practical control input to reduce the near field wavefront abberations due to the turbulent flow over the aperture.
Molecular-Based Optical Measurement Techniques for Transition and Turbulence in High-Speed Flow
NASA Technical Reports Server (NTRS)
Bathel, Brett F.; Danehy, Paul M.; Cutler, Andrew D.
2013-01-01
photogrammetry (for model attitude and deformation measurement) are excluded to limit the scope of this report. Other physical probes such as heat flux gauges, total temperature probes are also excluded. We further exclude measurement techniques that require particle seeding though particle based methods may still be useful in many high speed flow applications. This manuscript details some of the more widely used molecular-based measurement techniques for studying transition and turbulence: laser-induced fluorescence (LIF), Rayleigh and Raman Scattering and coherent anti-Stokes Raman scattering (CARS). These techniques are emphasized, in part, because of the prior experience of the authors. Additional molecular based techniques are described, albeit in less detail. Where possible, an effort is made to compare the relative advantages and disadvantages of the various measurement techniques, although these comparisons can be subjective views of the authors. Finally, the manuscript concludes by evaluating the different measurement techniques in view of the precision requirements described in this chapter. Additional requirements and considerations are discussed to assist with choosing an optical measurement technique for a given application.
Measurements of optical turbulence in the free atmosphere above Mount Maidanak in 2005-2007
NASA Astrophysics Data System (ADS)
Kornilov, V.; Ilyasov, S.; Vozyakova, O.; Tillaev, Yu.; Safonov, B.; Ibragimov, M.; Shatsky, N.; Egamberdiev, Sh.
2009-08-01
We present the results of our 2005-2007 campaign to measure the vertical distribution of optical turbulence above Mount Maidanak. The measurements were performed with the MASS instrument, a multi-aperture scintillation sensor that has been widely used for such studies in recent years at many observatories worldwide. Analysis of the data shows that the median seeing in the free atmosphere (at an altitude of 0.5 km and higher) is 0 ″46, while the isoplanatic angle is 2″.47. Given the large time constant (about 7 ms at good seeing), such conditions are favorable for using adaptive optics and interferometric measurements in the visible and near-infrared spectral ranges.
Suret, Pierre; Picozzi, Antonio; Randoux, Stéphane
2011-08-29
We study theoretically, numerically and experimentally the nonlinear propagation of partially incoherent optical waves in single mode optical fibers. We revisit the traditional treatment of the wave turbulence theory to provide a statistical kinetic description of the integrable scalar NLS equation. In spite of the formal reversibility and of the integrability of the NLS equation, the weakly nonlinear dynamics reveals the existence of an irreversible evolution toward a statistically stationary state. The evolution of the power spectrum of the field is characterized by the rapid growth of spectral tails that exhibit damped oscillations, until the whole spectrum ultimately reaches a steady state. The kinetic approach allows us to derive an analytical expression of the damped oscillations, which is found in agreement with the numerical simulations of both the NLS and kinetic equations. We report the experimental observation of this peculiar relaxation process of the integrable NLS equation.
Suret, Pierre; Picozzi, Antonio; Randoux, Stéphane
2011-08-29
We study theoretically, numerically and experimentally the nonlinear propagation of partially incoherent optical waves in single mode optical fibers. We revisit the traditional treatment of the wave turbulence theory to provide a statistical kinetic description of the integrable scalar NLS equation. In spite of the formal reversibility and of the integrability of the NLS equation, the weakly nonlinear dynamics reveals the existence of an irreversible evolution toward a statistically stationary state. The evolution of the power spectrum of the field is characterized by the rapid growth of spectral tails that exhibit damped oscillations, until the whole spectrum ultimately reaches a steady state. The kinetic approach allows us to derive an analytical expression of the damped oscillations, which is found in agreement with the numerical simulations of both the NLS and kinetic equations. We report the experimental observation of this peculiar relaxation process of the integrable NLS equation. PMID:21935152
SKA Weak Lensing I: Cosmological Forecasts and the Power of Radio-Optical Cross-Correlations
NASA Astrophysics Data System (ADS)
Harrison, Ian; Camera, Stefano; Zuntz, Joe; Brown, L.
2016-09-01
We construct forecasts for cosmological parameter constraints from weak gravitational lensing surveys involving the Square Kilometre Array (SKA). Considering matter content, dark energy and modified gravity parameters, we show that the first phase of the SKA (SKA1) can be competitive with other Stage III experiments such as the Dark Energy Survey (DES) and that the full SKA (SKA2) can potentially form tighter constraints than Stage IV optical weak lensing experiments, such as those that will be conducted with LSST, WFIRST-AFTA or Euclid-like facilities. Using weak lensing alone, going from SKA1 to SKA2 represents improvements by factors of ˜10 in matter, ˜10 in dark energy and ˜5 in modified gravity parameters. We also show, for the first time, the powerful result that comparably tight constraints (within ˜5%) for both Stage III and Stage IV experiments, can be gained from cross-correlating shear maps between the optical and radio wavebands, a process which can also eliminate a number of potential sources of systematic errors which can otherwise limit the utility of weak lensing cosmology.
Characterization of optical turbulence at the solar observatory at the Mount Teide, Tenerife
NASA Astrophysics Data System (ADS)
Sprung, Detlev; Sucher, Erik
2013-10-01
Optical turbulence represented by the structure function parameter of the refractive index Cn2 is regarded as one of the chief causes of image degradation of ground-based astronomical telescopes operating in visible or infrared wavebands. Especially, it affects the attainable spatial resolution. Therefore since the middle of September 2012 the optical turbulence has been monitored between two German solar telescopes at the Observatory in Tenerife /Canary Islands /Spain. It comprises the solar telescope GREGOR and the vacuum tower telescope VTT mounted on two 30 m high towers. Between the two towers at the level of the telescopes, Cn2 was measured using a Laser-Scintillometer SLS40 (Scintec, Rottenburg, Germany). The horizontal distance of the measurement path was 75 m. The first results of the measurements starting from the 15th September 2012 up to the end of December 2012 are presented and analyzed using simultaneous measured meteorological data of wind, temperature and humidity. Daily and seasonal variations are shown and discussed.
Spot detection accuracy analysis in turbulent channel for free space optical communication
NASA Astrophysics Data System (ADS)
Liu, Yan-Fei; Dai, Yong-Hong; Yu, Sheng-Lin; Xin, Shan; Chen, Jing; Ai, Yong
2015-10-01
Increasingly importance has been taken seriously for high frame rate CMOS camera to optical communication acquisition pointing and tacking (APT) system, with its compact structure, easy to developed and adapted to beacon light spot detection in atmospheric channel. As spot position accuracy directly determines the performance of space optical communication, it is very important to design a high precision spot center algorithm. Usually spot location algorithm uses gravity algorithm, shape center capturing algorithm or self-adaption threshold algorithm. In experiments we analyzed the characteristics of the spots which transmitted through atmospheric turbulence and studied light transmission characteristics in turbulent channel. We carried out a beacon light detection experiments in a distance of 3.4km, collected the beacon spots on CMOS camera and signal light power. We calculated spot position with two different algorithm and compared the calculation accuracy between field dispersive spot and ideal Gaussian laser spot. Experiment research show that, gravity center algorithm should be more suitable for beacon beam spot which accuracy can be improved about 1.3 pixels for a Gaussian spot. But the shape center algorithm has higher precision. The reasons were analyzed which made an important preparation for subsequent testing.
Libich, Jiri; Komanec, Matej; Zvanovec, Stanislav; Pesek, Petr; Popoola, Wasiu O; Ghassemlooy, Zabih
2015-02-01
This Letter presents original measurement results from an all-optical 10 Gbit/s free-space optics (FSO) relay link involving two FSO links and an all-optical switch. Considering the fact that reported analyses of relay links are dominated by analytical findings, the experimental results represent a vital resource for evaluating the performance of relay FSO links in the presence of atmospheric turbulence. Bit-error-rate (BER) performance of the relay system is tested for single and dual-hop links under several turbulence regimes. Furthermore, results from this measurement are used to ascertain real parameters of the outdoor links and to improve the accuracy of simulation results. Results show that using a dual-hop FSO link against a single FSO link could result in up to four orders of magnitude improvement in BER in the presence of atmospheric turbulence.
Single-shot observation of optical rogue waves in integrable turbulence using time microscopy
Suret, Pierre; Koussaifi, Rebecca El; Tikan, Alexey; Evain, Clément; Randoux, Stéphane; Szwaj, Christophe; Bielawski, Serge
2016-01-01
Optical fibres are favourable tabletop laboratories to investigate both coherent and incoherent nonlinear waves. In particular, exact solutions of the one-dimensional nonlinear Schrödinger equation such as fundamental solitons or solitons on finite background can be generated by launching periodic, specifically designed coherent waves in optical fibres. It is an open fundamental question to know whether these coherent structures can emerge from the nonlinear propagation of random waves. However the typical sub-picosecond timescale prevented—up to now—time-resolved observations of the awaited dynamics. Here, we report temporal ‘snapshots' of random light using a specially designed ‘time-microscope'. Ultrafast structures having peak powers much larger than the average optical power are generated from the propagation of partially coherent waves in optical fibre and are recorded with 250 femtoseconds resolution. Our experiment demonstrates the central role played by ‘breather-like' structures such as the Peregrine soliton in the emergence of heavy-tailed statistics in integrable turbulence. PMID:27713416
Single-shot observation of optical rogue waves in integrable turbulence using time microscopy
NASA Astrophysics Data System (ADS)
Suret, Pierre; Koussaifi, Rebecca El; Tikan, Alexey; Evain, Clément; Randoux, Stéphane; Szwaj, Christophe; Bielawski, Serge
2016-10-01
Optical fibres are favourable tabletop laboratories to investigate both coherent and incoherent nonlinear waves. In particular, exact solutions of the one-dimensional nonlinear Schrödinger equation such as fundamental solitons or solitons on finite background can be generated by launching periodic, specifically designed coherent waves in optical fibres. It is an open fundamental question to know whether these coherent structures can emerge from the nonlinear propagation of random waves. However the typical sub-picosecond timescale prevented--up to now--time-resolved observations of the awaited dynamics. Here, we report temporal `snapshots' of random light using a specially designed `time-microscope'. Ultrafast structures having peak powers much larger than the average optical power are generated from the propagation of partially coherent waves in optical fibre and are recorded with 250 femtoseconds resolution. Our experiment demonstrates the central role played by `breather-like' structures such as the Peregrine soliton in the emergence of heavy-tailed statistics in integrable turbulence.
Nelson, D.H.; Petrin, R.R.; MacKerrow, E.P.; Schmitt, M.J.; Foy, B.R.; Koskelo, A.C.; McVey, B.D.; Quick, C.R.; Porch, W.M.; Tiee, J.J.; Fite, C.B.; Archuleta, F.A.; Whitehead, M.C.; Walters, D.L.
1999-03-23
The measurement sensitivity of CO{sub 2} differential absorption lidar (DIAL) can be affected by a number of different processes. We have previously developed a Huygens-Fresnel wave optics propagation code to simulate the effects of two of these process: effects caused by beam propagation through atmospheric optical turbulence and effects caused by reflective speckle. Atmospheric optical turbulence affects the beam distribution of energy and phase on target. These effects include beam spreading, beam wander and scintillation which can result in increased shot-to-shot signal noise. In addition, reflective speckle alone has been shown to have a major impact on the sensitivity of CO{sub 2} DIAL. However, in real DIAL systems it is a combination of these phenomena, the interaction of atmospheric optical turbulence and reflective speckle, that influences the results. In this work, we briefly review a description of our model including the limitations along with previous simulation s of individual effects. The performance of our modified code with respect to experimental measurements affected by atmospheric optical turbulence and reflective speckle is examined. The results of computer simulations are directly compared with lidar measurements and show good agreement. In addition, advanced studies have been performed to demonstrate the utility of our model in assessing the effects for different lidar geometries on RMS noise and correlation ''size'' in the receiver plane.
Nelson, D.; Petrin, R.; MacKerrow, E.; Schmitt, M.; Foy, B.; Koskelo, A.; McVey, B.; Quick, C.; Porch, W.; Fite, C.; Archuleta, F.; Whitehead, M.; Tiee, J.; Walters, D.
1999-04-01
The measurement sensitivity of CO{sub 2} differential absorption lidar (DIAL) can be affected by a number of different processes. The authors have previously developed a Huygens-Fresnel wave optics propagation code to simulate the effects of two of these processes: effects caused by beam propagation through atmospheric optical turbulence and effects caused by reflective speckle. Atmospheric optical turbulence affects the beam distribution of energy and phase on target. These effects include beam spreading, beam wander and scintillation which can result in increased shot-to-shot signal noise. In addition, reflective speckle alone has been shown to have a major impact on the sensitivity of CO{sub 2} DIAL. However, in real DIAL systems it is a combination of these phenomena, the interaction of atmospheric optical turbulence and reflective speckle, that influences the results. The performance of the modified code with respect to experimental measurements affected by atmospheric optical turbulence and reflective speckle is examined. The results of computer simulations are directly compared with lidar measurements. The limitations of the model are also discussed. In addition, studies have been performed to determine the importance of key parameters in the simulation. The results of these studies and their impact on the overall results will be presented.
Investigation of anisoplanatic effect in adaptive optics for atmospheric turbulence correction
NASA Astrophysics Data System (ADS)
Li, Xinyang; Shao, Li; Hu, Shijie; Huang, Kui
2015-02-01
Laser Guide Star (LGS) is an artificial atmospheric turbulence probing source of adaptive optics (AO) for compensating for the wave-front error of interested object in real time, and for providing approximate diffraction-limited resolution recovery. Actually the unavoidable anisoplanatic error resulting from different light experience between the LGS and the object of interest through turbulent atmosphere will lead to an incomplete wave-front distortion compensation of the object. In this paper the statistics of anisoplanatic errors and their associated Zernike-modal variances have been systematically investigated for different LGS sources by means of numerical simulation, including Rayleigh LGS and Sodium LGS. The numerical results show that the probed wave-front expanded Zernike-modal decorrelation versus angular deviation between the LGS and the object of interest becomes much more sensitive for the higher altitude LGS. For minor angular deviations with LGS focal spots being still within the ray path from the object to the telescope, the reduction of the error from turbulence above the LGS altitude is still a leading cause to decrease the residual error variance after AO correction. However, for the greater angular deviations with LGS focal spots moving on the outside of the ray path from the object to the telescope, higher-altitude LGS could lead to an increasing residual error variance after AO complete correction with its wave-front as reference. At this point the adopted LGS operation mode and the AO system modal correction optimization should be taken into account for achieving a desired residual wave-front error.
A statistical model for road surface friction forecasting applying optical road weather measurements
NASA Astrophysics Data System (ADS)
Hippi, M.; Juga, I.; Nurmi, P.
2009-09-01
Road surface friction is defined as the grip between car tyre and underlying surface. Poor friction often plays a crucial role in wintertime car accidents. Friction can decrease dramatically during snowfall or when wet road surface temperature falls below zero. Even a thin layer of ice or snow can decrease friction substantially increasing the risk of accidents. Many studies have shown that road surface temperature, road conditions and friction can fluctuate dramatically within short distances under specific weather situations. Friction or grip can be improved with road maintenance activities like salting and gritting. Salting will melt the ice or snow layer, whereas gritting will improve the grip. Salting is effective only above -5C temperatures. Light snowfall together with low temperatures can result in very slippery driving conditions. Finnish Road Administration's observing network covers c. 500 road weather stations in Finland. Almost 100 of them are equipped with optical sensors (in winter 2008-2009). The number of optical sensors has increased remarkably during past few years. The optical measuring devices are Vaisala DSC111 sensors which measure the depth of water, snow and ice on the road surface and also produce an estimate of the state of road and prevailing friction. Observation data from road weather stations with optical sensors were collected from winter 2007/08, and a couple of representative (from a weather perspective) stations were selected for detailed statistical analysis. The purpose of the study was to find a statistical relationship between the observed values and, especially, the correlation between friction and other road weather parameters. Consequently, a model based on linear regression was developed. With the model friction being the dependent variable, the independent variables having highest correlations were the composite of ice and snow (water content) on the road, and the road surface temperature. In the case of a wet road
Hasegawa, Akira
2009-01-01
One important discovery in the twentieth century physics is the natural formation of a coherent or a well-ordered structure in continuous media, in contrary to degradation of the state as predicted earlier from the second law of thermodynamics. Here nonlinearity plays the essential role in its process. The discovery of soliton, a localized stable wave in a nonlinear and dispersive medium and the self-organization of fluid turbulence are of the major examples. A soliton is formed primarily in one-dimensional medium where the dispersion and nonlinearity play the essential role. Here the temporal evolution can be described by an infinite dimensional Hamiltonian system that is integrable. While a self-organization appears in an infinite dimensional non-Hamiltonian (or dissipative) system where more than two conservative quantities exist in the limit of no dissipation. In this manuscript, by showing examples of the optical soliton in dielectric fibers and self-organization of turbulence in a toroidal plasma in a magnetic field, we demonstrate these interesting discoveries. The manuscript is intended to describe these discoveries more on philosophical basis with some sacrifice on mathematical details so that the idea is conveyed to those in the wide area of sciences. PMID:19145067
NASA Astrophysics Data System (ADS)
Ghassemlooy, Zabih; Popoola, Wasiu O.; Ahmadi, Vahid; Leitgeb, Erich
In this paper, we analyse the error performance of transmitter/receiver array free-space optical (FSO) communication system employing binary phase shift keying (BPSK) subcarrier intensity modulation (SIM) in clear but turbulent atmospheric channel. Subcarrier modulation is employed to eliminate the need for adaptive threshold detector. Direct detection is employed at the receiver and each subcarrier is subsequently demodulated coherently. The effect of irradiance fading is mitigated with an array of lasers and photodetectors. The received signals are linearly combined using the optimal maximum ratio combining (MRC), the equal gain combining (EGC) and the selection combining (SelC). The bit error rate (BER) equations are derived considering additive white Gaussian noise and log normal intensity fluctuations. This work is part of the EU COST actions and EU projects.
Monitoring the optical turbulence in the surface layer at Dome C, Antarctica, with sonic anemometers
NASA Astrophysics Data System (ADS)
Aristidi, E.; Vernin, J.; Fossat, E.; Schmider, F.-X.; Travouillon, T.; Pouzenc, C.; Traullé, O.; Genthon, C.; Agabi, A.; Bondoux, E.; Challita, Z.; Mékarnia, D.; Jeanneaux, F.; Bouchez, G.
2015-12-01
The optical turbulence above Dome C in winter is mainly concentrated in the first tens of metres above the ground. Properties of this so-called surface layer (SL) were investigated during the period 2007-2012 by a set of sonic anemometers placed on a 45 m high tower. We present the results of this long-term monitoring of the refractive index structure constant C_n^2 within the SL, and confirm its thickness of 35 m. We give statistics of the contribution of the SL to the seeing and coherence time. We also investigate properties of large-scale structure functions of the temperature and show evidence of a second inertial zone at kilometric spatial scales.
Wu, Huiyun; Sheng, Shen; Huang, Zhisong; Zhao, Siqing; Wang, Hua; Sun, Zhenhai; Xu, Xiegu
2013-02-25
As a new attractive application of the vortex beams, power coupling of annular vortex beam propagating through a two- Cassegrain-telescope optical system in turbulent atmosphere has been investigated. A typical model of annular vortex beam propagating through a two-Cassegrain-telescope optical system is established, the general analytical expression of vortex beams with limited apertures and the analytical formulas for the average intensity distribution at the receiver plane are derived. Under the H-V 5/7 turbulence model, the average intensity distribution at the receiver plane and power coupling efficiency of the optical system are numerically calculated, and the influences of the optical topological charge, the laser wavelength, the propagation path and the receiver apertures on the power coupling efficiency are analyzed. These studies reveal that the average intensity distribution at the receiver plane presents a central dark hollow profile, which is suitable for power coupling by the Cassegrain telescope receiver. In the optical system with optimized parameters, power coupling efficiency can keep in high values with the increase of the propagation distance. Under the atmospheric turbulent conditions, great advantages of vortex beam in power coupling of the two-Cassegrain-telescope optical system are shown in comparison with beam without vortex.
Nelson, Matthew A.; Brown, Michael J.; Halverson, Scot A.; Bieringer, Paul E.; Annunzio, Andrew; Bieberbach, George; Meech, Scott
2015-09-25
We found that numerical-weather-prediction models are often used to supply the mean wind and turbulence fields for atmospheric transport and dispersion plume models as they provide dense horizontally- and vertically-resolved geographic coverage in comparison to typically sparse monitoring networks. Here, the Weather Research and Forecasting (WRF) model was run over the month-long period of the Joint Urban 2003 field campaign conducted in Oklahoma City and the simulated fields important to transport and dispersion models were compared to measurements from a number of sodars, tower-based sonic anemometers, and balloon soundings located in the greater metropolitan area. Time histories of computed wind speed, wind direction, turbulent kinetic energy (e), friction velocity (u* ), and reciprocal Obukhov length (1 / L) were compared to measurements over the 1-month field campaign. Vertical profiles of wind speed, potential temperature (θ ), and e were compared during short intensive operating periods. The WRF model was typically able to replicate the measured diurnal variation of the wind fields, but with an average absolute wind direction and speed difference of 35° and 1.9 m s^{-1} , respectively. Then, using the Mellor-Yamada-Janjic (MYJ) surface-layer scheme, the WRF model was found to generally underpredict surface-layer TKE but overpredict u* that was observed above a suburban region of Oklahoma City. The TKE-threshold method used by the WRF model’s MYJ surface-layer scheme to compute the boundary-layer height (h) consistently overestimated h derived from a θ gradient method whether using observed or modelled θ profiles.
Nelson, Matthew A.; Brown, Michael J.; Halverson, Scot A.; Bieringer, Paul E.; Annunzio, Andrew; Bieberbach, George; Meech, Scott
2015-09-25
We found that numerical-weather-prediction models are often used to supply the mean wind and turbulence fields for atmospheric transport and dispersion plume models as they provide dense horizontally- and vertically-resolved geographic coverage in comparison to typically sparse monitoring networks. Here, the Weather Research and Forecasting (WRF) model was run over the month-long period of the Joint Urban 2003 field campaign conducted in Oklahoma City and the simulated fields important to transport and dispersion models were compared to measurements from a number of sodars, tower-based sonic anemometers, and balloon soundings located in the greater metropolitan area. Time histories of computed windmore » speed, wind direction, turbulent kinetic energy (e), friction velocity (u* ), and reciprocal Obukhov length (1 / L) were compared to measurements over the 1-month field campaign. Vertical profiles of wind speed, potential temperature (θ ), and e were compared during short intensive operating periods. The WRF model was typically able to replicate the measured diurnal variation of the wind fields, but with an average absolute wind direction and speed difference of 35° and 1.9 m s-1 , respectively. Then, using the Mellor-Yamada-Janjic (MYJ) surface-layer scheme, the WRF model was found to generally underpredict surface-layer TKE but overpredict u* that was observed above a suburban region of Oklahoma City. The TKE-threshold method used by the WRF model’s MYJ surface-layer scheme to compute the boundary-layer height (h) consistently overestimated h derived from a θ gradient method whether using observed or modelled θ profiles.« less
NASA Astrophysics Data System (ADS)
Nelson, Matthew A.; Brown, Michael J.; Halverson, Scot A.; Bieringer, Paul E.; Annunzio, Andrew; Bieberbach, George; Meech, Scott
2016-02-01
Numerical-weather-prediction models are often used to supply the mean wind and turbulence fields for atmospheric transport and dispersion plume models as they provide dense horizontally- and vertically-resolved geographic coverage in comparison to typically sparse monitoring networks. Here, the Weather Research and Forecasting (WRF) model was run over the month-long period of the Joint Urban 2003 field campaign conducted in Oklahoma City and the simulated fields important to transport and dispersion models were compared to measurements from a number of sodars, tower-based sonic anemometers, and balloon soundings located in the greater metropolitan area. Time histories of computed wind speed, wind direction, turbulent kinetic energy ( e), friction velocity (u_*), and reciprocal Obukhov length (1 / L) were compared to measurements over the 1-month field campaign. Vertical profiles of wind speed, potential temperature (θ ), and e were compared during short intensive operating periods. The WRF model was typically able to replicate the measured diurnal variation of the wind fields, but with an average absolute wind direction and speed difference of 35°c and 1.9 m s^{-1}, respectively. Using the Mellor-Yamada-Janjic (MYJ) surface-layer scheme, the WRF model was found to generally underpredict surface-layer TKE but overpredict u_* that was observed above a suburban region of Oklahoma City. The TKE-threshold method used by the WRF model's MYJ surface-layer scheme to compute the boundary-layer height ( h) consistently overestimated h derived from a θ gradient method whether using observed or modelled θ profiles.
Cang, Ji; Liu, Xu
2011-09-01
The performance of partially coherent free-space optical links is investigated in the moderate to strong fluctuation regime of non-Kolmogorov turbulence. The expressions for large- and small-scale log-irradiance flux variance are obtained in non-Kolmogorov turbulence. By employing the gamma-gamma distribution of irradiance fluctuations, the effects of spatial coherence of the source, index of non-Kolmogorov spectrum, and size of the receiver on channel capacity for horizontal links are discussed. Results show that channel capacity presents fluctuating behaviors with the variation of alpha for longer links and increases for alpha values higher than 11/3.
Ma, Jing; Li, Kangning; Tan, Liying; Yu, Siyuan; Cao, Yubin
2015-09-01
The performances of satellite-to-ground downlink optical communications over Gamma-Gamma distributed atmospheric turbulence are studied for a coherent detection receiving system with spatial diversity. Maximum ratio combining (MRC) and selection combining (SC) techniques are considered as practical schemes to mitigate the atmospheric turbulence. Bit-error rate (BER) performances for binary phase-shift keying modulated coherent detection and outage probabilities are analyzed and compared for SC diversity using analytical results and for MRC diversity through an approximation method with different numbers of receiving aperture each with the same aperture area. To show the net diversity gain of a multiple aperture receiver system, BER performances and outage probabilities of MRC and SC multiple aperture receiver systems are compared with a single monolithic aperture with the same total aperture area (same total average incident optical power) for satellite-to-ground downlink optical communications. All the numerical results are verified by Monte-Carlo simulations. PMID:26368880
NASA Astrophysics Data System (ADS)
Li, Kangning; Ma, Jing; Belmonte, Aniceto; Tan, Liying; Yu, Siyuan
2015-12-01
The performances of satellite-to-ground downlink optical communications over Gamma-Gamma distributed turbulence are studied for a multiple-aperture receiver system. Equal gain-combining (EGC) and selection-combining (SC) techniques are considered as practical schemes to mitigate the atmospheric turbulence under thermal-noise-limited conditions. Bit-error rate (BER) performances for on-off keying-modulated direct detection and outage probabilities are analyzed and compared for SC diversity receptions using analytical results and for EGC diversity receptions through an approximation method. To show the net diversity gain of a multiple-aperture receiver system, BER performances and outage probabilities of EGC and SC receiver systems are compared with a single monolithic-aperture receiver system with the same total aperture area (same average total incident optical power) for satellite-to-ground downlink optical communications. All the numerical results are also verified by Monte-Carlo simulations.
Ma, Jing; Li, Kangning; Tan, Liying; Yu, Siyuan; Cao, Yubin
2015-09-01
The performances of satellite-to-ground downlink optical communications over Gamma-Gamma distributed atmospheric turbulence are studied for a coherent detection receiving system with spatial diversity. Maximum ratio combining (MRC) and selection combining (SC) techniques are considered as practical schemes to mitigate the atmospheric turbulence. Bit-error rate (BER) performances for binary phase-shift keying modulated coherent detection and outage probabilities are analyzed and compared for SC diversity using analytical results and for MRC diversity through an approximation method with different numbers of receiving aperture each with the same aperture area. To show the net diversity gain of a multiple aperture receiver system, BER performances and outage probabilities of MRC and SC multiple aperture receiver systems are compared with a single monolithic aperture with the same total aperture area (same total average incident optical power) for satellite-to-ground downlink optical communications. All the numerical results are verified by Monte-Carlo simulations.
Recent advances in turbulence prediction
NASA Astrophysics Data System (ADS)
Bhattacharya, Atreyee
2012-08-01
Turbulence in the upper troposphere and the lower stratosphere (8-14 kilometers in altitude) is a well-known aviation hazard; it is the major cause of injuries and occasional fatalities to passengers and crew members on commercial aircraft. Jet streams, thunderstorms, flow over mountains, and even the passage of other aircraft cause turbulence. However, the lack of precise observational data (which is still mainly from pilots reporting turbulence) and a clear understanding of the processes that cause turbulence make it difficult to accurately forecast aviation-scale turbulence. Hence, upper troposphere and lower stratosphere turbulence forecasting is an area of active research.
NASA Astrophysics Data System (ADS)
Nelson, Douglas H.; Petrin, Roger R.; MacKerrow, Edward P.; Schmitt, Mark J.; Quick, Charles R., Jr.; Zardecki, Andrew; Porch, William M.; Whitehead, Michael C.; Walters, Donald L.
1998-09-01
The measurement sensitivity of CO2 differential absorption LIDAR (DIAL) can be affected by a number of different processes. We will address the interaction of two of these processes: effects due to beam propagation through atmospheric turbulence and effects due to reflective speckle. Atmospheric turbulence affects the beam distribution of energy and phase on target. These effects include beam spreading, beam wander and scintillation which can result in increased shot-to-shot signal noise. In addition, reflective speckle alone has a major impact on the sensitivity of CO2 DIAL. The interaction of atmospheric turbulence and reflective speckle is of great importance in the performance of a DIAL system. A Huygens-Fresnel wave optics propagation code has previously been developed at the Naval Postgraduate School that models the effects of atmospheric turbulence as propagation through a series of phase screens with appropriate atmospheric statistical characteristics. This code has been modified to include the effects of reflective speckle. The performance of this modified code with respect to the combined effects of atmospheric turbulence and reflective speckle is examined. Results are compared with a combination of experimental data and analytical models.
Nelson, D.H.; Petrin, R.R.; MacKerrow, E.P.; Schmitt, M.J.; Quick, C.R.; Zardecki, A.; Porch, W.M.; Whitehead, M.; Walters, D.L.
1998-09-01
The measurement sensitivity of CO{sub 2} differential absorption LIDAR (DIAL) can be affected by a number of different processes. The authors address the interaction of two of these processes: effects due to beam propagation through atmospheric turbulence and effects due to reflective speckle. Atmospheric turbulence affects the beam distribution of energy and phase on target. These effects include beam spreading, beam wander and scintillation which can result in increased shot-to-shot signal noise. In addition, reflective speckle alone has a major impact on the sensitivity of CO{sub 2} DIAL. The interaction of atmospheric turbulence and reflective speckle is of great importance in the performance of a DIAL system. A Huygens-Fresnel wave optics propagation code has previously been developed at the Naval Postgraduate School that models the effects of atmospheric turbulence as propagation through a series of phase screens with appropriate atmospheric statistical characteristics. This code has been modified to include the effects of reflective speckle. The performance of this modified code with respect to the combined effects of atmospheric turbulence and reflective speckle is examined. Results are compared with a combination of experimental data and analytical models.
Berger, Thomas E.; Slater, Gregory; Hurlburt, Neal; Shine, Richard; Tarbell, Theodore; Title, Alan; Okamoto, Takenori J.; Ichimoto, Kiyoshi; Katsukawa, Yukio; Magara, Tetsuya; Suematsu, Yoshinori; Shimizu, Toshifumi
2010-06-20
Hinode/Solar Optical Telescope (SOT) observations reveal two new dynamic modes in quiescent solar prominences: large-scale (20-50 Mm) 'arches' or 'bubbles' that 'inflate' from below into prominences, and smaller-scale (2-6 Mm) dark turbulent upflows. These novel dynamics are related in that they are always dark in visible-light spectral bands, they rise through the bright prominence emission with approximately constant speeds, and the small-scale upflows are sometimes observed to emanate from the top of the larger bubbles. Here we present detailed kinematic measurements of the small-scale turbulent upflows seen in several prominences in the SOT database. The dark upflows typically initiate vertically from 5 to 10 Mm wide dark cavities between the bottom of the prominence and the top of the chromospheric spicule layer. Small perturbations on the order of 1 Mm or less in size grow on the upper boundaries of cavities to generate plumes up to 4-6 Mm across at their largest widths. All plumes develop highly turbulent profiles, including occasional Kelvin-Helmholtz vortex 'roll-up' of the leading edge. The flows typically rise 10-15 Mm before decelerating to equilibrium. We measure the flowfield characteristics with a manual tracing method and with the Nonlinear Affine Velocity Estimator (NAVE) 'optical flow' code to derive velocity, acceleration, lifetime, and height data for several representative plumes. Maximum initial speeds are in the range of 20-30 km s{sup -1}, which is supersonic for a {approx}10,000 K plasma. The plumes decelerate in the final few Mm of their trajectories resulting in mean ascent speeds of 13-17 km s{sup -1}. Typical lifetimes range from 300 to 1000 s ({approx}5-15 minutes). The area growth rate of the plumes (observed as two-dimensional objects in the plane of the sky) is initially linear and ranges from 20,000 to 30,000 km{sup 2} s{sup -1} reaching maximum projected areas from 2 to 15 Mm{sup 2}. Maximum contrast of the dark flows relative to
Study on Atmospheric Optical Turbulence above Mount Shatdzhatmaz in 2007-2013
NASA Astrophysics Data System (ADS)
Kornilov, V.; Safonov, B.; Kornilov, M.; Shatsky, N.; Voziakova, O.; Potanin, S.; Gorbunov, I.; Senik, V.; Cheryasov, D.
2014-05-01
We present the results of the atmospheric optical turbulence (OT) measurements performed atop Mount Shatdzhatmaz at the installation site of new 2.5 m telescope of the Sternberg Astronomical Institute. Nearly 300,000 vertical OT profiles from the ground up to an altitude of 23 km were obtained in the period of 2007 November-2013 June 2 with the combined multiaperture scintillation sensor (MASS) and differential image motion monitor (DIMM) instrument. The medians of the main OT characteristics, computed over the whole dataset are as follows: the integral seeing β0 = 0.96'', the free-atmosphere seeing βFA = 0.43'', and the isoplanatic angle θ0 = 2.07''. The median atmospheric time constant is τ0 = 6.57 ms. The revealed long-term variability of these parameters on scales of months and years implies the need to take it into account in astroclimatic campaign planning. For example, the annual variation in the monthly θ0 estimate amounts to 30%, while the time constant τ0 changes by a factor of 2.5. Evaluation of the potential of Mount Shatdzhatmaz in terms of high angular resolution observations indicates that in October-November, this site is as good as the best of studied summits in the world.
Edwards, M J; Hansen, J; Miles, A R; Froula, D; Gregori, G; Glenzer, S; Edens, A; Dittmire, T
2005-02-08
The possibility of studying compressible turbulent flows using gas targets driven by high power lasers and diagnosed with optical techniques is investigated. The potential advantage over typical laser experiments that use solid targets and x-ray diagnostics is more detailed information over a larger range of spatial scales. An experimental system is described to study shock - jet interactions at high Mach number. This consists of a mini-chamber full of nitrogen at a pressure {approx} 1 atms. The mini-chamber is situated inside a much larger vacuum chamber. An intense laser pulse ({approx}100J in {approx} 5ns) is focused on to a thin {approx} 0.3{micro}m thick silicon nitride window at one end of the mini-chamber. The window acts both as a vacuum barrier, and laser entrance hole. The ''explosion'' caused by the deposition of the laser energy just inside the window drives a strong blast wave out into the nitrogen atmosphere. The spherical shock expands and interacts with a jet of xenon introduced though the top of the mini-chamber. The Mach number of the interaction is controlled by the separation of the jet from the explosion. The resulting flow is visualized using an optical schlieren system using a pulsed laser source at a wavelength of 0.53 {micro}m. The technical path leading up to the design of this experiment is presented, and future prospects briefly considered. Lack of laser time in the final year of the project severely limited experimental results obtained using the new apparatus.
NASA Astrophysics Data System (ADS)
Stoneback, Matthew; Ishimaru, Akira; Reinhardt, Colin; Kuga, Yasuo
2013-03-01
We consider an optical beam propagated through the atmosphere and incident on an object causing a temperature rise. In clear air, the physical characteristics of the optical beam transmitted to the object surface are influenced primarily by the effect of atmospheric turbulence, which can be significant near the ground or ocean surface. We use a statistical model to quantify the expected power transfer through turbulent atmosphere and provide guidance toward the threshold of thermal blooming for the considered scenarios. The bulk thermal characteristics of the materials considered are used in a thermal diffusion model to determine the net temperature rise at the object surface due to the incident optical beam. These results of the study are presented in graphical form and are of particular interest to operators of high power laser systems operating over large distances through the atmosphere. Numerical examples include a CO2 laser (λ=10.6 μm) with: aperture size of 5 cm, varied pulse duration, and propagation distance of 0.5 km incident on 0.1-mm copper, 10-mm polyimide, 1-mm water, and 10-mm glass/resin composite targets. To assess the effect of near ground/ocean laser propagation, we compare turbulent (of varying degrees) and nonturbulent atmosphere.
Toselli, Italo; Korotkova, Olga
2015-06-01
We generalize a recently introduced model for nonclassic turbulent spatial power spectrum involving anisotropy along two mutually orthogonal axes transverse to the direction of beam propagation by including two scale-dependent weighting factors for these directions. Such a turbulent model may be pertinent to atmospheric fluctuations in the refractive index in stratified regions well above the boundary layer and employed for air-air communication channels. When restricting ourselves to an unpolarized, coherent Gaussian beam and a weak turbulence regime, we examine the effects of such a turbulence type on the OOK FSO link performance by including the results on scintillation flux, probability of fade, SNR, and BERs.
Forecasting seeing and parameters of long-exposure images by means of ARIMA
NASA Astrophysics Data System (ADS)
Kornilov, Matwey V.
2016-02-01
Atmospheric turbulence is the one of the major limiting factors for ground-based astronomical observations. In this paper, the problem of short-term forecasting seeing is discussed. The real data that were obtained by atmospheric optical turbulence (OT) measurements above Mount Shatdzhatmaz in 2007-2013 have been analysed. Linear auto-regressive integrated moving average (ARIMA) models are used for the forecasting. A new procedure for forecasting the image characteristics of direct astronomical observations (central image intensity, full width at half maximum, radius encircling 80 % of the energy) has been proposed. Probability density functions of the forecast of these quantities are 1.5-2 times thinner than the respective unconditional probability density functions. Overall, this study found that the described technique could adequately describe temporal stochastic variations of the OT power.
Cang, Ji; Liu, Xu
2011-09-26
Based on the generalized spectral model for non-Kolmogorov atmospheric turbulence, analytic expressions of the scintillation index (SI) are derived for plane, spherical optical waves and a partially coherent Gaussian beam propagating through non-Kolmogorov turbulence horizontally in the weak fluctuation regime. The new expressions relate the SI to the finite turbulence inner and outer scales, spatial coherence of the source and spectral power-law and then used to analyze the effects of atmospheric condition and link length on the performance of wireless optical communication links.
NASA Astrophysics Data System (ADS)
Rampy, Rachel A.
Since Galileo's first telescope some 400 years ago, astronomers have been building ever-larger instruments. Yet only within the last two decades has it become possible to realize the potential angular resolutions of large ground-based telescopes, by using adaptive optics (AO) technology to counter the blurring effects of Earth's atmosphere. And only within the past decade have the development of laser guide stars (LGS) extended AO capabilities to observe science targets nearly anywhere in the sky. Improving turbulence simulation strategies and LGS are the two main topics of my research. In the first part of this thesis, I report on the development of a technique for manufacturing phase plates for simulating atmospheric turbulence in the laboratory. The process involves strategic application of clear acrylic paint onto a transparent substrate. Results of interferometric characterization of the plates are described and compared to Kolmogorov statistics. The range of r0 (Fried's parameter) achieved thus far is 0.2--1.2 mm at 650 nm measurement wavelength, with a Kolmogorov power law. These plates proved valuable at the Laboratory for Adaptive Optics at University of California, Santa Cruz, where they have been used in the Multi-Conjugate Adaptive Optics testbed, during integration and testing of the Gemini Planet Imager, and as part of the calibration system of the on-sky AO testbed named ViLLaGEs (Visible Light Laser Guidestar Experiments). I present a comparison of measurements taken by ViLLaGEs of the power spectrum of a plate and the real sky turbulence. The plate is demonstrated to follow Kolmogorov theory well, while the sky power spectrum does so in a third of the data. This method of fabricating phase plates has been established as an effective and low-cost means of creating simulated turbulence. Due to the demand for such devices, they are now being distributed to other members of the AO community. The second topic of this thesis pertains to understanding and
NASA Astrophysics Data System (ADS)
Rampy, Rachel A.
Since Galileo's first telescope some 400 years ago, astronomers have been building ever-larger instruments. Yet only within the last two decades has it become possible to realize the potential angular resolutions of large ground-based telescopes, by using adaptive optics (AO) technology to counter the blurring effects of Earth's atmosphere. And only within the past decade have the development of laser guide stars (LGS) extended AO capabilities to observe science targets nearly anywhere in the sky. Improving turbulence simulation strategies and LGS are the two main topics of my research. In the first part of this thesis, I report on the development of a technique for manufacturing phase plates for simulating atmospheric turbulence in the laboratory. The process involves strategic application of clear acrylic paint onto a transparent substrate. Results of interferometric characterization of the plates are described and compared to Kolmogorov statistics. The range of r0 (Fried's parameter) achieved thus far is 0.2--1.2 mm at 650 nm measurement wavelength, with a Kolmogorov power law. These plates proved valuable at the Laboratory for Adaptive Optics at University of California, Santa Cruz, where they have been used in the Multi-Conjugate Adaptive Optics testbed, during integration and testing of the Gemini Planet Imager, and as part of the calibration system of the on-sky AO testbed named ViLLaGEs (Visible Light Laser Guidestar Experiments). I present a comparison of measurements taken by ViLLaGEs of the power spectrum of a plate and the real sky turbulence. The plate is demonstrated to follow Kolmogorov theory well, while the sky power spectrum does so in a third of the data. This method of fabricating phase plates has been established as an effective and low-cost means of creating simulated turbulence. Due to the demand for such devices, they are now being distributed to other members of the AO community. The second topic of this thesis pertains to understanding and
NASA Astrophysics Data System (ADS)
Miville-Deschênes, M.-A.; Duc, P.-A.; Marleau, F.; Cuillandre, J.-C.; Didelon, P.; Gwyn, S.; Karabal, E.
2016-08-01
Diffuse Galactic light has been observed in the optical since the 1930s. We propose that, when observed in the optical with deep imaging surveys, it can be used as a tracer of the turbulent cascade in the diffuse interstellar medium (ISM), down to scales of about 1 arcsec. Here we present a power spectrum analysis of the dust column density of a diffuse cirrus at high Galactic latitude (l ≈ 198°, b ≈ 32°) as derived from the combination of a MegaCam g-band image, obtained as part of the MATLAS large programme at the CFHT, with Planck radiance and WISE 12 μm data. The combination of these three datasets have allowed us to compute the density power spectrum of the H i over scales of more than three orders of magnitude. We found that the density field is well described by a single power law over scales ranging from 0.01 to 50 pc. The exponent of the power spectrum, γ = -2.9 ± 0.1, is compatible with what is expected for thermally bi-stable and turbulent H i. We did not find any steepening of the power spectrum at small scales indicating that the typical scale at which turbulent energy is dissipated in this medium is smaller than 0.01 pc. The ambipolar diffusion scenario that is usually proposed as the main dissipative agent, is consistent with our data only if the density of the cloud observed is higher than the typical values assumed for the cold neutral medium gas. We discuss the new avenue offered by deep optical imaging surveys for the study of the low density ISM structure and turbulence.
Deng, Peng; Kavehrad, Mohsen; Liu, Zhiwen; Zhou, Zhou; Yuan, Xiuhua
2013-07-01
We study the average capacity performance for multiple-input multiple-output (MIMO) free-space optical (FSO) communication systems using multiple partially coherent beams propagating through non-Kolmogorov strong turbulence, assuming equal gain combining diversity configuration and the sum of multiple gamma-gamma random variables for multiple independent partially coherent beams. The closed-form expressions of scintillation and average capacity are derived and then used to analyze the dependence on the number of independent diversity branches, power law α, refractive-index structure parameter, propagation distance and spatial coherence length of source beams. Obtained results show that, the average capacity increases more significantly with the increase in the rank of MIMO channel matrix compared with the diversity order. The effect of the diversity order on the average capacity is independent of the power law, turbulence strength parameter and spatial coherence length, whereas these effects on average capacity are gradually mitigated as the diversity order increases. The average capacity increases and saturates with the decreasing spatial coherence length, at rates depending on the diversity order, power law and turbulence strength. There exist optimal values of the spatial coherence length and diversity configuration for maximizing the average capacity of MIMO FSO links over a variety of atmospheric turbulence conditions.
NASA Astrophysics Data System (ADS)
Molin, S.; Dolfi, D.; Doisy, M.; Seraudie, A.; Arnal, D.; Coustols, E.; Mandle, J.
2010-09-01
We demonstrate the feasibility of detection of the nature (laminar/turbulent/transitional) of the aerodynamic boundary layer of a profile of a wing aircraft model, using a Distributed FeedBack (DFB) Fiber Laser as optical fiber sensor. Signals to be measured are pressure variations : ΔP~1Pa at few 100Hz in the laminar region and ΔP~10Pa at few kHz in the turbulent region. Intermittent regime occurring in-between these two regions (transition) is characterized by turbulent bursts in laminar flow. Relevant pressure variations have been obtained in a low-speed research-type wind tunnel of ONERA Centre of Toulouse. In order to validate the measurements, a "classical" hot film sensor, the application and use of which have been formerly developed and validated by ONERA, has been placed at the neighborhood of the fiber sensor. The hot film allows measurement of the boundary layer wall shear stress whose characteristics are a well known signature of the boundary layer nature (laminar, intermittent or turbulent) [1]. In the three regimes, signals from the fiber sensor and the hot film sensor are strongly correlated, which allows us to conclude that a DFB fiber laser sensor is a good candidate for detecting the boundary layer nature, and thus for future integration in an aircraft wing. The work presented here has been realized within the framework of "Clean Sky", a Joint Technology Initiative of the European Union.
El-Wakeel, Amr S; Mohammed, Nazmi A; Aly, Moustafa H
2016-09-10
In this work, a free space optical communication (FSO) link is proposed and utilized to explore and evaluate the FSO link performance under the joint occurrence of the atmospheric scattering and turbulence phenomena for 850 and 1550 nm operation. Diffraction and nondiffraction-limited systems are presented and evaluated for both wavelengths' operation, considering far-field conditions under different link distances. Bit error rate, pointing error angles, beam divergence angles, and link distance are the main performance indicators that are used to evaluate and compare the link performance under different system configurations and atmospheric phenomena combinations. A detailed study is performed to provide the merits of this work. For both far-field diffraction-limited and nondiffraction-limited systems, it is concluded that 1550 nm system operation is better than 850 nm for the whole presented joint occurrences of atmospheric scattering and turbulence.
El-Wakeel, Amr S; Mohammed, Nazmi A; Aly, Moustafa H
2016-09-10
In this work, a free space optical communication (FSO) link is proposed and utilized to explore and evaluate the FSO link performance under the joint occurrence of the atmospheric scattering and turbulence phenomena for 850 and 1550 nm operation. Diffraction and nondiffraction-limited systems are presented and evaluated for both wavelengths' operation, considering far-field conditions under different link distances. Bit error rate, pointing error angles, beam divergence angles, and link distance are the main performance indicators that are used to evaluate and compare the link performance under different system configurations and atmospheric phenomena combinations. A detailed study is performed to provide the merits of this work. For both far-field diffraction-limited and nondiffraction-limited systems, it is concluded that 1550 nm system operation is better than 850 nm for the whole presented joint occurrences of atmospheric scattering and turbulence. PMID:27661363
NASA Astrophysics Data System (ADS)
Ma, Jing; Li, Kangning; Tan, Liying; Yu, Siyuan; Cao, Yubin
2016-02-01
The error rate performances and outage probabilities of free-space optical (FSO) communications with spatial diversity are studied for Gamma-Gamma turbulent environments. Equal gain combining (EGC) and selection combining (SC) diversity are considered as practical schemes to mitigate turbulence. The exact bit-error rate (BER) expression and outage probability are derived for direct detection EGC multiple aperture receiver system. BER performances and outage probabilities are analyzed and compared for different number of sub-apertures each having aperture area A with EGC and SC techniques. BER performances and outage probabilities of a single monolithic aperture and multiple aperture receiver system with the same total aperture area are compared under thermal-noise-limited and background-noise-limited conditions. It is shown that multiple aperture receiver system can greatly improve the system communication performances. And these analytical tools are useful in providing highly accurate error rate estimation for FSO communication systems.
Blob identification algorithms applied to laser speckle to characterize optical turbulence
NASA Astrophysics Data System (ADS)
Cauble, Galen D.; Wayne, David T.
2015-09-01
Laser beam speckle resulting from atmospheric turbulence contains information about the propagation channel. The number and size of the speckle cells can be used to infer the spatial coherence and thus the Cn2 along a path. The challenge with this technique is the rapidly evolving speckle pattern and non-uniformity of the speckle cells. In this paper we investigate modern blob counting techniques used in biology, microscopy, and medical imaging. These methods are then applied to turbulent speckle images to estimate the number and size of the speckle cells. Speckle theory is reviewed for different beam types and different regimes of turbulence. Algorithms are generated to calculate path Cn2 from speckle information and path geometry. The algorithms are tested on speckle images from experimental data collected over a turbulent 1km path and compared to Cn2 measurements collected in parallel.
Boluda-Ruiz, Rubén; García-Zambrana, Antonio; Castillo-Vázquez, Carmen; Castillo-Vázquez, Beatriz
2014-06-30
In this paper, a novel adaptive cooperative protocol with multiple relays using detect-and-forward (DF) over atmospheric turbulence channels with pointing errors is proposed. The adaptive DF cooperative protocol here analyzed is based on the selection of the optical path, source-destination or different source-relay links, with a greater value of fading gain or irradiance, maintaining a high diversity order. Closed-form asymptotic bit error-rate (BER) expressions are obtained for a cooperative free-space optical (FSO) communication system with Nr relays, when the irradiance of the transmitted optical beam is susceptible to either a wide range of turbulence conditions, following a gamma-gamma distribution of parameters α and β, or pointing errors, following a misalignment fading model where the effect of beam width, detector size and jitter variance is considered. A greater robustness for different link distances and pointing errors is corroborated by the obtained results if compared with similar cooperative schemes or equivalent multiple-input multiple-output (MIMO) systems. Simulation results are further demonstrated to confirm the accuracy and usefulness of the derived results. PMID:24977911
Boluda-Ruiz, Rubén; García-Zambrana, Antonio; Castillo-Vázquez, Carmen; Castillo-Vázquez, Beatriz
2014-06-30
In this paper, a novel adaptive cooperative protocol with multiple relays using detect-and-forward (DF) over atmospheric turbulence channels with pointing errors is proposed. The adaptive DF cooperative protocol here analyzed is based on the selection of the optical path, source-destination or different source-relay links, with a greater value of fading gain or irradiance, maintaining a high diversity order. Closed-form asymptotic bit error-rate (BER) expressions are obtained for a cooperative free-space optical (FSO) communication system with Nr relays, when the irradiance of the transmitted optical beam is susceptible to either a wide range of turbulence conditions, following a gamma-gamma distribution of parameters α and β, or pointing errors, following a misalignment fading model where the effect of beam width, detector size and jitter variance is considered. A greater robustness for different link distances and pointing errors is corroborated by the obtained results if compared with similar cooperative schemes or equivalent multiple-input multiple-output (MIMO) systems. Simulation results are further demonstrated to confirm the accuracy and usefulness of the derived results.
Cui, Linyan; Xue, Bindang; Zheng, Shiling; Xue, Wenfang; Bai, Xiangzhi; Cao, Xiaoguang; Zhou, Fugen
2012-06-01
A new atmospheric spectral model and expressions of irradiance scintillation index are derived theoretically for optical wave propagating through moderate-to-strong non-Kolmogorov turbulence. They are developed under Andrews' assumption that small-scale irradiance fluctuations are modulated by large-scale irradiance fluctuations of the wave, and the geometrical optics approximation is adopted for mathematical development. A wide range of turbulence strength is considered instead of a limited range for weak turbulence. The atmospheric spectral model has a spectral power law value in the range of 3 to 4 instead of the standard power law value of 11/3. Numerical calculations are conducted to analyze the influences of spectral power law and turbulence strength.
Wang, Yao; Basu, Sukanta
2016-05-15
In this Letter, an artificial neural network (ANN) approach is proposed for the estimation of optical turbulence (Cn2) in the atmospheric surface layer. Five routinely available meteorological variables are used as the inputs. Observed Cn2 data near the Mauna Loa Observatory, Hawaii are utilized for validation. The proposed approach has demonstrated its prowess by capturing the temporal evolution of Cn2 remarkably well. More interestingly, this ANN approach is found to outperform a widely used similarity theory-based conventional formulation for all the prevalent atmospheric conditions (including strongly stratified conditions).
Wang, Yao; Basu, Sukanta
2016-05-15
In this Letter, an artificial neural network (ANN) approach is proposed for the estimation of optical turbulence (Cn2) in the atmospheric surface layer. Five routinely available meteorological variables are used as the inputs. Observed Cn2 data near the Mauna Loa Observatory, Hawaii are utilized for validation. The proposed approach has demonstrated its prowess by capturing the temporal evolution of Cn2 remarkably well. More interestingly, this ANN approach is found to outperform a widely used similarity theory-based conventional formulation for all the prevalent atmospheric conditions (including strongly stratified conditions). PMID:27176996
NASA Astrophysics Data System (ADS)
Zhao, Shengmei; Wang, Le; Zou, Li; Gong, Longyan; Cheng, Weiwen; Zheng, Baoyu; Chen, Hanwu
2016-10-01
A free-space optical (FSO) communication link with multiplexed orbital angular momentum (OAM) modes has been demonstrated to largely enhance the system capacity without a corresponding increase in spectral bandwidth, but the performance of the link is unavoidably degraded by atmospheric turbulence (AT). In this paper, we propose a turbulence mitigation scheme to improve AT tolerance of the OAM-multiplexed FSO communication link using both channel coding and wavefront correction. In the scheme, we utilize a wavefront correction method to mitigate the phase distortion first, and then we use a channel code to further correct the errors in each OAM mode. The improvement of AT tolerance is discussed over the performance of the link with or without channel coding/wavefront correction. The results show that the bit error rate performance has been improved greatly. The detrimental effect of AT on the OAM-multiplexed FSO communication link could be removed by the proposed scheme even in the relatively strong turbulence regime, such as Cn2 = 3.6 ×10-14m - 2 / 3.
Performance analysis for LDPC-coded optical PPM communication system in weak turbulence
NASA Astrophysics Data System (ADS)
Wang, Hongxing; Su, Yanqin; Zhang, Guangyi; Zhang, Tieying
2007-11-01
Atmosphere Laser Communication (ALC) has the great capability, the better quality of anti-jamming and security, so ALC is adapt to the military application in particular. But because ALC's channel is atmosphere, ALC will be influenced by Atmospheric fading and turbulence, which reduce communication reliability. As a result, studying the suitable modulation and coding becomes the important problems for ALC. From these, people has put forward plenty of modulation and coding technologies, including On-off keying (OOK), pulse position modulation (PPM), digital pulse interval modulation (DPIM), dual-header pulse interval modulation(DHPIM) and so on. Among these, the mean transmit power and error symbol rate of PPM are all less than the others, so PPM has some applied advantage. People has also studied channel coding technology for PPM in ALC, George Stephen Mecherle applied RS code to PPM and analyzed error bit performance in 1986, Jon Hamkins and Meera Srinivasan analyzed the error bit rate of applying Turbo code to PPM through APD detecting in 1998, J. Hamkins analyzed the error bit performance of 256-ray PPM for Turbo code in 1999, and HU Hongfei analyzed the combined mode and applying approach of binary LDPC and multi-system PPM. But all of these have not involved the influence of atmosphere weak turbulence. The paper introduces LDPC as the channel code to ALC, and combines with PPM, discusses the error performance of LDPC in weak turbulence, then compares the performance in weak turbulence, Gauss channel and uncoded system. The emulation results indicate that the LDPC-coded performance of Gauss channel is better than that in weak turbulence channel, and introducing LDPC can efficiently improve the error performance in Gauss channel and weak turbulence channel, which has some applied value.
NASA Technical Reports Server (NTRS)
Kalnay, Eugenia; Dalcher, Amnon
1987-01-01
It is shown that it is possible to predict the skill of numerical weather forecasts - a quantity which is variable from day to day and region to region. This has been accomplished using as predictor the dispersion (measured by the average correlation) between members of an ensemble of forecasts started from five different analyses. The analyses had been previously derived for satellite-data-impact studies and included, in the Northern Hemisphere, moderate perturbations associated with the use of different observing systems. When the Northern Hemisphere was used as a verification region, the prediction of skill was rather poor. This is due to the fact that such a large area usually contains regions with excellent forecasts as well as regions with poor forecasts, and does not allow for discrimination between them. However, when regional verifications were used, the ensemble forecast dispersion provided a very good prediction of the quality of the individual forecasts.
Xue, Bindang; Cui, Linyan; Xue, Wenfang; Bai, Xiangzhi; Zhou, Fugen
2011-05-01
A new generalized modified atmospheric spectral model is derived theoretically for wave propagating through non-Kolmogorov turbulence, which has been reported recently by increasing experimental evidence and theoretical investigation. The generalized, modified atmospheric spectrum considers finite turbulence inner and outer scales and has a spectral power law value in the range of 3 to 5 instead of the standard power law value of 11/3. When the inner scale and outer scale are set to zero and infinity, respectively, this spectral model is reduced to the classical non-Kolmogorov spectrum.
Optical remote sensing a potential tool for forecasting malaria in Orissa, India
NASA Astrophysics Data System (ADS)
Nizamuddin, Mohammad; Akhand, Kawsar; Roytman, Leonid; Kogan, Felix; Goldberg, Mitch
2013-05-01
Information on current and anticipated moisture and thermal condition from satellite data represents a source of affordable yet careful information for malaria forecasters to implement and control of epidemic. During the last decades Orissa state in India suffered from highest level of malaria incidence. This situation requires frequent monitoring of environmental conditions and dynamics of malaria occurrence. During 1985 to 2004 the NOAA AVHRR global vegetation index (GVI) dataset and its vegetation health (VH) have been studied and used as proxy for malaria fluctuation. This paper discusses applications of VH for early detecting and monitoring malaria incidence in Orissa. A significant relationship between satellite data and annual malaria incidences is found at least three months before the major malaria transmission period.
Yura, Harold T; Fields, Renny A
2011-06-20
Level crossing statistics is applied to the complex problem of atmospheric turbulence-induced beam wander for laser propagation from ground to space. A comprehensive estimate of the single-axis wander angle temporal autocorrelation function and the corresponding power spectrum is used to develop, for the first time to our knowledge, analytic expressions for the mean angular level crossing rate and the mean duration of such crossings. These results are based on an extension and generalization of a previous seminal analysis of the beam wander variance by Klyatskin and Kon. In the geometrical optics limit, we obtain an expression for the beam wander variance that is valid for both an arbitrarily shaped initial beam profile and transmitting aperture. It is shown that beam wander can disrupt bidirectional ground-to-space laser communication systems whose small apertures do not require adaptive optics to deliver uniform beams at their intended target receivers in space. The magnitude and rate of beam wander is estimated for turbulence profiles enveloping some practical laser communication deployment options and suggesting what level of beam wander effects must be mitigated to demonstrate effective bidirectional laser communication systems.
NASA Astrophysics Data System (ADS)
Jiang, Chen; Guo, Yinbiao; Yang, Qingqing; Han, Chunguang
2010-10-01
A new approach based on an artificial neural network (ANN) was presented for the prediction of machining precision of optical aspheric grinding. The ANN model is based on Globally Convergent Adaptive Quick Back Propagation algorithm (GCAOBP). A genetic algorithm (GA) was then applied to the trained ANN model to predict the gridding precision. The integrated GCAOBP-GA algorithm was successful in predicting the Root Mean Square of profile error (RMS) of optical aspheric workpiece in parallel grinding method using machining parameters. The results of experiments have shown that RMS of machined workpiece in parallel grinding can be predicted effectively through this approach.
NASA Astrophysics Data System (ADS)
Yamada, Hiromasa; Yamagishi, Yusuke; Sakakita, Hajime; Tsunoda, Syuichiro; Kasahara, Jiro; Fujiwara, Masanori; Kato, Susumu; Itagaki, Hirotomo; Kim, Jaeho; Kiyama, Satoru; Fujiwara, Yutaka; Ikehara, Yuzuru; Ikehara, Sanae; Nakanishi, Hayao; Shimizu, Nobuyuki
2016-01-01
To understand the mechanism of turbulent enhancement phenomena of a neutral gas flow containing plasma ejected from the nozzle of plasma equipment, the schlieren optical method was performed to visualize the neutral gas behavior. It was confirmed that the turbulent starting point became closer to the nozzle exit, as the amplitude of discharge voltage (electric field) increased. To study the effect of electric field on turbulent enhancement, two sets of external electrodes were arranged in parallel, and the gas from the nozzle was allowed to flow between the upper and lower electrodes. It was found that the neutral gas flow was bent, and the bending angle increased as the amplitude of the external electric field increased. The results obtained using a simple model analysis roughly coincide with experimental data. These results indicate that momentum transport from drifted ions induced by the electric field to neutral particles is an important factor that enhances turbulence.
Optical Remote-sensing Monitoring and Forecasting of Atmospheric Pollution in Huaibei Area, China
NASA Astrophysics Data System (ADS)
Li, Su-wen; Xie, Pin-hua; Jiang, En-hua; Zhang, Yong; Dai, Hai-feng
2012-12-01
Huaibei is an energy city. Coal as the primary energy consumption brings a large number of regional pollution in Huaibei area. Differential optical absorption spectroscopy (DOAS) as optical remote sensing technology has been applied to monitor regional average concentrations and inventory of nitrogen dioxide, sulfur dioxide and ozone. DOAS system was set up and applied to monitor the main air pollutants in Huaibei area. Monitoring data were obtained from 7 to 28 August, 2011. Monitoring results show measurements in controlling pollution are effective, and emissions of pollutants are up to the national standard in Huaibei area. Prediction model was also created to track changing trend of pollutions. These will provide raw data support for effective evaluation of environmental quality in Huaibei area.
Influence of atmospheric turbulence on the uplink propagation in an optical time transfer
NASA Astrophysics Data System (ADS)
Fridelance, Patricia
1997-08-01
The time transfer by laser link experiment T2L2 aims for a precision of 60 ps, which could be degraded by the atmospheric turbulence because of the strong variations of the photon number received by the satellite detector, from a measurement to another. The light intensity fluctuations in the satellite plane are estimated for the planned situation for which the beam radius at the atmosphere exit is significantly larger than the coherence length. Such speckle-type fluctuations are experimentally studied.
Influence of atmospheric turbulence on the uplink propagation in an optical time transfer.
Fridelance, P
1997-08-20
The time transfer by laser link experiment T2L2 aims for a precision of 60 ps, which could be degraded by the atmospheric turbulence because of the strong variations of the photon number received by the satellite detector, from a measurement to another. The light intensity fluctuations in the satellite plane are estimated for the planned situation for which the beam radius at the atmosphere exit is significantly larger than the coherence length. Such speckle-type fluctuations are experimentally studied.
Temporal decorrelation of optical turbulence as a function of altitude in the atmosphere
NASA Astrophysics Data System (ADS)
Avilés, J. L.; Avila, R.; Carrasco, E.; Sánchez, L. J.; Chun, M.; Butterley, T.; Wilson, R.; Urbiola, F. J.
2016-05-01
Here, we propose a new method to evaluate the Taylor's frozen-flow hypothesis with the Generalized SCIntillation Detection And Ranging technique (G-SCIDAR). Unlike the work previously reported in the literature, we take into consideration the wind-speed fluctuation effects when examining the spatiotemporal cross-covariance functions computed according to the G-SCIDAR method. We show that under the assumption of having turbulent layers driven by fluctuating wind-velocity vectors, it is correct examining the encircled volume of smeared cross-covariance peaks. The method was used to process 60 spatiotemporal cross-covariance functions of the stellar scintillation patterns retrieved at the 2.2 m telescope of the University of Hawaii along a two hours observation run. We found that most of the time the structure of atmospheric refraction-index inhomogeneities decorrelates linearly with time for individual turbulent layers. Moreover, contrary to the behaviour expected under the assumption of having a slowly evolving structure of turbulent eddies, being translated by a much greater wind-velocity vector, which should strengthen the hypothesis of a frozen flow, we found that the temporal decorrelation of such structure increases as the overall layer displacement velocity increases.
NASA Astrophysics Data System (ADS)
Yang, You-quan; Chi, Xue-fen; Shi, Jia-lin; Zhao, Lin-lin
2015-05-01
To facilitate the efficient support of quality-of-service (QoS) for promising free-space optical (FSO) communication systems, it is essential to model and analyze FSO channels in terms of delay QoS. However, most existing works focus on the average capacity and outage capacity for FSO, which are not enough to characterize the effective transmission data rate when delay-sensitive service is applied. In this paper, the effective capacity of FSO communication systems under statistical QoS provisioning constraints is investigated to meet heterogeneous traffic demands. A novel closed-form expression for effective capacity is derived under the combined effects of atmospheric turbulence conditions, pointing errors, beam widths, detector sizes and QoS exponents. The obtained results reveal the effects of some significant parameters on effective capacity, which can be used for the design of FSO systems carrying a wide range of services with diverse QoS requirements.
Hanson, Frank; Lasher, Mark
2010-06-01
We characterize and compare the effects of turbulence on underwater laser propagation with theory. Measurements of the coupling efficiency of the focused beam into a single-mode fiber are reported. A simple tip-tilt control system, based on the position of the image centroid in the focal plane, was shown to maintain good coupling efficiency for a beam radius equal to the transverse coherence length, r(0). These results are relevant to high bandwidth communication technology that requires good spatial mode quality.
NASA Astrophysics Data System (ADS)
Lynch, P.
2014-12-01
With the emergence of global aerosol models intended for operational forecasting use at global numerical weather prediction (NWP) centers, the International Cooperative for Aerosol Prediction (ICAP) was founded in 2010. One of the objectives of ICAP is to develop a global multi-model aerosol forecasting ensemble (ICAP-MME) for operational and basic research use. To increase the accuracy of aerosol forecasts, several of the NWP centers have incorporated assimilation of satellite and/or ground-based observations of aerosol optical thickness (AOT), the most widely available and evaluated aerosol parameter. The ICAP models are independent in their underlying meteorology, as well as aerosol sources, sinks, microphysics and chemistry. The diversity of aerosol representations in the aerosol forecast models results in differences in AOT. In addition, for models that include AOT assimilations, the diversity in assimilation methodology, the observed AOT data to be assimilated, and the pre-assimilation treatments of input data also leads to differences in the AOT analyses. Drawing from members of the ICAP latest generation of quasi-operational aerosol models, five day AOT forecasts and AOT analyses are analyzed from four multi-species models which have AOT assimilations: ECMWF, JMA, NASA GSFC/GMAO, and NRL/FNMOC. For forecast mode only, we also include the dust products from NOAA NGAC, BSC, and UK Met office in our analysis leading to a total of 7 dust models. AOT at 550nm from all models are validated at regionally representative Aerosol Robotic Network (AERONET) sites and a data assimilation grade multi-satellite aerosol analysis. These analyses are also compared with the recently developed AOT reanalysis at NRL. Here we will present the basic verification characteristics of the ICAP-MME, and identify regions of diversity between model analyses and forecasts. Notably, as in many other ensemble environments, the multi model ensemble consensus mean outperforms all of the
Lee, It Ee; Ghassemlooy, Zabih; Ng, Wai Pang; Khalighi, Mohammad-Ali; Liaw, Shien-Kuei
2016-01-01
Joint effects of aperture averaging and beam width on the performance of free-space optical communication links, under the impairments of atmospheric loss, turbulence, and pointing errors (PEs), are investigated from an information theory perspective. The propagation of a spatially partially coherent Gaussian-beam wave through a random turbulent medium is characterized, taking into account the diverging and focusing properties of the optical beam as well as the scintillation and beam wander effects. Results show that a noticeable improvement in the average channel capacity can be achieved with an enlarged receiver aperture in the moderate-to-strong turbulence regime, even without knowledge of the channel state information. In particular, it is observed that the optimum beam width can be reduced to improve the channel capacity, albeit the presence of scintillation and PEs, given that either one or both of these adverse effects are least dominant. We show that, under strong turbulence conditions, the beam width increases linearly with the Rytov variance for a relatively smaller PE loss but changes exponentially with steeper increments for higher PE losses. Our findings conclude that the optimal beam width is dependent on the combined effects of turbulence and PEs, and this parameter should be adjusted according to the varying atmospheric channel conditions. Therefore, we demonstrate that the maximum channel capacity is best achieved through the introduction of a larger receiver aperture and a beam-width optimization technique.
NASA Astrophysics Data System (ADS)
Gan, Chuen-Meei; Wu, Yonghua; Madhavan, B. L.; Gross, Barry; Moshary, Fred
2011-12-01
In this paper, the simulations of the Weather Research and Forecast (WRF) and Community Multiscale Air Quality (CMAQ) Models applied to the New York City (NYC) area are assessed with the aid of vertical profiling and column integrated remote sensing measurements. First, we find that when turbulent mixing processes are dominant, the WRF-derived planetary boundary layer (PBL) height exhibits a strong linear correlation ( R > 0.85) with lidar-derived PBL height. In these comparisons, we estimate the PBL height from the lidar measurements using a Wavelet Covariance Transform (WCT) approach that is modified to better isolate the convective layer from the residual layer (RL). Furthermore, the WRF-Lidar PBL height comparisons are made using different PBL parameterization schemes, including the Asymmetric Convective Model-version2 (ACM2) and the Modified Blackadar (BLK) scheme (which are both runs using hindcast data), as well as the Mellor-Yamada-Janjic (MYJ) scheme run in forecast mode. Our findings show that the correlations for these runs are high (>0.8), but the hindcast runs exhibit smaller overall dispersion (≈0.1) than the forecast runs. We also apply continuous 24-hour/7-day vertical ceilometer measurements to assess WRF-CMAQ model forecasts of surface PM 2.5 (particulate matter has aerodynamic diameter <2.5 μm). Strong overestimations in the surface PM 2.5 mass that are observed in the summer prior to sunrise are particularly shown to be strongly connected to underestimations of the PBL height and less to enhanced emissions. This interpretation is consistent with observations that TEOM (Tapered Element Oscillating MicroBalance) PM 2.5 measurements are better correlated to path-integrated CMAQ PM 2.5 than the near-surface measurements during these periods.
NASA Astrophysics Data System (ADS)
Gan, Chuen-Meei; Wu, Yonghua; Bomidi, L. M.; Gross, Barry; Moshary, Fred
2011-11-01
In this paper, the simulations of the Weather Research and Forecast (WRF) and Community Multiscale Air Quality (CMAQ) Models applied to the New York City (NYC) area are assessed with the aid of vertical profiling and column integrated remote sensing measurements. First, we find that when turbulent mixing processes are dominant, the WRFderived planetary boundary layer (PBL) height exhibits a strong linear correlation (R>0.85) with lidar-derived PBL height. In these comparisons, we estimate the PBL height from the lidar measurements using a Wavelet Covariance Transform (WCT) approach that is modified to better isolate the convective layer from the residual layer (RL). Furthermore, the WRF-Lidar PBL height comparisons are made using different PBL parameterization schemes, including the Asymmetric Convective Model-version2 (ACM2) and the Modified Blackadar (BLK) scheme (which are both runs using hindcast data), as well as the Mellor-Yamada-Janjic (MYJ) scheme run in forecast mode. Our findings show that the correlations for these runs are high (>0.8), but the hindcast runs exhibit smaller overall dispersion (~0.1) than the forecast runs. We also apply continuous 24-hour/7-day vertical ceilometer measurements to assess WRFCMAQ model forecasts of surface PM2.5 (particulate matter has aerodynamic diameter <2.5μm). Strong overestimations in the surface PM2.5 mass that are observed in the summer prior to sunrise are particularly shown to be strongly connected to underestimations of the PBL height and less to enhanced emissions. This interpretation is consistent with observations that TEOM (Tapered Element Oscillating MicroBalance) PM2.5 measurements are better correlated to pathintegrated CMAQ PM2.5 than the near-surface measurements during these periods.
Tan, Liying; Li, Mengnan; Yang, Qingbo; Ma, Jing
2015-03-20
In practice, due to the laser device and the inevitable error of the processing technique, the laser source emitted from the communication terminal is partially coherent, and is represented as a Gaussian Schell model (GSM). The cross-spectral density function based on the Gaussian model in previous research is replaced by the GSM. Thus the fiber-coupling efficiency equation of the GSM laser source through atmospheric turbulence is deduced. The GSM equation presents the effect of the source coherent parameter ζ on the fiber-coupling efficiency, which was not included previously. The effects of the source coherent parameter ζ on the spatial coherent radius and the fiber-coupling efficiency through atmospheric turbulence are numerically simulated and analyzed. The result manifests that the fiber-coupling efficiency invariably degrades with increasing ζ. The work in this paper is aimed to improve the redundancy design of fiber-coupling receiver systems by analyzing the fiber-coupling efficiency with the source coherent parameters.
Monteiro, A; Jarem, J
1993-01-10
The mutual coherence function (MCF) of strong-fluctuation theory as a result of optical energy passing through a transversely and longitudinally inhomogeneous aero-optic turbulent layer is studied. Solutions for the MCF equation are determined by decomposing the MCF solution into coherent and incoherent parts and by solving separately the equations that result from this decomposition. The MCF equations for an arbitrary three-dimensional inhomogeneous layer are presented. A simplified version of these equations for the case in which the turbulence inhomogeneity is longitudinally inhomogeneous and is transversely inhomogeneous in one dimension is also presented. A numerical method for solving the parabolic MCF equations by the Lax-Wendroff explicit finite-difference algorithm is given, and numerical examples of the MCF solution for three different inhomogeneous aero-optic layers are discussed. Equations to relate the point-spread function, the optical transfer function, and image formation to the MCF of an inhomogeneous aero-optic turbulence layer are derived. An approximate MCF Fourier integral solution is presented and compared with the exact finite-difference solution. A formula to estimate the validity of the approximate integral solution is given. PMID:20802679
NASA Astrophysics Data System (ADS)
Kaur, Prabhmandeep; Jain, Virander Kumar; Kar, Subrat
2014-12-01
In this paper, we investigate the performance of a Free Space Optic (FSO) link considering the impairments caused by the presence of various weather conditions such as very clear air, drizzle, haze, fog, etc., and turbulence in the atmosphere. Analytic expression for the outage probability is derived using the gamma-gamma distribution for turbulence and accounting the effect of weather conditions using the Beer-Lambert's law. The effect of receiver diversity schemes using aperture averaging and array receivers on the outage probability is studied and compared. As the aperture diameter is increased, the outage probability decreases irrespective of the turbulence strength (weak, moderate and strong) and weather conditions. Similar effects are observed when the number of direct detection receivers in the array are increased. However, it is seen that as the desired level of performance in terms of the outage probability decreases, array receiver becomes the preferred choice as compared to the receiver with aperture averaging.
Ren, Yongxiong; Wang, Zhe; Xie, Guodong; Li, Long; Willner, Asher J; Cao, Yinwen; Zhao, Zhe; Yan, Yan; Ahmed, Nisar; Ashrafi, Nima; Ashrafi, Solyman; Bock, Robert; Tur, Moshe; Willner, Alan E
2016-06-01
We explore the mitigation of atmospheric turbulence effects for orbital angular momentum (OAM)-based free-space optical (FSO) communications with multiple-input multiple-output (MIMO) architecture. Such a system employs multiple spatially separated aperture elements at the transmitter/receiver, and each transmitter aperture contains multiplexed data-carrying OAM beams. We propose to use spatial diversity combined with MIMO equalization to mitigate both weak and strong turbulence distortions. In a 2×2 FSO link with each transmitter aperture containing two multiplexed OAM modes of ℓ=+1 and ℓ=+3, we experimentally show that at least two OAM data channels could be recovered under both weak and strong turbulence distortions using selection diversity assisted with MIMO equalization.
NASA Astrophysics Data System (ADS)
Grant, Shanique L.
Emissions from local industries, particularly coal-fired power plants, have been shown to enhance the ambient pollutant budget in the Ohio River Valley (ORV) region. One pollutant that is of interest is PM2.5 due to its established link to respiratory illnesses, cardiopulmonary diseases and mortality. State and local agencies monitor the impact of the local point sources on the ambient concentrations at specific sites; however, the monitors do not provide satisfactory spatial coverage. An important metric for describing ambient particulate pollution is aerosol optical depth (AOD). It is a dimensionless geo-physical product measured remotely using satellites or ground-based light detection ranging instruments. This study focused on assessing the effectiveness of using satellite aerosol optical depth (AOD) as an indicator for PM2.5 in the ORV and two cities in Ohio. Three models, multi-linear regression (MLR), principal component analysis (PCA) -- MLR and neural network, were trained using 40% of the total dataset. The outcome was later tested to minimize error and further validated with another 40% of the dataset not included in the model development phase. Furthermore, to limit the effect of seasonality, four models representing each season were created for each city using meteorological variables known to influence PM2.5 and AOD concentration. GIS spatial analysis tool was employed to visualize and make spatial and temporal comparisons for the ORV region. Comparable spatial distributions were observed. Regression analysis showed that the highest and lowest correlations were in the summer and winter, respectively. Seasonal decomposition methods were used to evaluate trends at local Ohio monitoring stations to identify areas most suitable for improved air quality management. Over the six years of study, Cuyahoga County maintained PM2.5 concentrations above the national standard and in Hamilton County (Cincinnati) PM2.5 levels ranked above the national level for more
Brown, David M; Juarez, Juan C; Brown, Andrea M
2013-12-01
A laser differential image-motion monitor (DIMM) system was designed and constructed as part of a turbulence characterization suite during the DARPA free-space optical experimental network experiment (FOENEX) program. The developed link measurement system measures the atmospheric coherence length (r0), atmospheric scintillation, and power in the bucket for the 1550 nm band. DIMM measurements are made with two separate apertures coupled to a single InGaAs camera. The angle of arrival (AoA) for the wavefront at each aperture can be calculated based on focal spot movements imaged by the camera. By utilizing a single camera for the simultaneous measurement of the focal spots, the correlation of the variance in the AoA allows a straightforward computation of r0 as in traditional DIMM systems. Standard measurements of scintillation and power in the bucket are made with the same apertures by redirecting a percentage of the incoming signals to InGaAs detectors integrated with logarithmic amplifiers for high sensitivity and high dynamic range. By leveraging two, small apertures, the instrument forms a small size and weight configuration for mounting to actively tracking laser communication terminals for characterizing link performance.
Flatte; Gerber
2000-06-01
We have simulated optical propagation through atmospheric turbulence in which the spectrum near the inner scale follows that of Hill and Clifford [J. Opt. Soc. Am. 68, 892 (1978)] and the turbulence strength puts the propagation into the asymptotic strong-fluctuation regime. Analytic predictions for this regime have the form of power laws as a function of beta0(2), the irradiance variance predicted by weak-fluctuation (Rytov) theory, and l0, the inner scale. The simulations indeed show power laws for both spherical-wave and plane-wave initial conditions, but the power-law indices are dramatically different from the analytic predictions. Let sigmaI(2) - 1 = a(beta0(2)/betac(2))-b(l0/Rf)c, where we take the reference value of beta0(2) to be betac(2) = 60.6, because this is the center of our simulation region. For zero inner scale (for which c = 0), the analytic prediction is b = 0.4 and a = 0.17 (0.37) for a plane (spherical) wave. Our simulations for a plane wave give a = 0.234 +/- 0.007 and b = 0.50 +/- 0.07, and for a spherical wave they give a = 0.58 + /- 0.01 and b = 0.65 +/- 0.05. For finite inner scale the analytic prediction is b = 1/6, c = 7/18 and a = 0.76 (2.07) for a plane (spherical) wave. We find that to a reasonable approximation the behavior with beta0(2) and l0 indeed factorizes as predicted, and each part behaves like a power law. However, our simulations for a plane wave give a = 0.57 +/- 0.03, b = 0.33 +/- 0.03, and c = 0.45 +/- 0.06. For spherical waves we find a = 3.3 +/- 0.3, b = 0.45 +/- 0.05, and c = 0.8 +/- 0.1.
Stirring turbulence with turbulence
NASA Astrophysics Data System (ADS)
van de Water, Willem; Ergun Cekli, Hakki; Joosten, Rene
2011-11-01
We stir wind-tunnel turbulence with an active grid that consists of rods with attached vanes. The time-varying angle of these rods is controlled by random numbers. We study the response of turbulence on the statistical properties of these random numbers. The random numbers are generated by the Gledzer-Ohkitani-Yamada shell model, which is a simple dynamical model of turbulence that produces a velocity field displaying inertial-range scaling behavior. The range of scales can be adjusted by selection of shells. We find that the largest energy input and the smallest anisotropy are reached when the time scale of the random numbers matches that of the large eddies in the wind-tunnel turbulence. A large mismatch of these times creates a flow with interesting statistics, but it is not turbulence.
NASA Astrophysics Data System (ADS)
Konnik, Mikhail V.; De Dona, Jose
2014-07-01
Model-based optimal control such as Linear Quadratic Gaussian (LQG) control has been attracting considerable attention for adaptive optics systems. The ability of LQG to handle the complex dynamics of deformable mirrors and its relatively simple implementation makes LQG attractive for large adaptive optics systems. However, LQG has its own share of drawbacks, such as suboptimal handling of constraints on actuators movements and possible numerical problems in case of fast sampling rate discretization of the corresponding matrices. Unlike LQG, the Receding Horizon Control (RHC) technique provides control signals for a deformable mirror that are optimal within the prescribed constraints. This is achieved by reformulating the control problem as an online optimization problem that is solved at each sampling instance. In the unconstrained case, RHC produces the same control signals as LQG. However, when the control signals reach the constraints of actuator's allowable movement in a deformable mirror, RHC finds the control signals that are optimal within those constraints, rather than just clipping the unconstrained optimum as commonly done in LQG control. The article discusses the consequences of high-gain LQG control operation in the case when the constraints on the actuator's movement are reached. It is shown that clipping / saturating the control signals is not only suboptimal, but may be hazardous for the surface of a deformable mirror. The results of numerical simulations indicate that high-gain LQG control can lead to abrupt changes and spikes in the control signal when saturation occurs. The article further discusses a possible link between high-gain LQG and the waffle mode in the closed-loop operation of astronomical adaptive optics systems. Performance evaluation of Receding Horizon Control in terms of atmospheric disturbance rejection and a comparison with Linear Quadratic Gaussian control are performed. The results of the numerical simulations suggest that the
Chen, Chunyi; Yang, Huamin; Zhou, Zhou; Zhang, Weizhi; Kavehrad, Mohsen; Tong, Shoufeng; Wang, Tianshu
2013-12-01
The temporal covariance function of irradiance-flux fluctua-tions for Gaussian Schell-model (GSM) beams propagating in atmospheric turbulence is theoretically formulated by making use of the method of effective beam parameters. Based on this formulation, new expressions for the root-mean-square (RMS) bandwidth of the irradiance-flux temporal spectrum due to GSM beams passing through atmospheric turbulence are derived. With the help of these expressions, the temporal fade statistics of the irradiance flux in free-space optical (FSO) communication systems, using spatially partially coherent sources, impaired by atmospheric turbulence are further calculated. Results show that with a given receiver aperture size, the use of a spatially partially coherent source can reduce both the fractional fade time and average fade duration of the received light signal; however, when atmospheric turbulence grows strong, the reduction in the fractional fade time becomes insignificant for both large and small receiver apertures and in the average fade duration turns inconsiderable for small receiver apertures. It is also illustrated that if the receiver aperture size is fixed, changing the transverse correlation length of the source from a larger value to a smaller one can reduce the average fade frequency of the received light signal only when a threshold parameter in decibels greater than the critical threshold level is specified.
NASA Astrophysics Data System (ADS)
Saide, P. E.; Carmichael, G. R.; Liu, Z.; Schwartz, C. S.; Lin, H. C.; da Silva, A. M.; Hyer, E.
2013-10-01
An aerosol optical depth (AOD) three-dimensional variational data assimilation technique is developed for the Gridpoint Statistical Interpolation (GSI) system for which WRF-Chem forecasts are performed with a detailed sectional model, the Model for Simulating Aerosol Interactions and Chemistry (MOSAIC). Within GSI, forward AOD and adjoint sensitivities are performed using Mie computations from the WRF-Chem optical properties module, providing consistency with the forecast. GSI tools such as recursive filters and weak constraints are used to provide correlation within aerosol size bins and upper and lower bounds for the optimization. The system is used to perform assimilation experiments with fine vertical structure and no data thinning or re-gridding on a 12 km horizontal grid over the region of California, USA, where improvements on analyses and forecasts is demonstrated. A first set of simulations was performed, comparing the assimilation impacts of using the operational MODIS (Moderate Resolution Imaging Spectroradiometer) dark target retrievals to those using observationally constrained ones, i.e., calibrated with AERONET (Aerosol RObotic NETwork) data. It was found that using the observationally constrained retrievals produced the best results when evaluated against ground based monitors, with the error in PM2.5 predictions reduced at over 90% of the stations and AOD errors reduced at 100% of the monitors, along with larger overall error reductions when grouping all sites. A second set of experiments reveals that the use of fine mode fraction AOD and ocean multi-wavelength retrievals can improve the representation of the aerosol size distribution, while assimilating only 550 nm AOD retrievals produces no or at times degraded impact. While assimilation of multi-wavelength AOD shows positive impacts on all analyses performed, future work is needed to generate observationally constrained multi-wavelength retrievals, which when assimilated will generate size
ETA-CMAQ MODELING SYSTEM'S CAPABILITY TO PROVIDE PM 2.5 AND AEROSOL OPTICAL THICKNESS FORECAST
In 2003, NOAA and the U.S. EPA signed a Memorandum of Agreement to work together to develop a National Air Quality Forecasting (AQF) capability. To meet this goal, NOAA's National Weather Service (NWS), the Office of Atmospheric Research (OAR) and the U.S. EPA developed and eval...
Robey, H.F.; Albrecht, G.F.; Moore, T.R.
1990-04-06
A new optical technique for quantitatively measuring the spectral density of passive scalar fluctuations in a turbulent flow has been developed. The technique exploits the photorefractive properties of BaTiO{sub 3} to separate the optical signal of the turbulent field from the coherent illumination background. It is a major improvement over existing techniques in that it is non-intrusive, has excellent frequency response and spatial resolution, and is capable of simultaneously measuring two components of the three-dimensional spectral density, {Phi}{theta}({kappa}). The technique is thus especially well suited to the directly study of anisotropic flows. We have applied this technique to study the spectrum of temperature fluctuations in a fully developed turbulent channel flow with heat addition. The flow is highly anisotropic, yet the spectrum in directions transverse to the flow is seen to exhibit an inertial--convective subrange behavior which is characteristic of isotropic flows. The spectral behavior in the flow direction, due to the direct influence of the mean strain rate, is observed to be markedly different. 17 refs., 7 figs.
Stirring turbulence with turbulence
NASA Astrophysics Data System (ADS)
Cekli, Hakki Ergun; Joosten, René; van de Water, Willem
2015-12-01
We stir wind-tunnel turbulence with an active grid that consists of rods with attached vanes. The time-varying angle of these rods is controlled by random numbers. We study the response of turbulence on the statistical properties of these random numbers. The random numbers are generated by the Gledzer-Ohkitani-Yamada shell model, which is a simple dynamical model of turbulence that produces a velocity field displaying inertial-range scaling behavior. The range of scales can be adjusted by selection of shells. We find that the largest energy input and the smallest anisotropy are reached when the time scale of the random numbers matches that of the largest eddies of the wind-tunnel turbulence. A large mismatch of these times creates a highly intermittent random flow with interesting but quite anomalous statistics.
NASA Astrophysics Data System (ADS)
Lee, Sojin; Song, Chul-han; Park, Rae Seol; Park, Mi Eun; Han, Kyung man; Kim, Jhoon; Choi, Myungje; Ghim, Young Sung; Woo, Jung-Hun
2016-04-01
To improve short-term particulate matter (PM) forecasts in South Korea, the initial distribution of PM composition, particularly over the upwind regions, is primarily important. To prepare the initial PM composition, the aerosol optical depth (AOD) data retrieved from a geostationary equatorial orbit (GEO) satellite sensor, GOCI (Geostationary Ocean Color Imager) which covers a part of Northeast Asia (113-146° E; 25-47° N), were used. Although GOCI can provide a higher number of AOD data in a semicontinuous manner than low Earth orbit (LEO) satellite sensors, it still has a serious limitation in that the AOD data are not available at cloud pixels and over high-reflectance areas, such as desert and snow-covered regions. To overcome this limitation, a spatiotemporal-kriging (STK) method was used to better prepare the initial AOD distributions that were converted into the PM composition over Northeast Asia. One of the largest advantages in using the STK method in this study is that more observed AOD data can be used to prepare the best initial AOD fields compared with other methods that use single frame of observation data around the time of initialization. It is demonstrated in this study that the short-term PM forecast system developed with the application of the STK method can greatly improve PM10 predictions in the Seoul metropolitan area (SMA) when evaluated with ground-based observations. For example, errors and biases of PM10 predictions decreased by ˜ 60 and ˜ 70{%}, respectively, during the first 6 h of short-term PM forecasting, compared with those without the initial PM composition. In addition, the influences of several factors on the performances of the short-term PM forecast were explored in this study. The influences of the choices of the control variables on the PM chemical composition were also investigated with the composition data measured via PILS-IC (particle-into-liquid sampler coupled with ion chromatography) and low air-volume sample
Jarem, J M
1994-01-10
The mutual coherence function (MCF) that results when a double point source illuminates a transversely and longitudinally inhomogeneous turbulence layer is considered. The analysis was carried out by (1) decomposition of the free-space MCF from the double point source into four separate interference terms, (2) calculation of the MCF that resulted from each of these terms when the optical wave that arose from these terms propagated through the inhomogeneous turbulence layer, and (3) addition of the solutions together to form the overall MCF solution of the optical system. The analysis was carried out in a transverse center-difference coordinate system. Two of the four terms were shown to vary rapidly in the center coordinate variables, and the other two were shown to vary rapidly in the difference coordinate variables. Because two of the terms showed rapid interference effects in the center coordinate variable and the other two in the difference coordinate variable, two different spatial-spectral algorithms were developed in the paper to analyze the MCF's that arose from each of the two types of rapid interference variation. The spatial-spectral MCF equations that arose from the analysis were solved numerically by the Lax-Wendroff finite-difference method. Several numerical plots of the center and difference interference MCF's that resulted when a double point source was incident upon a transversely inhomogeneous aero-optic layer were given. Plots of the variation of the interference MCF's with angular separation of the double point source are shown. PMID:20862014
Group-kinetic theory and modeling of atmospheric turbulence
NASA Technical Reports Server (NTRS)
Tchen, C. M.
1989-01-01
A group kinetic method is developed for analyzing eddy transport properties and relaxation to equilibrium. The purpose is to derive the spectral structure of turbulence in incompressible and compressible media. Of particular interest are: direct and inverse cascade, boundary layer turbulence, Rossby wave turbulence, two phase turbulence; compressible turbulence, and soliton turbulence. Soliton turbulence can be found in large scale turbulence, turbulence connected with surface gravity waves and nonlinear propagation of acoustical and optical waves. By letting the pressure gradient represent the elementary interaction among fluid elements and by raising the Navier-Stokes equation to higher dimensionality, the master equation was obtained for the description of the microdynamical state of turbulence.
NASA Technical Reports Server (NTRS)
Seasholtz, R. G.; Goldman, L. J.
1982-01-01
A technique for measuring a small optical axis velocity component in a flow with a large transverse velocity component is presented. Experimental results are given for a subsonic free jet operating in a laboratory environment, and for a 0.508 meter diameter turbine stator cascade. Satisfactory operation of the instrument was demonstrated in the stator cascade facility with an ambient acoustic noise level during operation of about 105 dB. In addition, the turbulence intensity measured with the interferometer was consistent with previous measurements taken with a fringe type laser anemometer.
NASA Astrophysics Data System (ADS)
Wilson, R. W.; Butterley, T.; Osborn, J.
2009-09-01
SLODAR turbulence monitors have been installed and operated at the Cerro Paranal, Mauna Kea and SAAO Sutherland observatories. The instruments, developed at Durham University, provide real-time measurements of the atmospheric turbulence strength, altitude and velocity, for site characterization and for real-time support of adaptive optics for astronomy. We present sample results and compare contemporaneous data obtained with SLODAR, MASS and DIMM monitors at the ESO Paranal observatory.
Cui, Linyan
2015-03-01
Analytical expressions for the variance of angle of arrival (AOA) fluctuations based on the Rytov approximation theory are derived for plane and spherical waves' propagation through weak anisotropic non-Kolmogorov turbulence atmosphere. The anisotropic spectrum model based on the assumption of circular symmetry in the orthogonal plane throughout the path is adopted and it includes the same degree of anisotropy along the direction of propagation for all the turbulence cells size in the inertial sub-range. The derived expressions consider a single anisotropic coefficient describing the turbulence anisotropic property and a general spectral power law value in the range 3 to 4. They reduce correctly to the previously published analytic expressions for the cases of plane and spherical waves' propagation through weak isotropic non-Kolmogorov turbulence for the special case of anisotropic factor equaling one. To reduce the complexity of the analytical results, the asymptotic-fit expressions are also derived and they fit well with the close-form ones. These results are useful for understanding the potential impact of deviations from the standard isotropic non-Kolmogorov turbulence atmosphere.
Ding, Jiachen; Li, Mi; Tang, Minghui; Li, Yan; Song, Yuejiang
2013-09-15
Minimum shift keying (MSK) has been widely used in fiber optical communication and free-space optical communication. In order to introduce MSK into satellite laser communication, the bit-error rate (BER) performance of the MSK scheme is investigated in uplink communications under the influence of atmospheric turbulence consisting of weak fluctuation and beam wander. Numerical results indicate that the BER performance of MSK is much better than the performance of on-off keying (OOK). With the laser power being 4 W, the improvement is 5 dB in coherent demodulation and 15 dB in delay coherent demodulation. Furthermore, compared with OOK, optimal values of the divergence angle, receiver diameter, and transmitter beam radius are easier and more practical to achieve in the MSK scheme. The work can benefit ground-to-satellite laser uplink communication system design.
NASA Astrophysics Data System (ADS)
Valley, M. T.; Dudorov, V. V.; Kolosov, V. V.; Filimonov, G. A.
2006-11-01
The error caused by atmospheric turbulence, in determining the orientation angle of an object (a series of reflectors) has been studied. The orientation angle was determined by studying the image of the object. Numerical modeling was performed involving construction of the image of a series of reflectors as if they were observed through a turbulent medium, calculation of the coordinates of reflector mass centers, finding of the line closest to the reflector mass centers, and determination of its slope angle. Variance of the slope angle fluctuations is calculated.
Comparison of Kolmogorov's and coherent turbulence.
Lukin, V P; Bol'basova, L A; Nosov, V V
2014-04-01
Features of optical wave fluctuations while propagating through a randomly inhomogeneous turbulent medium with a finite outer scale are considered, including conditions when areas with dominating influence of one large-scale coherent structure are observed in the atmosphere, for which the spectrum of atmospheric turbulence can differ significantly from the Kolmogorov model spectrum. Using an approximate model of the spectrum for coherent turbulence, described earlier in our works, the variance of jitter of an optical image is calculated (under the applicability condition for the smooth perturbation method). The comparison of these equations with known similar equations for Kolmogorov turbulence has shown that the variance of fluctuations is significantly weaker in coherent turbulence than in the Kolmogorov theory under similar conditions. This means that phase fluctuations of optical radiation decrease significantly in coherent turbulence. The importance of this conclusion is noted for interpretation of the results of optical sounding of atmospheric turbulence.
NASA Technical Reports Server (NTRS)
1988-01-01
ROFFS stands for Roffer's Ocean Fishing Forecasting Service, Inc. Roffer combines satellite and computer technology with oceanographic information from several sources to produce frequently updated charts sometimes as often as 30 times a day showing clues to the location of marlin, sailfish, tuna, swordfish and a variety of other types. Also provides customized forecasts for racing boats and the shipping industry along with seasonal forecasts that allow the marine industry to formulate fishing strategies based on foreknowledge of the arrival and departure times of different fish. Roffs service exemplifies the potential for benefits to marine industries from satellite observations. Most notable results are reduced search time and substantial fuel savings.
NASA Astrophysics Data System (ADS)
Sprung, D.; Sucher, E.; Ramkilowan, A.; Griffith, D. J.
2014-10-01
Optical turbulence represented by the structure function parameter of the refractive index Cn 2 is a relevant parameter for the performance of electro-optical systems and characterization of the atmospheric influence on imaging. It was investigated during a field trial above an Highveld grassland in the atmospheric surface layer at the Rietvlei Nature Reserve close to Pretoria in South Africa from 18th June to 30th June 2013. This campaign was performed to compare different measurement techniques analyzing the diurnal formation of the vertical distribution of optical turbulence up to a height of 16 m above ground. The chosen time period was characterized by a pronounced diurnal cycle of the meteorological conditions, i.e. low variations from day to day. Ultra sonic anemometers were used to measure high frequency time series (50 Hz) of temperature at single points. From the statistical analysis of these time series Cn 2 was derived. Three instruments were mounted at a portable mast in the center of slant path measurements over a horizontal distance of 1000 m using large aperture scintillometers (Boundary layer scintillometer BLS 900). Averaging over a time period of 5 minutes, the results of both methods are compared. The agreement in the results of optical turbulence is quite good. Discrepancies and agreement are analyzed with respect to the atmospheric stability and other meteorological parameters. Lowest values of Cn 2 at 4.6 m above ground amount to about 8*10-17 m-2/3, daily maxima to 6*10-13 m-2/3. Additional to the nearly constant meteorological conditions in the diurnal cycle, the uniformity of the terrain let the results of this measurement campaign an ideal data set for investigating methodological questions regarding a comparison of single point measurements with integrated measurements over a horizontal distance. Four stability regimes were identified in the diurnal cycle and investigated. These are convective conditions during the day, neutral
NASA Astrophysics Data System (ADS)
Robert, Clélia; Conan, Jean-Marc; Wolf, Peter
2016-06-01
Bidirectional ground-satellite laser links suffer from turbulence-induced scintillation and phase distortion. We study how turbulence impacts on coherent detection capacity and on the associated phase noise that restricts clock transfer precision. We evaluate the capacity to obtain a two-way cancellation of atmospheric effects despite the asymmetry between up and down link that limits the link reciprocity. For ground-satellite links, the asymmetry is induced by point-ahead angle and possibly the use, for the ground terminal, of different transceiver diameters, in reception and emission. The quantitative analysis is obtained thanks to refined end- to-end simulations under realistic turbulence and wind conditions as well as satellite cinematic. These temporally resolved simulations allow characterizing the coherent detection in terms of time series of heterodyne efficiency for different system parameters. We show that Tip/Tilt correction on ground is mandatory at reception for the down link and as a pre-compensation of the up link. Good correlation between up and down phase noise is obtained even with asymmetric apertures of the ground transceiver and in spite of pointing ahead angle. The reduction to less than 1 rad2 of the two-way differential phase noise is very promising for clock comparisons.
Yi, Xiang; Liu, Zengji; Yue, Peng
2012-02-13
By use of the generalized von Kármán spectrum model that features both inner scale and outer scale parameters for non-Kolmogorov turbulence and the extended Rytov method that incorporates a modified amplitude spatial-frequency filter function under strong-fluctuation conditions, theoretical expressions are developed for the scintillation index of a horizontally propagating plane wave and spherical wave that are valid under moderate-to-strong irradiance fluctuations. Numerical results show that the obtained expressions also compare well with previous results in weak-fluctuation regimes. Based on these general models, the impacts of finite inner and outer scales on the scintillation index of an optical wave are examined under various non-Kolmogorov fluctuation conditions.
NASA Astrophysics Data System (ADS)
Krishnan, Prabu; Sriram Kumar, D.
2014-12-01
Free-space optical communication (FSO) is emerging as a captivating alternative to work out the hindrances in the connectivity problems. It can be used for transmitting signals over common lands and properties that the sender or receiver may not own. The performance of an FSO system depends on the random environmental conditions. The bit error rate (BER) performance of differential phase shift keying FSO system is investigated. A distributed strong atmospheric turbulence channel with pointing error is considered for the BER analysis. Here, the system models are developed for single-input, single-output-FSO (SISO-FSO) and single-input, multiple-output-FSO (SIMO-FSO) systems. The closed-form mathematical expressions are derived for the average BER with various combining schemes in terms of the Meijer's G function.
PREFACE: Turbulent Mixing and Beyond Turbulent Mixing and Beyond
NASA Astrophysics Data System (ADS)
Abarzhi, Snezhana I.; Gauthier, Serge; Rosner, Robert
2008-10-01
The goals of the International Conference `Turbulent Mixing and Beyond' are to expose the generic problem of Turbulence and Turbulent Mixing in Unsteady Flows to a wide scientific community, to promote the development of new ideas in tackling the fundamental aspects of the problem, to assist in the application of novel approaches in a broad range of phenomena, where the non-canonical turbulent processes occur, and to have a potential impact on technology. The Conference provides the opportunity to bring together scientists from the areas which include, but are not limited to, high energy density physics, plasmas, fluid dynamics, turbulence, combustion, material science, geophysics, astrophysics, optics and telecommunications, applied mathematics, probability and statistics, and to have their attention focused on the long-standing formidable task. The Turbulent Mixing and Turbulence in Unsteady Flows, including multiphase flows, plays a key role in a wide variety of phenomena, ranging from astrophysical to nano-scales, under either high or low energy density conditions. Inertial confinement and magnetic fusion, light-matter interaction and non-equilibrium heat transfer, properties of materials under high strain rates, strong shocks, explosions, blast waves, supernovae and accretion disks, stellar non-Boussinesq and magneto-convection, planetary interiors and mantle-lithosphere tectonics, premixed and non-premixed combustion, oceanography, atmospheric flows, unsteady boundary layers, hypersonic and supersonic flows, are a few examples to list. A grip on unsteady turbulent processes is crucial for cutting-edge technology such as laser-micromachining and free-space optical telecommunications, and for industrial applications in aeronautics. Unsteady Turbulent Processes are anisotropic, non-local and multi-scale, and their fundamental scaling, spectral and invariant properties depart from the classical Kolmogorov scenario. The singular aspects and similarity of the
Gilles, L; Ellerbroek, B L
2010-11-01
Real-time turbulence profiling is necessary to tune tomographic wavefront reconstruction algorithms for wide-field adaptive optics (AO) systems on large to extremely large telescopes, and to perform a variety of image post-processing tasks involving point-spread function reconstruction. This paper describes a computationally efficient and accurate numerical technique inspired by the slope detection and ranging (SLODAR) method to perform this task in real time from properly selected Shack-Hartmann wavefront sensor measurements accumulated over a few hundred frames from a pair of laser guide stars, thus eliminating the need for an additional instrument. The algorithm is introduced, followed by a theoretical influence function analysis illustrating its impulse response to high-resolution turbulence profiles. Finally, its performance is assessed in the context of the Thirty Meter Telescope multi-conjugate adaptive optics system via end-to-end wave optics Monte Carlo simulations.
ERIC Educational Resources Information Center
Taylor, Kelley R.
2010-01-01
This article presents a sample legal battle that illustrates school officials' "reasonable forecasts" of substantial disruption in the school environment. In 2006, two students from a Texas high school came to school carrying purses decorated with images of the Confederate flag. The school district has a zero-tolerance policy for clothing or…
NASA Technical Reports Server (NTRS)
Mauldin, L. E.
1994-01-01
Business travel planning within an organization is often a time-consuming task. Travel Forecaster is a menu-driven, easy-to-use program which plans, forecasts cost, and tracks actual vs. planned cost for business-related travel of a division or branch of an organization and compiles this information into a database to aid the travel planner. The program's ability to handle multiple trip entries makes it a valuable time-saving device. Travel Forecaster takes full advantage of relational data base properties so that information that remains constant, such as per diem rates and airline fares (which are unique for each city), needs entering only once. A typical entry would include selection with the mouse of the traveler's name and destination city from pop-up lists, and typed entries for number of travel days and purpose of the trip. Multiple persons can be selected from the pop-up lists and multiple trips are accommodated by entering the number of days by each appropriate month on the entry form. An estimated travel cost is not required of the user as it is calculated by a Fourth Dimension formula. With this information, the program can produce output of trips by month with subtotal and total cost for either organization or sub-entity of an organization; or produce outputs of trips by month with subtotal and total cost for international-only travel. It will also provide monthly and cumulative formats of planned vs. actual outputs in data or graph form. Travel Forecaster users can do custom queries to search and sort information in the database, and it can create custom reports with the user-friendly report generator. Travel Forecaster 1.1 is a database program for use with Fourth Dimension Runtime 2.1.1. It requires a Macintosh Plus running System 6.0.3 or later, 2Mb of RAM and a hard disk. The standard distribution medium for this package is one 3.5 inch 800K Macintosh format diskette. Travel Forecaster was developed in 1991. Macintosh is a registered trademark of
Horton, W.; Hu, G.
1998-07-01
The origin of plasma turbulence from currents and spatial gradients in plasmas is described and shown to lead to the dominant transport mechanism in many plasma regimes. A wide variety of turbulent transport mechanism exists in plasmas. In this survey the authors summarize some of the universally observed plasma transport rates.
NASA Astrophysics Data System (ADS)
Gruber, M. A.; Fochesatto, G. J.; Kane, D. L.; Edgar, C.
2012-12-01
Scintillometer measurements of turbulence inner scale length and/or refractive index structure functions allow for indirect retrieval of boundary layer turbulent fluxes on large spacial scales and on short temporal scales relative to eddy covariance techniques. For the past several decades, scintillometer measurement strategies have been compared to other boundary layer measurement techniques; they demonstrate advantages in applications such as the validation and parameterization of satellite remote sensing over a wide variety of terrain, as a source of ground level data for input into large scale models, and in agricultural irrigation management. In past analyses of scintillometer data, the relevant set of nonlinear coupled Monin-Obukhov similarity equations has been solved with a cyclically iterative numerical approximation, and analyses of error propagation from source measurements to derived variables have been attempted without explicit solution to this set of equations. A new analytic method of explicit solution is presented which allows for arbitrarily small and easily quantifiable computational error, guaranteed convergence, faster computation, simpler computer code, and, most importantly, which makes the variable inter-dependency explicit, allowing for direct evaluation of global partial derivative terms in error propagation equations. Results from this method show that many sensitivity functions derived in the previous literature are over-estimated in magnitude, in some cases drastically. Past estimates of computational error resulting from the canonical cyclically iterative procedure are re-visited. Explicit variable inter-dependency is shown to resolve spurious correlations in interpretive validations of scintillometer retrievals. General sensitivity functions are expanded for the use of path weighting functions over heterogeneous terrain in a way which is practical for field implementation. Advantages of the new methods are demonstrated in a case study
AIR QUALITY FORECAST VERIFICATION USING SATELLITE DATA
NOAA 's operational geostationary satellite retrievals of aerosol optical depths (AODs) were used to verify National Weather Service (NWS) experimental (research mode) particulate matter (PM2.5) forecast guidance issued during the summer 2004 International Consortium for Atmosp...
ERIC Educational Resources Information Center
Hanratty, Thomas J.
1980-01-01
This paper gives an account of research on the structure of turbulence close to a solid boundary. Included is a method to study the flow close to the wall of a pipe without interferring with it. (Author/JN)
NASA Astrophysics Data System (ADS)
Nazarenko, Sergey
2015-07-01
Wave turbulence is the statistical mechanics of random waves with a broadband spectrum interacting via non-linearity. To understand its difference from non-random well-tuned coherent waves, one could compare the sound of thunder to a piece of classical music. Wave turbulence is surprisingly common and important in a great variety of physical settings, starting with the most familiar ocean waves to waves at quantum scales or to much longer waves in astrophysics. We will provide a basic overview of the wave turbulence ideas, approaches and main results emphasising the physics of the phenomena and using qualitative descriptions avoiding, whenever possible, involved mathematical derivations. In particular, dimensional analysis will be used for obtaining the key scaling solutions in wave turbulence - Kolmogorov-Zakharov (KZ) spectra.
Cui, Linyan; Xue, Bindang; Zhou, Fugen
2013-11-01
The effects of moderate-to-strong non-Kolmogorov turbulence on the angle of arrival (AOA) fluctuations for plane and spherical waves are investigated in detail both analytically and numerically. New analytical expressions for the variance of AOA fluctuations are derived for moderate-to-strong non-Kolmogorov turbulence. The new expressions cover a wider range of non-Kolmogorov turbulence strength and reduce correctly to previously published analytic expressions for the cases of plane and spherical wave propagation through both weak non-Kolmogorov turbulence and moderate-to-strong Kolmogorov turbulence cases. The final results indicate that, as turbulence strength becomes greater, the expressions developed with the Rytov theory deviate from those given in this work. This deviation becomes greater with stronger turbulence, up to moderate-to-strong turbulence strengths. Furthermore, general spectral power law has significant influence on the variance of AOA fluctuations in non-Kolmogorov turbulence. These results are useful for understanding the potential impact of deviations from the standard Kolmogorv spectrum.
Super Ensemble-based Aviation Turbulence Guidance (SEATG) for Air Traffic Management (ATM)
NASA Astrophysics Data System (ADS)
Kim, Jung-Hoon; Chan, William; Sridhar, Banavar; Sharman, Robert
2014-05-01
Super Ensemble (ensemble of ten turbulence metrics from time-lagged ensemble members of weather forecast data)-based Aviation Turbulence Guidance (SEATG) is developed using Weather Research and Forecasting (WRF) model and in-situ eddy dissipation rate (EDR) observations equipped on commercial aircraft over the contiguous United States. SEATG is a sequence of five procedures including weather modeling, calculating turbulence metrics, mapping EDR-scale, evaluating metrics, and producing final SEATG forecast. This uses similar methodology to the operational Graphic Turbulence Guidance (GTG) with three major improvements. First, SEATG use a higher resolution (3-km) WRF model to capture cloud-resolving scale phenomena. Second, SEATG computes turbulence metrics for multiple forecasts that are combined at the same valid time resulting in an time-lagged ensemble of multiple turbulence metrics. Third, SEATG provides both deterministic and probabilistic turbulence forecasts to take into account weather uncertainties and user demands. It is found that the SEATG forecasts match well with observed radar reflectivity along a surface front as well as convectively induced turbulence outside the clouds on 7-8 Sep 2012. And, overall performance skill of deterministic SEATG against the observed EDR data during this period is superior to any single turbulence metrics. Finally, probabilistic SEATG is used as an example application of turbulence forecast for air-traffic management. In this study, a simple Wind-Optimal Route (WOR) passing through the potential areas of probabilistic SEATG and Lateral Turbulence Avoidance Route (LTAR) taking into account the SEATG are calculated at z = 35000 ft (z = 12 km) from Los Angeles to John F. Kennedy international airports. As a result, WOR takes total of 239 minutes with 16 minutes of SEATG areas for 40% of moderate turbulence potential, while LTAR takes total of 252 minutes travel time that 5% of fuel would be additionally consumed to entirely
Turnipseed, D. Phil
2011-01-01
Forecast Mekong is part of the U.S. Department of State's Lower Mekong Initiative, which was launched in 2009 by Secretary Hillary Clinton and the Foreign Ministers of Cambodia, Laos, Thailand, and Vietnam to enhance partnerships between the U.S. and the Lower Mekong River countries in the areas of environment, health, education, and infrastructure. The U.S. Geological Survey (USGS) is working in close cooperation with the U.S. Department of State to use research and data from the Lower Mekong Basin to provide hands-on results that will help decision makers in Lower Mekong River countries in the planning and design for restoration, conservation, and management efforts in the basin.
Passive adaptive imaging through turbulence
NASA Astrophysics Data System (ADS)
Tofsted, David
2016-05-01
Standard methods for improved imaging system performance under degrading optical turbulence conditions typically involve active adaptive techniques or post-capture image processing. Here, passive adaptive methods are considered where active sources are disallowed, a priori. Theoretical analyses of short-exposure turbulence impacts indicate that varying aperture sizes experience different degrees of turbulence impacts. Smaller apertures often outperform larger aperture systems as turbulence strength increases. This suggests a controllable aperture system is advantageous. In addition, sub-aperture sampling of a set of training images permits the system to sense tilts in different sub-aperture regions through image acquisition and image cross-correlation calculations. A four sub-aperture pattern supports corrections involving five realizable operating modes (beyond tip and tilt) for removing aberrations over an annular pattern. Progress to date will be discussed regarding development and field trials of a prototype system.
Adams, Allan; Chesler, Paul M; Liu, Hong
2014-04-18
We construct turbulent black holes in asymptotically AdS4 spacetime by numerically solving Einstein's equations. Using the AdS/CFT correspondence we find that both the dual holographic fluid and bulk geometry display signatures of an inverse cascade with the bulk geometry being well approximated by the fluid-gravity gradient expansion. We argue that statistically steady-state black holes dual to d dimensional turbulent flows have horizons whose area growth has a fractal-like structure with fractal dimension D=d+4/3.
Turbulence in Compressible Flows
NASA Technical Reports Server (NTRS)
1997-01-01
Lecture notes for the AGARD Fluid Dynamics Panel (FDP) Special Course on 'Turbulence in Compressible Flows' have been assembled in this report. The following topics were covered: Compressible Turbulent Boundary Layers, Compressible Turbulent Free Shear Layers, Turbulent Combustion, DNS/LES and RANS Simulations of Compressible Turbulent Flows, and Case Studies of Applications of Turbulence Models in Aerospace.
Turbulence mitigation methods and their evaluation
NASA Astrophysics Data System (ADS)
van Eekeren, Adam W. M.; Dijk, Judith; Schutte, Klamer
2014-10-01
In general, long range detection, recognition and identification in visual and infrared imagery are hampered by turbulence caused by atmospheric conditions. The amount of turbulence is often indicated by the refractive-index structure parameter Cn2. The value of this parameter and its variation is determined by the turbulence effects over the optical path. Especially along horizontal optical paths near the surface (land-to-land scenario) large values and fluctuations of Cn2 occur, resulting in an extremely blurred and shaky image sequence. Another important parameter is the isoplanatic angle, θ0, which is the angle where the turbulence is approximately constant. Over long horizontal paths the values of θ0 are typically very small; much smaller than the field-of-view of the camera. Typical image artefacts that are caused by turbulence are blur, tilt and scintillation. These artefacts occur often locally in an image. Therefore turbulence corrections are required in each image patch of the size of the isoplanatic angle. Much research has been devoted to the field of turbulence mitigation. One of the main advantages of turbulence mitigation is that it enables visual recognition over larger distances by reducing the blur and motion in imagery. In many (military) scenarios this is of crucial importance. In this paper we give a brief overview of two software approaches to mitigate the visual artifacts caused by turbulence. These approaches are very diverse in complexity. It is shown that a more complex turbulence mitigation approach is needed to improve the imagery containing medium turbulence. The basic turbulence mitigation method is only capable of mitigating low turbulence.
Talbot, L.; Cheng, R.K.
1993-12-01
Turbulent combustion is the dominant process in heat and power generating systems. Its most significant aspect is to enhance the burning rate and volumetric power density. Turbulent mixing, however, also influences the chemical rates and has a direct effect on the formation of pollutants, flame ignition and extinction. Therefore, research and development of modern combustion systems for power generation, waste incineration and material synthesis must rely on a fundamental understanding of the physical effect of turbulence on combustion to develop theoretical models that can be used as design tools. The overall objective of this program is to investigate, primarily experimentally, the interaction and coupling between turbulence and combustion. These processes are complex and are characterized by scalar and velocity fluctuations with time and length scales spanning several orders of magnitude. They are also influenced by the so-called {open_quotes}field{close_quotes} effects associated with the characteristics of the flow and burner geometries. The authors` approach is to gain a fundamental understanding by investigating idealized laboratory flames. Laboratory flames are amenable to detailed interrogation by laser diagnostics and their flow geometries are chosen to simplify numerical modeling and simulations and to facilitate comparison between experiments and theory.
NASA Technical Reports Server (NTRS)
Bardina, Jorge E.
1995-01-01
The objective of this work is to develop, verify, and incorporate the baseline two-equation turbulence models which account for the effects of compressibility into the three-dimensional Reynolds averaged Navier-Stokes (RANS) code and to provide documented descriptions of the models and their numerical procedures so that they can be implemented into 3-D CFD codes for engineering applications.
NASA Astrophysics Data System (ADS)
Lee, S.; Song, C. H.; Park, R. S.; Park, M. E.; Han, K. M.; Kim, J.; Choi, M.; Ghim, Y. S.; Woo, J.-H.
2016-01-01
To improve short-term particulate matter (PM) forecasts in South Korea, the initial distribution of PM composition, particularly over the upwind regions, is primarily important. To prepare the initial PM composition, the aerosol optical depth (AOD) data retrieved from a geostationary equatorial orbit (GEO) satellite sensor, GOCI (Geostationary Ocean Color Imager) which covers a part of Northeast Asia (113-146° E; 25-47° N), were used. Although GOCI can provide a higher number of AOD data in a semicontinuous manner than low Earth orbit (LEO) satellite sensors, it still has a serious limitation in that the AOD data are not available at cloud pixels and over high-reflectance areas, such as desert and snow-covered regions. To overcome this limitation, a spatiotemporal-kriging (STK) method was used to better prepare the initial AOD distributions that were converted into the PM composition over Northeast Asia. One of the largest advantages in using the STK method in this study is that more observed AOD data can be used to prepare the best initial AOD fields compared with other methods that use single frame of observation data around the time of initialization. It is demonstrated in this study that the short-term PM forecast system developed with the application of the STK method can greatly improve PM10 predictions in the Seoul metropolitan area (SMA) when evaluated with ground-based observations. For example, errors and biases of PM10 predictions decreased by ˜ 60 and ˜ 70 %, respectively, during the first 6 h of short-term PM forecasting, compared with those without the initial PM composition. In addition, the influences of several factors on the performances of the short-term PM forecast were explored in this study. The influences of the choices of the control variables on the PM chemical composition were also investigated with the composition data measured via PILS-IC (particle-into-liquid sampler coupled with ion chromatography) and low air-volume sample
Bulk Comptonization by turbulence in accretion discs
NASA Astrophysics Data System (ADS)
Kaufman, J.; Blaes, O. M.
2016-06-01
Radiation pressure dominated accretion discs around compact objects may have turbulent velocities that greatly exceed the electron thermal velocities within the disc. Bulk Comptonization by the turbulence may therefore dominate over thermal Comptonization in determining the emergent spectrum. Bulk Comptonization by divergenceless turbulence is due to radiation viscous dissipation only. It can be treated as thermal Comptonization by solving the Kompaneets equation with an equivalent `wave' temperature, which is a weighted sum over the power present at each scale in the turbulent cascade. Bulk Comptonization by turbulence with non-zero divergence is due to both pressure work and radiation viscous dissipation. Pressure work has negligible effect on photon spectra in the limit of optically thin turbulence, and in this limit radiation viscous dissipation alone can be treated as thermal Comptonization with a temperature equivalent to the full turbulent power. In the limit of extremely optically thick turbulence, radiation viscous dissipation is suppressed, and the evolution of local photon spectra can be understood in terms of compression and expansion of the strongly coupled photon and gas fluids. We discuss the consequences of these effects for self-consistently resolving and interpreting turbulent Comptonization in spectral calculations in radiation magnetohydrodynamic simulations of high luminosity accretion flows.
RELATIVISTIC ACCRETION MEDIATED BY TURBULENT COMPTONIZATION
Socrates, Aristotle E-mail: socrates@astro.princeton.ed
2010-08-10
Black hole and neutron star accretion flows display unusually high levels of hard coronal emission in comparison to all other optically thick, gravitationally bound, turbulent astrophysical systems. Since these flows sit in deep relativistic gravitational potentials, their random bulk motions approach the speed of light, therefore allowing turbulent Comptonization to be an important effect. We show that the inevitable production of hard X-ray photons results from turbulent Comptonization in the limit where the turbulence is trans-sonic and the accretion power approaches the Eddington limit. In this regime, the turbulent Compton y-parameter approaches unity and the turbulent Compton temperature is a significant fraction of the electron rest mass energy, in agreement with the observed phenomena.
NASA Technical Reports Server (NTRS)
Lambert, Winifred C.
2000-01-01
This report describes the outcome of Phase 1 of the AMU's Improved Anvil Forecasting task. Forecasters in the 45th Weather Squadron and the Spaceflight Meteorology Group have found that anvil forecasting is a difficult task when predicting LCC and FR violations. The purpose of this task is to determine the technical feasibility of creating an anvil-forecasting tool. Work on this study was separated into three steps: literature search, forecaster discussions, and determination of technical feasibility. The literature search revealed no existing anvil-forecasting techniques. However, there appears to be growing interest in anvils in recent years. If this interest continues to grow, more information will be available to aid in developing a reliable anvil-forecasting tool. The forecaster discussion step revealed an array of methods on how better forecasting techniques could be developed. The forecasters have ideas based on sound meteorological principles and personal experience in forecasting and analyzing anvils. Based on the information gathered in the discussions with the forecasters, the conclusion of this report is that it is technically feasible at this time to develop an anvil forecasting technique that will significantly contribute to the confidence in anvil forecasts.
NASA Astrophysics Data System (ADS)
Newell, Alan C.; Rumpf, Benno
2011-01-01
In this article, we state and review the premises on which a successful asymptotic closure of the moment equations of wave turbulence is based, describe how and why this closure obtains, and examine the nature of solutions of the kinetic equation. We discuss obstacles that limit the theory's validity and suggest how the theory might then be modified. We also compare the experimental evidence with the theory's predictions in a range of applications. Finally, and most importantly, we suggest open challenges and encourage the reader to apply and explore wave turbulence with confidence. The narrative is terse but, we hope, delivered at a speed more akin to the crisp pace of a Hemingway story than the wordjumblingtumbling rate of a Joycean novel.
NASA Technical Reports Server (NTRS)
Rubesin, Morris W.
1987-01-01
Recent developments at several levels of statistical turbulence modeling applicable to aerodynamics are briefly surveyed. Emphasis is on examples of model improvements for transonic, two-dimensional flows. Experience with the development of these improved models is cited to suggest methods of accelerating the modeling process necessary to keep abreast of the rapid movement of computational fluid dynamics into the computation of complex three-dimensional flows.
The impact of Sun-weather research on forecasting
NASA Technical Reports Server (NTRS)
Larsen, M. F.
1979-01-01
The possible impact of Sun-weather research on forecasting is examined. The type of knowledge of the effect is evaluated to determine if it is in a form that can be used for forecasting purposes. It is concluded that the present understanding of the effect does not lend itself readily to applications for forecast purposes. The limits of present predictive skill are examined and it is found that skill is most lacking for prediction of the smallest scales of atmospheric motion. However, it is not expected that Sun-weather research will have any significant impact on forecasting the smaller scales since predictability at these scales is limited by the finite grid size resolution and the time scales of turbulent diffusion. The predictability limits for the largest scales are on the order of several weeks although presently only a one week forecast is achievable.
PREFACE Turbulent Mixing and Beyond
NASA Astrophysics Data System (ADS)
Abarzhi, Snezhana I.; Gauthier, Serge; Niemela, Joseph J.
2010-12-01
confined plasmas, magneto-convection, magneto-rotational instability, dynamo; Canonical plasmas: coupled plasmas, anomalous resistance, ionosphere; Physics of atmosphere: environmental fluid dynamics, weather forecasting, turbulent flows in stratified media and atmosphere, non-Boussinesq convection; Geophysics and Earth science: mantle-lithosphere tectonics, oceanography, turbulent convection under rotation, planetary interiors; Combustion: dynamics of flames and fires, deflagration-to-detonation transition, blast waves and explosions, flows with chemical reactions, flows in jet engines; Mathematical aspects of non-equilibrium dynamics: vortex dynamics, singularities, discontinuities, asymptotic dynamics, weak solutions, well- and ill-posedness, continuous transports out of thermodynamic equilibrium; Stochastic processes and probabilistic description: long-tail distributions and anomalous diffusion, data assimilation and processing methodologies, error estimate and uncertainty quantification, statistically unsteady processes; Advanced numerical simulations: continuous DNS/LES/RANS, molecular dynamics, Monte-Carlo, predictive modeling, validation and verification of numerical models; Experimental diagnostics: model experiments in high energy density and low energy density regimes, plasma diagnostics, fluid flow visualizations and control, opto-fluidics, novel optical methods, holography, advanced technologies. TMB-2009 was organized by the following members of the Organizing Committee: Snezhana I Abarzhi (chairperson, Chicago, USA) Malcolm J Andrews (Los Alamos National Laboratory, USA) Sergei I Anisimov (Landau Institute for Theoretical Physics, Russia) Hiroshi Azechi (Institute of Laser Engineering, Osaka, Japan) Serge Gauthier (Commissariat à l'Energie Atomique, France) Christopher J Keane (Lawrence Livermore National Laboratory, USA) Robert Rosner (Argonne National Laboratory, USA) Katepalli R Sreenivasan (International Centre for Theoretical Physics, Italy) Alexander
Highley, D.D.; Hilmes, T.J. )
1993-07-01
This article discusses the use and training of artificial neural networks (ANNs) for load forecasting. The topics of the article include a brief overview of neural networks, interest in ANNs, training of neural networks, a case study in load forecasting, and the potential for using an artificial neural network to perform short-term load forecasting.
Quantifying Atmospheric Impacts on Space Optical Imaging and Communications
NASA Astrophysics Data System (ADS)
Alliss, R.; Felton, B.
2011-09-01
background (CSB). The CSB represents a recent depiction (one month weighted average) of what the scene looks like, radiometrically, in the absence of clouds so that it can be compared with imagery at the requested analysis time. If the actual imagery compared to the CSB differs by more than a specified threshold then clouds are indicated. Cloud properties such as cloud top heights and bases and optical depths are subsequently derived. The result represents a high spatial and temporal resolution climatology that can be used to derive accurate Cloud Free Line of Sight (CFLOS) statistics in order to quantify atmospheric effects on optical imaging and communication systems. For example, clouds over the State of Hawaii are quite variable in frequency ranging from less than 15% in some of the sheltered coastal waters and local summits to greater than 70% on the mauka (windward) sides of the islands. Vertical optical depths from the summit can range from 0.5dB to greater than 50dB. Optical turbulence is characterized by the refractive index structure function Cn2, which in turn is used to calculate atmospheric seeing parameters. While attempts have been made to characterize Cn2 using empirical models, it can be calculated more directly from Numerical Weather Prediction (NWP) simulations using pressure, temperature, thermal stability, vertical wind shear, turbulent Prandtl number, and turbulence kinetic energy (TKE). A modified version of the Weather Research and Forecast (WRF) model is used to generate Cn2 throughout the atmospheric column, allowing for ground-to-space seeing estimates of ro. Simulations are performed using the Maui High Performance Computing Centers (MHPCC) Mana cluster. Detailed results from both the clouds and turbulence simulations will be shown at the conference with specific applications to space imaging and communication systems.
NASA Astrophysics Data System (ADS)
Wilde, B. H.; Rosen, P. A.; Foster, J. M.; Perry, T. S.; Steinkamp, M. J.; Robey, H. F.; Khokhlov, A. M.; Gittings, M. L.; Coker, R. F.; Keiter, P. A.; Knauer, J. P.; Drake, R. P.; Remington, B. A.; Bennett, G. R.; Sinars, D. B.; Campbell, R. B.; Mehlhorn, T. A.
2003-10-01
Over the last few years we have fielded numerous supersonic jet experiments on the NOVA and OMEGA lasers and Sandia's pulsed-power Z-machine in a collaboration between Los Alamos National Laboratory, the Atomic Weapons Establishment, Lawrence Livermore National Laboratory, and Sandia National Laboratory. These experiments are being conducted to help validate our radiation-hydrodynamic codes, especially the newly developing ASC codes. One of the outstanding questions is whether these types of jets should turn turbulent given their high Reynolds number. Recently we have modified our experiments to have more Kelvin-Helmholtz shear, run much later in time and therefore have a better chance of going turbulent. In order to diagnose these large (several mm) jets at very late times ( 1000 ns) we are developing point-projection imaging on both the OMEGA laser, the Sandia Z-Machine, and ultimately at NIF. Since these jets have similar Euler numbers to jets theorized to be produced in supernovae explosions, we are also collaborating with the astrophysics community to help in the validation of their new codes. This poster will present a review of the laser and pulsed-power experiments and a comparison of the data to simulations by the codes from the various laboratories. We will show results of simulations wherein these jets turn highly 3-dimensional and show characteristics of turbulence. With the new data, we hope to be able to validate the sub-grid-scale turbulent mix models (e. g. BHR) that are being incorporated into our codes.*This work is performed under the auspices of the U. S. Department of Energy by the Los Alamos National Laboratory Laboratory under Contract No. W-7405-ENG-36, Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48, the Laboratory for Laser Energetics under Contract No. DE-FC03-92SF19460, Sandia National Laboratories under Contract No. DE-AC04-94AL85000, the Office of Naval Research, and the NASA Astrophysical Theory Grant.
NASA Astrophysics Data System (ADS)
Meneguz, Elena; Turp, Debi; Wells, Helen
2015-04-01
It is well known that encounters with moderate or severe turbulence can lead to passenger injuries and incur high costs for airlines from compensation and litigation. As one of two World Area Forecast Centres (WAFCs), the Met Office has responsibility for forecasting en-route weather hazards worldwide for aviation above a height of 10,000 ft. Observations from commercial aircraft provide a basis for gaining a better understanding of turbulence and for improving turbulence forecasts through verification. However there is currently a lack of information regarding the possible cause of the observed turbulence, or whether the turbulence occurred within cloud. Such information would be invaluable for the development of forecasting techniques for particular types of turbulence and for forecast verification. Of all the possible sources of turbulence, convective activity is believed to be a major cause of turbulence. Its relative importance over the Europe and North Atlantic area has not been yet quantified in a systematic way: in this study, a new approach is developed to automate identification of turbulent encounters in the proximity of convective clouds. Observations of convection are provided from two independent sources: a surface based lightning network and satellite imagery. Lightning observations are taken from the Met Office Arrival Time Detections network (ATDnet). ATDnet has been designed to identify cloud-to-ground flashes over Europe but also detects (a smaller fraction of) strikes over the North Atlantic. Meteosat Second Generation (MSG) satellite products are used to identify convective clouds by applying a brightness temperature filtering technique. The morphological features of cold cloud tops are also investigated. The system is run for all in situ turbulence reports received from airlines for a total of 12 months during summer 2013 and 2014 for the domain of interest. Results of this preliminary short term climatological study show significant intra
PREFACE: Turbulent Mixing and Beyond Turbulent Mixing and Beyond
NASA Astrophysics Data System (ADS)
Abarzhi, Snezhana I.; Gauthier, Serge; Rosner, Robert
2008-10-01
The goals of the International Conference `Turbulent Mixing and Beyond' are to expose the generic problem of Turbulence and Turbulent Mixing in Unsteady Flows to a wide scientific community, to promote the development of new ideas in tackling the fundamental aspects of the problem, to assist in the application of novel approaches in a broad range of phenomena, where the non-canonical turbulent processes occur, and to have a potential impact on technology. The Conference provides the opportunity to bring together scientists from the areas which include, but are not limited to, high energy density physics, plasmas, fluid dynamics, turbulence, combustion, material science, geophysics, astrophysics, optics and telecommunications, applied mathematics, probability and statistics, and to have their attention focused on the long-standing formidable task. The Turbulent Mixing and Turbulence in Unsteady Flows, including multiphase flows, plays a key role in a wide variety of phenomena, ranging from astrophysical to nano-scales, under either high or low energy density conditions. Inertial confinement and magnetic fusion, light-matter interaction and non-equilibrium heat transfer, properties of materials under high strain rates, strong shocks, explosions, blast waves, supernovae and accretion disks, stellar non-Boussinesq and magneto-convection, planetary interiors and mantle-lithosphere tectonics, premixed and non-premixed combustion, oceanography, atmospheric flows, unsteady boundary layers, hypersonic and supersonic flows, are a few examples to list. A grip on unsteady turbulent processes is crucial for cutting-edge technology such as laser-micromachining and free-space optical telecommunications, and for industrial applications in aeronautics. Unsteady Turbulent Processes are anisotropic, non-local and multi-scale, and their fundamental scaling, spectral and invariant properties depart from the classical Kolmogorov scenario. The singular aspects and similarity of the
A radiosonde thermal sensor technique for measurement of atmospheric turbulence
NASA Technical Reports Server (NTRS)
Bufton, J. L.
1975-01-01
A new system was developed to measure vertical profiles of microthermal turbulence in the free atmosphere. It combines thermal sensor technology with radiosonde balloon systems. The resultant data set from each thermosonde flight is a profile of the strength and distribution of microthermal fluctuations which act as tracers for turbulence. The optical strength of this turbulence is computed and used to predict optical and laser beam propagation statistics. A description of the flight payload, examples of turbulence profiles, and comparison with simultaneous stellar observations are included.
Statistical turbulence theory and turbulence phenomenology
NASA Technical Reports Server (NTRS)
Herring, J. R.
1973-01-01
The application of deductive turbulence theory for validity determination of turbulence phenomenology at the level of second-order, single-point moments is considered. Particular emphasis is placed on the phenomenological formula relating the dissipation to the turbulence energy and the Rotta-type formula for the return to isotropy. Methods which deal directly with most or all the scales of motion explicitly are reviewed briefly. The statistical theory of turbulence is presented as an expansion about randomness. Two concepts are involved: (1) a modeling of the turbulence as nearly multipoint Gaussian, and (2) a simultaneous introduction of a generalized eddy viscosity operator.
NASA Technical Reports Server (NTRS)
Davis, R. E.; Champine, R. A.; Ehernberger, L. J.
1979-01-01
The results of 46 clear air turbulence (CAT) probing missions conducted with an extensively instrumented B-57B aircraft are summarized. Turbulence samples were obtained under diverse conditions including mountain waves, jet streams, upper level fronts and troughs, and low altitude mechanical and thermal turbulence. CAT was encouraged on 20 flights comprising 77 data runs. In all, approximately 4335 km were flown in light turbulence, 1415 km in moderate turbulence, and 255 km in severe turbulence during the program. The flight planning, operations, and turbulence forecasting aspects conducted with the B-57B aircraft are presented.
Jenu, M.Z.M.; Bebbington, D.H.O.
1994-11-01
The split-step method was used to derive the full spatial dependence of the fourth moment of a plane-wave propagating in a two-dimensional turbulent atmosphere with a power-law spectrum for two values of the scattering parameter {gamma}{sub {ital k}} = 0 and 1 [J. Opt. Soc. Am. A {bold 2}, 2133 (1985)]. The changes in {gamma}{sub {ital k}} were obtained by the use of two different values of the inner scale of turbulence {ital l}{sub 0} while the operating wavelength and turbulent strength were kept constant. In this way the influence of {ital l}{sub 0} on the field statistics can be obtained. The results of intensity scintillation index {sigma}{sub {ital I}}{sup 2} and covariance function {ital b}{sub {ital I}} are also presented. The agreement of {sigma}{sub {ital I}}{sup 2} with the results of the reference cited above especially for {gamma}{sub {ital k}} = 0 is good. We also used the results of {ital b}{sub {ital I}} to study the asymptotic dependence of the characteristic correlation length on {zeta}, where {zeta} is the propagation-range scale.
Reflective ghost imaging through turbulence
Hardy, Nicholas D.; Shapiro, Jeffrey H.
2011-12-15
Recent work has indicated that ghost imaging may have applications in standoff sensing. However, most theoretical work has addressed transmission-based ghost imaging. To be a viable remote-sensing system, the ghost imager needs to image rough-surfaced targets in reflection through long, turbulent optical paths. We develop, within a Gaussian-state framework, expressions for the spatial resolution, image contrast, and signal-to-noise ratio of such a system. We consider rough-surfaced targets that create fully developed speckle in their returns and Kolmogorov-spectrum turbulence that is uniformly distributed along all propagation paths. We address both classical and nonclassical optical sources, as well as a computational ghost imager.
Sources and dynamics of turbulence in the upper troposphere and lower stratosphere: A review
NASA Astrophysics Data System (ADS)
Sharman, R. D.; Trier, S. B.; Lane, T. P.; Doyle, J. D.
2012-06-01
Turbulence is a well-known hazard to aviation that is responsible for numerous injuries each year, with occasional fatalities, and is the underlying cause of many people's fear of air travel. Not only are turbulence encounters a safety issue, they also result in millions of dollars of operational costs to airlines, leading to increased costs passed on to the consumer. For these reasons, pilots, dispatchers, and air traffic controllers attempt to avoid turbulence wherever possible. Accurate forecasting of aviation-scale turbulence has been hampered in part by a lack of understanding of the underlying dynamical processes. However, more precise observations of turbulence encounters together with recent research into turbulence generation processes is helping to elucidate the detailed dynamical processes involved and is laying the foundation for improved turbulence forecasting and avoidance. In this paper we briefly review some of the more important recent observational, theoretical, and modeling results related to turbulence at cruise altitudes for commercial aircraft (i.e., the upper troposphere and lower stratosphere), and their implications for aviation turbulence forecasting.
Laser beam propagation in atmospheric turbulence
NASA Technical Reports Server (NTRS)
Murty, S. S. R.
1979-01-01
The optical effects of atmospheric turbulence on the propagation of low power laser beams are reviewed in this paper. The optical effects are produced by the temperature fluctuations which result in fluctuations of the refractive index of air. The commonly-used models of index-of-refraction fluctuations are presented. Laser beams experience fluctuations of beam size, beam position, and intensity distribution within the beam due to refractive turbulence. Some of the observed effects are qualitatively explained by treating the turbulent atmosphere as a collection of moving gaseous lenses of various sizes. Analytical results and experimental verifications of the variance, covariance and probability distribution of intensity fluctuations in weak turbulence are presented. For stronger turbulence, a saturation of the optical scintillations is observed. The saturation of scintillations involves a progressive break-up of the beam into multiple patches; the beam loses some of its lateral coherence. Heterodyne systems operating in a turbulent atmosphere experience a loss of heterodyne signal due to the destruction of coherence.
Correction methods for underwater turbulence degraded imaging
NASA Astrophysics Data System (ADS)
Kanaev, A. V.; Hou, W.; Restaino, S. R.; Matt, S.; Gładysz, S.
2014-10-01
The use of remote sensing techniques such as adaptive optics and image restoration post processing to correct for aberrations in a wavefront of light propagating through turbulent environment has become customary for many areas including astronomy, medical imaging, and industrial applications. EO imaging underwater has been mainly concentrated on overcoming scattering effects rather than dealing with underwater turbulence. However, the effects of turbulence have crucial impact over long image-transmission ranges and under extreme turbulence conditions become important over path length of a few feet. Our group has developed a program that attempts to define under which circumstances application of atmospheric remote sensing techniques could be envisioned. In our experiments we employ the NRL Rayleigh-Bénard convection tank for simulated turbulence environment at Stennis Space Center, MS. A 5m long water tank is equipped with heating and cooling plates that generate a well measured thermal gradient that in turn produces various degrees of turbulence. The image or laser beam spot can be propagated along the tank's length where it is distorted by induced turbulence. In this work we report on the experimental and theoretical findings of the ongoing program. The paper will introduce the experimental setup, the techniques used, and the measurements made as well as describe novel methods for postprocessing and correction of images degraded by underwater turbulence.
Forecaster priorities for improving probabilistic flood forecasts
NASA Astrophysics Data System (ADS)
Wetterhall, Fredrik; Pappenberger, Florian; Alfieri, Lorenzo; Cloke, Hannah; Thielen, Jutta
2014-05-01
Hydrological ensemble prediction systems (HEPS) have in recent years been increasingly used for the operational forecasting of floods by European hydrometeorological agencies. The most obvious advantage of HEPS is that more of the uncertainty in the modelling system can be assessed. In addition, ensemble prediction systems generally have better skill than deterministic systems both in the terms of the mean forecast performance and the potential forecasting of extreme events. Research efforts have so far mostly been devoted to the improvement of the physical and technical aspects of the model systems, such as increased resolution in time and space and better description of physical processes. Developments like these are certainly needed; however, in this paper we argue that there are other areas of HEPS that need urgent attention. This was also the result from a group exercise and a survey conducted to operational forecasters within the European Flood Awareness System (EFAS) to identify the top priorities of improvement regarding their own system. They turned out to span a range of areas, the most popular being to include verification of an assessment of past forecast performance, a multi-model approach for hydrological modelling, to increase the forecast skill on the medium range (>3 days) and more focus on education and training on the interpretation of forecasts. In light of limited resources, we suggest a simple model to classify the identified priorities in terms of their cost and complexity to decide in which order to tackle them. This model is then used to create an action plan of short-, medium- and long-term research priorities with the ultimate goal of an optimal improvement of EFAS in particular and to spur the development of operational HEPS in general.
Weather forecasting expert system study
NASA Technical Reports Server (NTRS)
1985-01-01
Weather forecasting is critical to both the Space Transportation System (STS) ground operations and the launch/landing activities at NASA Kennedy Space Center (KSC). The current launch frequency places significant demands on the USAF weather forecasters at the Cape Canaveral Forecasting Facility (CCFF), who currently provide the weather forecasting for all STS operations. As launch frequency increases, KSC's weather forecasting problems will be great magnified. The single most important problem is the shortage of highly skilled forecasting personnel. The development of forecasting expertise is difficult and requires several years of experience. Frequent personnel changes within the forecasting staff jeopardize the accumulation and retention of experience-based weather forecasting expertise. The primary purpose of this project was to assess the feasibility of using Artificial Intelligence (AI) techniques to ameliorate this shortage of experts by capturing aria incorporating the forecasting knowledge of current expert forecasters into a Weather Forecasting Expert System (WFES) which would then be made available to less experienced duty forecasters.
Weather assessment and forecasting
NASA Technical Reports Server (NTRS)
1977-01-01
Data management program activities centered around the analyses of selected far-term Office of Applications (OA) objectives, with the intent of determining if significant data-related problems would be encountered and if so what alternative solutions would be possible. Three far-term (1985 and beyond) OA objectives selected for analyses as having potential significant data problems were large-scale weather forecasting, local weather and severe storms forecasting, and global marine weather forecasting. An overview of general weather forecasting activities and their implications upon the ground based data system is provided. Selected topics were specifically oriented to the use of satellites.
NASA Astrophysics Data System (ADS)
Doerner, R.; Hübinger, B.; Martienssen, W.
1994-07-01
The exponential separation of initially adjacent trajectories restricts the predictability of deterministic chaotic motions. The predictability depends on the initial state from where the trajectory starts that shall be forecasted. By calculating the predictability simultaneously with the forecast, we are able to reject forecasts with low reliability immediately, thereby decreasing drastically the average forecast error. We test this scheme experimentally on Chua's circuit [Komuro, Tokunaga, Matsumoto, Chua, and Hotta, Int. J. Bifurc. Chaos 1, 139 (1991)], basing all calculations only on a time series of a single scalar variable.
A controlled laboratory environment to study EO signal degradation due to underwater turbulence
NASA Astrophysics Data System (ADS)
Matt, Silvia; Hou, Weilin; Goode, Wesley; Liu, Guigen; Han, Ming; Kanaev, Andrey; Restaino, Sergio
2015-05-01
Temperature microstructure in the ocean can lead to localized changes in the index of refraction and can distort underwater electro-optical (EO) signal transmission. A similar phenomenon is well-known from atmospheric optics and generally referred to as "optical turbulence". Though turbulent fluctuations in the ocean distort EO signal transmission and can impact various underwater applications, from diver visibility to active and passive remote sensing, there have been few studies investigating the subject. To provide a test bed for the study of impacts from turbulent flows on underwater EO signal transmission, and to examine and mitigate turbulence effects, we set up a laboratory turbulence environment allowing the variation of turbulence intensity. Convective turbulence is generated in a large Rayleigh- Bénard tank and the turbulent flow is quantified using high-resolution Acoustic Doppler Velocimeter profilers and fast thermistor probes. The turbulence measurements are complemented by computational fluid dynamics simulations of convective turbulence emulating the tank environment. These numerical simulations supplement the sparse laboratory measurements. The numerical data compared well to the laboratory data and both conformed to the Kolmogorov spectrum of turbulence and the Batchelor spectrum of temperature fluctuations. The controlled turbulence environment can be used to assess optical image degradation in the tank in relation to turbulence intensity, as well as to apply adaptive optics techniques. This innovative approach that combines optical techniques, turbulence measurements and numerical simulations can help understand how to mitigate the effects of turbulence impacts on underwater optical signal transmission, as well as advance optical techniques to probe oceanic processes.
Measuring plasma turbulence using low coherence microwave radiation
Smith, D. R.
2012-02-20
Low coherence backscattering (LCBS) is a proposed diagnostic technique for measuring plasma turbulence and fluctuations. LCBS is an adaptation of optical coherence tomography, a biomedical imaging technique. Calculations and simulations show LCBS measurements can achieve centimeter-scale spatial resolution using low coherence microwave radiation. LCBS measurements exhibit several advantages over standard plasma turbulence measurement techniques including immunity to spurious reflections and measurement access in hollow density profiles. Also, LCBS is scalable for 1-D profile measurements and 2-D turbulence imaging.
NASA Technical Reports Server (NTRS)
Mcmahon, J.
1972-01-01
Opinions or plans of qualified experts in the field are used for forecasting future requirements for air navigational facilities and services of international civil aviation. ICAO periodically collects information from Stators and operates on anticipated future operations, consolidates this information, and forecasts the future level of activity at different airports.
Ohira, Yutaka
2013-04-10
We consider particle acceleration by large-scale incompressible turbulence with a length scale larger than the particle mean free path. We derive an ensemble-averaged transport equation of energetic charged particles from an extended transport equation that contains the shear acceleration. The ensemble-averaged transport equation describes particle acceleration by incompressible turbulence (turbulent shear acceleration). We find that for Kolmogorov turbulence, the turbulent shear acceleration becomes important on small scales. Moreover, using Monte Carlo simulations, we confirm that the ensemble-averaged transport equation describes the turbulent shear acceleration.
Challenging Issues on fog forecast with a three-dimensional fog forecast model
NASA Astrophysics Data System (ADS)
Masbou, M.
2012-12-01
Fog has a significant impact on economical aspect (traffic management and safety) as well as on environmental issues (fresh water source for the population and the biosphere in arid region). However, reliable fog and visibility forecasts stay challenging issue. Fog is generally a small scale phenomenon which is mostly affected by local advective transport, radiation, topography, vegetation, turbulent mixing at the surface as well as its microphysical structure. In order to consider these intertwined processes, the three-dimensional fog forecast model, COSMO-FOG, with a high vertical resolution with different microphysical complexity has been developed. This model includes a microphysical parameterisation based on the one-dimensional fog forecast model. The implementation of the cloud water droplets as a new prognostic variable allows a detailed definition of the sedimentation processes and the variations in visibility. Moreover, the turbulence scheme, based on a Mellor-Yamada 2.5 order and a closure of a 2nd order has been modified to improve the model behaviour in case of a stable atmosphere structure, occurring typically during night radiative fog episodes. The potential of COSMO-FOG will be presented in some realistic fog situations (flat, bumpy and complex terrain). The fog spatial extension will be compared with MSG satellite products for fog and low cloud. The interplays between dynamical, thermodynamical patterns and the soil-atmosphere interactions will be presented.
The problem of atmospheric turbulence
NASA Technical Reports Server (NTRS)
Toomre, J.; HILL; MERRYFIELD; GOUGH
1984-01-01
All ground-based observations of the solar five-minute oscillations are affected by turbulence in the Earth's atmosphere that leads to substantial refractive index variations. The turbulent motions serve to mix an air mass that is thermally stratified in the vertical, thereby producing intermittent thermal fluctuations over a wide range of heights in the atmosphere. These thermal structures yield refractive index changes that deflect the light path in a complicated way, producing intricate variations of amplitude and phase in what might have started out as simple plane waves. Since the fluid turbulence is statistical in nature, so too is the optical turbulence which is an integral measure of the refractive index changes along the light travel path. All of this produces what is usually called atmospheric seeing, which consists of image motion, blurring and distortion across the field of view. The effects of atmospheric seeing upon observations of five-minute oscillations carried out from the ground were assessed. This will help to provide a baseline estimate of the scienctific benefits that might accrue if one were able to observe the same oscillations from a space observatory unfettered by seeing effects.
Evaluation of turbulence mitigation methods
NASA Astrophysics Data System (ADS)
van Eekeren, Adam W. M.; Huebner, Claudia S.; Dijk, Judith; Schutte, Klamer; Schwering, Piet B. W.
2014-05-01
Atmospheric turbulence is a well-known phenomenon that diminishes the recognition range in visual and infrared image sequences. There exist many different methods to compensate for the effects of turbulence. This paper focuses on the performance of two software-based methods to mitigate the effects of low- and medium turbulence conditions. Both methods are capable of processing static and dynamic scenes. The first method consists of local registration, frame selection, blur estimation and deconvolution. The second method consists of local motion compensation, fore- /background segmentation and weighted iterative blind deconvolution. A comparative evaluation using quantitative measures is done on some representative sequences captured during a NATO SET 165 trial in Dayton. The amount of blurring and tilt in the imagery seem to be relevant measures for such an evaluation. It is shown that both methods improve the imagery by reducing the blurring and tilt and therefore enlarge the recognition range. Furthermore, results of a recognition experiment using simulated data are presented that show that turbulence mitigation using the first method improves the recognition range up to 25% for an operational optical system.
The impact of turbulent fluctuations on light propagation in a controlled environment
NASA Astrophysics Data System (ADS)
Matt, Silvia; Hou, Weilin; Goode, Wesley
2014-05-01
Underwater temperature and salinity microstructure can lead to localized changes in the index of refraction and can be a limiting factor in oceanic environments. This optical turbulence can affect electro-optical (EO) signal transmissions that impact various applications, from diver visibility to active and passive remote sensing. To quantify the scope of the impacts from turbulent flows on EO signal transmission, and to examine and mitigate turbulence effects, we perform experiments in a controlled turbulence environment allowing the variation of turbulence intensity. This controlled turbulence setup is implemented at the Naval Research Laboratory Stennis Space Center (NRLSSC). Convective turbulence is generated in a classical Rayleigh-Benard tank and the turbulent flow is quantified using a state-of-the-art suite of sensors that includes high-resolution Acoustic Doppler Velocimeter profilers and fast thermistor probes. The measurements are complemented by very high- resolution non-hydrostatic numerical simulations. These computational fluid dynamics simulations allow for a more complete characterization of the convective flow in the laboratory tank than would be provided by measurements alone. Optical image degradation in the tank is assessed in relation to turbulence intensity. The unique approach of integrating optical techniques, turbulence measurements and numerical simulations helps advance our understanding of how to mitigate the effects of turbulence impacts on underwater optical signal transmission, as well as of the use of optical techniques to probe oceanic processes.
Imaging through turbulence using a plenoptic sensor
NASA Astrophysics Data System (ADS)
Wu, Chensheng; Ko, Jonathan; Davis, Christopher C.
2015-09-01
Atmospheric turbulence can significantly affect imaging through paths near the ground. Atmospheric turbulence is generally treated as a time varying inhomogeneity of the refractive index of the air, which disrupts the propagation of optical signals from the object to the viewer. Under circumstances of deep or strong turbulence, the object is hard to recognize through direct imaging. Conventional imaging methods can't handle those problems efficiently. The required time for lucky imaging can be increased significantly and the image processing approaches require much more complex and iterative de-blurring algorithms. We propose an alternative approach using a plenoptic sensor to resample and analyze the image distortions. The plenoptic sensor uses a shared objective lens and a microlens array to form a mini Keplerian telescope array. Therefore, the image obtained by a conventional method will be separated into an array of images that contain multiple copies of the object's image and less correlated turbulence disturbances. Then a highdimensional lucky imaging algorithm can be performed based on the collected video on the plenoptic sensor. The corresponding algorithm will select the most stable pixels from various image cells and reconstruct the object's image as if there is only weak turbulence effect. Then, by comparing the reconstructed image with the recorded images in each MLA cell, the difference can be regarded as the turbulence effects. As a result, the retrieval of the object's image and extraction of turbulence effect can be performed simultaneously.
Forecasting the solar activity cycle: new insights
NASA Astrophysics Data System (ADS)
Nandy, Dibyendu; Karak, Bidya Binay
2013-07-01
Having advance knowledge of solar activity is important because the Sun's magnetic output governs space weather and impacts technologies reliant on space. However, the irregular nature of the solar cycle makes solar activity predictions a challenging task. This is best achieved through appropriately constrained solar dynamo simulations and as such the first step towards predictions is to understand the underlying physics of the solar dynamo mechanism. In Babcock-Leighton type dynamo models, the poloidal field is generated near the solar surface whereas the toroidal field is generated in the solar interior. Therefore a finite time is necessary for the coupling of the spatially segregated source layers of the dynamo. This time delay introduces a memory in the dynamo mechanism which allows forecasting of future solar activity. Here we discuss how this forecasting ability of the solar cycle is affected by downward turbulent pumping of magnetic flux. With significant turbulent pumping the memory of the dynamo is severely degraded and thus long term prediction of the solar cycle is not possible; only a short term prediction of the next cycle peak may be possible based on observational data assimilation at the previous cycle minimum.
Generalized atmospheric turbulence MTF for wave propagating through non-Kolmogorov turbulence.
Cui, Lin-yan; Xue, Bin-dang; Cao, Xiao-guang; Dong, Jian-kang; Wang, Jie-ning
2010-09-27
A generalized exponential spectrum model is derived, which considers finite turbulence inner and outer scales and has a general spectral power law value between the range 3 to 5 instead of standard power law value 11/3. Based on this generalized spectrum model, a new generalized long exposure turbulence modulation transfer function (MTF) is obtained for optical plane and spherical wave propagating through horizontal path in weak fluctuation turbulence. When the inner scale and outer scale are set to zero and infinite, respectively, the new generalized MTF is reduced to the classical generalized MTF derived from the non-Kolmogorov spectrum.
Simultaneous video stabilization and moving object detection in turbulence.
Oreifej, Omar; Li, Xin; Shah, Mubarak
2013-02-01
Turbulence mitigation refers to the stabilization of videos with nonuniform deformations due to the influence of optical turbulence. Typical approaches for turbulence mitigation follow averaging or dewarping techniques. Although these methods can reduce the turbulence, they distort the independently moving objects, which can often be of great interest. In this paper, we address the novel problem of simultaneous turbulence mitigation and moving object detection. We propose a novel three-term low-rank matrix decomposition approach in which we decompose the turbulence sequence into three components: the background, the turbulence, and the object. We simplify this extremely difficult problem into a minimization of nuclear norm, Frobenius norm, and l1 norm. Our method is based on two observations: First, the turbulence causes dense and Gaussian noise and therefore can be captured by Frobenius norm, while the moving objects are sparse and thus can be captured by l1 norm. Second, since the object's motion is linear and intrinsically different from the Gaussian-like turbulence, a Gaussian-based turbulence model can be employed to enforce an additional constraint on the search space of the minimization. We demonstrate the robustness of our approach on challenging sequences which are significantly distorted with atmospheric turbulence and include extremely tiny moving objects.
Distinguishing ichthyogenic turbulence from geophysical turbulence
NASA Astrophysics Data System (ADS)
Pujiana, Kandaga; Moum, James N.; Smyth, William D.; Warner, Sally J.
2015-05-01
Measurements of currents and turbulence beneath a geostationary ship in the equatorial Indian Ocean during a period of weak surface forcing revealed unexpectedly strong turbulence beneath the surface mixed layer. Coincident with the turbulence was a marked reduction of the current speeds registered by shipboard Doppler current profilers, and an increase in their variability. At a mooring 1 km away, measurements of turbulence and currents showed no such anomalies. Correlation with the shipboard echo sounder measurements indicate that these nighttime anomalies were associated with fish aggregations beneath the ship. The fish created turbulence by swimming against the strong zonal current in order to remain beneath the ship, and their presence affected the Doppler speed measurements. The principal characteristics of the resultant ichthyogenic turbulence are (i) low wave number roll-off of shear spectra in the inertial subrange relative to geophysical turbulence, (ii) Thorpe overturning scales that are small compared with the Ozmidov scale, and (iii) low mixing efficiency. These factors extend previous findings by Gregg and Horne (2009) to a very different biophysical regime and support the general conclusion that the biological contribution to mixing the ocean via turbulence is negligible.
NASA Technical Reports Server (NTRS)
Scoggins, J. R.; Clark, T. L.; Possiel, N. C.
1975-01-01
Procedures for forecasting clear air turbulence in the stratosphere over the western United States from rawinsonde data are described and results presented. Approaches taken to relate meteorological parameters to regions of turbulence and nonturbulence encountered by the XB-70 during 46 flights at altitudes between 12-20 km include: empirical probabilities, discriminant function analysis, and mountainwave theory. Results from these techniques were combined into a procedure to forecast regions of clear air turbulence with an accuracy of 70-80 percent. A computer program was developed to provide an objective forecast directly from the rawinsonde sounding data.
NASA Astrophysics Data System (ADS)
Zentgraf, Florian; Baum, Elias; Böhm, Benjamin; Dreizler, Andreas; Peterson, Brian
2016-04-01
Planar particle image velocimetry (PIV) and tomographic PIV (TPIV) measurements are utilized to analyze turbulent statistical theory quantities and the instantaneous turbulence within a single-cylinder optical engine. Measurements are performed during the intake and mid-compression stroke at 800 and 1500 RPM. TPIV facilitates the evaluation of spatially resolved Reynolds stress tensor (RST) distributions, anisotropic Reynolds stress invariants, and instantaneous turbulent vortical structures. The RST analysis describes distributions of individual velocity fluctuation components that arise from unsteady turbulent flow behavior as well as cycle-to-cycle variability (CCV). A conditional analysis, for which instantaneous PIV images are sampled by their tumble center location, reveals that CCV and turbulence have similar contributions to RST distributions at the mean tumble center, but turbulence is dominant in regions peripheral to the tumble center. Analysis of the anisotropic Reynolds stress invariants reveals the spatial distribution of axisymmetric expansion, axisymmetric contraction, and 3D isotropy within the cylinder. Findings indicate that the mid-compression flow exhibits a higher tendency toward 3D isotropy than the intake flow. A novel post-processing algorithm is utilized to classify the geometry of instantaneous turbulent vortical structures and evaluate their frequency of occurrence within the cylinder. Findings are coupled with statistical theory quantities to provide a comprehensive understanding of the distribution of turbulent velocity components, the distribution of anisotropic states of turbulence, and compare the turbulent vortical flow distribution that is theoretically expected to what is experimentally observed. The analyses reveal requisites of important turbulent flow quantities and discern their sensitivity to the local flow topography and engine operation.
Statistical evaluation of forecasts
NASA Astrophysics Data System (ADS)
Mader, Malenka; Mader, Wolfgang; Gluckman, Bruce J.; Timmer, Jens; Schelter, Björn
2014-08-01
Reliable forecasts of extreme but rare events, such as earthquakes, financial crashes, and epileptic seizures, would render interventions and precautions possible. Therefore, forecasting methods have been developed which intend to raise an alarm if an extreme event is about to occur. In order to statistically validate the performance of a prediction system, it must be compared to the performance of a random predictor, which raises alarms independent of the events. Such a random predictor can be obtained by bootstrapping or analytically. We propose an analytic statistical framework which, in contrast to conventional methods, allows for validating independently the sensitivity and specificity of a forecasting method. Moreover, our method accounts for the periods during which an event has to remain absent or occur after a respective forecast.
Studying Turbulence Using Numerical Simulation Databases, 2. Proceedings of the 1988 Summer Program
NASA Technical Reports Server (NTRS)
1988-01-01
The focus of the program was on the use of direct numerical simulations of turbulent flow for study of turbulence physics and modeling. A special interest was placed on turbulent mixing layers. The required data for these investigations were generated from four newly developed codes for simulation of time and spatially developing incompressible and compressible mixing layers. Also of interest were the structure of wall bounded turbulent and transitional flows, evaluation of diagnostic techniques for detection of organized motions, energy transfer in isotropic turbulence, optical propagation through turbulent media, and detailed analysis of the interaction of vortical structures.
Numerical weather forecasting with anelastic model
NASA Astrophysics Data System (ADS)
Wójcik, Damian; Kurowski, Marcin; Piotrowski, Zbigniew; Rosa, Bogdan; Ziemiański, Michał
2013-04-01
Research conducted at Polish Institute of Meteorology and Water Management, National Research Institute, in collaboration with Consortium for Small Scale Modeling (COSMO) are aimed at developing new conservative dynamical core for next generation operational weather prediction model. Within the frames of the project a new prototype model has been developed. The dynamical core of the model is based on anelastic set of equation and numerics adopted from the EULAG model. An employment of EULAG allowed to profit from its desirable conservative properties and numerical robustness confirmed in number of benchmark tests and widely documented in scientific literature. The first stage of the project has been already successfully completed. Its main achievement is a hybrid model capable to compute weather forecast. The model consists of EULAG dynamical core implemented into the software environment of the operational COSMO model and basic COSMO physical parameterizations involving turbulence, friction, radiation, moist processes and surface fluxes (COSMO-EULAG). The presentation shows the case studies comparing results of 24-hour forecasts calculated via the hybrid model with analogous results obtained with the Runge-Kutta dynamical core standard for the COSMO operational applications. The experiments are performed with 2.2 km resolution over Alpine domain of operational MeteoSwiss numerical forecasts. The results demonstrate that the short-term forecasts employing different dynamical cores are qualitatively and quantitatively similar, especially in the middle and upper troposphere. Near the surface the COSMO-EULAG results, while similar to the Runge-Kutta ones, show more small-scale variability. It is seen that the anelastic approximation does not impose measurable adverse affects on the forecast. The presentation shows also results of another class of experiments. They involve 24-hour forecast with COSMO-EULAG over realistic Alpine domain with the horizontal resolutions of
Introduction to quantum turbulence
Barenghi, Carlo F.; Skrbek, Ladislav; Sreenivasan, Katepalli R.
2014-01-01
The term quantum turbulence denotes the turbulent motion of quantum fluids, systems such as superfluid helium and atomic Bose–Einstein condensates, which are characterized by quantized vorticity, superfluidity, and, at finite temperatures, two-fluid behavior. This article introduces their basic properties, describes types and regimes of turbulence that have been observed, and highlights similarities and differences between quantum turbulence and classical turbulence in ordinary fluids. Our aim is also to link together the articles of this special issue and to provide a perspective of the future development of a subject that contains aspects of fluid mechanics, atomic physics, condensed matter, and low-temperature physics. PMID:24704870
Modeling Compressed Turbulence
Israel, Daniel M.
2012-07-13
From ICE to ICF, the effect of mean compression or expansion is important for predicting the state of the turbulence. When developing combustion models, we would like to know the mix state of the reacting species. This involves density and concentration fluctuations. To date, research has focused on the effect of compression on the turbulent kinetic energy. The current work provides constraints to help development and calibration for models of species mixing effects in compressed turbulence. The Cambon, et al., re-scaling has been extended to buoyancy driven turbulence, including the fluctuating density, concentration, and temperature equations. The new scalings give us helpful constraints for developing and validating RANS turbulence models.
Probabilistic river forecast methodology
NASA Astrophysics Data System (ADS)
Kelly, Karen Suzanne
1997-09-01
The National Weather Service (NWS) operates deterministic conceptual models to predict the hydrologic response of a river basin to precipitation. The output from these models are forecasted hydrographs (time series of the future river stage) at certain locations along a river. In order for the forecasts to be useful for optimal decision making, the uncertainty associated with them must be quantified. A methodology is developed for this purpose that (i) can be implemented with any deterministic hydrologic model, (ii) receives a probabilistic forecast of precipitation as input, (iii) quantifies all sources of uncertainty, (iv) operates in real-time and within computing constraints, and (v) produces probability distributions of future river stages. The Bayesian theory which supports the methodology involves transformation of a distribution of future precipitation into one of future river stage, and statistical characterization of the uncertainty in the hydrologic model. This is accomplished by decomposing total uncertainty into that associated with future precipitation and that associated with the hydrologic transformations. These are processed independently and then integrated into a predictive distribution which constitutes a probabilistic river stage forecast. A variety of models are presented for implementation of the methodology. In the most general model, a probability of exceedance associated with a given future hydrograph specified. In the simplest model, a probability of exceedance associated with a given future river stage is specified. In conjunction with the Ohio River Forecast Center of the NWS, the simplest model is used to demonstrate the feasibility of producing probabilistic river stage forecasts for a river basin located in headwaters. Previous efforts to quantify uncertainty in river forecasting have only considered selected sources of uncertainty, been specific to a particular hydrologic model, or have not obtained an entire probability
An overview of health forecasting.
Soyiri, Ireneous N; Reidpath, Daniel D
2013-01-01
Health forecasting is a novel area of forecasting, and a valuable tool for predicting future health events or situations such as demands for health services and healthcare needs. It facilitates preventive medicine and health care intervention strategies, by pre-informing health service providers to take appropriate mitigating actions to minimize risks and manage demand. Health forecasting requires reliable data, information and appropriate analytical tools for the prediction of specific health conditions or situations. There is no single approach to health forecasting, and so various methods have often been adopted to forecast aggregate or specific health conditions. Meanwhile, there are no defined health forecasting horizons (time frames) to match the choices of health forecasting methods/approaches that are often applied. The key principles of health forecasting have not also been adequately described to guide the process. This paper provides a brief introduction and theoretical analysis of health forecasting. It describes the key issues that are important for health forecasting, including: definitions, principles of health forecasting, and the properties of health data, which influence the choices of health forecasting methods. Other matters related to the value of health forecasting, and the general challenges associated with developing and using health forecasting services are discussed. This overview is a stimulus for further discussions on standardizing health forecasting approaches and methods that will facilitate health care and health services delivery.
Oceanic turbulence effects on long-exposure and short-exposure imaging
NASA Astrophysics Data System (ADS)
Pu, Huan; Ji, Xiaoling
2016-10-01
Based on the power spectrum of oceanic turbulence, the modulation transfer functions and the optical resolution for long-exposure and short-exposure imaging through oceanic turbulence are studied in detail. The analytical formulae for the seeing parameter and the tilt variance in oceanic turbulence are derived, and it is found that the relationship between the seeing parameter and the spatial coherence width in oceanic turbulence is just like that in atmospheric turbulence. Furthermore, the model of underwater imaging shown in this paper considers both temperature and salinity fluctuations for oceanic turbulence. It is found that, compared with the dominating salinity-induced turbulence, the range of angular spatial frequency where oceanic turbulence plays the major role rather than particle scattering is higher for the dominating temperature-induced turbulence.
Cui, Linyan; Xue, Bindang; Zhou, Fugen
2016-04-01
In this study, the modified anisotropic turbulence refractive-index fluctuations spectral model is derived based on the extended Rytov approximation theory for the theoretical investigations of optical plane and spherical waves propagating through moderate-to-strong anisotropic non-Kolmogorov turbulence. The anisotropic factor which parameterizes the asymmetry of turbulence cells or eddies in the horizontal and vertical directions is introduced. The general spectral power law in the range of 3-4 is also considered compared with the conventional classic value of 11/3 for Kolmogorov turbulence. Based on the modified anisotropic turbulence refractive-index fluctuations spectrum, the analytic expressions of the irradiance scintillation index are also derived for optical plane and spherical waves propagating through moderate-to-strong anisotropic non-Kolmogorov turbulence. They are applicable in a wide range of turbulence strengths and can reduce correctly to the previously published results in the special cases of weak anisotropic turbulence and moderate-to-strong isotropic turbulence. Calculations are performed to analyze the derived models.
Coupling of turbulent and non-turbulent flow regimes within pyroclastic density currents
NASA Astrophysics Data System (ADS)
Breard, Eric C. P.; Lube, Gert; Jones, Jim R.; Dufek, Josef; Cronin, Shane J.; Valentine, Greg A.; Moebis, Anja
2016-10-01
Volcanic eruptions are at their most deadly when pyroclastic density currents sweep across landscapes to devastate everything in their path. The internal dynamics underpinning these hazards cannot be directly observed. Here we present a quantitative view inside pyroclastic density currents by synthesizing their natural flow behaviour in large-scale experiments. The experiments trace flow dynamics from initiation to deposition, and can explain the sequence and evolution of real-world deposits. We show that, inside pyroclastic density currents, the long-hypothesized non-turbulent underflow and fully turbulent ash-cloud regions are linked through a hitherto unrecognized middle zone of intermediate turbulence and concentration. Bounded by abrupt jumps in turbulence, the middle zone couples underflow and ash-cloud regions kinematically. Inside this zone, strong feedback between gas and particle phases leads to the formation of mesoscale turbulence clusters. These extremely fast-settling dendritic structures dictate the internal stratification and evolution of pyroclastic density currents and allow the underflows to grow significantly during runout. Our experiments reveal how the underflow and ash-cloud regions are dynamically related--insights that are relevant to the forecasting of pyroclastic density current behaviour in volcanic hazard models.
Forced unsteady deceleration of a turbulent boundary layer from a temporal perspective
NASA Technical Reports Server (NTRS)
Brereton, G. J.
1992-01-01
The behavior of a turbulent boundary layer which has been subjected to a local ramp-like deceleration in the external velocity field, which leads to forced separation, has been studied experimentally. The data of this study are re-interpreted in light of more recent findings concerning the temporal nature of boundary layer turbulence in the presence of forced unsteady shear. In particular, the robustness of the near-wall turbulent motions to organized deformation is recognized. Their resilence during unsteady shearing action promotes continued efficient turbulent mixing and rapid redistribution of turbulent kinetic energy during forced transients. In aerodynamic problems, the rapid nature of the adjustment of the turbulence field to a new temporal boundary condition necessitates equally rapid remedial measures to be taken if means of control/prevention of forced unsteady separation are to be deployed to maximum effect. This requirement suggests exploration of the use of simple, real-time statistical forecasting techniques, based upon time-series analysis of easily-measurable features of the flow, to help assure timely deployment of mechanisms of boundary-layer control. This paper focuses upon the nature of turbulence in boundary layers undergoing forced deceleration which would lead to separation. A preliminary form of a forecasting model is presented and evaluated. Using observations of the previous two large eddies passing a detector, it forecasts the behavior of the future large eddy rather well.
Reverse Energy Cascade in Turbulent Weakly Ionized Plasmas
NASA Technical Reports Server (NTRS)
Williams, Kyron; Appartaim, R.; Belay, K.; Johnson, J. A., III
1998-01-01
in optical spectra. A determination of the role which changing turbulent parameters might play on optical signatures behind a reflected shock wave should therefore provide a useful tool for the evolution of theoretical models for turbulence.
Perez, Joaquin; Zvanovec, Stanislav; Ghassemlooy, Zabih; Popoola, Wasiu O
2014-02-10
Optical beams propagating through the turbulent atmospheric channel suffer from both the attenuation and phase distortion. Since future wireless networks are envisaged to be deployed in the ad hoc mesh topology, this paper presents the experimental laboratory characterization of mitigation of turbulence induced signal fades for two ad hoc scenarios. Results from measurements of the thermal structure constant along the propagation channels, changes of the coherence lengths for different turbulence regimes and the eye diagrams for partially correlated turbulences in free space optical channels are discussed. Based on these results future deployment of optical ad hoc networks can be more straightforwardly planned.
Optimal beam focusing through turbulence.
Charnotskii, Mikhail
2015-11-01
Beam spread and beam wandering are the most perceptible effects of atmospheric turbulence on propagating laser beams. The width of the mean irradiance profile is typically used to characterize the beam spread. This so-called long-term (LT) statistic allows for a relatively simple theoretical description. However, the LT beam size is not a very practical measure of the beam spread because its measurements are sensitive to the movements of the source and detector, and to the large-scale variations of the refractive index that are not associated with turbulence. The short-term (ST) beam spread is measured relative to the instantaneous position of the beam center and is free of these drawbacks, but has not been studied as thoroughly as the LT spread. We present a theoretical model for the ST beam irradiance that is based on the parabolic equation for the beam wave propagation in random media, and the Markov approximation for calculation of the statistics of the optical field, and discuss an approximation that allows introduction of the isoplanatic ST point spread function (PSF). Unlike the LT PSF, the ST PSF depends on the overall beam geometry. This allows optimization of the initial beam field in terms of minimizing the ST beam size at the observation plane. Calculations supporting this conjecture are presented for the simple case of the coherent Gaussian beam, and Kolmogorov turbulence.
Optimal beam focusing through turbulence.
Charnotskii, Mikhail
2015-11-01
Beam spread and beam wandering are the most perceptible effects of atmospheric turbulence on propagating laser beams. The width of the mean irradiance profile is typically used to characterize the beam spread. This so-called long-term (LT) statistic allows for a relatively simple theoretical description. However, the LT beam size is not a very practical measure of the beam spread because its measurements are sensitive to the movements of the source and detector, and to the large-scale variations of the refractive index that are not associated with turbulence. The short-term (ST) beam spread is measured relative to the instantaneous position of the beam center and is free of these drawbacks, but has not been studied as thoroughly as the LT spread. We present a theoretical model for the ST beam irradiance that is based on the parabolic equation for the beam wave propagation in random media, and the Markov approximation for calculation of the statistics of the optical field, and discuss an approximation that allows introduction of the isoplanatic ST point spread function (PSF). Unlike the LT PSF, the ST PSF depends on the overall beam geometry. This allows optimization of the initial beam field in terms of minimizing the ST beam size at the observation plane. Calculations supporting this conjecture are presented for the simple case of the coherent Gaussian beam, and Kolmogorov turbulence. PMID:26560908
PREFACE Turbulent Mixing and Beyond
NASA Astrophysics Data System (ADS)
Abarzhi, Snezhana I.; Gauthier, Serge; Niemela, Joseph J.
2010-12-01
The goals of the International Conference 'Turbulent Mixing and Beyond', TMB-2009, are to expose the generic problem of non-equilibrium turbulent processes to a broad scientific community, to promote the development of new ideas in tackling the fundamental aspects of the problem, to assist in the application of novel approaches in a broad range of phenomena, where the turbulent processes occur, and to have a potential impact on technology. The Conference provides the opportunity to bring together researchers from different areas, which include but are not limited to fluid dynamics, plasmas, high energy density physics, astrophysics, material science, combustion, atmospheric and Earth sciences, nonlinear and statistical physics, applied mathematics, probability and statistics, data processing and computations, optics and telecommunications, and to have their attention focused on the long-standing formidable task of non-equilibrium processes. Non-equilibrium turbulent processes play a key role in a broad variety of phenomena spanning astrophysical to atomistic scales and high or low energy density regimes. Inertial confinement and magnetic fusion, light-matter interaction and non-equilibrium heat transfer, strong shocks and explosions, material transformation under high strain rate, supernovae and accretion disks, stellar non-Boussinesq and magneto-convection, planetary interiors and mantle-lithosphere tectonics, premixed and non-premixed combustion, non-canonical wall-bounded flows, hypersonic and supersonic boundary layers, dynamics of atmosphere and oceanography, are just a few examples. A grip on non-equilibrium turbulent processes is crucial for cutting-edge technology such as laser micro-machining, nano-electronics, free-space optical telecommunications, and for industrial applications in the areas of aeronautics and aerodynamics. Non-equilibrium turbulent processes are anisotropic, non-local, multi-scale and multi-phase, and often are driven by shocks or
Kerstein, A.R.
1996-12-31
One-Dimensional Turbulence is a new turbulence modeling strategy involving an unsteady simulation implemented in one spatial dimension. In one dimension, fine scale viscous and molecular-diffusive processes can be resolved affordably in simulations at high turbulence intensity. The mechanistic distinction between advective and molecular processes is thereby preserved, in contrast to turbulence models presently employed. A stochastic process consisting of mapping {open_quote}events{close_quote} applied to a one-dimensional velocity profile represents turbulent advection. The local event rate for given eddy size is proportional to the velocity difference across the eddy. These properties cause an imposed shear to induce an eddy cascade analogous in many respects to the eddy cascade in turbulent flow. Many scaling and fluctuation properties of self-preserving flows, and of passive scalars introduced into these flows, are reproduced.
Turbulence generation by waves
Kaftori, D.; Nan, X.S.; Banerjee, S.
1995-12-31
The interaction between two-dimensional mechanically generated waves, and a turbulent stream was investigated experimentally in a horizontal channel, using a 3-D LDA synchronized with a surface position measuring device and a micro-bubble tracers flow visualization with high speed video. Results show that although the wave induced orbital motion reached all the way to the wall, the characteristics of the turbulence wall structures and the turbulence intensity close to the wall were not altered. Nor was the streaky nature of the wall layer. On the other hand, the mean velocity profile became more uniform and the mean friction velocity was increased. Close to the free surface, the turbulence intensity was substantially increased as well. Even in predominantly laminar flows, the introduction of 2-D waves causes three dimensional turbulence. The turbulence enhancement is found to be proportional to the wave strength.
NASA Technical Reports Server (NTRS)
Kaplan, Michael L.; Lux, Kevin M.; Cetola, Jeffrey D.; Huffman, Allan W.; Riordan, Allen J.; Slusser, Sarah W.; Lin, Yuh-Lang; Charney, Joseph J.; Waight, Kenneth T.
2004-01-01
Real-time prediction of environments predisposed to producing moderate-severe aviation turbulence is studied. We describe the numerical model and its postprocessing system designed for said prediction of environments predisposed to severe aviation turbulence as well as presenting numerous examples of its utility. The numerical model is MASS version 5.13, which is integrated over three different grid matrices in real time on a university work station in support of NASA Langley Research Center s B-757 turbulence research flight missions. The postprocessing system includes several turbulence-related products, including four turbulence forecasting indices, winds, streamlines, turbulence kinetic energy, and Richardson numbers. Additionally, there are convective products including precipitation, cloud height, cloud mass fluxes, lifted index, and K-index. Furthermore, soundings, sounding parameters, and Froude number plots are also provided. The horizontal cross-section plot products are provided from 16 000 to 46 000 ft in 2000-ft intervals. Products are available every 3 hours at the 60- and 30-km grid interval and every 1.5 hours at the 15-km grid interval. The model is initialized from the NWS ETA analyses and integrated two times a day.
Tactical missile turbulence problems
NASA Technical Reports Server (NTRS)
Dickson, Richard E.
1987-01-01
Of particular interest is atmospheric turbulence in the atmospheric boundary layer, since this affects both the launch and terminal phase of flight, and the total flight for direct fire systems. Brief discussions are presented on rocket artillery boost wind problems, mean wind correction, turbulent boost wind correction, the Dynamically Aimed Free Flight Rocket (DAFFR) wind filter, the DAFFR test, and rocket wake turbulence problems. It is concluded that many of the turbulence problems of rockets and missiles are common to those of aircraft, such as structural loading and control system design. However, these problems have not been solved at this time.
Triggering filamentation using turbulence
NASA Astrophysics Data System (ADS)
Eeltink, D.; Berti, N.; Marchiando, N.; Hermelin, S.; Gateau, J.; Brunetti, M.; Wolf, J. P.; Kasparian, J.
2016-09-01
We study the triggering of single filaments due to turbulence in the beam path for a laser of power below the filamenting threshold. Turbulence can act as a switch between the beam not filamenting and producing single filaments. This positive effect of turbulence on the filament probability, combined with our observation of off-axis filaments, suggests the underlying mechanism is modulation instability caused by transverse perturbations. We hereby experimentally explore the interaction of modulation instability and turbulence, commonly associated with multiple filaments, in the single-filament regime.
NASA Astrophysics Data System (ADS)
Maximova, Lyudmila
1987-07-01
For the first time Soviet scientists have set up a bioseismological proving ground which will stage a systematic extensive experiment of using birds, ants, mountain rodents including marmots, which can dig holes in the Earth's interior to a depth of 50 meters, for the purpose of earthquake forecasting. Biologists have accumulated extensive experimental data on the impact of various electromagnetic fields, including fields of weak intensity, on living organisms. As far as mammals are concerned, electromagnetic waves with frequencies close to the brain's biorhythms have the strongest effect. How these observations can be used to forecast earthquakes is discussed.
US industrial battery forecast
Hollingsworth, V. III
1996-09-01
Last year was strong year for the US industrial battery market with growth in all segments. Sales of industrial batteries in North America grew 19.2% in 1995, exceeding last year`s forecasted growth rate of 11.6%. The results of the recently completed BCI Membership Survey forecast 1996 sales to be up 10.5%, and to continue to increase at a 10.4% compound annual rate through the year 2000. This year`s survey includes further detail on the stationary battery market with the inclusion of less than 25 Ampere-Hour batteries for the first time.
Inhomogeneous turbulence in magnetic reconnection
NASA Astrophysics Data System (ADS)
Yokoi, Nobumitsu
2016-07-01
Turbulence is expected to play an essential role in enhancing magnetic reconnection. Turbulence associated with magnetic reconnection is highly inhomogeneous: it is generated by inhomogeneities of the field configuration such as the velocity shear, temperature gradient, density stratification, magnetic shear, etc. This self-generated turbulence affects the reconnection through the turbulent transport. In this reconnection--turbulence interaction, localization of turbulent transport due to dynamic balance between several turbulence effects plays an essential role. For investigating inhomogeneous turbulence in a strongly nonlinear regime, closure or turbulence modeling approaches provide a powerful tool. A turbulence modeling approach for the magnetic reconnection is introduced. In the model, the mean-field equations with turbulence effects incorporated are solved simultaneously with the equations of turbulent statistical quantities that represent spatiotemporal properties of turbulence under the effect of large-scale field inhomogeneities. Numerical simulations of this Reynolds-averaged turbulence model showed that self-generated turbulence enhances magnetic reconnection. It was pointed out that reconnection states may be divided into three category depending on the turbulence level: (i) laminar reconnection; (ii) turbulent reconnection, and (iii) turbulent diffusion. Recent developments in this direction are also briefly introduced, which includes the magnetic Prandtl number dependence, spectral evolution, and guide-field effects. Also relationship of this fully nonlinear turbulence approach with other important approaches such as plasmoid instability reconnection will be discussed.
ERIC Educational Resources Information Center
Bivin, David; Rooney, Patrick Michael
1999-01-01
This study used Tobit analysis to estimate retention probabilities and credit hours at two universities. Tobit was judged as appropriate for this problem because it recognizes the lower bound of zero on credit hours and incorporates this bound into parameter estimates and forecasts. Models are estimated for credit hours in a single year and…
Education Planning: Pupil Forecasting.
ERIC Educational Resources Information Center
Royal Inst. of Public Administration, Reading (England). Local Government Operational Research Unit.
This computer-based system of enrollment projection predicts up to seven years ahead the number of school children of each age and sex who will be in school. The main distinguishing feature of the system is the ability to detect well in advance small changes in the geographical distribution of children. Forecasts are made for zones that will yield…
Federal Forecasters Directory, 1995.
ERIC Educational Resources Information Center
National Center for Education Statistics (ED), Washington, DC.
This directory lists employees of the federal government who are involved in forecasting for policy formation and trend prediction purposes. Job title, agency, business address, phone or e-mail number, and specialty areas are listed for each employee. Employees are listed for the following agencies: (1) Bureau of the Census; (2) Bureau of Economic…
External Environmental Forecast.
ERIC Educational Resources Information Center
Lapin, Joel D.
Representing current viewpoints of academics, futures experts, and social observers, this external environmental forecast presents projections and information of particular relevance to the future of Catonsville Community College. The following topics are examined: (1) population changes and implications for higher education; (2) state and local…
Evolving forecasting classifications and applications in health forecasting
Soyiri, Ireneous N; Reidpath, Daniel D
2012-01-01
Health forecasting forewarns the health community about future health situations and disease episodes so that health systems can better allocate resources and manage demand. The tools used for developing and measuring the accuracy and validity of health forecasts commonly are not defined although they are usually adapted forms of statistical procedures. This review identifies previous typologies used in classifying the forecasting methods commonly used in forecasting health conditions or situations. It then discusses the strengths and weaknesses of these methods and presents the choices available for measuring the accuracy of health-forecasting models, including a note on the discrepancies in the modes of validation. PMID:22615533
NASA Technical Reports Server (NTRS)
Montgomery, David
1988-01-01
Three areas of study in MHD turbulence are considered. These are the turbulent relaxation of the toroidal Z pinch, density fluctuations in MHD fluids, and MHD cellular automata. A Boolean computer game that updates a cellular representation in parallel and that has macroscopic averages converging to solutions of the two-dimensional MHD equations is discussed.
Samanta, Devranjan; Dubief, Yves; Holzner, Markus; Schäfer, Christof; Morozov, Alexander N; Wagner, Christian; Hof, Björn
2013-06-25
Turbulence is ubiquitous in nature, yet even for the case of ordinary Newtonian fluids like water, our understanding of this phenomenon is limited. Many liquids of practical importance are more complicated (e.g., blood, polymer melts, paints), however; they exhibit elastic as well as viscous characteristics, and the relation between stress and strain is nonlinear. We demonstrate here for a model system of such complex fluids that at high shear rates, turbulence is not simply modified as previously believed but is suppressed and replaced by a different type of disordered motion, elasto-inertial turbulence. Elasto-inertial turbulence is found to occur at much lower Reynolds numbers than Newtonian turbulence, and the dynamical properties differ significantly. The friction scaling observed coincides with the so-called "maximum drag reduction" asymptote, which is exhibited by a wide range of viscoelastic fluids.
Samanta, Devranjan; Dubief, Yves; Holzner, Markus; Schäfer, Christof; Morozov, Alexander N.; Wagner, Christian; Hof, Björn
2013-01-01
Turbulence is ubiquitous in nature, yet even for the case of ordinary Newtonian fluids like water, our understanding of this phenomenon is limited. Many liquids of practical importance are more complicated (e.g., blood, polymer melts, paints), however; they exhibit elastic as well as viscous characteristics, and the relation between stress and strain is nonlinear. We demonstrate here for a model system of such complex fluids that at high shear rates, turbulence is not simply modified as previously believed but is suppressed and replaced by a different type of disordered motion, elasto-inertial turbulence. Elasto-inertial turbulence is found to occur at much lower Reynolds numbers than Newtonian turbulence, and the dynamical properties differ significantly. The friction scaling observed coincides with the so-called “maximum drag reduction” asymptote, which is exhibited by a wide range of viscoelastic fluids. PMID:23757498
NASA Astrophysics Data System (ADS)
2004-04-01
New Detailed VLT Images of Saturn's Largest Moon Optimizing space missions Titan, the largest moon of Saturn was discovered by Dutch astronomer Christian Huygens in 1655 and certainly deserves its name. With a diameter of no less than 5,150 km, it is larger than Mercury and twice as large as Pluto. It is unique in having a hazy atmosphere of nitrogen, methane and oily hydrocarbons. Although it was explored in some detail by the NASA Voyager missions, many aspects of the atmosphere and surface still remain unknown. Thus, the existence of seasonal or diurnal phenomena, the presence of clouds, the surface composition and topography are still under debate. There have even been speculations that some kind of primitive life (now possibly extinct) may be found on Titan. Titan is the main target of the NASA/ESA Cassini/Huygens mission, launched in 1997 and scheduled to arrive at Saturn on July 1, 2004. The ESA Huygens probe is designed to enter the atmosphere of Titan, and to descend by parachute to the surface. Ground-based observations are essential to optimize the return of this space mission, because they will complement the information gained from space and add confidence to the interpretation of the data. Hence, the advent of the adaptive optics system NAOS-CONICA (NACO) [1] in combination with ESO's Very Large Telescope (VLT) at the Paranal Observatory in Chile now offers a unique opportunity to study the resolved disc of Titan with high sensitivity and increased spatial resolution. Adaptive Optics (AO) systems work by means of a computer-controlled deformable mirror that counteracts the image distortion induced by atmospheric turbulence. It is based on real-time optical corrections computed from image data obtained by a special camera at very high speed, many hundreds of times each second (see e.g. ESO Press Release 25/01 , ESO PR Photos 04a-c/02, ESO PR Photos 19a-c/02, ESO PR Photos 21a-c/02, ESO Press Release 17/02, and ESO Press Release 26/03 for earlier NACO
Causes of non-Kolmogorov turbulence in the atmosphere.
Lukin, V P; Nosov, E V; Nosov, V V; Torgaev, A V
2016-04-20
In the present work, we briefly describe a model for atmospheric turbulence energy on the basis of experimental data obtained in Siberia. A series of new studies is considered and the results of our long-term experimental observations are summarized. The results of these studies form the basis for an explanation of some effects in interactions between optical waves and atmospheric turbulence. Our numerous experimental results point to the possible generation of so-called coherent turbulence in the atmosphere. When analyzing the problem, we proceeded based on our own experimental data and comprehension that the coherent turbulence is a result of the action of self-organizing nonlinear processes, which run in continuous media, including atmospheric air. The experimental data confirmed the effect of attenuation of light fluctuations in coherent turbulence.
Influence of atmospheric turbulence on OAM-based FSO system with use of realistic link model
NASA Astrophysics Data System (ADS)
Li, Ming; Yu, Zhongyuan; Cvijetic, Milorad
2016-04-01
We study the influence of atmospheric turbulence on OAM-based free-space optical (FSO) communication by using the Pump turbulence spectrum model which accurately characterizes the realistic FSO link. A comprehensive comparison is made between the Pump and Kolmogorov spectrum models with respect to the turbulence impact. The calculated results show that obtained turbulence-induced crosstalk is lower, which means that a higher channel capacity is projected when the realistic Pump spectrum is used instead of the Kolmogorov spectrum. We believe that our results prove that performance of practical OAM-based FSO is better than one predicted by using the original Kolmogorov turbulence model.
Sea Fog Forecasting with Lagrangian Models
NASA Astrophysics Data System (ADS)
Lewis, J. M.
2014-12-01
In 1913, G. I. Taylor introduced us to a Lagrangian view of sea fog formation. He conducted his study off the coast of Newfoundland in the aftermath of the Titanic disaster. We briefly review Taylor's classic work and then apply these same principles to a case of sea fog formation and dissipation off the coast of California. The resources used in this study consist of: 1) land-based surface and upper-air observations, 2) NDBC (National Data Buoy Center) observations from moored buoys equipped to measure dew point temperature as well as the standard surface observations at sea (wind, sea surface temperature, pressure, and air temperature), 3) satellite observations of cloud, and 4) a one-dimensional (vertically directed) boundary layer model that tracks with the surface air motion and makes use of sophisticated turbulence-radiation parameterizations. Results of the investigation indicate that delicate interplay and interaction between the radiation and turbulence processes makes accurate forecasts of sea fog onset unlikely in the near future. This pessimistic attitude stems from inadequacy of the existing network of observations and uncertainties in modeling dynamical processes within the boundary layer.
Turbulence-induced persistence in laser beam wandering.
Zunino, Luciano; Gulich, Damián; Funes, Gustavo; Pérez, Darío G
2015-07-01
We have experimentally confirmed the presence of long-memory correlations in the wandering of a thin Gaussian laser beam over a screen after propagating through a turbulent medium. A laboratory-controlled experiment was conducted in which coordinate fluctuations of the laser beam were recorded at a sufficiently high sampling rate for a wide range of turbulent conditions. Horizontal and vertical displacements of the laser beam centroid were subsequently analyzed by implementing detrended fluctuation analysis. This is a very well-known and widely used methodology to unveil memory effects from time series. Results obtained from this experimental analysis allow us to confirm that both coordinates behave as highly persistent signals for strong turbulent intensities. This finding is relevant for a better comprehension and modeling of the turbulence effects in free-space optical communication systems and other applications related to propagation of optical signals in the atmosphere.
Turbulence-induced persistence in laser beam wandering.
Zunino, Luciano; Gulich, Damián; Funes, Gustavo; Pérez, Darío G
2015-07-01
We have experimentally confirmed the presence of long-memory correlations in the wandering of a thin Gaussian laser beam over a screen after propagating through a turbulent medium. A laboratory-controlled experiment was conducted in which coordinate fluctuations of the laser beam were recorded at a sufficiently high sampling rate for a wide range of turbulent conditions. Horizontal and vertical displacements of the laser beam centroid were subsequently analyzed by implementing detrended fluctuation analysis. This is a very well-known and widely used methodology to unveil memory effects from time series. Results obtained from this experimental analysis allow us to confirm that both coordinates behave as highly persistent signals for strong turbulent intensities. This finding is relevant for a better comprehension and modeling of the turbulence effects in free-space optical communication systems and other applications related to propagation of optical signals in the atmosphere. PMID:26125388
NASA Astrophysics Data System (ADS)
Rehill, Brendan; Ed J. Walsh Collaboration; Philipp Schlatter, Luca Brandt Collaboration; Tamer A. Zaki Collaboration; Donald M. McEligot Collaboration
2011-11-01
Within the boundary layer transition region turbulent spots emerge and grow to form the fully-turbulent boundary layer. This paper examines the turbulent statistics within turbulent spots in a transitional boundary layer subject to free-stream turbulence intensity of 4 . 7 % . Conditionally sampled DNS results, where the laminar and turbulent contributions to the transition region are separated, are used to obtain the relevant statistics. Conditional sampling of the data provides some improvement over the more classical time-space-averaged data reduction techniques, through providing more insight into the true turbulent statistics within turbulent spots. The statistics are compared to the lowest fully-turbulent DNS available in the literature to identify how the turbulent spots develop and form the fully-turbulent state. Stokes Institute, University of Limerick, Limerick, Ireland
NASA Technical Reports Server (NTRS)
Wilkinson, Stephen P.; Lindemann, A. Margrethe; Beeler, George B.; Mcginley, Catherine B.; Goodman, Wesley L.; Balasubramanian, R.
1986-01-01
A variety of wall turbulence control devices which were experimentally investigated are discussed; these include devices for burst control, alteration of outer flow structures, large eddy substitution, increased heat transfer efficiency, and reduction of wall pressure fluctuations. Control of pre-burst flow was demonstrated with a single, traveling surface depression which is phase-locked to elements of the burst production process. Another approach to wall turbulence control is to interfere with the outer layer coherent structures. A device in the outer part of a boundary layer was shown to suppress turbulence and reduce drag by opposing both the mean and unsteady vorticity in the boundary layer. Large eddy substitution is a method in which streamline curvature is introduced into the boundary layer in the form of streamwise vortices. Riblets, which were already shown to reduce turbulent drag, were also shown to exhibit superior heat transfer characteristics. Heat transfer efficiency as measured by the Reynolds Analogy Factor was shown to be as much as 36 percent greater than a smooth flat plate in a turbulent boundary layer. Large Eddy Break-Up (LEBU) which are also known to reduce turbulent drag were shown to reduce turbulent wall pressure fluctuation.
Modeling turbulent flame propagation
Ashurst, W.T.
1994-08-01
Laser diagnostics and flow simulation techniques axe now providing information that if available fifty years ago, would have allowed Damkoehler to show how turbulence generates flame area. In the absence of this information, many turbulent flame speed models have been created, most based on Kolmogorov concepts which ignore the turbulence vortical structure, Over the last twenty years, the vorticity structure in mixing layers and jets has been shown to determine the entrainment and mixing behavior and these effects need to be duplicated by combustion models. Turbulence simulations reveal the intense vorticity structure as filaments and simulations of passive flamelet propagation show how this vorticity Creates flame area and defines the shape of the expected chemical reaction surface. Understanding how volume expansion interacts with flow structure should improve experimental methods for determining turbulent flame speed. Since the last decade has given us such powerful new tools to create and see turbulent combustion microscopic behavior, it seems that a solution of turbulent combustion within the next decade would not be surprising in the hindsight of 2004.
Forecasting carbon dioxide emissions.
Zhao, Xiaobing; Du, Ding
2015-09-01
This study extends the literature on forecasting carbon dioxide (CO2) emissions by applying the reduced-form econometrics approach of Schmalensee et al. (1998) to a more recent sample period, the post-1997 period. Using the post-1997 period is motivated by the observation that the strengthening pace of global climate policy may have been accelerated since 1997. Based on our parameter estimates, we project 25% reduction in CO2 emissions by 2050 according to an economic and population growth scenario that is more consistent with recent global trends. Our forecasts are conservative due to that we do not have sufficient data to fully take into account recent developments in the global economy.
NASA Astrophysics Data System (ADS)
Turco, M.; Milelli, M.
2009-09-01
To the authors' knowledge there are relatively few studies that try to answer this topic: "Are humans able to add value to computer-generated forecasts and warnings ?". Moreover, the answers are not always positive. In particular some postprocessing method is competitive or superior to human forecast (see for instance Baars et al., 2005, Charba et al., 2002, Doswell C., 2003, Roebber et al., 1996, Sanders F., 1986). Within the alert system of ARPA Piemonte it is possible to study in an objective manner if the human forecaster is able to add value with respect to computer-generated forecasts. Every day the meteorology group of the Centro Funzionale of Regione Piemonte produces the HQPF (Human QPF) in terms of an areal average for each of the 13 regional warning areas, which have been created according to meteo-hydrological criteria. This allows the decision makers to produce an evaluation of the expected effects by comparing these HQPFs with predefined rainfall thresholds. Another important ingredient in this study is the very dense non-GTS network of rain gauges available that makes possible a high resolution verification. In this context the most useful verification approach is the measure of the QPF and HQPF skills by first converting precipitation expressed as continuous amounts into ‘‘exceedance'' categories (yes-no statements indicating whether precipitation equals or exceeds selected thresholds) and then computing the performances for each threshold. In particular in this work we compare the performances of the latest three years of QPF derived from two meteorological models COSMO-I7 (the Italian version of the COSMO Model, a mesoscale model developed in the framework of the COSMO Consortium) and IFS (the ECMWF global model) with the HQPF. In this analysis it is possible to introduce the hypothesis test developed by Hamill (1999), in which a confidence interval is calculated with the bootstrap method in order to establish the real difference between the
Forecasting Infectious Disease Outbreaks
NASA Astrophysics Data System (ADS)
Shaman, J. L.
2015-12-01
Dynamic models of infectious disease systems abound and are used to study the epidemiological characteristics of disease outbreaks, the ecological mechanisms affecting transmission, and the suitability of various control and intervention strategies. The dynamics of disease transmission are non-linear and consequently difficult to forecast. Here, we describe combined model-inference frameworks developed for the prediction of infectious diseases. We show that accurate and reliable predictions of seasonal influenza outbreaks can be made using a mathematical model representing population-level influenza transmission dynamics that has been recursively optimized using ensemble data assimilation techniques and real-time estimates of influenza incidence. Operational real-time forecasts of influenza and other infectious diseases have been and are currently being generated.
Forecasting carbon dioxide emissions.
Zhao, Xiaobing; Du, Ding
2015-09-01
This study extends the literature on forecasting carbon dioxide (CO2) emissions by applying the reduced-form econometrics approach of Schmalensee et al. (1998) to a more recent sample period, the post-1997 period. Using the post-1997 period is motivated by the observation that the strengthening pace of global climate policy may have been accelerated since 1997. Based on our parameter estimates, we project 25% reduction in CO2 emissions by 2050 according to an economic and population growth scenario that is more consistent with recent global trends. Our forecasts are conservative due to that we do not have sufficient data to fully take into account recent developments in the global economy. PMID:26081307
Near-field turbulence effects on quantum-key distribution
Shapiro, Jeffrey H.
2003-02-01
Bounds on average power transfer over a near-field optical path through atmospheric turbulence are used to deduce bounds on the sift and error probabilities of a free-space quantum-key distribution system that uses the Bennett-Brassard 1984 (BB84) protocol. It is shown that atmospheric turbulence imposes at most a modest decrease in the sift probability and a modest increase in the conditional probability of error given that a sift event has occurred.
Long-distance Bessel beam propagation through Kolmogorov turbulence.
Birch, Philip; Ituen, Iniabasi; Young, Rupert; Chatwin, Chris
2015-11-01
Free-space optical communication has the potential to transmit information with both high speed and security. However, since it is unguided it suffers from losses due to atmospheric turbulence and diffraction. To overcome the diffraction limits the long-distance propagation of Bessel beams is considered and compared against Gaussian beam properties. Bessel beams are shown to have a number of benefits over Gaussian beams when propagating through atmospheric turbulence.
Propagation of rotational field correlation through atmospheric turbulence.
Nairat, Mazen; Voelz, David
2014-04-01
A general formulation is presented that describes the propagation of the rotational field correlation of an optical beam through atmospheric turbulence. The associated influence on the orbital angular momentum (OAM) of a single photon is described analytically. The analysis predicts the probability of change in the OAM state due to the process of propagating through turbulence. The probability of a change in an OAM state depends on the Fresnel number and on the ratio of the beam diameter to the Fried parameter.
Common omissions and misconceptions of wave propagation in turbulence: discussion.
Charnotskii, Mikhail
2012-05-01
This review paper addresses typical mistakes and omissions that involve theoretical research and modeling of optical propagation through atmospheric turbulence. We discuss the disregard of some general properties of narrow-angle propagation in refractive random media, the careless use of simplified models of turbulence, and omissions in the calculations of the second moment of the propagating wave. We also review some misconceptions regarding short-exposure imaging, propagation of polarized waves, and calculations of the scintillation index of the beam waves.
Turbulence Detection and Mitigation Element
NASA Technical Reports Server (NTRS)
Bogue, Rod
2003-01-01
This paper presents viewgraphs on turbulence detection and mitigation technologies in weather accident prevention. The topics include: 1) Organization; 2) Scope of Turbulence Effort; 3) Background; 4) Turbulence Detection and Mitigation Program Metrics; 5) Approach; 6) Turbulence Team Relationships; 7) WBS Structure; 8) Deliverables; 9) TDAM Changes; 10) FY-01 Results/Accomplishments; 11) Out-year Plans; and 12) Element Status.
Technology 2005 : Reviews & Forecasts
NASA Astrophysics Data System (ADS)
Kimura, Ken
Nine Technical Committees (TC's) of the Fundamentals and Materials Society of IEE Japan have contributed their Review & Forecast articles to the present. Special Issue of the IEEJ Transaction on Fundamentals and Materials. So you can survey the state-of-the-art of the 9 different technical fields with these articles. The series of reviews were submitted in reply to the request by experts in the respective fields.
Satellite freeze forecast system
NASA Technical Reports Server (NTRS)
Martsolf, J. D. (Principal Investigator)
1983-01-01
Provisions for back-up operations for the satellite freeze forecast system are discussed including software and hardware maintenance and DS/1000-1V linkage; troubleshooting; and digitized radar usage. The documentation developed; dissemination of data products via television and the IFAS computer network; data base management; predictive models; the installation of and progress towards the operational status of key stations; and digital data acquisition are also considered. The d addition of dew point temperature into the P-model is outlined.
Frost Forecasting for Fruitgrowers
NASA Technical Reports Server (NTRS)
Martsolf, J. D.; Chen, E.
1983-01-01
Progress in forecasting from satellite data reviewed. University study found data from satellites displayed in color and used to predict frost are valuable aid to agriculture. Study evaluated scheme to use Earth-temperature data from Geostationary Operational Environmental Satellite in computer model that determines when and where freezing temperatures endanger developing fruit crops, such as apples, peaches and cherries in spring and citrus crops in winter.
2008-01-25
BOUT is a parallelized 3D nonlocal electromagnetic turbulence code. The principal calculations are the boundary plasma turbulence in a realistic magnetic geometry. BOUT uses fluid Braginskii equations for plasma vorticity, density, electron and ion temperature and Parallel mementum. With sources added in the core-edge region and sinks in the scrape-off-layer (SOL), BOUT follows the self-consistent profile evolution together with turbulence. BOUT also includes coupling to a magnetohyfrodynamic equlibrium (EFIT package) and a two-dimensional hydrodynamic edgemore » transport model (UEDGE package).« less
Periodically kicked turbulence
Lohse
2000-10-01
Periodically kicked turbulence is theoretically analyzed within a mean-field theory. For large enough kicking strength A and kicking frequency f the Reynolds number grows exponentially and then runs into some saturation. The saturation level Re(sat) can be calculated analytically; different regimes can be observed. For large enough Re we find Re(sat) approximately Af, but intermittency can modify this scaling law. We suggest an experimental realization of periodically kicked turbulence to study the different regimes we theoretically predict and thus to better understand the effect of forcing on fully developed turbulence. PMID:11089041
NASA Technical Reports Server (NTRS)
Case, Jonathan L.; Wheeler, Mark M.; Merceret, Francis J. (Technical Monitor)
2002-01-01
The nocturnal land breeze at the Kennedy Space Center (KSC) and Cape Canaveral Air Force Station (CCAFS) is both operationally significant and challenging to forecast. The occurrence and timing of land breezes impact low-level winds, atmospheric stability, low temperatures, and fog development. Accurate predictions of the land breeze are critical for toxic material dispersion forecasts associated with space launch missions, since wind direction and low-level stability can change noticeably with the onset of a land breeze. This report presents a seven-year observational study of land breezes over east-central Florida from 1995 to 2001. This comprehensive analysis was enabled by the high-resolution tower observations over KSC/CCAFS. Five-minute observations of winds, temperature, and moisture along with 9 15-MHz Doppler Radar Wind Profiler data were used to analyze specific land-breeze cases, while the tower data were used to construct a composite climatology. Utilities derived from this climatology were developed to assist forecasters in determining the land-breeze occurrence, timing, and movement based on predicted meteorological conditions.
NASA Technical Reports Server (NTRS)
Macdonald, R. B.; Hall, F. G.
1980-01-01
The needs for and remote sensing means of global crop forecasting are discussed, and key results of the Large Area Crop Inventory Experiment (LACIE) are presented. Current crop production estimates provided by foreign countries are shown often to be inadequate, and the basic elements of crop production forecasts are reviewed. The LACIE project is introduced as a proof-of-concept experiment designed to assimilate remote sensing technology, monitor global wheat production, evaluate key technical problems, modify the technique accordingly and demonstrate the feasibility of a global agricultural monitoring system. The global meteorological data, sampling and aggregation techniques, Landsat data analysis procedures and yield forecast procedures used in the experiment are outlined. Accuracy assessment procedures employed to evaluate LACIE technology performance are presented, and improvements in system efficiency and capacity during the three years of operation are pointed out. Results of LACIE estimates of Soviet, U.S. and Canadian wheat production are presented which demonstrate the feasibility and accuracy of the remote-sensing approach for global food and fiber monitoring.
Modeling of turbulent chemical reaction
NASA Technical Reports Server (NTRS)
Chen, J.-Y.
1995-01-01
Viewgraphs are presented on modeling turbulent reacting flows, regimes of turbulent combustion, regimes of premixed and regimes of non-premixed turbulent combustion, chemical closure models, flamelet model, conditional moment closure (CMC), NO(x) emissions from turbulent H2 jet flames, probability density function (PDF), departures from chemical equilibrium, mixing models for PDF methods, comparison of predicted and measured H2O mass fractions in turbulent nonpremixed jet flames, experimental evidence of preferential diffusion in turbulent jet flames, and computation of turbulent reacting flows.
Unified models of E-layer plasma turbulence from density gradients and Hall currents
NASA Astrophysics Data System (ADS)
Hassan, Ehab; Litt, Sandeep; Horton, Wendell; Smolyakov, Andrei; Skiff, Fred
2013-10-01
The Earth's ionosphere is rich with plasma irregularities of scale-lengths extend from few centimeters to hundreds of kilometers. The combination of small-scale turbulence with large coherent structures is at the forefront of basic plasma turbulence theory. A new unified model for the small-scale plasma turbulence called Type-I and Type-II in the E-region ionosphere is presented. Simulations and a proposed laboratory experiment for these plasma waves in a weakly ionized plasma are reported. The ions [Argon in the lab and NO+ in the ionosphere] are collisional and the electrons ExB drifts produce Hall currents. The dispersion relations are analyzed for both density gradient and electron current driven instabilities. A basic understanding of the turbulence is important for forecasting disruptions in GNSS communication signals from RF signal scattering produced by the E-layer plasma turbulence on the 10cm to 10m scales lengths. NSF:AGS-0964692.
Large-eddy simulations of contrails in a turbulent atmosphere
NASA Astrophysics Data System (ADS)
Picot, J.; Paoli, R.; Thouron, O.; Cariolle, D.
2014-11-01
In this work, the evolution of contrails in the vortex and dissipation regimes is studied by means of fully three-dimensional large-eddy simulation (LES) coupled to a Lagrangian particle tracking method to treat the ice phase. This is the first paper where fine-scale atmospheric turbulence is generated and sustained by means of a stochastic forcing that mimics the properties of stably stratified turbulent flows as those occurring in the upper troposphere lower stratosphere. The initial flow-field is composed by the turbulent background flow and a wake flow obtained from separate LES of the jet regime. Atmospheric turbulence is the main driver of the wake instability and the structure of the resulting wake is sensitive to the intensity of the perturbations, primarily in the vertical direction. A stronger turbulence accelerates the onset of the instability, which results in shorter contrail decent and more effective mixing in the interior of the plume. However, the self-induced turbulence that is produced in the wake after the vortex break-up dominates over background turbulence at the end of the vortex regime and dominates the mixing with ambient air. This results in global microphysical characteristics such as ice mass and optical depth that are be slightly affected by the intensity of atmospheric turbulence. On the other hand, the background humidity and temperature have a first order effect on the survival of ice crystals and particle size distribution, which is in line with recent and ongoing studies in the literature.
EU pharmaceutical expenditure forecast
Urbinati, Duccio; Rémuzat, Cécile; Kornfeld, Åsa; Vataire, Anne-Lise; Cetinsoy, Laurent; Aballéa, Samuel; Mzoughi, Olfa; Toumi, Mondher
2014-01-01
Background and Objectives With constant incentives for healthcare payers to contain their pharmaceutical budgets, forecasting has become critically important. Some countries have, for instance, developed pharmaceutical horizon scanning units. The objective of this project was to build a model to assess the net effect of the entrance of new patented medicinal products versus medicinal products going off-patent, with a defined forecast horizon, on selected European Union (EU) Member States’ pharmaceutical budgets. This model took into account population ageing, as well as current and future country-specific pricing, reimbursement, and market access policies (the project was performed for the European Commission; see http://ec.europa.eu/health/healthcare/key_documents/index_en.htm). Method In order to have a representative heterogeneity of EU Member States, the following countries were selected for the analysis: France, Germany, Greece, Hungary, Poland, Portugal, and the United Kingdom. A forecasting period of 5 years (2012–2016) was chosen to assess the net pharmaceutical budget impact. A model for generics and biosimilars was developed for each country. The model estimated a separate and combined effect of the direct and indirect impacts of the patent cliff. A second model, estimating the sales development and the risk of development failure, was developed for new drugs. New drugs were reviewed individually to assess their clinical potential and translate it into commercial potential. The forecast was carried out according to three perspectives (healthcare public payer, society, and manufacturer), and several types of distribution chains (retail, hospital, and combined retail and hospital). Probabilistic and deterministic sensitivity analyses were carried out. Results According to the model, all countries experienced drug budget reductions except Poland (+€41 million). Savings were expected to be the highest in the United Kingdom (−€9,367 million), France
Containerless Ripple Turbulence
NASA Technical Reports Server (NTRS)
Putterman, Seth; Wright, William; Duval, Walter; Panzarella, Charles
2002-01-01
One of the longest standing unsolved problems in physics relates to the behavior of fluids that are driven far from equilibrium such as occurs when they become turbulent due to fast flow through a grid or tidal motions. In turbulent flows the distribution of vortex energy as a function of the inverse length scale [or wavenumber 'k'] of motion is proportional to 1/k(sup 5/3) which is the celebrated law of Kolmogorov. Although this law gives a good description of the average motion, fluctuations around the average are huge. This stands in contrast with thermally activated motion where large fluctuations around thermal equilibrium are highly unfavorable. The problem of turbulence is the problem of understanding why large fluctuations are so prevalent which is also called the problem of 'intermittency'. Turbulence is a remarkable problem in that its solution sits simultaneously at the forefront of physics, mathematics, engineering and computer science. A recent conference [March 2002] on 'Statistical Hydrodynamics' organized by the Los Alamos Laboratory Center for Nonlinear Studies brought together researchers in all of these fields. Although turbulence is generally thought to be described by the Navier-Stokes Equations of fluid mechanics the solution as well as its existence has eluded researchers for over 100 years. In fact proof of the existence of such a solution qualifies for a 1 M$ millennium prize. As part of our NASA funded research we have proposed building a bridge between vortex turbulence and wave turbulence. The latter occurs when high amplitude waves of various wavelengths are allowed to mutually interact in a fluid. In particular we have proposed measuring the interaction of ripples [capillary waves] that run around on the surface of a fluid sphere suspended in a microgravity environment. The problem of ripple turbulence poses similar mathematical challenges to the problem of vortex turbulence. The waves can have a high amplitude and a strong nonlinear
Containerless Ripple Turbulence
NASA Astrophysics Data System (ADS)
Putterman, Seth; Wright, William; Duval, Walter; Panzarella, Charles
2002-11-01
One of the longest standing unsolved problems in physics relates to the behavior of fluids that are driven far from equilibrium such as occurs when they become turbulent due to fast flow through a grid or tidal motions. In turbulent flows the distribution of vortex energy as a function of the inverse length scale [or wavenumber 'k'] of motion is proportional to 1/k5/3 which is the celebrated law of Kolmogorov. Although this law gives a good description of the average motion, fluctuations around the average are huge. This stands in contrast with thermally activated motion where large fluctuations around thermal equilibrium are highly unfavorable. The problem of turbulence is the problem of understanding why large fluctuations are so prevalent which is also called the problem of 'intermittency'. Turbulence is a remarkable problem in that its solution sits simultaneously at the forefront of physics, mathematics, engineering and computer science. A recent conference [March 2002] on 'Statistical Hydrodynamics' organized by the Los Alamos Laboratory Center for Nonlinear Studies brought together researchers in all of these fields. Although turbulence is generally thought to be described by the Navier-Stokes Equations of fluid mechanics the solution as well as its existence has eluded researchers for over 100 years. In fact proof of the existence of such a solution qualifies for a 1 M millennium prize. As part of our NASA funded research we have proposed building a bridge between vortex turbulence and wave turbulence. The latter occurs when high amplitude waves of various wavelengths are allowed to mutually interact in a fluid. In particular we have proposed measuring the interaction of ripples [capillary waves] that run around on the surface of a fluid sphere suspended in a microgravity environment. The problem of ripple turbulence poses similar mathematical challenges to the problem of vortex turbulence. The waves can have a high amplitude and a strong nonlinear
Turbulent flow through screens
NASA Technical Reports Server (NTRS)
Mehta, R. D.
1984-01-01
A detailed experimental investigation has been carried out on the effects of different types of screens on turbulent flow, in particular turbulent boundary layers. The effect of a screen on a turbulent boundary layer is to give it a 'new lease of life'. The boundary layer turbulence is reorganized and the thickness reduced, thus making it less susceptible to separation. The aerodynamic properties of plastic screens are found to differ significantly from those of the conventional metal screens, evidently because of differences in the weaving properties. The 'overshoot' in mean velocity profile near the boudnary layer edge is shown to be a result of the effect of screen inclination on pressure drop coefficient. A more accurate formulation for the deflection coefficient of a screen is also proposed.
NASA Astrophysics Data System (ADS)
Creppy, Adama; Praud, Olivier; Druart, Xavier; Kohnke, Philippa L.; Plouraboué, Franck
2015-09-01
Collective motion of self-sustained swarming flows has recently provided examples of small-scale turbulence arising where viscous effects are dominant. We report the first observation of universal enstrophy cascade in concentrated swarming sperm consistent with a body of evidence built from various independent measurements. We found a well-defined k-3 power-law decay of a velocity field power spectrum and relative dispersion of small beads consistent with theoretical predictions in 2D turbulence. Concentrated living sperm displays long-range, correlated whirlpool structures of a size that provides an integral scale of turbulence. We propose a consistent explanation for this quasi-2D turbulence based on self-structured laminated flow forced by steric interactions and alignment, a state of active matter that we call "swarming liquid crystal." We develop scaling arguments consistent with this interpretation.
Turbulent Mixing Characteristics in Stratocumulus Clouds
NASA Astrophysics Data System (ADS)
Wang, S.; Wang, Q.; Bucholtz, A.; Zheng, X.
2010-12-01
Turbulence mixing in stratocumulus clouds plays fundamental roles in impacting aerosol-cloud microphysics, regulating cloud macroscopic distribution both in space and time, and interacting with large- and meso-scale meteorological conditions. Understanding the turbulence mixing is a key in understanding physical processes in stratocumulus. This work aims at providing some turbulence mixing characteristics within the entrainment zone using a large-eddy simulation (LES) technique in selected observation cases from two recent field campaigns: Physics of Stratocumulus Top (POST) and VAMOS Ocean-Cloud-Atmosphere-Land Study- Regional experiment (VOCALS-Rex). LES simulation results of two cases of observed stratocumulus clouds will be discussed. The first one is a nighttime cloud case observed on 8 August 2008 during POST. This case is characterized by a relatively weak inversion (~ 5K), weak wind shear across the inversion and strong moisture variability. The other is a daytime cloud case observed on 29 October 2008. This case is characterized by a strong inversion (15 K) and relatively strong wind shear ( ~7 m s-1) across the inversion, which is due to a westward upslope of the PBL height. We apply COAMPS-LES to both cases with initial soundings derived from the observations and large-scale conditions calculated using COAMPS real-time forecasts. Observed longwave radiative (LW) flux from POST is used to validate a simple LW radiation parameterization. Basic turbulence statistics are also computed from the observations; and they are used to evaluate the LES simulations. Analyses of the simulations are focused on the probability density function of Richardson number within the entrainment zone and mixing line characteristics, which can be used to understand the mixing processes produced by the wind shear, radiative cooling and evaporation.
Synchronization of clocks through 12 km of strongly turbulent air over a city
NASA Astrophysics Data System (ADS)
Sinclair, Laura C.; Swann, William C.; Bergeron, Hugo; Baumann, Esther; Cermak, Michael; Coddington, Ian; Deschênes, Jean-Daniel; Giorgetta, Fabrizio R.; Juarez, Juan C.; Khader, Isaac; Petrillo, Keith G.; Souza, Katherine T.; Dennis, Michael L.; Newbury, Nathan R.
2016-10-01
We demonstrate real-time, femtosecond-level clock synchronization across a low-lying, strongly turbulent, 12-km horizontal air path by optical two-way time transfer. For this long horizontal free-space path, the integrated turbulence extends well into the strong turbulence regime corresponding to multiple scattering with a Rytov variance up to 7 and with the number of signal interruptions exceeding 100 per second. Nevertheless, optical two-way time transfer is used to synchronize a remote clock to a master clock with femtosecond-level agreement and with a relative time deviation dropping as low as a few hundred attoseconds. Synchronization is shown for a remote clock based on either an optical or microwave oscillator and using either tip-tilt or adaptive-optics free-space optical terminals. The performance is unaltered from optical two-way time transfer in weak turbulence across short links. These results confirm that the two-way reciprocity of the free-space time-of-flight is maintained both under strong turbulence and with the use of adaptive optics. The demonstrated robustness of optical two-way time transfer against strong turbulence and its compatibility with adaptive optics is encouraging for future femtosecond clock synchronization over very long distance ground-to-air free-space paths.
Measurements of atmospheric turbulence
NASA Technical Reports Server (NTRS)
Murrow, Harold N.
1987-01-01
Various types of atmospheric turbulence measurements are addressed for the purpose of stimulating discussion relative to available data. An outline of these various types of measurements are discussed. Some specific results of detailed characterization studies made at NASA Langley are emphasized. The most recent reports on statistics of turbulence encounters for various types of aircraft operations are summarized. Special severe encounter studies and reference to remote sensing are also included. Wind shear is considered to be a special topic and is not covered.
NASA Astrophysics Data System (ADS)
Cote, O.; Dobosy, R.; Roadcap, J.; Crawford, T.; Hacker, J.
Four turbulence measurement campaigns were performed in the winter sub-tropical jet streams of south coastal Japan and Australia during 1998-2001 with the objective to capture the dynamics of severe refractive and clear air turbulence events. The aircraft used was the GROB 520T EGRETT, which is owned and operated by Airborne Research Australia a unit of Flinders University of South Australia. Severe turbulence events are difficult to forecast and measure but are of critical importance to commercial air safety (NASA -FAA) and the High-Energy Laser (HEL) propagation disturbances. Measurements have shown that weak turbulence/severe turbulence events are associated with anisotropy/isotropy of the turbulent velocity spectra/structure parameters. Strong turbulence events are associated with Froude number that are near unity; weak turbulence with Froude numbers 1. The role that fluctuating velocity-pressure gradient correlation in maintaining strong turbulence, the limited success of Richardson number as a predictor, and limitations of diagnostic prediction schemes based on mesoscale model output will be considered.
NASA Astrophysics Data System (ADS)
Chan, P. W.
2009-03-01
The Hong Kong International Airport (HKIA) is situated in an area of complex terrain. Turbulent flow due to terrain disruption could occur in the vicinity of HKIA when winds from east to southwest climb over Lantau Island, a mountainous island to the south of the airport. Low-level turbulence is an aviation hazard to the aircraft flying into and out of HKIA. It is closely monitored using remote-sensing instruments including Doppler LIght Detection And Ranging (LIDAR) systems and wind profilers in the airport area. Forecasting of low-level turbulence by numerical weather prediction models would be useful in the provision of timely turbulence warnings to the pilots. The feasibility of forecasting eddy dissipation rate (EDR), a measure of turbulence intensity adopted in the international civil aviation community, is studied in this paper using the Regional Atmospheric Modelling System (RAMS). Super-high resolution simulation (within the regime of large eddy simulation) is performed with a horizontal grid size down to 50 m for some typical cases of turbulent airflow at HKIA, such as spring-time easterly winds in a stable boundary layer and gale-force southeasterly winds associated with a typhoon. Sensitivity of the simulation results with respect to the choice of turbulent kinetic energy (TKE) parameterization scheme in RAMS is also examined. RAMS simulation with Deardorff (1980) TKE scheme is found to give the best result in comparison with actual EDR observations. It has the potential for real-time forecasting of low-level turbulence in short-term aviation applications (viz. for the next several hours).
NASA Astrophysics Data System (ADS)
Garbet, X.; Esteve, D.; Sarazin, Y.; Dif-Pradalier, G.; Ghendrih, P.; Grandgirard, V.; Latu, G.; Smolyakov, A.
2014-11-01
The Ohm's law is modified when turbulent processes are accounted for. Besides an hyper-resistivity, already well known, pinch terms appear in the electron momentum flux. Moreover it appears that turbulence is responsible for a source term in the Ohm's law, called here turbulent current drive. Two terms contribute to this source. The first term is a residual stress in the momentum flux, while the second contribution is an electro-motive force. A non zero average parallel wave number is needed to get a finite source term. Hence a symmetry breaking mechanism must be invoked, as for ion momentum transport. E × B shear flows and turbulence intensity gradients are shown to provide similar contributions. Moreover this source term has to compete with the collision friction term (resistivity). The effect is found to be significant for a large scale turbulence in spite of an unfavorable scaling with the ratio of the electron to ion mass. Turbulent current drive appears to be a weak effect in the plasma core, but could be substantial in the plasma edge where it may produce up to 10 % of the local current density.
Hydrological Forecasting Practices in Brazil
NASA Astrophysics Data System (ADS)
Fan, Fernando; Paiva, Rodrigo; Collischonn, Walter; Ramos, Maria-Helena
2016-04-01
This work brings a review on current hydrological and flood forecasting practices in Brazil, including the main forecasts applications, the different kinds of techniques that are currently being employed and the institutions involved on forecasts generation. A brief overview of Brazil is provided, including aspects related to its geography, climate, hydrology and flood hazards. A general discussion about the Brazilian practices on hydrological short and medium range forecasting is presented. Detailed examples of some hydrological forecasting systems that are operational or in a research/pre-operational phase using the large scale hydrological model MGB-IPH are also presented. Finally, some suggestions are given about how the forecasting practices in Brazil can be understood nowadays, and what are the perspectives for the future.
NASA Astrophysics Data System (ADS)
Ouyang, Bing; Hou, Weilin; Gong, Cuiling; Caimi, Frank M.; Dalgleish, Fraser R.; Vuorenkoski, Anni K.
2016-05-01
The Compressive Line Sensing (CLS) active imaging system has been demonstrated to be effective in scattering mediums, such as turbid coastal water through simulations and test tank experiments. Since turbulence is encountered in many atmospheric and underwater surveillance applications, a new CLS imaging prototype was developed to investigate the effectiveness of the CLS concept in a turbulence environment. Compared with earlier optical bench top prototype, the new system is significantly more robust and compact. A series of experiments were conducted at the Naval Research Lab's optical turbulence test facility with the imaging path subjected to various turbulence intensities. In addition to validating the system design, we obtained some unexpected exciting results - in the strong turbulence environment, the time-averaged measurements using the new CLS imaging prototype improved both SNR and resolution of the reconstructed images. We will discuss the implications of the new findings, the challenges of acquiring data through strong turbulence environment, and future enhancements.
Parameter estimation and forecasting for multiplicative log-normal cascades.
Leövey, Andrés E; Lux, Thomas
2012-04-01
We study the well-known multiplicative log-normal cascade process in which the multiplication of Gaussian and log normally distributed random variables yields time series with intermittent bursts of activity. Due to the nonstationarity of this process and the combinatorial nature of such a formalism, its parameters have been estimated mostly by fitting the numerical approximation of the associated non-Gaussian probability density function to empirical data, cf. Castaing et al. [Physica D 46, 177 (1990)]. More recently, alternative estimators based upon various moments have been proposed by Beck [Physica D 193, 195 (2004)] and Kiyono et al. [Phys. Rev. E 76, 041113 (2007)]. In this paper, we pursue this moment-based approach further and develop a more rigorous generalized method of moments (GMM) estimation procedure to cope with the documented difficulties of previous methodologies. We show that even under uncertainty about the actual number of cascade steps, our methodology yields very reliable results for the estimated intermittency parameter. Employing the Levinson-Durbin algorithm for best linear forecasts, we also show that estimated parameters can be used for forecasting the evolution of the turbulent flow. We compare forecasting results from the GMM and Kiyono et al.'s procedure via Monte Carlo simulations. We finally test the applicability of our approach by estimating the intermittency parameter and forecasting of volatility for a sample of financial data from stock and foreign exchange markets.
Grid-scale fluctuations and forecast error in wind power
NASA Astrophysics Data System (ADS)
Bel, G.; Connaughton, C. P.; Toots, M.; Bandi, M. M.
2016-02-01
Wind power fluctuations at the turbine and farm scales are generally not expected to be correlated over large distances. When power from distributed farms feeds the electrical grid, fluctuations from various farms are expected to smooth out. Using data from the Irish grid as a representative example, we analyze wind power fluctuations entering an electrical grid. We find that not only are grid-scale fluctuations temporally correlated up to a day, but they possess a self-similar structure—a signature of long-range correlations in atmospheric turbulence affecting wind power. Using the statistical structure of temporal correlations in fluctuations for generated and forecast power time series, we quantify two types of forecast error: a timescale error ({e}τ ) that quantifies deviations between the high frequency components of the forecast and generated time series, and a scaling error ({e}\\zeta ) that quantifies the degree to which the models fail to predict temporal correlations in the fluctuations for generated power. With no a priori knowledge of the forecast models, we suggest a simple memory kernel that reduces both the timescale error ({e}τ ) and the scaling error ({e}\\zeta ).
Forecasting droughts in East Africa
NASA Astrophysics Data System (ADS)
Mwangi, E.; Wetterhall, F.; Dutra, E.; Di Giuseppe, F.; Pappenberger, F.
2014-02-01
The humanitarian crises caused by the recent droughts (2008-2009 and 2010-2011) in East Africa have illustrated that the ability to make accurate drought forecasts with sufficient lead time is essential. The use of dynamical model precipitation forecasts in combination with drought indices, such as the Standardized Precipitation Index (SPI), can potentially lead to a better description of drought duration, magnitude and spatial extent. This study evaluates the use of the European Centre for Medium-Range Weather Forecasts (ECMWF) products in forecasting droughts in East Africa. ECMWF seasonal precipitation shows significant skill for March-May and October-December rain seasons when evaluated against measurements from the available in situ stations from East Africa. The forecast for October-December rain season has higher skill than for the March-May season. ECMWF forecasts add value to the consensus forecasts produced during the Greater Horn of Africa Climate Outlook Forum (GHACOF), which is the present operational product for precipitation forecast over East Africa. Complementing the original ECMWF precipitation forecasts with SPI provides additional information on the spatial extent and intensity of the drought event.
Hydrologic Forecasting and Hydropower Production
NASA Astrophysics Data System (ADS)
Wigmosta, M. S.; Voisin, N.; Lettenmaier, D. P.; Coleman, A.; Mishra, V.; Schaner, N. A.
2011-12-01
Hydroelectric power production is one of many competing demands for available water along with other priority uses such as irrigation, thermoelectric cooling, municipal, recreation, and environmental performance. Increasingly, hydroelectric generation is being used to offset the intermittent nature of some renewable energy sources such as wind-generated power. An accurate forecast of the magnitude and timing of water supply assists managers in integrated planning and operations to balance competing water uses against current and future supply while protecting against the possibility of water or energy shortages and excesses with real-time actions. We present a medium-range to seasonal ensemble streamflow forecasting system where uncertainty in forecasts is addressed explicitly. The integrated forecast system makes use of remotely-sensed data and automated spatial and temporal data assimilation. Remotely-sensed snow cover, observed snow water equivalent, and observed streamflow data are used to update the hydrologic model state prior to the forecast. In forecast mode, the hydrology model is forced by calibrated ensemble weather/climate forecasts. This system will be fully integrated into a water optimization toolset to inform reservoir and power operations, and guide environmental performance decision making. This flow forecast system development is carried out in agreement with the National Weather Service so that the system can later be incorporated into the NOAA eXperimental Ensemble Forecast Service (XEFS).
Solar Indices Forecasting Tool
NASA Astrophysics Data System (ADS)
Henney, Carl John; Shurkin, Kathleen; Arge, Charles; Hill, Frank
2016-05-01
Progress to forecast key space weather parameters using SIFT (Solar Indices Forecasting Tool) with the ADAPT (Air Force Data Assimilative Photospheric flux Transport) model is highlighted in this presentation. Using a magnetic flux transport model, ADAPT, we estimate the solar near-side field distribution that is used as input into empirical models for predicting F10.7(solar 10.7 cm, 2.8 GHz, radio flux), the Mg II core-to-wing ratio, and selected bands of solar far ultraviolet (FUV) and extreme ultraviolet (EUV) irradiance. Input to the ADAPT model includes the inferred photospheric magnetic field from the NISP ground-based instruments, GONG & VSM. Besides a status update regarding ADAPT and SIFT models, we will summarize the findings that: 1) the sum of the absolute value of strong magnetic fields, associated with sunspots, is shown to correlate well with the observed daily F10.7 variability (Henney et al. 2012); and 2) the sum of the absolute value of weak magnetic fields, associated with plage regions, is shown to correlate well with EUV and FUV irradiance variability (Henney et al. 2015). This work utilizes data produced collaboratively between Air Force Research Laboratory (AFRL) and the National Solar Observatory (NSO). The ADAPT model development is supported by AFRL. The input data utilized by ADAPT is obtained by NISP (NSO Integrated Synoptic Program). NSO is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under a cooperative agreement with the National Science Foundation (NSF). The 10.7 cm solar radio flux data service, utilized by the ADAPT/SIFT F10.7 forecasting model, is operated by the National Research Council of Canada and National Resources Canada, with the support of the Canadian Space Agency.
High-resolution ground layer turbulence from inside the CFHT dome using a lunar scintillometer
NASA Astrophysics Data System (ADS)
Pfrommer, T.; Hickson, P.
2015-04-01
For ground layer adaptive optics systems, knowledge of the local height- and time- resolved ground layer (GL) turbulence is crucial to link local topography with optical turbulence. Such turbulence profiles have been obtained in the years 2009 and 2010 over 250 hours on Mauna Kea, Hawaii. Results from measurements inside the Canada-France-Hawaii Telescope (CFHT) dome indicate severe degradation of image quality due to a poorly vented dome and thus provide input for dome modifications and design aspects for a new ground layer adaptive optics system. The outside median GL seeing above 6 metres was determined to be 0.48±0.01”.
Evolution of phase singularities of vortex beams propagating in atmospheric turbulence.
Ge, Xiao-Lu; Wang, Ben-Yi; Guo, Cheng-Shan
2015-05-01
Optical vortex beams propagating through atmospheric turbulence are studied by numerical modeling, and the phase singularities of the vortices existing in the turbulence-distorted beams are calculated. It is found that the algebraic sum of topological charges (TCs) of all the phase singularities existing in test aperture is approximately equal to the TC of the input vortex beam. This property provides us a possible approach for determining the TC of the vortex beam propagating through the atmospheric turbulence, which could have potential application in optical communication using optical vortices.
NASA Technical Reports Server (NTRS)
1979-01-01
Weather forecasters are usually very precise in reporting such conditions as temperature, wind velocity and humidity. They also provide exact information on barometric pressure at a given moment, and whether the barometer is "rising" or "falling"- but not how rapidly or how slowly it is rising or falling. Until now, there has not been available an instrument which measures precisely the current rate of change of barometric pressure. A meteorological instrument called a barograph traces the historical ups and downs of barometric pressure and plots a rising or falling curve, but, updated every three hours, it is only momentarily accurate at each updating.
Turnipseed, D. Phil
2011-01-01
In 2009, U.S. Secretary of State Hillary R. Clinton joined with the Foreign Ministers of Cambodia, Laos, Thailand, and Vietnam in launching the Lower Mekong Initiative to enhance U.S. engagement with the Lower Mekong countries in the areas of environment, health, education, and infrastructure. Part of the Lower Mekong Initiative, the U.S. Geological Survey's Forecast Mekong project is engaging the United States in scientific research relevant to environmental issues in the Lower Mekong River countries and is staying the course in support of the Mekong Nations with a suite of new projects for 2011.
Forecasting in Complex Systems
NASA Astrophysics Data System (ADS)
Rundle, J. B.; Holliday, J. R.; Graves, W. R.; Turcotte, D. L.; Donnellan, A.
2014-12-01
Complex nonlinear systems are typically characterized by many degrees of freedom, as well as interactions between the elements. Interesting examples can be found in the areas of earthquakes and finance. In these two systems, fat tails play an important role in the statistical dynamics. For earthquake systems, the Gutenberg-Richter magnitude-frequency is applicable, whereas for daily returns for the securities in the financial markets are known to be characterized by leptokurtotic statistics in which the tails are power law. Very large fluctuations are present in both systems. In earthquake systems, one has the example of great earthquakes such as the M9.1, March 11, 2011 Tohoku event. In financial systems, one has the example of the market crash of October 19, 1987. Both were largely unexpected events that severely impacted the earth and financial systems systemically. Other examples include the M9.3 Andaman earthquake of December 26, 2004, and the Great Recession which began with the fall of Lehman Brothers investment bank on September 12, 2013. Forecasting the occurrence of these damaging events has great societal importance. In recent years, national funding agencies in a variety of countries have emphasized the importance of societal relevance in research, and in particular, the goal of improved forecasting technology. Previous work has shown that both earthquakes and financial crashes can be described by a common Landau-Ginzburg-type free energy model. These metastable systems are characterized by fat tail statistics near the classical spinodal. Correlations in these systems can grow and recede, but do not imply causation, a common source of misunderstanding. In both systems, a common set of techniques can be used to compute the probabilities of future earthquakes or crashes. In this talk, we describe the basic phenomenology of these systems and emphasize their similarities and differences. We also consider the problem of forecast validation and verification
Interactive Forecasting with the National Weather Service River Forecast System
NASA Technical Reports Server (NTRS)
Smith, George F.; Page, Donna
1993-01-01
The National Weather Service River Forecast System (NWSRFS) consists of several major hydrometeorologic subcomponents to model the physics of the flow of water through the hydrologic cycle. The entire NWSRFS currently runs in both mainframe and minicomputer environments, using command oriented text input to control the system computations. As computationally powerful and graphically sophisticated scientific workstations became available, the National Weather Service (NWS) recognized that a graphically based, interactive environment would enhance the accuracy and timeliness of NWS river and flood forecasts. Consequently, the operational forecasting portion of the NWSRFS has been ported to run under a UNIX operating system, with X windows as the display environment on a system of networked scientific workstations. In addition, the NWSRFS Interactive Forecast Program was developed to provide a graphical user interface to allow the forecaster to control NWSRFS program flow and to make adjustments to forecasts as necessary. The potential market for water resources forecasting is immense and largely untapped. Any private company able to market the river forecasting technologies currently developed by the NWS Office of Hydrology could provide benefits to many information users and profit from providing these services.
Evolution of branch points for a laser beam propagating through an uplink turbulent atmosphere.
Ge, Xiao-Lu; Liu, Xuan; Guo, Cheng-Shan
2014-03-24
Evolution of branch points in the distorted optical field is studied when a laser beam propagates through turbulent atmosphere along an uplink path. Two categories of propagation events are mainly explored for the same propagation height: fixed wavelength with change of the turbulence strength and fixed turbulence strength with change of the wavelength. It is shown that, when the beam propagates to a certain height, the density of the branch-points reaches its maximum and such a height changes with the turbulence strength but nearly remains constant with different wavelengths. The relationship between the density of branch-points and the Rytov number is also given. A fitted formula describing the relationship between the density of branch-points and propagation height with different turbulence strength and wavelength is found out. Interestingly, this formula is very similar to the formula used for describing the Blackbody radiation in physics. The results obtained may be helpful for atmospheric optics, astronomy and optical communication.
The Aeroacoustics of Turbulent Coanda Wall Jets
NASA Astrophysics Data System (ADS)
Lubert, Caroline; Fox, Jason
2007-11-01
Turbulent Coanda wall jets have become increasingly widely used in a variety of industrial applications in recent years, due to the substantial flow deflection that they afford. A related characteristic is the enhanced turbulence levels and entrainment they offer, compared with conventional jet flows. This characteristic is, however, generally accompanied by a significant increase in the noise levels associated with devices employing this effect. As a consequence, the potential offered by Coanda devices is yet to be fully realized. This problem provides the impetus for the research detailed in this poster. To date, some work has been done on developing a mathematical model of the Turbulent Mixing Noise emitted by such a device, assuming that the surface adjoining the turbulent flow was essentially 2-D. This poster extends this fundamental model, through a combination of mathematical modeling and acoustical and optical experiments. The effect of a variety of parameters, including nozzle configuration and jet exit velocity will be discussed, and ways of reducing or attenuating the noise generated by such flow, whilst still maintaining the crucial flow characteristics, will be presented.
Radiatively Driven Turbulence at the Cloud Top
NASA Astrophysics Data System (ADS)
de Lozar, Alberto; Mellado, Juan Pedro
2012-11-01
We use Direct Numerical Simulations to investigate a radiatively-driven smoke cloud-top mixing layer. This configuration mimics relevant aspects of stratocumuls clouds, in particular the mixing across an inversion that bounds a radiatively driven turbulent flow. A 1D formulation is employed for the radiation calculations. Below the inversion a convective boundary layer propagates downwards into the cloud-bulk. The convective boundary layer decouples from the inversion properties other than the injected buoyancy flux. This buoyancy flux is equal to the total radiative cooling minus the cooling of the inversion layer where the cloud mixes with the free atmosphere. An exact equation at a properly defined inversion point divides the inversion cooling into three components: a molecular flux, a turbulent flux and the direct radiative cooling by the smoke inside the inversion layer. The normalized turbulent flux levels to a constant value (0 . 175 +/- 0 . 05), which is independent of the stratification. As suggested by earlies studies, we observe that the turbulent entrainment only occurs at the small scales and that eddies larger than four optical lengths (50 m in a typical DYCOMS-II cloud) perform little or no entrainment.
Turbulence in Natural Environments
NASA Astrophysics Data System (ADS)
Banerjee, Tirtha
Problems in the area of land/biosphere-atmosphere interaction, hydrology, climate modeling etc. can be systematically organized as a study of turbulent flow in presence of boundary conditions in an increasing order of complexity. The present work is an attempt to study a few subsets of this general problem of turbulence in natural environments- in the context of neutral and thermally stratified atmospheric surface layer, the presence of a heterogeneous vegetation canopy and the interaction between air flow and a static water body in presence of flexible protruding vegetation. The main issue addressed in the context of turbulence in the atmospheric surface layer is whether it is possible to describe the macro-states of turbulence such as mean velocity and turbulent velocity variance in terms of the micro-states of the turbulent flow, i.e., a distribution of turbulent kinetic energy across a multitude of scales. This has been achieved by a `spectral budget approach' which is extended for thermal stratification scenarios as well, in the process unifying the seemingly different and unrelated theories of turbulence such as Kolmogorov's hypothesis, Heisenberg's eddy viscosity, Monin Obukhov Similarity Theory (MOST) etc. under a common framework. In the case of a more complex scenario such as presence of a vegetation canopy with edges and gaps, the question that is addressed is in what detail the turbulence is needed to be resolved in order to capture the bulk flow features such as recirculation patterns. This issue is addressed by a simple numerical framework and it has been found out that an explicit prescription of turbulence is not necessary in presence of heterogeneities such as edges and gaps where the interplay between advection, pressure gradients and drag forces are sufficient to capture the first order dynamics. This result can be very important for eddy-covariance flux calibration strategies in non-ideal environments and the developed numerical model can be
Turbulence and Stochastic Processes
NASA Astrophysics Data System (ADS)
Celani, Antonio; Mazzino, Andrea; Pumir, Alain
sec:08-1In 1931 the monograph Analytical Methods in Probability Theory appeared, in which A.N. Kolmogorov laid the foundations for the modern theory of Markov processes [1]. According to Gnedenko: "In the history of probability theory it is difficult to find other works that changed the established points of view and basic trends in research work in such a decisive way". Ten years later, his article on fully developed turbulence provided the framework within which most, if not all, of the subsequent theoretical investigations have been conducted [2] (see e.g. the review by Biferale et al. in this volume [3]. Remarkably, the greatest advances made in the last few years towards a thorough understanding of turbulence developed from the successful marriage between the theory of stochastic processes and the phenomenology of turbulent transport of scalar fields. In this article we will summarize these recent developments which expose the direct link between the intermittency of transported fields and the statistical properties of particle trajectories advected by the turbulent flow (see also [4], and, for a more thorough review, [5]. We also discuss the perspectives of the Lagrangian approach beyond passive scalars, especially for the modeling of hydrodynamic turbulence.
UV index forecasts and measurements of health-effective radiation.
Feister, Uwe; Laschewski, Gudrun; Grewe, Rolf-Dieter
2011-01-10
While erythemal irradiance as a potentially damaging effect to the skin has been extensively studied and short-term forecasts have been issued to the public to reduce detrimental immediate and long-term effects such as sunburn and skin cancer by overexposure, beneficial effects to human health such as vitamin D(3) production by UV radiation and melatonin suppression by blue visible light have attained more and more attention, though both of them have not become part of forecasting yet. Using 4years of solar radiation data measured at the mid-latitude site Lindenberg (52°N), and forecast daily maximum UV index values, an overall good correspondence has been found. The data base of solar UV radiation and illuminance has also been used to analyze effects of clouds and aerosols on the effective irradiance. Optically thick clouds can strongly modify the ratios between erythemal and vitamin D(3) effective irradiance such that direct radiative transfer modeling of the latter in future UV forecasts should be preferably used. If parameterizations of vitamin D(3) effective irradiance from erythemal irradiance are used instead, the optical cloud depth would have to be taken into account to avoid an overestimation of vitamin D(3) with parameterizations neglecting cloud optical depth. Particular emphasis for the beneficial effects has been laid in our study on low exposure. Daily doses of solar irradiation for both vitamin D(3) and melatonin suppression do not reach minimum threshold doses even with clear sky and unobstructed horizon during the winter months.
Regional-seasonal weather forecasting
Abarbanel, H.; Foley, H.; MacDonald, G.; Rothaus, O.; Rudermann, M.; Vesecky, J.
1980-08-01
In the interest of allocating heating fuels optimally, the state-of-the-art for seasonal weather forecasting is reviewed. A model using an enormous data base of past weather data is contemplated to improve seasonal forecasts, but present skills do not make that practicable. 90 references. (PSB)
The pioneers of weather forecasting
NASA Astrophysics Data System (ADS)
Ballard, Susan
2016-01-01
In The Weather Experiment author Peter Moore takes us on a compelling journey through the early history of weather forecasting, bringing to life the personalities, lives and achievements of the men who put in place the building blocks required for forecasts to be possible.
Thirty Meter Telescope Site Testing VI: Turbulence Profiles
NASA Astrophysics Data System (ADS)
Els, S. G.; Travouillon, T.; Schöck, M.; Riddle, R.; Skidmore, W.; Seguel, J.; Bustos, E.; Walker, D.
2009-05-01
The results on the vertical distribution of optical turbulence above the five mountains which were investigated by the site testing for the Thirty Meter Telescope (TMT) are reported. On San Pedro Mártir in Mexico; the 13 North site on Mauna Kea; and three mountains in northern Chile: Cerro Tolar, Cerro Armazones, and Cerro Tolonchar; MASS-DIMM turbulence profilers have been operated over at least two years. Acoustic turbulence profilers—SODARs—were also operated at these sites. The obtained turbulence profiles indicate that at all sites the lowest 200 m are the main source of the total seeing observed, with the Chilean sites showing a weaker ground layer than the other two sites. The two northern hemisphere sites have weaker turbulence at altitudes above 500 m, with 13N showing the weakest turbulence at 16 km, responsible for the large isoplanatic angle at this site. The influence of the jetstream and wind speeds close to the ground on the clear sky turbulence strength throughout the atmosphere are discussed, as well as seasonal and nocturnal variations. This is the sixth article in a series discussing the TMT site testing project.
Yang, Huan; Zimmerman, Aaron; Lehner, Luis
2015-02-27
We demonstrate that rapidly spinning black holes can display a new type of nonlinear parametric instability-which is triggered above a certain perturbation amplitude threshold-akin to the onset of turbulence, with possibly observable consequences. This instability transfers from higher temporal and azimuthal spatial frequencies to lower frequencies-a phenomenon reminiscent of the inverse cascade displayed by (2+1)-dimensional fluids. Our finding provides evidence for the onset of transitory turbulence in astrophysical black holes and predicts observable signatures in black hole binaries with high spins. Furthermore, it gives a gravitational description of this behavior which, through the fluid-gravity duality, can potentially shed new light on the remarkable phenomena of turbulence in fluids.
Yang, Huan; Zimmerman, Aaron; Lehner, Luis
2015-02-27
We demonstrate that rapidly spinning black holes can display a new type of nonlinear parametric instability-which is triggered above a certain perturbation amplitude threshold-akin to the onset of turbulence, with possibly observable consequences. This instability transfers from higher temporal and azimuthal spatial frequencies to lower frequencies-a phenomenon reminiscent of the inverse cascade displayed by (2+1)-dimensional fluids. Our finding provides evidence for the onset of transitory turbulence in astrophysical black holes and predicts observable signatures in black hole binaries with high spins. Furthermore, it gives a gravitational description of this behavior which, through the fluid-gravity duality, can potentially shed new light on the remarkable phenomena of turbulence in fluids. PMID:25768746
Weather Forecasting Systems and Methods
NASA Technical Reports Server (NTRS)
Mecikalski, John (Inventor); MacKenzie, Wayne M., Jr. (Inventor); Walker, John Robert (Inventor)
2014-01-01
A weather forecasting system has weather forecasting logic that receives raw image data from a satellite. The raw image data has values indicative of light and radiance data from the Earth as measured by the satellite, and the weather forecasting logic processes such data to identify cumulus clouds within the satellite images. For each identified cumulus cloud, the weather forecasting logic applies interest field tests to determine a score indicating the likelihood of the cumulus cloud forming precipitation and/or lightning in the future within a certain time period. Based on such scores, the weather forecasting logic predicts in which geographic regions the identified cumulus clouds will produce precipitation and/or lighting within during the time period. Such predictions may then be used to provide a weather map thereby providing users with a graphical illustration of the areas predicted to be affected by precipitation within the time period.
Turbulent forced diffusion flames
Arpaci, V.S.; Li, C.Y.
1995-07-01
It is the purpose of this study to introduce a turbulent microscale appropriate for forced diffusion flames and to propose models for fuel consumption and skin friction in terms of this scale. The study consists of four sections. Following the introduction, Section 2 recapitulates the laminar theories of reacting boundary layers in terms of dimensional arguments and proposes models for fuel consumption and skin friction. Section 3 extends these arguments by introducing a microscale appropriate for turbulent flames and, in terms of this scale, develops models for fuel consumption and skin friction, correlates the experimental data on skin friction, and Section 4 concludes the study.
Correlated imaging through atmospheric turbulence
Zhang Pengli; Gong Wenlin; Shen Xia; Han Shensheng
2010-09-15
Correlated imaging through atmospheric turbulence is studied, and the analytical expressions describing turbulence effects on image resolution are derived. Compared with direct imaging, correlated imaging can reduce the influence of turbulence to a certain extent and reconstruct high-resolution images. The result is backed up by numerical simulations, in which turbulence-induced phase perturbations are simulated by random-phase screens inserted into propagation paths.
Reliable probabilistic forecasts from an ensemble reservoir inflow forecasting system
NASA Astrophysics Data System (ADS)
Bourdin, Dominique R.; Nipen, Thomas N.; Stull, Roland B.
2014-04-01
This paper describes a probabilistic reservoir inflow forecasting system that explicitly attempts to sample from major sources of uncertainty in the modeling chain. Uncertainty in hydrologic forecasts arises due to errors in the hydrologic models themselves, their parameterizations, and in the initial and boundary conditions (e.g., meteorological observations or forecasts) used to drive the forecasts. The Member-to-Member (M2M) ensemble presented herein uses individual members of a numerical weather model ensemble to drive two different distributed hydrologic models, each of which is calibrated using three different objective functions. An ensemble of deterministic hydrologic states is generated by spinning up the daily simulated state using each model and parameterization. To produce probabilistic forecasts, uncertainty models are used to fit probability distribution functions (PDF) to the bias-corrected ensemble. The parameters of the distribution are estimated based on statistical properties of the ensemble and past verifying observations. The uncertainty model is able to produce reliable probability forecasts by matching the shape of the PDF to the shape of the empirical distribution of forecast errors. This shape is found to vary seasonally in the case-study watershed. We present an "intelligent" adaptation to a Probability Integral Transform (PIT)-based probability calibration scheme that relabels raw cumulative probabilities into calibrated cumulative probabilities based on recent past forecast performance. As expected, the intelligent scheme, which applies calibration corrections only when probability forecasts are deemed sufficiently unreliable, improves reliability without the inflation of ignorance exhibited in certain cases by the original PIT-based scheme.
Forecasting geomagnetic activities from the Boyle Index
NASA Astrophysics Data System (ADS)
Bala, R.; Reiff, P. H.
2010-12-01
The Boyle Index (BI), Φ =10-4}( {v{2}/{km/sec) + 11.7({(B)/(nT)})sin 3}{(θ /2) kV, has been successful in predicting the geomagnetic activity since its inception in October 2003. It is available in near-real-time from http://space.rice.edu/ISTP/wind.html and provides space weather predictions of geomagnetic indices (Kp, Dst and the AE) in real time through neural network algorithms. In addition, it provides free email alerts to its 700+ subscribers whenever the magnetospheric activity levels exceed certain pre-defined thresholds. We are constantly improving our algorithms, in the interest of either including more data or improving the accuracy and lead-time of forecasts. For example, with the inclusion of two more years of data (2008 and 2009) in the training, we have the advantage of modeling one of the deepest solar minimums, which has been exceptionally low in terms of the activity level. Our algorithms have been successful in capturing the effects of ``preconditioning" and the non-linearity in the solar wind parameters (for example, see figure 1). This paper presents our new attempts to include the effects of solar turbulence by incorporating the standard deviations in the solar wind parameters along with the BI, for greater the turbulence the higher the energy input into the magnetosphere as some of the previous studies have shown. Furthermore, we will also present how 3-hour averaged 1-hour sliding window scheme have improved our predictions with lead times of 3 hours or longer. Our predictions from a recent activity, 03 August 2010.
Twelve mortal sins of the turbulence propagation science
NASA Astrophysics Data System (ADS)
Charnotskii, Mikhail
2011-09-01
In this review paper we discuss a series of typical mistakes and omissions that are made by engineers and scientists involved in the theoretical research and modeling of the optical propagation through atmospheric turbulence. We show how the use of the oversimplified Gaussian spectral model of turbulence delivers the completely erroneous results for the beam wander. We address a series of common omissions related to calculations of the average beam intensity: unnecessary use of the approximations when rigorous result is available, invalid application of the RMS beam size to the turbulence-distorted beams, overlooking the simple theoretical result - average beam intensity is a convolution with the turbulent Point Spread Function (PSF). We discuss the meaning and potential dangers of the use of the quadratic structure function for modeling of the turbulent perturbations. We will also address the issues related to the energy conservation principle and reciprocity that have very important consequences for the turbulence propagation, but are frequently overlooked in the current literature. We discuss a series of misconceptions that very common in of the Scintillation Index (SI) calculations. We will clarify the infamous misunderstanding of the Rytov's approximation: vanishing scintillation at the beam focus, and show the correct weak and strong scintillation solutions for the SI at the beam focus. We discuss the flaws of the Fried model of the short-term PSF, and direct to the more accurate PSF model. We will briefly review the propagation of the polarized optical waves through turbulence and discuss the inadequacy of the recently published calculations of the electromagnetic beams calculations. We discuss some common errors in representation of the calculation results for the non-Kolmogorov turbulence.
Irradiance scintillation index on slant atmospheric turbulence: simple approach
NASA Astrophysics Data System (ADS)
Fayed, Heba A.; El Aziz, Ahmed Abd; Aly, Asmaa M.; Aly, Moustafa H.
2016-05-01
Turbulence plays an important role in investigating the irradiance scintillation index (SI) for a free-space optical wave propagating through atmospheric turbulence. The Hufnagel-Valley model is used in most studies, where the SI of the slant path is obtained using numerical analysis. A polynomial is proposed for the refractive index structure parameter, on which a closed form is derived for the irradiance SI of a spherical optical wave propagating through a slant atmospheric turbulence. This is used to study signal-to-noise ratio and bit error rate for system performance evaluation. The obtained results demonstrate the simplicity of using the derived closed form of SI compared to statistical methods. The derived expression takes less computational time for SI, which reflects positively on the system performance, which is an essential issue in vehicular mobile applications, in particular.
Forecasting droughts in East Africa
NASA Astrophysics Data System (ADS)
Mwangi, Emmah; Wetterhall, Fredrik; Dutra, Emanuel; Di Giuseppe, Francesca; Pappenberger, Florian
2014-05-01
The humanitarian crisis caused by the recent droughts (2008-2009 and 2010-2011) in East Africa have illustrated that the ability to make accurate drought predictions with sufficient lead time is essential. The use of dynamical model forecasts in combination with drought indices, such as the Standardized Precipitation Index (SPI), can potentially to lead to a better description of drought duration, magnitude and spatial extent. This study evaluates the use of the European Centre for Medium-Range Weather Forecasts (ECMWF) products in forecasting droughts in East Africa. ECMWF seasonal precipitation shows significant skill for both rain seasons when evaluated against measurements from the available in-situ stations from East Africa. The forecast for October-December rain season has higher skill than for the March-May season. ECMWF forecasts add value to the statistical forecasts produced during the Greater Horn of Africa Climate Outlook Forums (GHACOF), which is the present operational product. Complementing the raw precipitation forecasts with SPI provides additional information on the spatial extent and intensity of the drought event.
Atmospheric composition forecasting in Europe
NASA Astrophysics Data System (ADS)
Menut, L.; Bessagnet, B.
2010-01-01
The atmospheric composition is a societal issue and, following new European directives, its forecast is now recommended to quantify the air quality. It concerns both gaseous and particles species, identified as potential problems for health. In Europe, numerical systems providing daily air quality forecasts are numerous and, mostly, operated by universities. Following recent European research projects (GEMS, PROMOTE), an organization of the air quality forecast is currently under development. But for the moment, many platforms exist, each of them with strengths and weaknesses. This overview paper presents all existing systems in Europe and try to identify the main remaining gaps in the air quality forecast knowledge. As modeling systems are now able to reasonably forecast gaseous species, and in a lesser extent aerosols, the future directions would concern the use of these systems with ensemble approaches and satellite data assimilation. If numerous improvements were recently done on emissions and chemistry knowledge, improvements are still needed especially concerning meteorology, which remains a weak point of forecast systems. Future directions will also concern the use of these forecast tools to better understand and quantify the air pollution impact on health.
Zhou, Yuan; Yuan, Yangsheng; Qu, Jun; Huang, Wei
2016-05-16
Analytical formulas are derived for the average intensity, the root-mean-square (rms) angular width, and the M^{2}-factor of Laguerre-Gaussian correlated Schell-model (LGCSM) beam propagating in non-Kolmogorov turbulence. The influence of the beam and turbulence parameters on the LGCSM beam is numerically calculated. It is shown that the quality of the LGCSM beam can be improved by choosing appropriate beam or turbulence parameter values. It is also found that the LGCSM beam has advantage over the Gaussian Schell-model (GSM) beam for reducing the turbulence-induced degradation. Our results will have some theoretical reference value for optical communications.
Multilevel turbulence simulations
Tziperman, E.
1994-12-31
The authors propose a novel method for the simulation of turbulent flows, that is motivated by and based on the Multigrid (MG) formalism. The method, called Multilevel Turbulence Simulations (MTS), is potentially more efficient and more accurate than LES. In many physical problems one is interested in the effects of the small scales on the larger ones, or in a typical realization of the flow, and not in the detailed time history of each small scale feature. MTS takes advantage of the fact that the detailed simulation of small scales is not needed at all times, in order to make the calculation significantly more efficient, while accurately accounting for the effects of the small scales on the larger scale of interest. In MTS, models of several resolutions are used to represent the turbulent flow. The model equations in each coarse level incorporate a closure term roughly corresponding to the tau correction in the MG formalism that accounts for the effects of the unresolvable scales on that grid. The finer resolution grids are used only a small portion of the simulation time in order to evaluate the closure terms for the coarser grids, while the coarse resolution grids are then used to accurately and efficiently calculate the evolution of the larger scales. The methods efficiency relative to direct simulations is of the order of the ratio of required integration time to the smallest eddies turnover time, potentially resulting in orders of magnitude improvement for a large class of turbulence problems.
Cygankiewicz, Iwona
2013-01-01
Heart rate turbulence (HRT) is a baroreflex-mediated biphasic reaction of heart rate in response to premature ventricular beats. Heart rate turbulence is quantified by: turbulence onset (TO) reflecting the initial acceleration of heart rate following premature beat and turbulence slope (TS) describing subsequent deceleration of heart rate. Abnormal HRT identifies patients with autonomic dysfunction or impaired baroreflex sensitivity due to variety of disorders, but also may reflect changes in autonomic nervous system induced by different therapeutic modalities such as drugs, revascularization, or cardiac resynchronization therapy. More importantly, impaired HRT has been shown to identify patients at high risk of all-cause mortality and sudden death, particularly in postinfarction and congestive heart failure patients. It should be emphasized that abnormal HRT has a well-established role in stratification of postinfarction and heart failure patients with relatively preserved left ventricular ejection fraction. The ongoing clinical trials will document whether HRT can be used to guide implantation of cardioverter-defibrillators in this subset of patients, not covered yet by ICD guidelines. This review focuses on the current state-of-the-art knowledge regarding clinical significance of HRT in detection of autonomic dysfunction and regarding the prognostic significance of this parameter in predicting all-cause mortality and sudden death.
Premixed turbulent flame calculation
NASA Technical Reports Server (NTRS)
El-Tahry, S.; Rutland, C. J.; Ferziger, J. H.; Rogers, M. M.
1987-01-01
The importance of turbulent premixed flames in a variety of applications has led to a substantial amount of effort towards improving the understanding of these flames. Although these efforts have increased the understanding, many questions still remain. The use of direct numerical simulation (DNS) in solving these questions is examined.
Spirituality in Turbulent Times.
ERIC Educational Resources Information Center
Wheatley, Margaret J.
2002-01-01
Discusses the importance of spiritual leadership in turbulent, uncertain times. Describes several spiritual principles--for example, life is cyclical; all life is interconnected. Offers six suggestions for personal health: Start day peacefully, learn to be mindful, slow things down, create own measures, expect surprise, practice gratefulness. (PKP)
NASA Technical Reports Server (NTRS)
Bass, J; Agostini, L
1955-01-01
The theory of turbulence reached its full growth at the end of the 19th century as a result of the work by Boussinesq and Reynolds. It then underwent a long period of stagnation which ended under the impulse given to it by the development of wind tunnels caused by the needs of aviation. Numerous researchers, attempted to put Reynolds' elementary statistical theory into a more precise form. During the war, some isolated scientists - von Weizsacker and Heisenberg in Germany, Kolmogoroff in Russia, Onsager in the U.S.A. - started a program of research. By a system of assumptions which make it possible to approach the structure of turbulence in well-defined limiting conditions quantitatively, they obtained a certain number of laws on the correlations and the spectrum. Since the late reports have improved the mathematical language of turbulence, it was deemed advisable to start with a detailed account of the mathematical methods applicable to turbulence, inspired at first by the work of the French school, above all for the basic principles, then the work of the foreigners, above all for the theory of the spectrum.
Cygankiewicz, Iwona
2013-01-01
Heart rate turbulence (HRT) is a baroreflex-mediated biphasic reaction of heart rate in response to premature ventricular beats. Heart rate turbulence is quantified by: turbulence onset (TO) reflecting the initial acceleration of heart rate following premature beat and turbulence slope (TS) describing subsequent deceleration of heart rate. Abnormal HRT identifies patients with autonomic dysfunction or impaired baroreflex sensitivity due to variety of disorders, but also may reflect changes in autonomic nervous system induced by different therapeutic modalities such as drugs, revascularization, or cardiac resynchronization therapy. More importantly, impaired HRT has been shown to identify patients at high risk of all-cause mortality and sudden death, particularly in postinfarction and congestive heart failure patients. It should be emphasized that abnormal HRT has a well-established role in stratification of postinfarction and heart failure patients with relatively preserved left ventricular ejection fraction. The ongoing clinical trials will document whether HRT can be used to guide implantation of cardioverter-defibrillators in this subset of patients, not covered yet by ICD guidelines. This review focuses on the current state-of-the-art knowledge regarding clinical significance of HRT in detection of autonomic dysfunction and regarding the prognostic significance of this parameter in predicting all-cause mortality and sudden death. PMID:24215748
Aircraft Dynamic Modeling in Turbulence
NASA Technical Reports Server (NTRS)
Morelli, Eugene A.; Cunninham, Kevin
2012-01-01
A method for accurately identifying aircraft dynamic models in turbulence was developed and demonstrated. The method uses orthogonal optimized multisine excitation inputs and an analytic method for enhancing signal-to-noise ratio for dynamic modeling in turbulence. A turbulence metric was developed to accurately characterize the turbulence level using flight measurements. The modeling technique was demonstrated in simulation, then applied to a subscale twin-engine jet transport aircraft in flight. Comparisons of modeling results obtained in turbulent air to results obtained in smooth air were used to demonstrate the effectiveness of the approach.
Remarks on turbulent constitutive relations
NASA Technical Reports Server (NTRS)
Shih, Tsan-Hsing; Lumley, John L.
1993-01-01
The paper demonstrates that the concept of turbulent constitutive relations can be used to construct general models for various turbulent correlations. Some of the Generalized Cayley-Hamilton formulas for relating tensor products of higher extension to tensor products of lower extension are introduced. The combination of dimensional analysis and invariant theory can lead to 'turbulent constitutive relations' (or general turbulence models) for, in principle, any turbulent correlations. As examples, the constitutive relations for Reynolds stresses and scalar fluxes are derived. The results are consistent with ones from Renormalization Group (RNG) theory and two-scale Direct-Interaction Approximation (DIA) method, but with a more general form.
Workshop on Computational Turbulence Modeling
NASA Technical Reports Server (NTRS)
1993-01-01
This document contains presentations given at Workshop on Computational Turbulence Modeling held 15-16 Sep. 1993. The purpose of the meeting was to discuss the current status and future development of turbulence modeling in computational fluid dynamics for aerospace propulsion systems. Papers cover the following topics: turbulence modeling activities at the Center for Modeling of Turbulence and Transition (CMOTT); heat transfer and turbomachinery flow physics; aerothermochemistry and computational methods for space systems; computational fluid dynamics and the k-epsilon turbulence model; propulsion systems; and inlet, duct, and nozzle flow.
NASA Technical Reports Server (NTRS)
Rubinstein, R. (Editor); Rumsey, C. L. (Editor); Salas, M. D. (Editor); Thomas, J. L. (Editor); Bushnell, Dennis M. (Technical Monitor)
2001-01-01
Advances in turbulence modeling are needed in order to calculate high Reynolds number flows near the onset of separation and beyond. To this end, the participants in this workshop made the following recommendations. (1) A national/international database and standards for turbulence modeling assessment should be established. Existing experimental data sets should be reviewed and categorized. Advantage should be taken of other efforts already under-way, such as that of the European Research Community on Flow, Turbulence, and Combustion (ERCOFTAC) consortium. Carefully selected "unit" experiments will be needed, as well as advances in instrumentation, to fill the gaps in existing datasets. A high priority should be given to document existing turbulence model capabilities in a standard form, including numerical implementation issues such as grid quality and resolution. (2) NASA should support long-term research on Algebraic Stress Models and Reynolds Stress Models. The emphasis should be placed on improving the length-scale equation, since it is the least understood and is a key component of two-equation and higher models. Second priority should be given to the development of improved near-wall models. Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES) would provide valuable guidance in developing and validating new Reynolds-averaged Navier-Stokes (RANS) models. Although not the focus of this workshop, DNS, LES, and hybrid methods currently represent viable approaches for analysis on a limited basis. Therefore, although computer limitations require the use of RANS methods for realistic configurations at high Reynolds number in the foreseeable future, a balanced effort in turbulence modeling development, validation, and implementation should include these approaches as well.
Velocity Measurements of Turbulent Wake Flow Over a Circular Cylinder
NASA Astrophysics Data System (ADS)
Shih, Chang-Lung; Chen, Wei-Cheng; Chang, Keh-Chin; Wang, Muh-Rong
2016-06-01
There are two general concerns in the velocity measurements of turbulence. One is the temporal characteristics which governs the turbulent mixing process. Turbulence is rotational and is characterized by high levels of fluctuating vorticity. In order to obtain the information of vorticity dynamics, the spatial characteristics is the other concern. These varying needs can be satisfied by using a variety of diagnostic techniques such as invasive physical probes and non-invasive optical instruments. Probe techniques for the turbulent measurements are inherently simple and less expensive than optical methods. However, the presence of a physical probe may alter the flow field, and velocity measurements usually become questionable when probing recirculation zones. The non-invasive optical methods are mostly made of the foreign particles (or seeding) instead of the fluid flow and are, thus, of indirect method. The difference between the velocities of fluid and foreign particles is always an issue to be discussed particularly in the measurements of complicated turbulent flows. Velocity measurements of the turbulent wake flow over a circular cylinder will be made by using two invasive instruments, namely, a cross-type hot-wire anemometry (HWA) and a split-fiber hot-film anemometry (HFA), and a non-invasive optical instrument, namely, particle image velocimetry (PIV) in this study. Comparison results show that all three employed diagnostic techniques yield similar measurements in the mean velocity while somewhat deviated results in the root-mean-squared velocity, particularly for the PIV measurements. It is demonstrated that HFA possesses more capability than HWA in the flow measurements of wake flow. Wake width is determined in terms of either the flatness factor or shear-induced vorticity. It is demonstrated that flow data obtained with the three employed diagnostic techniques are capable of yielding accurate determination of wake width.
IACATS AIV: AIV process for a versatile turbulence simulator
NASA Astrophysics Data System (ADS)
Ramos Zapata, Gonzalo; Belenguer-Dávila, Tomás; Pastor Santos, Carmen; Sánchez Rodríguez, Antonio; Moreno Raso, Javier; Argelaguet, Heribert; Serrano, Javier
2010-07-01
IACATS is an atmospheric turbulence, stars and telescope simulator for the evaluation of on ground telescopes instrumentation developed by INTA (optics) and LIDAX (opto-mechanics) for the IAC (Instituto de Astrofísica de Canarias). Three telescopes have been simulated, matching the f number, focal plane, and optical interface of the actual telescopes. An optical breadboard was designed and built containing the required opto-mechanics for simulating the telescopes, and various levels of turbulence required. In addition to the telescope simulator optics, a set of three phase plates have been procured and conveniently combined in order to reproduce the atmospheric turbulence required by the IAC. A wave front sensor has been also included in order to evaluate the deformation that the phase plates, or the simulated turbulence, produce in the wave front coming from the illumination system and star simulator. Finally, a specific illumination system was developed including different working wavelengths in order to fulfil the requirements. The description of the illumination system itself has been done in a separate publication.. In the following lines, the characteristics of the IACATS instrument as well as the results obtained from the AIV (Assembly and Integration Verification) process are reported on.
Partially coherent beam propagation in atmospheric turbulence [invited].
Gbur, Greg
2014-09-01
Partially coherent beams hold much promise in free-space optical communications for their resistance to the deleterious effects of atmospheric turbulence. We describe the basic theoretical and computational tools used to investigate these effects, and review the research to date.
Turbulence effects on thermal blooming.
Gebhardt, F G; Smith, D C; Buser, R G; Rohde, R S
1973-08-01
Theoretical and experimental studies have been carried out to determine the importance of mechanical turbulence, i.e., velocity fluctuations, on the propagation of high power cw CO(2) laser radiation in the atmosphere. The experimental results were obtained using artificially generated turbulence and show, in agreement with theory based on a diffusion model, that the turbulence tends to replace the asymmetric bending, focusing, and spreading by the mean wind with a symmetric blooming. For sufficiently strong velocity fluctuations, say, greater than two to three times the mean velocity, the turbulence can reduce thermal blooming effects and increase the beam irradiance. Smaller turbulence levels, however, may actually result in decreasing the beam irradiance somewhat. From these results and estimates of the properties of turbulent diffusion in the atmosphere it appears that under typical conditions the mechanical turbulence will not significantly reduce the wind-dominated thermal distortion effects.
Characterizing the uncertainty in river stage forecasts conditional on point forecast values
NASA Astrophysics Data System (ADS)
Yan, Jun; Liao, Gong-Yi; Gebremichael, Mekonnen; Shedd, Robert; Vallee, David R.
2012-12-01
Uncertainty information about river level forecast is as important as the forecast itself for forecast users. This paper presents a flexible, statistical approach that processes deterministic forecasts into probabilistic forecasts. The model is a smoothly changing conditional distribution of river stage given point forecast and other information available, such as lagged river level at the time of forecasting. The parametric distribution is a four-parameter skewt distribution, with each parameter modeled as a smooth function of the point forecast and the 1 day ago observed river level. The model was applied to 9 years of daily 6 h lead forecasts and 24 h lead forecasts in the warm season and their matching observations at the Plymouth station on the Pemigewasset River in New Hampshire. For each point forecast, the conditional distribution and resulting prediction intervals provide uncertainty information that are potentially very important to forecast users and algorithm developers in decision making and improvement of forecast quality.
Propagation of a higher-order cosh-Gaussian beam in turbulent atmosphere.
Zhou, Guoquan
2011-02-28
The propagation of a higher-order cosh-Gaussian beam through a paraxial and real ABCD optical system in turbulent atmosphere has been investigated. The analytical expressions for the average intensity, the effective beam size, and the kurtosis parameter of a higher-order cosh-Gaussian beam through a paraxial and real ABCD optical system are derived in turbulent atmosphere. The average intensity distribution and the spreading properties of a higher-order cosh-Gaussian in turbulent atmosphere are numerically demonstrated. The influences of the beam parameters and the structure constant of the atmospheric turbulence on the propagation of a higher-order cosh-Gaussian beam in turbulent atmosphere are also examined in detail.
NASA Astrophysics Data System (ADS)
Basart, Sara; Terradellas, Enric; Cuevas, Emilio; Jorba, Oriol; Benincasa, Francesco; Baldasano, Jose M.
2015-04-01
The World Meteorological Organization's Sand and Dust Storm Warning Advisory and Assessment System (WMO SDS-WAS, http://sds-was.aemet.es/) project has the mission to enhance the ability of countries to deliver timely and quality sand and dust storm forecasts, observations, information and knowledge to users through an international partnership of research and operational communities. The good results obtained by the SDS-WAS Northern Africa, Middle East and Europe (NAMEE) Regional Center and the demand of many national meteorological services led to the deployment of operational dust forecast services. On June 2014, the first WMO Regional Meteorological Center Specialized on Atmospheric Sand and Dust Forecast, the Barcelona Dust Forecast Center (BDFC; http://dust.aemet.es/), was publicly presented. The Center operationally generates and distributes predictions for the NAMEE region. The dust forecasts are based on the NMMB/BSC-Dust model developed at the Barcelona Supercomputing Center (BSC-CNS). The present contribution will describe the main objectives and capabilities of BDFC. One of the activities performed by the BDFC is to establish a protocol to routinely exchange products from dust forecast models as dust load, dust optical depth (AOD), surface concentration, surface extinction and deposition. An important step in dust forecasting is the evaluation of the results that have been generated. This process consists of the comparison of the model results with multiple kinds of observations (i.e. AERONET and MODIS) and is aimed to facilitate the understanding of the model capabilities, limitations, and appropriateness for the purpose for which it was designed. The aim of this work is to present different evaluation approaches and to test the use of different observational products in the evaluation system.
Spreading and wandering of Gaussian–Schell model laser beams in an anisotropic turbulent ocean
NASA Astrophysics Data System (ADS)
Wu, Yuqian; Zhang, Yixin; Zhu, Yun; Hu, Zhengda
2016-09-01
The effect of anisotropic turbulence on the spreading and wandering of Gaussian–Schell model (GSM) laser beams propagating in an ocean is studied. The long-term spreading of a GSM beam propagating through the paraxial channel of a turbulent ocean is also developed. Expressions of random wander for such laser beams are derived in an anisotropic turbulent ocean based on the extended Huygens–Fresnel principle. We investigate the influence of parameters in a turbulent ocean on the beam wander and spreading. Our results indicate that beam spreading and random beam wandering are smaller without considering the anisotropy of turbulence in the oceanic channel. Salinity fluctuation has a greater contribution to both the beam spreading and beam wander than that of temperature fluctuations in a turbulent ocean. Our results could be helpful for designing a free-space optical wireless communication system in an oceanic environment.
Spreading and wandering of Gaussian-Schell model laser beams in an anisotropic turbulent ocean
NASA Astrophysics Data System (ADS)
Wu, Yuqian; Zhang, Yixin; Zhu, Yun; Hu, Zhengda
2016-09-01
The effect of anisotropic turbulence on the spreading and wandering of Gaussian-Schell model (GSM) laser beams propagating in an ocean is studied. The long-term spreading of a GSM beam propagating through the paraxial channel of a turbulent ocean is also developed. Expressions of random wander for such laser beams are derived in an anisotropic turbulent ocean based on the extended Huygens-Fresnel principle. We investigate the influence of parameters in a turbulent ocean on the beam wander and spreading. Our results indicate that beam spreading and random beam wandering are smaller without considering the anisotropy of turbulence in the oceanic channel. Salinity fluctuation has a greater contribution to both the beam spreading and beam wander than that of temperature fluctuations in a turbulent ocean. Our results could be helpful for designing a free-space optical wireless communication system in an oceanic environment.
Satellite sensing of submerged fossil turbulence and zombie turbulence
NASA Astrophysics Data System (ADS)
Gibson, Carl H.
2004-11-01
Surface brightness anomalies from a submerged municipal wastewater outfall trapped by buoyancy in an area 0.1 km^2 are surprisingly detected from space satellites in areas > 200 km^2. How is this possible? Microstructure measurements near the outfall diffuser reveal enhanced turbulence and temperature dissipation rates above the 50 m trapping depth. Near-vertical radiation of internal waves by fossil and zombie turbulence microstructure patches produce wind ripple smoothing with 30-50 m internal wave patterns in surface Fourier brightness anomalies near the outfall. Detections at 10-14 km distances are at 100-220 m bottom boundary layer (BBL) fossil turbulence scales. Advected outfall fossils form zombie turbulence patches in internal wave patterns as they extract energy, vorticity, turbulence and ambient vertical internal wavelength information as their density gradients are tilted by the waves. As the zombies fossilize, patterned energy radiates near-vertically to produce the detected Fourier anomalies. Zombie turbulence patches beam extracted energy in a preferred direction with a special frequency, like energized metastable molecules in a chemical maser. Thus, kilowatts to produce the submerged field of advected fossil outfall turbulence patches are amplified by beamed zombie turbulence maser action (BZTMA) into megawatts of turbulence dissipation to affect sea surface brightness on wide surface areas using gigawatts of BBL fossil turbulence wave energy available.
Expressing oceanic turbulence parameters by atmospheric turbulence structure constant.
Baykal, Yahya
2016-02-20
The parameters composing oceanic turbulence are the wavelength, link length, rate of dissipation of kinetic energy per unit mass of fluid, rate of dissipation of mean-squared temperature, Kolmogorov microscale, and the ratio of temperature to salinity contributions to the refractive index spectrum. The required physical entities such as the average intensity and the scintillation index in the oceanic medium are formulated by using the power spectrum of oceanic turbulence, which is described by oceanic turbulence parameters. On the other hand, there exists a rich archive of formulations and results for the above-mentioned physical entities in atmospheric turbulence, where the parameters describing the turbulence are the wavelength, the link length, and the structure constant. In this paper, by equating the spherical wave scintillation index solutions in the oceanic and atmospheric turbulences, we have expressed the oceanic turbulence parameters by an equivalent structure constant used in turbulent atmosphere. Such equivalent structure constant will help ease reaching solutions of similar entities in an oceanic turbulent medium by employing the corresponding existing solutions, which are valid in an atmospheric turbulent medium.
Value of Wind Power Forecasting
Lew, D.; Milligan, M.; Jordan, G.; Piwko, R.
2011-04-01
This study, building on the extensive models developed for the Western Wind and Solar Integration Study (WWSIS), uses these WECC models to evaluate the operating cost impacts of improved day-ahead wind forecasts.
Method Forecasts Global Energy Substitution
ERIC Educational Resources Information Center
Chemical and Engineering News, 1975
1975-01-01
Describes a model developed to forecast energy demands and determine trends in demand for primary fuels. The energy model essentially considers primary energy sources as competing commodities in a market. (MLH)
Latin American Battery Forecast Report
Malacon, S.
1995-12-31
A forecast of battery production in Latin America is described. The economic influence and political difficulties which have influenced the market are discussed. Data is presented for original equipment shipments and replacement batteries.
Dynamic Stochastic Superresolution of sparsely observed turbulent systems
Branicki, M.; Majda, A.J.
2013-05-15
of the turbulent signal and the observation time relative to the decorrelation time of the turbulence at a given spatial scale in a fashion elucidated here. The DSS technique exploiting a simple Gaussian closure of the nonlinear stochastic forecast model emerges as the most suitable trade-off between the superresolution skill and computational complexity associated with estimating the cross-correlations between the aliasing modes of the sparsely observed turbulent signal. Such techniques offer a promising and efficient approach to constraining unresolved turbulent fluxes through stochastic superparameterization and a subsequent improvement in coarse-grained filtering and prediction of the next generation atmosphere–ocean system (AOS) models.
Dynamic Stochastic Superresolution of sparsely observed turbulent systems
NASA Astrophysics Data System (ADS)
Branicki, M.; Majda, A. J.
2013-05-01
the turbulent signal and the observation time relative to the decorrelation time of the turbulence at a given spatial scale in a fashion elucidated here. The DSS technique exploiting a simple Gaussian closure of the nonlinear stochastic forecast model emerges as the most suitable trade-off between the superresolution skill and computational complexity associated with estimating the cross-correlations between the aliasing modes of the sparsely observed turbulent signal. Such techniques offer a promising and efficient approach to constraining unresolved turbulent fluxes through stochastic superparameterization and a subsequent improvement in coarse-grained filtering and prediction of the next generation atmosphere-ocean system (AOS) models.
Practical Meteor Stream Forecasting
NASA Technical Reports Server (NTRS)
Cooke, William J.; Suggs, Robert M.
2003-01-01
Inspired by the recent Leonid meteor storms, researchers have made great strides in our ability to predict enhanced meteor activity. However, the necessary calibration of the meteor stream models with Earth-based ZHRs (Zenith Hourly Rates) has placed emphasis on the terran observer and meteor activity predictions are published in such a manner to reflect this emphasis. As a consequence, many predictions are often unusable by the satellite community, which has the most at stake and the greatest interest in meteor forecasting. This paper suggests that stream modelers need to pay more attention to the needs of this community and publish not just durations and times of maxima for Earth, but everything needed to characterize the meteor stream in and out of the plane of the ecliptic, which, at a minimum, consists of the location of maximum stream density (ZHR) and the functional form of the density decay with distance from this point. It is also suggested that some of the terminology associated with meteor showers may need to be more strictly defined in order to eliminate the perception of crying wolf by meteor scientists. An outburst is especially problematic, as it usually denotes an enhancement by a factor of 2 or more to researchers, but conveys the notion of a sky filled with meteors to satellite operators and the public. Experience has also taught that predicted ZHRs often lead to public disappointment, as these values vastly overestimate what is seen.
Preparing for an Uncertain Forecast
ERIC Educational Resources Information Center
Karolak, Eric
2011-01-01
Navigating the world of government relations and public policy can be a little like predicting the weather. One can't always be sure what's in store or how it will affect him/her down the road. But there are common patterns and a few basic steps that can help one best prepare for a change in the forecast. Though the forecast is uncertain, early…
Turbulence, Chondrules, and Planetesimals
NASA Technical Reports Server (NTRS)
Cuzzi, Jeffrey; Hogan, Robert C.; Dobrovolskis, Anthony R.; Paque, Julie M.
1998-01-01
It has been shown both numerically and experimentally that 3-D turbulence concentrates aerodynamically size-selected particles by orders of magnitude. In a previous review chapter, in "Chondrules and the protoplanetary disk" we illustrated the initial predictions of Turbulent Concentration (TC) as applied to the solar nebula. We predicted the particle size which will be most effectively concentrated by turbulence; it is the particle which has a gas drag stopping time equal to the overturn time of the smallest (Kolmogorov scale) eddy. The primary uncertainty is the level of nebula turbulence, or Reynolds number Re, which can be expressed in terms of the standard nebula eddy viscosity parameter alpha = Re(nu)(sub m)/cH, where nu(sub m) is molecular viscosity, c is sound speed, and H is vertical scale height. Several studies, and observed lifetimes of circumstellar disks, have suggested that the level of nebula turbulence can be described by alpha = 10(exp -2) - 10(exp -4). There is some recent concern about how energy is provided to maintain this turbulence, but the issue remains open. We adopt a canonical minimum mass nebula with a range of alpha > 0. We originally showed that chondrule-sized particles are selected for concentration in the terrestrial planet region if alpha = 10(exp -3) - 10(exp -4). In addition, Paque and Cuzzi found that the size distribution of chondrules is an excellent match for theoretical predictions. One then asks by what concentration factor C these particles can be concentrated; our early numerical results indicated an increase of C with alpha, and were supported by simple scaling arguments, but the extrapolation range was quite large and the predictions (C 10(exp 5) - 10(exp 6) not unlikely) uncertain. The work presented here, which makes use of our recent demonstration that the particle density field is a multifractal with flow-independent properties provides a far more secure ground for such predictions. We also indicate how fine
Forecasting droughts in East Africa
NASA Astrophysics Data System (ADS)
Mwangi, E.; Wetterhall, F.; Dutra, E.; Di Giuseppe, F.; Pappenberger, F.
2013-08-01
The humanitarian crisis caused by the recent droughts (2008-2009 and 2010-2011) in the East African region have illustrated that the ability to make accurate drought predictions with adequate lead time is essential. The use of dynamical model forecasts and drought indices, such as Standardized Precipitation Index (SPI), promises to lead to a better description of drought duration, magnitude and spatial extent. This study evaluates the use of the European Centre for Medium-Range Weather Forecasts (ECMWF) products in forecasting droughts in East Africa. ECMWF seasonal precipitation shows significant skill for both rain seasons when evaluated against measurements from the available in-situ stations from East Africa. The October-December rain season has higher skill that the March-May season. ECMWF forecasts add value to the statistical forecasts produced during the Greater Horn of Africa Climate Outlook Forums (GHACOF) which is the present operational product. Complementing the raw precipitation forecasts with SPI provides additional information on the spatial extend and intensity of the drought event.
Municipal water consumption forecast accuracy
NASA Astrophysics Data System (ADS)
Fullerton, Thomas M.; Molina, Angel L.
2010-06-01
Municipal water consumption planning is an active area of research because of infrastructure construction and maintenance costs, supply constraints, and water quality assurance. In spite of that, relatively few water forecast accuracy assessments have been completed to date, although some internal documentation may exist as part of the proprietary "grey literature." This study utilizes a data set of previously published municipal consumption forecasts to partially fill that gap in the empirical water economics literature. Previously published municipal water econometric forecasts for three public utilities are examined for predictive accuracy against two random walk benchmarks commonly used in regional analyses. Descriptive metrics used to quantify forecast accuracy include root-mean-square error and Theil inequality statistics. Formal statistical assessments are completed using four-pronged error differential regression F tests. Similar to studies for other metropolitan econometric forecasts in areas with similar demographic and labor market characteristics, model predictive performances for the municipal water aggregates in this effort are mixed for each of the municipalities included in the sample. Given the competitiveness of the benchmarks, analysts should employ care when utilizing econometric forecasts of municipal water consumption for planning purposes, comparing them to recent historical observations and trends to insure reliability. Comparative results using data from other markets, including regions facing differing labor and demographic conditions, would also be helpful.
Survey of air cargo forecasting techniques
NASA Technical Reports Server (NTRS)
Kuhlthan, A. R.; Vermuri, R. S.
1978-01-01
Forecasting techniques currently in use in estimating or predicting the demand for air cargo in various markets are discussed with emphasis on the fundamentals of the different forecasting approaches. References to specific studies are cited when appropriate. The effectiveness of current methods is evaluated and several prospects for future activities or approaches are suggested. Appendices contain summary type analyses of about 50 specific publications on forecasting, and selected bibliographies on air cargo forecasting, air passenger demand forecasting, and general demand and modalsplit modeling.
HESS Opinions "Forecaster priorities for improving probabilistic flood forecasts"
NASA Astrophysics Data System (ADS)
Wetterhall, F.; Pappenberger, F.; Alfieri, L.; Cloke, H. L.; Thielen-del Pozo, J.; Balabanova, S.; Daňhelka, J.; Vogelbacher, A.; Salamon, P.; Carrasco, I.; Cabrera-Tordera, A. J.; Corzo-Toscano, M.; Garcia-Padilla, M.; Garcia-Sanchez, R. J.; Ardilouze, C.; Jurela, S.; Terek, B.; Csik, A.; Casey, J.; Stankūnavičius, G.; Ceres, V.; Sprokkereef, E.; Stam, J.; Anghel, E.; Vladikovic, D.; Alionte Eklund, C.; Hjerdt, N.; Djerv, H.; Holmberg, F.; Nilsson, J.; Nyström, K.; Sušnik, M.; Hazlinger, M.; Holubecka, M.
2013-11-01
Hydrological ensemble prediction systems (HEPS) have in recent years been increasingly used for the operational forecasting of floods by European hydrometeorological agencies. The most obvious advantage of HEPS is that more of the uncertainty in the modelling system can be assessed. In addition, ensemble prediction systems generally have better skill than deterministic systems both in the terms of the mean forecast performance and the potential forecasting of extreme events. Research efforts have so far mostly been devoted to the improvement of the physical and technical aspects of the model systems, such as increased resolution in time and space and better description of physical processes. Developments like these are certainly needed; however, in this paper we argue that there are other areas of HEPS that need urgent attention. This was also the result from a group exercise and a survey conducted to operational forecasters within the European Flood Awareness System (EFAS) to identify the top priorities of improvement regarding their own system. They turned out to span a range of areas, the most popular being to include verification of an assessment of past forecast performance, a multi-model approach for hydrological modelling, to increase the forecast skill on the medium range (>3 days) and more focus on education and training on the interpretation of forecasts. In light of limited resources, we suggest a simple model to classify the identified priorities in terms of their cost and complexity to decide in which order to tackle them. This model is then used to create an action plan of short-, medium- and long-term research priorities with the ultimate goal of an optimal improvement of EFAS in particular and to spur the development of operational HEPS in general.
BER evaluations for multimode beams in underwater turbulence
NASA Astrophysics Data System (ADS)
Altay Arpali, Serap; Baykal, Yahya; Arpali, Çağlar
2016-07-01
In underwater optical communication links, bit error rate (BER) is an important performance criterion. For this purpose, the effects of oceanic turbulence on multimode laser beam incidences are studied and compared in terms of average BER (
Fossils of big bang turbulence
NASA Astrophysics Data System (ADS)
Gibson, C. H.
2004-12-01
A model is proposed connecting turbulence, fossil turbulence, and the big bang origin of the universe. While details are incomplete, the model is consistent with our knowledge of these processes and is supported by observations. Turbulence arises in a hot-big-bang quantum-gravitational-dynamics scenario at Planck scales. Chaotic, eddy-like-motions produce an exothermic Planck particle cascade from 10-35 m at 1032 K to 108 larger, 104 cooler, quark-gluon scales. A Planck-Kerr instability gives high-Reynolds-number (Re 106) turbulent combustion, space-time-energy-entropy and turbulent mixing. Batchelor-Obukhov-Corrsin turbulent-temperature fluctuations are preserved as the first fossil-turbulence by inflation stretching the patterns beyond the horizon ct of causal connection faster than light speed c in time t 10-33 seconds. Fossil-big-bang-temperature-turbulence re-enters the horizon and imprints nucleosynthesis of H-He densities that seed fragmentation by gravity at 1012 s in the low Reynolds number plasma before its transition to gas at t 1013 s and T 3000 K. Multi-scaling coefficients of the cosmic-microwave-background (CMB) temperature anisotropies closely match those for high Reynolds number turbulence, Bershadskii and Sreenivasan 2002, 2003. CMB spectra support the interpretation that big-bang-turbulence-fossils triggered fragmentation of the viscous plasma at supercluster to galaxy mass scales from 1046 to 1042 kg, Gibson 1996, 2000, 2004ab.
Turbulence in molecular clouds
NASA Astrophysics Data System (ADS)
Dickman, R. L.
The basic aim of this paper is to offer a primer of basic concepts and methods of analysis for observationally-oriented individuals who wish to work in the rapidly developing area of molecular cloud turbulence. First the difficulties which beset early attempts to determine the nature of gas motions within molecular clouds are reviewed. Some aspects of turbulence as a hydrodynamic phenomenon are considered next along with an introduction to the statistical vocabulary of the subject which is required to understand the methods for analyzing observational data. A simple and useful approximation for estimating the velocity correlation length of a molecular cloud is also described. The paper concludes with a final perspective, which considers the extent to which size-velocity dispersion correlations can serve as a probe of chaotic velocity fields in molecular clouds.
Homogeneous quantum electrodynamic turbulence
NASA Technical Reports Server (NTRS)
Shebalin, John V.
1992-01-01
The electromagnetic field equations and Dirac equations for oppositely charged wave functions are numerically time-integrated using a spatial Fourier method. The numerical approach used, a spectral transform technique, is based on a continuum representation of physical space. The coupled classical field equations contain a dimensionless parameter which sets the strength of the nonlinear interaction (as the parameter increases, interaction volume decreases). For a parameter value of unity, highly nonlinear behavior in the time-evolution of an individual wave function, analogous to ideal fluid turbulence, is observed. In the truncated Fourier representation which is numerically implemented here, the quantum turbulence is homogeneous but anisotropic and manifests itself in the nonlinear evolution of equilibrium modal spatial spectra for the probability density of each particle and also for the electromagnetic energy density. The results show that nonlinearly interacting fermionic wave functions quickly approach a multi-mode, dynamic equilibrium state, and that this state can be determined by numerical means.
NASA Astrophysics Data System (ADS)
O'dell, C. R.
1986-10-01
It has been known for many decades that the Reynolds number in HII regions must be very high and that the corresponding fine scale flow must be turbulent. Even though the theoretical relation between turbulent element separation and random velocity was derived by Kolmogoroff over forty years ago, there have been only a few attempts to test this theory and its corresponding assumptions. An attempt by Munch for M42 with marginal velocity resolution lead to ambiguous results, although more recent studies by Jean Rene Roy and his colleagues have been more credible. The internal velocities of a number of HII regions were systematically studied and the theory was tested with considerable certainty. The results should be important for the determination of the energy balance of HII regions and the relation of small scale motion to the process of star formation.
Controlled-Turbulence Bioreactors
NASA Technical Reports Server (NTRS)
Wolf, David A.; Schwartz, Ray; Trinh, Tinh
1989-01-01
Two versions of bioreactor vessel provide steady supplies of oxygen and nutrients with little turbulence. Suspends cells in environment needed for sustenance and growth, while inflicting less damage from agitation and bubbling than do propeller-stirred reactors. Gentle environments in new reactors well suited to delicate mammalian cells. One reactor kept human kidney cells alive for as long as 11 days. Cells grow on carrier beads suspended in liquid culture medium that fills cylindrical housing. Rotating vanes - inside vessel but outside filter - gently circulates nutrient medium. Vessel stationary; magnetic clutch drives filter cylinder and vanes. Another reactor creates even less turbulence. Oxygen-permeable tubing wrapped around rod extending along central axis. Small external pump feeds oxygen to tubing through rotary coupling, and oxygen diffuses into liquid medium.
Precision tropopause turbulence measurements
NASA Astrophysics Data System (ADS)
Otten, Leonard John, III; Jones, Al; Black, Don G.; Lane, Joshua; Hugo, Ron; Beyer, Jeffery; Roggemann, Michael C.
2000-11-01
Limited samples of the turbulence structure in the tropopause suggest that conventional models for atmospheric turbulence may not apply through this portion of the atmosphere. This paper discusses the instrumentation requirements, design and calibration of a balloon borne sensor suite designed to accurately measure the distribution and spectral spatial character of the index of refraction fluctuations through the tropopause. The basis for the data system is a 16 bit dynamic range, high data rate sample and hold instrumentation package. Calibration and characterization of the constant current anemometers used in the measurements show them to have a frequency response greater than 170 Hz at the -3 Db point and sufficient resolution to measure a Cn2 of 1 x 10-19 cm-2/3. A novel technique was developed that integrates the over 20 signals into two time correlated telemetry streams. The entire system has been assembled for a flight in the late summer of 2000.
Homogeneous quantum electrodynamic turbulence
Shebalin, J.V.
1992-10-01
The electromagnetic field equations and Dirac equations for oppositely charged wave functions are numerically time-integrated using a spatial Fourier method. The numerical approach used, a spectral transform technique, is based on a continuum representation of physical space. The coupled classical field equations contain a dimensionless parameter which sets the strength of the nonlinear interaction (as the parameter increases, interaction volume decreases). For a parameter value of unity, highly nonlinear behavior in the time-evolution of an individual wave function, analogous to ideal fluid turbulence, is observed. In the truncated Fourier representation which is numerically implemented here, the quantum turbulence is homogeneous but anisotropic and manifests itself in the nonlinear evolution of equilibrium modal spatial spectra for the probability density of each particle and also for the electromagnetic energy density. The results show that nonlinearly interacting fermionic wave functions quickly approach a multi-mode, dynamic equilibrium state, and that this state can be determined by numerical means.
Spherical Model for Turbulence
NASA Astrophysics Data System (ADS)
Mou, Chung-Yu.
A new set of models for homogeneous, isotropic turbulence is considered in which the Navier-Stokes equations for incompressible fluid flow are generalized to a set of N coupled equations in N velocity fields. It is argued that in order to be useful these models must embody a new group of symmetries, and a general formalism is laid out for their construction. The work is motivated by similar techniques that have had extraordinary success in improving the theoretical understanding of equilibrium phase transitions in condensed matter systems. The key result is that these models simplify when N is large. The so-called spherical limit, N to infty, can be solved exactly, yielding a closed pair of nonlinear integral equations for the response and correlation functions. These equations, known as Kraichnan's Direct Interaction Approximation (DIA) equations, are, for the first time, solved fully in the scale-invariant turbulent regime, and the implications of these solutions for real turbulence (N = 1) are discussed. In particular, it is argued that previously applied renormalization group techniques, based on an expansion in the exponent, y, that characterizes the driving spectrum, are incorrect, and that the Kolmogorov exponent zeta has a nontrivial dependence on N, with zeta(N toinfty) = {3over2}. This value is remarkably close to the experimental result, zeta~{5over3}, which must therefore result from higher order corrections in powers of {1over N}. Prospects for calculating these corrections are briefly discussed: though daunting, such a calculations would, for the first time, provide a controlled perturbation expansion for the Kolmogorov, and other, exponents. Our techniques may also be applied to other nonequilibrium dynamical problems, such as the KPZ equation for interface growth, and perhaps to turbulence in nonlinear wave systems.
Spherical model for turbulence
NASA Astrophysics Data System (ADS)
Mou, Chung-Yu
A new set of models for homogeneous, isotropic turbulence is considered in which the Navier-Stokes equations for incompressible fluid flow are generalized to a set of N coupled equations in N velocity fields. It is argued that in order to be useful these models must embody a new group of symmetries, and a general formalism is laid out for their construction. The work is motivated by similar techniques that have had extraordinary success in improving the theoretical understanding of equilibrium phase transitions in condensed matter systems. The key result is that these models simplify when N is large. The so-called spherical limit, N approaches infinity, can be solved exactly, yielding a closed pair of nonlinear integral equations for the response and correlation functions. These equations, known as Kraichnan's Direct Interaction Approximation (DIA) equations, are, for the first time, solved fully in the scale-invariant turbulent regime, and the implications of these solutions for real turbulence (N = 1) are discussed. In particular, it is argued that previously applied renormalization group techniques, based on an expansion in the exponent, y, that characterizes the driving spectrum, are incorrect, and that the Kolmogorov exponent zeta has a nontrivial dependence on N, with zeta(N approaches infinity) = 3/2. This value is remarkably close to the experimental result, zeta approximately equals 5/3, which must therefore result from higher order corrections in powers of 1/N. Prospects for calculating these corrections are briefly discussed: though daunting, such a calculation would, for the first time, provide a controlled perturbation expansion for the Kolmogorov, and other exponents. Our techniques may also be applied to other nonequilibrium dynamical problems, such as the KPZ equation for interface growth, and perhaps to turbulence in nonlinear wave systems.
Turbulent General Magnetic Reconnection
NASA Astrophysics Data System (ADS)
Eyink, G. L.
2015-07-01
Plasma flows with a magnetohydrodynamic (MHD)-like turbulent inertial range, such as the solar wind, require a generalization of general magnetic reconnection (GMR) theory. We introduce the slip velocity source vector per unit arclength of field line, the ratio of the curl of the non-ideal electric field in the generalized Ohm’s Law and magnetic field strength. It diverges at magnetic nulls, unifying GMR with null-point reconnection. Only under restrictive assumptions is the slip velocity related to the gradient of quasi-potential (which is the integral of parallel electric field along magnetic field lines). In a turbulent inertial range, the non-ideal field becomes tiny while its curl is large, so that line slippage occurs even while ideal MHD becomes accurate. The resolution is that ideal MHD is valid for a turbulent inertial range only in a weak sense that does not imply magnetic line freezing. The notion of weak solution is explained in terms of renormalization group (RG) type theory. The weak validity of the ideal Ohm’s law in the inertial range is shown via rigorous estimates of the terms in the generalized Ohm’s Law. All non-ideal terms are irrelevant in the RG sense and large-scale reconnection is thus governed solely by ideal dynamics. We discuss the implications for heliospheric reconnection, in particular for deviations from the Parker spiral model. Solar wind observations show that reconnection in a turbulence-broadened heliospheric current sheet, which is consistent with Lazarian-Vishniac theory, leads to slip velocities that cause field lines to lag relative to the spiral model.
Stability, transition and turbulence
NASA Technical Reports Server (NTRS)
Hussaini, M. Y.
1987-01-01
A glimpse is provided of the research program in stability, transition, and turbulence based on numerical simulations. This program includes both the so-called abrupt and the restrained transition processes. Attention is confined to the prototype problems of channel flow and the parallel boundary layer in the former category and the Taylor-Couette flow in the latter category. It covers both incompressible flows and supersonic flows. Some representative results are presented.
Stability, transition and turbulence
NASA Technical Reports Server (NTRS)
Hussaini, M. Y.
1987-01-01
A glimpse is provided of the research program in stability, transition and turbulence based on numerical simulations. This program includes both the so-called abrupt and the restrained transition processes. Attention is confined to the prototype problems of channel flow and the parallel boundary layer in the former category and the Taylor-Couette flow in the latter category. It covers both incompressible flows and supersonic flows. Some representative results are presented.
NASA Astrophysics Data System (ADS)
Belotserkovskii, Oleg
2001-06-01
The main principles for constructing of mathematical models for fully developed free shear turbulence and hydrodynamic instabilities are considered in the report. Such a “rational” modeling is applied for a variety of unsteady multidimensional problems. For the wide class of phenomena, by the large Reynolds numbers within the low-frequency and inertial intervals of turbulent motion, the effect of molecular viscosity and of the small elements of flow in the largest part of perturbation domain are not practically essential neither for the general characteristics of macroscopic structures of the flow developed, nor the flow pattern as a whole. This makes it possible not to take into consideration the effects of molecular viscosity when studying the dynamics of large vortices, and to implement the study of those on the basis of models of the ideal gas (using the methods of “rational” averaging, but without application of semi-empirical models of turbulence). Among the problems, which have been studied by such a way, there are those of the jet-type flow in the wake behind the body, the motions of ship frames with stern shearing, the formation of anterior stalling zones by the flow about blunted bodies with jets or needles directed to meet the flow, etc. As applications the problems of instability development and of spreading of smoke cloud from large-scale source of the fire are considered.
NASA Astrophysics Data System (ADS)
Boucheron, L.; Al-Ghraibah, Amani; McAteer, J.; Cao, H.; Jackiewicz, J.; McNamara, B.; Voelz, D.; Calabro, B.; DeGrave, K.; Kirk, M.; Madadi, A.; Petsov, A.; Taylor, G.
2011-05-01
Solar active regions are the source of many energetic and geo-effective events such as solar flares and coronal mass ejections (CMEs). Understanding how these complex source regions evolve and produce these events is of fundamental importance, not only to solar physics, but also to the demands of space weather forecasting. We propose to investigate the physical properties of active region magnetic fields using fractal-, gradient-, neutral line-, emerging flux-, wavelet- and general image-based techniques, and to correlate them to solar activity. The combination of these projects with solarmonitor.org and the international Max Millenium Campaign presents an opportunity for accurate and timely flare predictions for the first time. Many studies have attempted to relate solar flares to their concomitant magnetic field distributions. However, a consistent, causal relationship between the magnetic field on the photosphere and the production of solar flares is unknown. Often the local properties of the active region magnetic field - critical in many theories of activity - are lost in the global definition of their diagnostics, in effect smoothing out variations that occur on small spatial scales. Mindful of this, our overall goal is to create measures that are sensitive to both the global and the small-scale nature of energy storage and release in the solar atmosphere in order to study solar flare prediction. This set of active region characteristics will be automatically explored for discriminating features through the use of feature selection methods. Such methods search a feature space while optimizing a criterion - the prediction of a flare in this case. The large size of the datasets used in this project make it well suited for an exploration of a large feature space. This work is funded through a New Mexico State University Interdisciplinary Research Grant.
Coherent optical adaptive techniques.
Bridges, W B; Brunner, P T; Lazzara, S P; Nussmeier, T A; O'Meara, T R; Sanguinet, J A; Brown, W P
1974-02-01
The theory of multidither adaptive optical radar phased arrays is briefly reviewed as an introduction to the experimental results obtained with seven-element linear and three-element triangular array systems operating at 0.6328 microm. Atmospheric turbulence compensation and adaptive tracking capabilities are demonstrated.
Modeling the turbulent kinetic energy equation for compressible, homogeneous turbulence
NASA Technical Reports Server (NTRS)
Aupoix, B.; Blaisdell, G. A.; Reynolds, William C.; Zeman, Otto
1990-01-01
The turbulent kinetic energy transport equation, which is the basis of turbulence models, is investigated for homogeneous, compressible turbulence using direct numerical simulations performed at CTR. It is shown that the partition between dilatational and solenoidal modes is very sensitive to initial conditions for isotropic decaying turbulence but not for sheared flows. The importance of the dilatational dissipation and of the pressure-dilatation term is evidenced from simulations and a transport equation is proposed to evaluate the pressure-dilatation term evolution. This transport equation seems to work well for sheared flows but does not account for initial condition sensitivity in isotropic decay. An improved model is proposed.
Suppression of turbulent resistivity in turbulent Couette flow
NASA Astrophysics Data System (ADS)
Si, Jiahe; Colgate, Stirling A.; Sonnenfeld, Richard G.; Nornberg, Mark D.; Li, Hui; Colgate, Arthur S.; Westpfahl, David J.; Romero, Van D.; Martinic, Joe
2015-07-01
Turbulent transport in rapidly rotating shear flow very efficiently transports angular momentum, a critical feature of instabilities responsible both for the dynamics of accretion disks and the turbulent power dissipation in a centrifuge. Turbulent mixing can efficiently transport other quantities like heat and even magnetic flux by enhanced diffusion. This enhancement is particularly evident in homogeneous, isotropic turbulent flows of liquid metals. In the New Mexico dynamo experiment, the effective resistivity is measured using both differential rotation and pulsed magnetic field decay to demonstrate that at very high Reynolds number rotating shear flow can be described entirely by mean flow induction with very little contribution from correlated velocity fluctuations.
Suppression of turbulent resistivity in turbulent Couette flow
Si, Jiahe Sonnenfeld, Richard G.; Colgate, Arthur S.; Westpfahl, David J.; Romero, Van D.; Martinic, Joe; Colgate, Stirling A.; Li, Hui; Nornberg, Mark D.
2015-07-15
Turbulent transport in rapidly rotating shear flow very efficiently transports angular momentum, a critical feature of instabilities responsible both for the dynamics of accretion disks and the turbulent power dissipation in a centrifuge. Turbulent mixing can efficiently transport other quantities like heat and even magnetic flux by enhanced diffusion. This enhancement is particularly evident in homogeneous, isotropic turbulent flows of liquid metals. In the New Mexico dynamo experiment, the effective resistivity is measured using both differential rotation and pulsed magnetic field decay to demonstrate that at very high Reynolds number rotating shear flow can be described entirely by mean flow induction with very little contribution from correlated velocity fluctuations.
Statistical earthquake focal mechanism forecasts
NASA Astrophysics Data System (ADS)
Kagan, Yan Y.; Jackson, David D.
2014-04-01
Forecasts of the focal mechanisms of future shallow (depth 0-70 km) earthquakes are important for seismic hazard estimates and Coulomb stress, and other models of earthquake occurrence. Here we report on a high-resolution global forecast of earthquake rate density as a function of location, magnitude and focal mechanism. In previous publications we reported forecasts of 0.5° spatial resolution, covering the latitude range from -75° to +75°, based on the Global Central Moment Tensor earthquake catalogue. In the new forecasts we have improved the spatial resolution to 0.1° and the latitude range from pole to pole. Our focal mechanism estimates require distance-weighted combinations of observed focal mechanisms within 1000 km of each gridpoint. Simultaneously, we calculate an average rotation angle between the forecasted mechanism and all the surrounding mechanisms, using the method of Kagan & Jackson proposed in 1994. This average angle reveals the level of tectonic complexity of a region and indicates the accuracy of the prediction. The procedure becomes problematical where longitude lines are not approximately parallel, and where shallow earthquakes are so sparse that an adequate sample spans very large distances. North or south of 75°, the azimuths of points 1000 km away may vary by about 35°. We solved this problem by calculating focal mechanisms on a plane tangent to the Earth's surface at each forecast point, correcting for the rotation of the longitude lines at the locations of earthquakes included in the averaging. The corrections are negligible between -30° and +30° latitude, but outside that band uncorrected rotations can be significantly off. Improved forecasts at 0.5° and 0.1° resolution are posted at http://eq.ess.ucla.edu/kagan/glob_gcmt_index.html.
NASA Astrophysics Data System (ADS)
Velluet, M.-T.; Vorontsov, Mikhail; Schwering, Piet; Marchi, Gabriele; Nicolas, Stephane; Riker, Jim
2012-06-01
The performance of optical systems is degraded by atmospheric turbulence. Over propagation distances that exceed several kilometers, it is difficult to evaluate its impact because of terrain variability - a factor that should be taken into account. However, to optimize performance, the turbulence characteristics and its effect on optical wave propagation along the propagation path should be known. The understanding of turbulence impact is one of the main objectives of the NATO group SET 165: "Adaptive Optics (AO) for laser beam delivery, passive and active imaging and turbulence mitigation". In this paper we describe experiments performed by the NATO SET 165 research group, namely, a set of atmospheric experiments over a 7 km distance, and discuss some preliminary results of data processing. The experiments were conducted at the University of Dayton Intelligent Optics Laboratory (UD/IOL) in October 2011. It benefited significantly from the available optical setups and the infrastructure on the UD/IOL site.
Continuum modeling of crowd turbulence.
Golas, Abhinav; Narain, Rahul; Lin, Ming C
2014-10-01
With the growth in world population, the density of crowds in public places has been increasing steadily, leading to a higher incidence of crowd disasters at high densities. Recent research suggests that emergent chaotic behavior at high densities-known collectively as crowd turbulence-is to blame. Thus, a deeper understanding of crowd turbulence is needed to facilitate efforts to prevent and plan for chaotic conditions in high-density crowds. However, it has been noted that existing algorithms modeling collision avoidance cannot faithfully simulate crowd turbulence. We hypothesize that simulation of crowd turbulence requires modeling of both collision avoidance and frictional forces arising from pedestrian interactions. Accordingly, we propose a model for turbulent crowd simulation, which incorporates a model for interpersonal stress and acceleration constraints similar to real-world pedestrians. Our simulated results demonstrate a close correspondence with observed metrics for crowd turbulence as measured in known crowd disasters.
Atmospheric Quantum Channels with Weak and Strong Turbulence
NASA Astrophysics Data System (ADS)
Vasylyev, D.; Semenov, A. A.; Vogel, W.
2016-08-01
The free-space transfer of high-fidelity optical signals between remote locations has many applications, including both classical and quantum communication, precision navigation, clock synchronization, etc. The physical processes that contribute to signal fading and loss need to be carefully analyzed in the theory of light propagation through the atmospheric turbulence. Here we derive the probability distribution for the atmospheric transmittance including beam wandering, beam shape deformation, and beam-broadening effects. Our model, referred to as the elliptic beam approximation, applies to weak, weak-to-moderate, and strong turbulence and hence to the most important regimes in atmospheric communication scenarios.
Atmospheric Quantum Channels with Weak and Strong Turbulence.
Vasylyev, D; Semenov, A A; Vogel, W
2016-08-26
The free-space transfer of high-fidelity optical signals between remote locations has many applications, including both classical and quantum communication, precision navigation, clock synchronization, etc. The physical processes that contribute to signal fading and loss need to be carefully analyzed in the theory of light propagation through the atmospheric turbulence. Here we derive the probability distribution for the atmospheric transmittance including beam wandering, beam shape deformation, and beam-broadening effects. Our model, referred to as the elliptic beam approximation, applies to weak, weak-to-moderate, and strong turbulence and hence to the most important regimes in atmospheric communication scenarios.
Atmospheric Quantum Channels with Weak and Strong Turbulence.
Vasylyev, D; Semenov, A A; Vogel, W
2016-08-26
The free-space transfer of high-fidelity optical signals between remote locations has many applications, including both classical and quantum communication, precision navigation, clock synchronization, etc. The physical processes that contribute to signal fading and loss need to be carefully analyzed in the theory of light propagation through the atmospheric turbulence. Here we derive the probability distribution for the atmospheric transmittance including beam wandering, beam shape deformation, and beam-broadening effects. Our model, referred to as the elliptic beam approximation, applies to weak, weak-to-moderate, and strong turbulence and hence to the most important regimes in atmospheric communication scenarios. PMID:27610835
Turbulence and Mixing in the Columbia River Plume
NASA Astrophysics Data System (ADS)
Kilcher, L. F.; Nash, J.; Moum, J.
2004-12-01
Thin bouyant plumes represent a technical challenge for in-situ observations. In July 2004 a unique set of measurements were taken in which our vertical microstructure profiler, Chameleon, and acoustics (300 kHz ADCP and 120 kHz echosounder) were modified to measure the O(1-5 m) thick plume. The Chameleon profiles included measurements of density, fluorescence, optical backscatter and turbulent energy dissipation. Intense turbulence was observed in plume fronts (with 30 m vertical displacements), at the plume base (with O(1 s-1) shear) and in O(20 m) thick bottom boundary layers. Preliminary results from 10 days of observations will be presented and discussed.
Zilberman, Arkadi; Golbraikh, Ephim; Kopeika, Norman S
2008-12-01
Turbulence properties of communication links (optical and microwave) in terms of log-amplitude variance are studied on the basis of a three-layer model of refractive index fluctuation spectrum in the free atmosphere. We suggest a model of turbulence spectra (Kolmogorov and non-Kolmogorov) changing with altitude on the basis of obtained experimental and theoretical data for turbulence profile in the troposphere and lower stratosphere.
Zilberman, Arkadi; Golbraikh, Ephim; Kopeika, Norman S
2008-12-01
Turbulence properties of communication links (optical and microwave) in terms of log-amplitude variance are studied on the basis of a three-layer model of refractive index fluctuation spectrum in the free atmosphere. We suggest a model of turbulence spectra (Kolmogorov and non-Kolmogorov) changing with altitude on the basis of obtained experimental and theoretical data for turbulence profile in the troposphere and lower stratosphere.
Quantum ghost imaging through turbulence
Dixon, P. Ben; Howland, Gregory A.; Howell, John C.; Chan, Kam Wai Clifford; O'Sullivan-Hale, Colin; Rodenburg, Brandon; Hardy, Nicholas D.; Shapiro, Jeffrey H.; Simon, D. S.; Sergienko, A. V.; Boyd, R. W.
2011-05-15
We investigate the effect of turbulence on quantum ghost imaging. We use entangled photons and demonstrate that for a specific experimental configuration the effect of turbulence can be greatly diminished. By decoupling the entangled photon source from the ghost-imaging central image plane, we are able to dramatically increase the ghost-image quality. When imaging a test pattern through turbulence, this method increases the imaged pattern visibility from V=0.15{+-}0.04 to 0.42{+-}0.04.
Predicting two-dimensional turbulence
NASA Astrophysics Data System (ADS)
Cerbus, R. T.; Goldburg, W. I.
2015-04-01
Prediction is a fundamental objective of science. It is more difficult for chaotic and complex systems like turbulence. Here we use information theory to quantify spatial prediction using experimental data from a turbulent soap film. At high Reynolds number, Re, where a cascade exists, turbulence becomes easier to predict as the inertial range broadens. The development of a cascade at low Re is also detected.
Realistic weather simulations and forecast verification with COSMO-EULAG
NASA Astrophysics Data System (ADS)
Wójcik, Damian; Piotrowski, Zbigniew; Rosa, Bogdan; Ziemiański, Michał
2015-04-01
Research conducted at Polish Institute of Meteorology and Water Management, National Research Institute, in collaboration with Consortium for Small Scale Modeling (COSMO) resulted in the development of a new prototype model COSMO-EULAG. The dynamical core of the new model is based on anelastic set of equation and numerics adopted from the EULAG model. The core is coupled, with the 1st degree of accuracy, to the COSMO physical parameterizations involving turbulence, friction, radiation, moist processes and surface fluxes. The tool is capable to compute weather forecast in mountainous area for the horizontal resolutions ranging from 2.2 km to 0.1 km and with slopes reaching 82 degree of inclination. An employment of EULAG allows to profit from its desirable conservative properties and numerical robustness confirmed in number of benchmark tests and widely documented in scientific literature. In this study we show a realistic case study of Alpine summer convection simulated by COSMO-EULAG. It compares the convection-permitting realization of the flow using 2.2 km horizontal grid size, typical for contemporary very high resolution regional NWP forecast, with realization of LES type using grid size of 100 m. The study presents comparison of flow, cloud and precipitation structure together with the reference results of standard compressible COSMO Runge-Kutta model forecast in 2.2 km horizontal resolution. The case study results are supplemented by COSMO-EULAG forecast verification results for Alpine domain in 2.2 km horizontal resolution. Wind, temperature, cloud, humidity and precipitation scores are being presented. Verification period covers one summer month (June 2013) and one autumn month (November 2013). Verification is based on data collected by a network of approximately 200 stations (surface data verification) and 6 stations (upper-air verification) located in the Alps and vicinity.
Turbulent Distortion of Condensate Accretion
NASA Technical Reports Server (NTRS)
Hazoume, R.; Orou Chabi, J.; Johnson, J. A., III
1997-01-01
When a simple model for the relationship between the density-temperature fluctuation correlation and mean values is used, we determine that the rate of change of turbulent intensity can influence directly the accretion rate of droplets. Considerable interest exists in the accretion rate for condensates in nonequilibrium flow with icing and the potential role which reactant accretion can play in nonequilibrium exothermic reactant processes. Turbulence is thought to play an important role in such flows. It has already been experimentally determined that turbulence influences the sizes of droplets in the heterogeneous nucleation of supersaturated vapors. This paper addresses the issue of the possible influence of turbulence on the accretion rate of droplets.
Turbulence effect on cloud radiation.
Matsuda, K; Onishi, R; Kurose, R; Komori, S
2012-06-01
The effect of turbulent clustering of water droplets on radiative transfer is investigated by means of both a three-dimensional direct numerical simulation of particle-laden homogeneous isotropic turbulence and a radiative transfer simulation based on a Monte Carlo photon tracing method. The results show that turbulent clustering causes the formation of void regions of droplets and hence increases the direct transmittance. This effect decreases as the turbulent Reynolds number increases and is estimated to be negligibly small under the conditions in real clouds.
Nonlocality in homogeneous superfluid turbulence
NASA Astrophysics Data System (ADS)
Dix, O. M.; Zieve, R. J.
2014-10-01
Simulating superfluid turbulence using the localized induction approximation allows neighboring parallel vortices to proliferate. In many circumstances a turbulent tangle becomes unsustainable, degenerating into a series of parallel, noninteracting vortex lines. Calculating with the fully nonlocal Biot-Savart law prevents this difficulty but also increases computation time. Here we use a truncated Biot-Savart integral to investigate the effects of nonlocality on homogeneous turbulence. We find that including the nonlocal interaction up to roughly the spacing between nearest-neighbor vortex segments prevents the parallel alignment from developing, yielding an accurate model of homogeneous superfluid turbulence with less computation time.
Turbulent Dynamos and Magnetic Helicity
Ji, Hantao
1999-04-01
It is shown that the turbulent dynamo alpha-effect converts magnetic helicity from the turbulent field to the mean field when the turbulence is electromagnetic while the magnetic helicity of the mean-field is transported across space when the turbulence is elcetrostatic or due to the elcetron diamagnetic effect. In all cases, however, the dynamo effect strictly conserves the total helicity expect for a battery effect which vanishes in the limit of magnetohydrodynamics. Implications for astrophysical situations, especially for the solar dynamo, are discussed.
Fennec dust forecast intercomparison over the Sahara in June 2011
NASA Astrophysics Data System (ADS)
Chaboureau, Jean-Pierre; Flamant, Cyrille; Dauhut, Thibaut; Kocha, Cécile; Lafore, Jean-Philippe; Lavaysse, Chistophe; Marnas, Fabien; Mokhtari, Mohamed; Pelon, Jacques; Reinares Martínez, Irene; Schepanski, Kerstin; Tulet, Pierre
2016-06-01
In the framework of the Fennec international programme, a field campaign was conducted in June 2011 over the western Sahara. It led to the first observational data set ever obtained that documents the dynamics, thermodynamics and composition of the Saharan atmospheric boundary layer (SABL) under the influence of the heat low. In support to the aircraft operation, four dust forecasts were run daily at low and high resolutions with convection-parameterizing and convection-permitting models, respectively. The unique airborne and ground-based data sets allowed the first ever intercomparison of dust forecasts over the western Sahara. At monthly scale, large aerosol optical depths (AODs) were forecast over the Sahara, a feature observed by satellite retrievals but with different magnitudes. The AOD intensity was correctly predicted by the high-resolution models, while it was underestimated by the low-resolution models. This was partly because of the generation of strong near-surface wind associated with thunderstorm-related density currents that could only be reproduced by models representing convection explicitly. Such models yield emissions mainly in the afternoon that dominate the total emission over the western fringes of the Adrar des Iforas and the Aïr Mountains in the high-resolution forecasts. Over the western Sahara, where the harmattan contributes up to 80 % of dust emission, all the models were successful in forecasting the deep well-mixed SABL. Some of them, however, missed the large near-surface dust concentration generated by density currents and low-level winds. This feature, observed repeatedly by the airborne lidar, was partly forecast by one high-resolution model only.
Communicating Storm Surge Forecast Uncertainty
NASA Astrophysics Data System (ADS)
Troutman, J. A.; Rhome, J.
2015-12-01
When it comes to tropical cyclones, storm surge is often the greatest threat to life and property along the coastal United States. The coastal population density has dramatically increased over the past 20 years, putting more people at risk. Informing emergency managers, decision-makers and the public about the potential for wind driven storm surge, however, has been extremely difficult. Recently, the Storm Surge Unit at the National Hurricane Center in Miami, Florida has developed a prototype experimental storm surge watch/warning graphic to help communicate this threat more effectively by identifying areas most at risk for life-threatening storm surge. This prototype is the initial step in the transition toward a NWS storm surge watch/warning system and highlights the inundation levels that have a 10% chance of being exceeded. The guidance for this product is the Probabilistic Hurricane Storm Surge (P-Surge) model, which predicts the probability of various storm surge heights by statistically evaluating numerous SLOSH model simulations. Questions remain, however, if exceedance values in addition to the 10% may be of equal importance to forecasters. P-Surge data from 2014 Hurricane Arthur is used to ascertain the practicality of incorporating other exceedance data into storm surge forecasts. Extracting forecast uncertainty information through analyzing P-surge exceedances overlaid with track and wind intensity forecasts proves to be beneficial for forecasters and decision support.
CME Ensemble Forecasting - A Primer
NASA Astrophysics Data System (ADS)
Pizzo, V. J.; de Koning, C. A.; Cash, M. D.; Millward, G. H.; Biesecker, D. A.; Codrescu, M.; Puga, L.; Odstrcil, D.
2014-12-01
SWPC has been evaluating various approaches for ensemble forecasting of Earth-directed CMEs. We have developed the software infrastructure needed to support broad-ranging CME ensemble modeling, including composing, interpreting, and making intelligent use of ensemble simulations. The first step is to determine whether the physics of the interplanetary propagation of CMEs is better described as chaotic (like terrestrial weather) or deterministic (as in tsunami propagation). This is important, since different ensemble strategies are to be pursued under the two scenarios. We present the findings of a comprehensive study of CME ensembles in uniform and structured backgrounds that reveals systematic relationships between input cone parameters and ambient flow states and resulting transit times and velocity/density amplitudes at Earth. These results clearly indicate that the propagation of single CMEs to 1 AU is a deterministic process. Thus, the accuracy with which one can forecast the gross properties (such as arrival time) of CMEs at 1 AU is determined primarily by the accuracy of the inputs. This is no tautology - it means specifically that efforts to improve forecast accuracy should focus upon obtaining better inputs, as opposed to developing better propagation models. In a companion paper (deKoning et al., this conference), we compare in situ solar wind data with forecast events in the SWPC operational archive to show how the qualitative and quantitative findings presented here are entirely consistent with the observations and may lead to improved forecasts of arrival time at Earth.
Forecasting seasonal outbreaks of influenza.
Shaman, Jeffrey; Karspeck, Alicia
2012-12-11
Influenza recurs seasonally in temperate regions of the world; however, our ability to predict the timing, duration, and magnitude of local seasonal outbreaks of influenza remains limited. Here we develop a framework for initializing real-time forecasts of seasonal influenza outbreaks, using a data assimilation technique commonly applied in numerical weather prediction. The availability of real-time, web-based estimates of local influenza infection rates makes this type of quantitative forecasting possible. Retrospective ensemble forecasts are generated on a weekly basis following assimilation of these web-based estimates for the 2003-2008 influenza seasons in New York City. The findings indicate that real-time skillful predictions of peak timing can be made more than 7 wk in advance of the actual peak. In addition, confidence in those predictions can be inferred from the spread of the forecast ensemble. This work represents an initial step in the development of a statistically rigorous system for real-time forecast of seasonal influenza.
Advances in Solar Power Forecasting
NASA Astrophysics Data System (ADS)
Haupt, S. E.; Kosovic, B.; Drobot, S.
2014-12-01
The National Center for Atmospheric Research and partners are building a blended SunCast Solar Power Forecasting system. This system includes several short-range nowcasting models and improves upon longer range numerical weather prediction (NWP) models as part of the "Public-Private-Academic Partnership to Advance Solar Power Forecasting." The nowcasting models being built include statistical learning models that include cloud regime prediction, multiple sky imager-based advection models, satellite image-based advection models, and rapid update NWP models with cloud assimilation. The team has also integrated new modules into the Weather Research and Forecasting Model (WRF) to better predict clouds, aerosols, and irradiance. The modules include a new shallow convection scheme; upgraded physics parameterizations of clouds; new radiative transfer modules that specify GHI, DNI, and DIF prediction; better satellite assimilation methods; and new aerosol estimation methods. These new physical models are incorporated into WRF-Solar, which is then integrated with publically available NWP models via the Dynamic Integrated Forecast (DICast) system as well as the Nowcast Blender to provide seamless forecasts at partner utility and balancing authority commercial solar farms. The improvements will be described and results to date discussed.
Experiments in turbulence induced super-resolution in surveillance imagery
NASA Astrophysics Data System (ADS)
Lambert, Andrew; Li, Feng; Bowman, David; Fraser, Donald
2008-11-01
Surveillance imaging from long-range requires use of telescopic optics, and fast electro-optic sensors. The intervening air introduces distortion of the imagery and its spatial frequency content, and does so such that regions of the image suffer dissimilar distortion, visible in the first instance as a time varying geometrical warp, and then as region specific blurring or "speckle". The severity of this, and hence the reduction in size of regions exhibiting similar distortion, is a function of the field of view of the telescope, the height above ground of the imaging path, the range to the target, and climatic conditions. Image processing algorithms must be run on the sequence of imagery to correct these distortions, on the assumption that exposure time has effectively "frozen" the turbulence. These are absent of knowledge of the actual scene under investigation. Successful algorithms do manage to correct the apparent warping, and in doing so they yield both information on the bulk turbulent medium, and allow for reconstruction of spatial frequency content of the scene that would have been lost by the capability of the optics had their been no turbulence. This is known as turbulence-induced super-resolution. To confirm the success of algorithms in both correction and reconstruction of such super-resolution we have devised a field experiment where the truth image is known and which uses other methods to evaluate the turbulence for collaboration of the results. We report here a new algorithm, which has proved successful in satellite remote sensing, for restoring this imagery to quality beyond the diffraction limits set by the optics.
3rd International Conference on Turbulent Mixing and Beyond
NASA Astrophysics Data System (ADS)
Abarzhi, Snezhana I.; Gauthier, Serge; Keane, Christopher J.; Niemela, Joseph J.
2013-07-01
: material transformation under high strain rates, equation of state, impact dynamics, mixing at nano- and micro-scales. • Astrophysics: supernovae, interstellar medium, star formation, stellar interiors, early Universe, cosmic-microwave background, accretion discs. • Magneto-hydrodynamics: magnetic fusion and magnetically confined plasmas, magneto-convection, magneto-rotational instability, dynamo. • Canonical plasmas: coupled plasmas, anomalous resistance, ionosphere. • Physics of atmosphere: environmental fluid dynamics, forecasting, turbulent flows in stratified media and atmosphere. • Geophysics and Earth science: mantle-lithosphere tectonics, oceanography, turbulent convection under rotation, planetary interiors. • Combustion: dynamics of flames and fires, deflagration-to-detonation transition, blast waves and explosions, flows with chemical reactions, reactive flows in jet engines. • Theoretical aspects of non-equilibrium dynamics: vortex dynamics, singularities, discontinuities, asymptotic dynamics, weak solutions, well- and ill-posedness, continuous transports out of thermodynamic equilibrium. • Stochastic processes and probabilistic description: long-tail distributions and anomalous diffusion, data assimilation and processing methodologies, error estimate and uncertainty quantification, statistically unsteady processes. • Advanced numerical simulations: continuous DNS/LES/RANS, molecular dynamics, Monte-Carlo, predictive modelling, validation and verification of numerical models. • Experiments and experimental diagnostics: model experiments in high energy density and low energy density regimes, plasma diagnostics, fluid flow visualizations and control, opto-fluidics, novel optical method, holography, advanced technologies. The abstracts of the 207 accepted presentations of 443 authors were published in Proceedings. Abstracts. The Third International Conference 'Turbulent Mixing and Beyond', 21 -28 August 2011. Copyright (ISBN 92-95003-45-4). All
Gaylord, J
2009-04-30
The purpose of this study is to specify the design for an initial optics supply planning system for NIF, and to present quality assurance and test plans for the construction of the system as specified. The National Ignition Facility (NIF) is a large laser facility that is just starting operations. Thousands of specialized optics are required to operate the laser, and must be exchanged over time based on the laser shot plan and predictions of damage. Careful planning and tracking of optic exchanges is necessary because of the tight inventory of spare optics, and the long lead times for optics procurements and production changes. Automated inventory forecasting and production planning tools are required to replace existing manual processes. The optics groups members who are expected to use the supply planning system are the stakeholders for this project, and are divided into three groups. Each of these groups participated in a requirements specification that was used to develop this design. (1) Optics Management--These are the top level stakeholdersk, and the final decision makers. This group is the interface to shot operations, is ultimately responsible for optics supply, and decides which exchanges will be made. (2) Work Center Managers--This group manages the on site optics processing work centers. They schedule the daily work center operations, and are responsible for developing long term processing, equipment, and staffing plans. (3) Component Engineers--This group manages the vendor contracts for the manufacture of new optics and the off site rework of existing optics. They are responsible for sourcing vendors, negotiating contracts, and managing vendor processes. The scope of this analysis is to describe the structure and design details of a system that will meet all requirements that were described by stakeholders and documented in the analysis model for this project. The design specifies the architecture, components, interfaces, and data stores of the system
Fluid dynamics: In pursuit of turbulence
NASA Astrophysics Data System (ADS)
Knebel, Johannes; Weber, Markus F.; Frey, Erwin
2016-03-01
In the transition from laminar to turbulent pipe flow, puffs of turbulence form, split and decay. The phenomenology and lifetime of these turbulent puffs exhibit population dynamics that also drive predator-prey ecosystems on the edge of extinction.
Some Basic Laws of Isotropic Turbulent Flow
NASA Technical Reports Server (NTRS)
Loitsianskii, L. G.
1945-01-01
An Investigation is made of the diffusion of artificially produced turbulence behind screens or other turbulence producers. The method is based on the author's concept of disturbance moment as a certain theoretically well-founded measure of turbulent disturbances.
Smooth Sailing for Weather Forecasting
NASA Technical Reports Server (NTRS)
2002-01-01
Through a cooperative venture with NASA's Stennis Space Center, WorldWinds, Inc., developed a unique weather and wave vector map using space-based radar satellite information and traditional weather observations. Called WorldWinds, the product provides accurate, near real-time, high-resolution weather forecasts. It was developed for commercial and scientific users. In addition to weather forecasting, the product's applications include maritime and terrestrial transportation, aviation operations, precision farming, offshore oil and gas operations, and coastal hazard response support. Target commercial markets include the operational maritime and aviation communities, oil and gas providers, and recreational yachting interests. Science applications include global long-term prediction and climate change, land-cover and land-use change, and natural hazard issues. Commercial airlines have expressed interest in the product, as it can provide forecasts over remote areas. WorldWinds, Inc., is currently providing its product to commercial weather outlets.
Aggregate vehicle travel forecasting model
Greene, D.L.; Chin, Shih-Miao; Gibson, R.
1995-05-01
This report describes a model for forecasting total US highway travel by all vehicle types, and its implementation in the form of a personal computer program. The model comprises a short-run, econometrically-based module for forecasting through the year 2000, as well as a structural, scenario-based longer term module for forecasting through 2030. The short-term module is driven primarily by economic variables. It includes a detailed vehicle stock model and permits the estimation of fuel use as well as vehicle travel. The longer-tenn module depends on demographic factors to a greater extent, but also on trends in key parameters such as vehicle load factors, and the dematerialization of GNP. Both passenger and freight vehicle movements are accounted for in both modules. The model has been implemented as a compiled program in the Fox-Pro database management system operating in the Windows environment.
Turbulent supersonic channel flow
NASA Astrophysics Data System (ADS)
Lechner, Richard; Sesterhenn, Jörn; Friedrich, Rainer
2001-01-01
The effects of compressibility are studied in low Reynolds number turbulent supersonic channel flow via a direct numerical simulation. A pressure-velocity-entropy formulation of the compressible Navier-Stokes equations which is cast in a characteristic, non-conservative form and allows one to specify exact wall boundary conditions, consistent with the field equations, is integrated using a fifth-order compact upwind scheme for the Euler part, a fourth-order Padé scheme for the viscous terms and a third-order low-storage Runge-Kutta time integration method. Coleman et al fully developed supersonic channel flow at M?=?1.5 and Re?=?3000 is used to test the method. The nature of fluctuating variables is investigated in detail for the wall layer and the core region based on scatter plots. Fluctuations conditioned on sweeps and ejections in the wall layer are especially instructive, showing that positive temperature, entropy and total temperature fluctuations are mainly due to sweep events in this specific situation of wall cooling. The effect of compressibility on the turbulence structure is in many respects similar to that found in homogeneous shear turbulence and in mixing layers. The normal components of the Reynolds stress anisotropy tensor are increased due to compressibility, while the shear stress component is slightly reduced. Characteristic of the Reynolds stress transport is a suppression of the production of the longitudinal and the shear stress component, a suppression of all velocity-pressure-gradient correlations and most of the dissipation rates. Comparison with incompressible channel flow data reveals that compressibility effects manifest themselves in the wall layer only.
Operational on-line coupled chemical weather forecasts for Europe with WRF/Chem
NASA Astrophysics Data System (ADS)
Hirtl, Marcus; Mantovani, Simone; Krüger, Bernd C.; Flandorfer, Claudia; Langer, Matthias
2014-05-01
Air quality is a key element for the well-being and quality of life of European citizens. Air pollution measurements and modeling tools are essential for the assessment of air quality according to EU legislation. The responsibilities of ZAMG as the national weather service of Austria include the support of the federal states and the public in questions connected to the protection of the environment in the frame of advisory and counseling services as well as expert opinions. ZAMG conducts daily Air-Quality forecasts using the on-line coupled model WRF/Chem. Meteorology is simulated simultaneously with the emissions, turbulent mixing, transport, transformation, and fate of trace gases and aerosols. The emphasis of the application is on predicting pollutants over Austria. Two domains are used for the simulations: the mother domain covers Europe with a resolution of 12 km, the inner domain includes the alpine region with a horizontal resolution of 4 km; 45 model levels are used in the vertical direction. The model runs 2 times per day for a period of 72 hours and is initialized with ECMWF forecasts. On-line coupled models allow considering two-way interactions between different atmospheric processes including chemistry (both gases and aerosols), clouds, radiation, boundary layer, emissions, meteorology and climate. In the operational set-up direct-, indirect and semi-direct effects between meteorology and air chemistry are enabled. The model is running on the HPCF (High Performance Computing Facility) of the ZAMG. In the current set-up 1248 CPUs are used. As the simulations need a big amount of computing resources, a method to safe I/O-time was implemented. Every MPI task writes all its output into the shared memory filesystem of the compute nodes. Once the WRF/Chem integration is finished, all split NetCDF-files are merged and saved on the global file system. The merge-routine is based on parallel-NetCDF. With this method the model runs about 30% faster on the SGI
NASA Astrophysics Data System (ADS)
Haeri, M. B.; Putterman, S. J.; Garcia, A.; Roberts, P. H.
1993-01-01
The nonlinear quantum kinetic equation for the interaction of sound waves is solved via analytic and numerical techniques. In the classical regime energy cascades to higher frequency (ω) according to the steady-state power law ω-3/2. In the quantum limit, the system prefers a reverse cascade of energy which follows the power law ω-6. Above a critical flux, a new type of spectrum appears which is neither self-similar nor close to equilibrium. This state of nonlinear quantum wave turbulence represents a flow of energy directly from the classical source to the quantum degrees of freedom.