Arkadi Zilberman

Propagation of electromagnetic waves in Kolmogorov and non-Kolmogorov atmospheric turbulence: three-layer altitude model

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.

Generalized atmospheric turbulence: implications regarding imaging and communications

At present, system design usually assumes the Kolmogorov model of refractive index fluctuation spectra in the atmosphere. However, experimental data indicates that in the atmospheric boundary layer and at higher altitudes the turbulence can be different from Kolmogorovs type. In optical communications, analytical models of mean irradiance and scintillation index have been developed for a traditional Kolmogorov spectrum and must be revised for non-Kolmogorov turbulence. The image quality (resolution, MTF, etc.) is essentially dependent on the properties of turbulent media. Turbulence MTF must be generalized to include non-Kolmogorov statistics. The change in fluctuation correlations of the refractive index can lead to a considerable change in both the MTF form and the resolution value. In this work, on the basis of experimental observations and modeling, generalized atmospheric turbulence statistics including both Kolmogorov and non-Kolmogorov path components are discussed, and their influence on imaging and communications through the atmosphere estimated for different scenarios of vertical and slant-path propagation. The atmospheric model of an arbitrary (non-Kolmogorov) spectrum is applied to estimate the statistical quantities associated with optical communication links (e.g., scintillation and fading statistics) and imaging systems. Implications can be significant for optical communication, imaging through the atmosphere, and remote sensing.

Computer Backplane With Free Space Optical Links: Air Turbulence Effects

Over recent decades, there have been increasing demands for high data-rate backplanes for enhanced performance in computers. The present technology of electronic backplanes cannot meet the required data-rate demands for next-generation computers, indicating a need for a technology shift from the electronic to the optic domain. In this paper, we develop a mathematical model to describe the effect of air turbulence on a short range free space optical communication link, such as would be found in computer backplane communication, and conduct experiments to validate the model. The air turbulence under discussion resembles that which would result from the high temperature of chips on the board together with the ventilation of the air by the chip fan. In our experiment, the communication performance, expressed as bit error rate (BER), is presented as a function of the location of the turbulence source and the log amplitude variance. The log amplitude variance was evaluated by two independent methods. One of the main results of this study is the indication that the performance of the backplane deteriorates even for very small values of air turbulence strength. This is exacerbated by the fact that extremely low BER performance is required at the backplane (e.g., from 10-14 to 10- 18 ). We also demonstrate that increasing the distance between the turbulence source and the optical link reduces the influence of the air turbulence in an exponential manner. This fact is important for the design of future-generation optical backplanes. It is noted that operation at wavelengths around 1550 nm yields communication performance that is less severely degraded by air turbulence effects than at 670 nm.

The influence of several changes in atmospheric states over semi-arid areas on the incidence of mental health disorders.

The incidence of suicide attempts [Deliberate Self Harm (DSH); ICD-10: X60–X84] and psychotic attacks (PsA; ICD-10, F20–F29) in association with atmospheric states, typical for areas close to big deserts, was analyzed. A retrospective study is based on the 4,325 cases of DSH and PsA registered in the Mental Health Center (MHC) of Ben-Gurion University (Be’er-Sheva, Israel) during 2001–2003. Pearson and Spearman test correlations were used; the statistical significance was tested at p < 0.1. The influence of temperature and humidity on suicide attempts (NSU) and psychotic attacks (NPS) was weakly pronounced (p > 0.1). Correlation coefficients between NSU and NPS and speed WS of westerly wind reaches 0.3 (p < 0.05), while their dependence on easterly WS was weaker (p > 0.09). Variations in easterly wind direction WD influence NSU and NPS values (p < 0.04), but no corresponding correlation with westerly winds was found (p > 0.3). Obviously ,in transition areas located between different regions ,the main role of air streams in meteorological–biological impact can scarcely be exaggerated. An unstable balance in the internal state of a weather-sensitive person is disturbed when the atmospheric state is changed by specific desert winds, which can provoke significant perturbations in meteorological parameters. Results indicate the importance of wind direction, defining mainly the atmospheric situation in semi-arid areas: changes in direction of the easterly wind influence NSU and NPS, while changes in WS are important for mental health under westerly air streams. Obviously, NSU and NPS are more affected by the disturbance of weather from its normal state, for a given season, to which the local population is accustomed, than by absolute values of meteorological parameters.

Performance limitation of laser satellite communication due to vibrations and atmospheric turbulence: down-link scenario

SUMMARY In this paper, we analyse the effects of vibrations and the atmosphere on the performance of a broadband laser inter-satellite link (BLISL) which was studied within the framework of the BLISL joint Israeli– German applied research project. The use of optical radiation as a carrier between satellites and in satelliteto-ground links enables transmission using very narrow beam divergence angles. Due to the narrow beam divergence angle and the large distance between the satellite and the ground station or airplane the pointing is a complicated process. Further complication results from vibration of the pointing system caused by two fundamental mechanisms of a stochastic nature: (1) tracking noise created by the electro-optic tracker and (2) vibrations caused by internal satellite mechanical mechanisms. Additionally an inhomogeneity in the temperature and pressure of the atmosphere leads to variations of the refractive index along the transmission path. These variations of refractive index as well as pointing vibrations can cause fluctuations in the intensity and the phase of the received signal leading to an increase in link error probability. In this paper, we develop a bit error probability (BEP) model that takes into account both pointing vibrations and turbulence-induced log amplitude fluctuations (i.e. signal intensity fading) in a regime in which the receiver aperture D0 is smaller than the turbulence coherence diameter d0: Our results indicate that BLISL can achieve a BEP of 10 � 9 and data rate of 1Gbps with normalized pointing vibration of GT *s 2 ¼ 0:05 and turbulence of sX ¼ 0:3: Copyright # 2003 John Wiley & Sons, Ltd.

Measured profiles of aerosols and turbulence for elevations of 2 to 20 km and consequences of widening of laser beams

A new lidar system for measuring simultaneously aerosol extinction, size distribution and turbulence profiles up to 20 km altitude has been developed. On the basis of measurements and a Monte Carlo beam propagation model, the atmospheric aerosol contributions to laser beam widening for a horizontal propagation path at various elevations is estimated and compared with beam widening caused by turbulence.

Laser beam wander in the atmosphere: implications for optical turbulence vertical profile sensing with imaging LIDAR

A summary of different approaches for laser beam wander statistics estimation is presented. The principles of an imaging LIDAR technique for remote measurements of refractive turbulence vertical profile based on image motion analysis of a secondary source created by a laser beam at a given altitude are described. The turbulence-induced beam displacement statistics and angle-of-arrival variance of backscattered wave-front are analyzed for different sensing configurations. This study has implications for airborne reconnaissance image restoration, optical satellite communication, adaptive optics, and atmospheric effects on laser weaponry.

LIDAR measurements of atmospheric turbulence vertical profiles

An imaging LIDAR system for measuring vertical profile of the atmospheric refractive index turbulence has been developed and its performance demonstrated. The turbulence profile retrieval technique is based on image motion analysis. In the present work LIDAR measurements of Cn2 vertical profiles are demonstrated. Unlike the existing turbulence models, the experimental results show the various strata and layers in the vertical turbulence profiles.

Laser beam widening as a function of elevation in the atmosphere for horizontal propagation

A new lidar system for measuring near simultaneously aerosol extinction, size distribution and turbulence profiles up to 20 km altitude has been developed. On the basis of measurements and a Monte Carlo beam propagation model, the atmospheric aerosol contributions to laser beam widening for a horizontal propagation path at various elevations is estimated and compared with beam widening caused by turbulence.

Prediction of data stream parameters in atmospheric turbulent wireless communication links

A unified approach for calculation of information data stream parameters in the atmospheric optical communication channel is presented based on irradiance fluctuations of optical wave propagation through turbulence and on a generalized Ricean K-parameter distribution. The effects of turbulence are described via the well-known Kolmogorov scheme of turbulent structure relaxation in terms of stochastic scintillation theory described by the gamma-gamma distribution along with measurements of the values of the refractive index structure parameter, C(n)(2). The relation between the Ricean parameter K and the signal scintillation parameter sigma(I)(2) is considered to develop a unified description of the corresponding probability density function (pdf) of signal fading within an atmospheric wireless communication link. Through the corresponding pdf and parameter K, signal data stream parameters such as the signal-to-noise ratio (SNR), bit error rate (BER), and capacity of the optical atmospheric channel (C) are estimated. Such an approach permits the reliable prediction of the effects of fading caused by different levels of turbulence and agrees with experimental data observed at different atmospheric levels, at the heights of both 100-200 m and above 1-2 km. It is shown that at heights of 100-200 m, effects of fading, caused by turbulence, occur much more frequently than those at the heights of 1-2 km. Data stream parameters such as channel capacity, SNR, and spectral efficiency become stronger at higher altitudes, while at the same time the BER becomes relatively negligible.