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1

Twisted electromagnetic sinc Schell-model beam and its transmission in a turbulent atmosphere

Zhang Changyou, Fu Wenyu

Optica Applicata

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2024

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Vol. 54, nr 1

15--29

EN

We present the twisted electromagnetic sinc-correlation Schell-model (EM TSSM) beam as an extension of the cylindrical sinc Schell-model beam and analyze the necessary source parameter conditions to generate a physically viable beam. Furthermore, we thoroughly investigate the propagation properties of the EM TSSM beam in atmospheric turbulence using the extended Huygens–Fresnel integral, explicitly focusing on spectral intensity, degree of polarization (DOP), and degree of coherence (DOC). It shows that the twisted phase has a noticeable impact on the intensity profiles of these beams, causing them to exhibit rotation and self-splitting while still maintaining their shape in free space. Moreover, during propagation through a turbulent atmosphere, it exhibits self-combining properties over a long range and recovers the plat-topped distribution. Compared with the sinc Schell-model beam without the twisted phase, the DOP distribution of such a beam can rotate around its distribution center. As these beams propagate through turbulent atmospheres, they can self-heal their DOP distribution within specific ranges affected by atmospheric turbulence. A twist factor causes non-unidirectional rotation of the DOC distribution in free space. The DOC gradually transforms from multi-strip profiles into a Gaussian-like distribution. Furthermore, the beam parameters play a crucial role in shaping the DOC. The results will be useful in optical trapping and optical communication.

2

An approach to investigating the feasibility of free-space optical communication technology deployment under scintillation effects

Mahmood Aras S.

Opto-Electronics Review

|

2023

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Vol. 31, No. 3

art. no. e147037

EN

Local weather conditions have an impact on the availability of free-space optical (FSO) communication. The variation in meteorological parameters, such as temperature, humidity, and wind speed, leads to variations of the refractive index along the transmission path. These refractive index inhomogeneities produced by atmospheric turbulence induce optical turbulence which is responsible for random fluctuations in the intensity of the laser beam that carries the signal (irradiance) called scintillations that can significantly degrade the performance of FSO systems. This paper aims to investigate the feasibility of deploying FSO communication technology under scintillation effects in any urban region and atmospheric environment. To achieve that, firstly by utilizing the Hufnagel-Vally day with the Sadot and Kopeika models together, the scintillation strength for a specified region, Sulaimani City in north-eastern Iraq as an example, has been estimated through the calculation of the refractive index structure parameter (Cn²) over a period of 10 years and it was found to be at the strong turbulence level. Secondly, from the same estimated parameter, the scintillation attenuation of the signal carrying the laser beam intensity can be calculated to investigate the feasibility of FSO communication using Optysistem-7 software. The optimal link distance for northeastern Iraq (Sulaimani City) has been found to be within the limit of about 5.5 km. Analysing the max. Q-factor, bit-error rate and signal to noise ratio for an average of 120 months between 2013-2022 assessed the best and worst seasons for FSO.

3

Variable antennas positions solution to reduce pointing errors due to wind speed and temperature coupled effects during free space optical link using matrix Rician pointing error model

Teuma Mbezi Michel, Eke Samuel, Som Idelette Hermine Judith, Mouangue Ruben Martin

Optica Applicata

|

2023

|

Vol. 53, nr 3

393--406

EN

Pointing errors (PE) during free space optical (FSO) transmission can be caused by laser beam wander due to thermal and wind dynamic instability. The aim of this work is to study the coupled effects of temperature and wind speed on PE using matrix Rician pointing error (MRPE) model; then show how variable antennas height can reduce PE due to wind speed and temperature coupled effects. To achieve this purposes, average PE expression was established using MRPE model. Then considering a Gaussian beam wave and Monin–Obukhov similarity functions for the structure parameters of temperature, explicit relationship was established between average PE, temperature and wind speed. It comes out of this study that under dynamic turbulence, one can appropriately modify temperature to reduce PE due to dynamic instability and reciprocally. Depending on turbulence large cells or frozen turbulence eddies distribution, PE can be reduced by appropriately modified antennas height or the distance between transmitter and receiver. That is why this work suggests to install variable or dynamic antennas (rather than fixed ones) which could intelligently modify its positions according to laser beam wander created by atmospheric turbulence.

4

FSO system performance analysis based on novel Gamma–Chi-square irradiance PDF model

Todorović Jelena, Spalević Petar, Panić Stefan, Milosavljević Bojana, Gligorijević Milan

Optica Applicata

|

2021

|

Vol. 51, nr 3

335--348

EN

In order to provide a novel analytically traceable free space optics (FSO) channel model for describing turbulence based irradiance fluctuations, following basic scintillation theory principles, we have derived closed-form expression for probability density function (PDF) of a new statistical Gamma–Chi-square model. Further, capitalizing on provided model, error performances of FSO system over on-off keying (OOK) transmission scheme both in the presence of atmospheric turbulence and misalignment fading (pointing error) is investigated. For both cases, the average bit error rate (ABER) at the receiving side of the system is determined in an analytically closed form. The results are graphically presented in order to analyze the impact of different levels of turbulence, as well as other relevant parameters, on the quality of the received signal in the OOK modulated FSO system.

5

The impact of standard deviation of wind on the bomb flight in atmospheric turbulence

Kowaleczko Grzegorz, Grajewski Krzysztof, Kobiela Szymon, Kaźmierczak Romuald

Journal of KONBiN

|

2021

|

Vol. 51, iss. 2

79--91

EN

The paper provides the simulation results of a small-diameter guided training bomb released during atmospheric turbulence. The simulation utilized a guided bombed devised at ITWL. Aerodynamic characteristics of the bomb were obtained from wind tunnel tests and from calculations made by the PRODAS programme. The simulation programme was developed based on a mathematical model describing a spatial motion of an aerial bomb moving in atmospheric turbulence. To describe a turbulence component, the model of stochastic processes proposed by Shinozuki was used. The manuscript includes examples of diagrams of basic parameters showing the bomb flight in a disturbed atmosphere. The analysis of the impact of the standard deviation of the wind on the change in the parameters of bomb flight was performed. The relationships between the parameters of bomb flight and the possibility to hit the target were provided.

PL

W artykule przedstawiono wyniki symulacji lotu ćwiczebnej bomby kierowanej małego wagomiaru zrzuconej w warunkach atmosfery turbulentnej. Do symulacji użyto bomby kierowanej zaprojektowanej w ITWL. Charakterystyki aerodynamiczne bomby otrzymano z badań w tunelu aerodynamicznym i obliczeń wykonanych w komercyjnym programie PRODAS. Program symulacyjny opracowany został na podstawie modelu matematycznego opisującego ruch przestrzenny bomby lotniczej poruszającej się w warunkach turbulentnej atmosfery. Do opisu składowej turbulencji wykorzystano model procesów stochastycznych zaproponowany przez Shinozukiego. W artykule pokazano przykładowe przebiegi podstawowych parametrów opisujących lot bomby w zaburzonej atmosferze. Dokonano analizy wpływu odchylenia standardowego wiatru na zmianę parametrów lotu bomby. Przedstawiono zależności występujące między parametrami lotu bomby a możliwością trafienia w cel.

6

Effect of Atmospheric Turbulence on the Striking Accuracy of Guided Bombs

Grajewski Krzysztof, Kowaleczko Grzegorz, Pietraszek Mariusz

Problemy Mechatroniki : uzbrojenie, lotnictwo, inżynieria bezpieczeństwa

|

2020

|

Vol. 11, Nr 1 (39)

31--48

EN

This paper presents the test results of a simulation of an air-to-surface guided bomb drop in a turbulent atmosphere. The guided bomb was developed from a practice bomb built and upgraded by the Air Force Institute of Technology. The paper presents the test results of a numerical simulation of an air-to-surface guided bomb drop ran in a proprietary software environment. The numerical simulation inputs included aerodynamic characteristics calculated with PRODAS software and verified by wind tunnel tests. The stochastic components of atmospheric turbulence were simulated with a stochastic process model proposed by Shinozuki. Examples of the guided bomb drop simulation results are given in the paper. The effect of atmospheric turbulence parameters, i.e. standard deviation, σ and turbulence scale, Lw on the striking accuracy and ground impact scatter, are also shown.

PL

W artykule przedstawiono wyniki przeprowadzonych symulacji zrzutu bomby w turbulentnej atmosferze. Bomba ta powstała na bazie bomby ćwiczebnej zbudowanej i zmodernizowanej w Instytucie Technicznym Wojsk Lotniczych. W artykule przedstawiono wyniki numerycznej symulacji z wykorzystaniem autorskiego oprogramowania. W obliczeniach użyto charakterystyki aerodynamiczne wyliczone programem PRODAS, które weryfikowano badaniami w tunelu aerodynamicznym. Do opisu składowej turbulencji wykorzystano model procesów stochastycznych zaproponowany przez Shinozukiego. Przedstawiono przykładowe wyniki symulacji zrzutu bomby. Pokazano wpływ parametrów turbulencji atmosfery - odchylenia standardowego i skali turbulencji σ, Lw, na celność i rozrzut.

7

Spreading properties of a multi-Gaussian Schell-model vortex beam in slanted atmospheric turbulence

Chang Shuai, Song Yansong, Dong Yan, Dong Keyan

Optica Applicata

|

2020

|

Vol. 50, nr 1

83--94

EN

The cross-spectral density function of a multi-Gaussian Schell-model vortex (MGSMV) beam propagating through slanted atmospheric turbulence was derived, and the influences of the MGSMV beam parameter and slanted atmospheric turbulence on the spreading properties of a MGSMV beam are studied. One can find that a MGSMV beam propagating in slanted atmospheric turbulence can evolve into the flat-topped beam, and a MGSMV beam with larger index N and topological charge M propagating in slanted atmospheric turbulence will lose the dark hollow center and evolve into the Gaussian beam more slowly than the MGSMV beam with smaller index N and topological charge M. It is also found that a MGSMV beam propagating in slanted atmospheric turbulence with larger strucutre parameter C will evolve into Gaussian beam faster, but the influences of zenith angle α on the spreading properties of MGSMV beam in the far field can be ignored.

8

Characteristics of C2µ derived from ultrasonic anemometer in an urban boundary layer

Al-Jiboori Monim H., Jaber Sundus H.

Przegląd Naukowy Inżynieria i Kształtowanie Środowiska

|

2019

|

Vol. 28, No. 1

14--24

EN

Fast-response observations of three components of wind and air temperature have been applied to calculate the refractive index function coefficient (C2µ ), which is needed to describe optical wave propagation in a turbulent medium. These were measured by 3D ultrasonic anemometer installed on the roof of the building of Atmospheric Science Department which is 19 m above ground level. Refractive index function coefficient was calculated for various periods of three seasons: winter, spring and summer.Diurnal variations of (C2µ) have been made at the surface layer for these seasons. The results show that high values ofmean (C2µ) occurred during the day time more than at night, also they occurred more in summer than in winter and spring. The results of (Cµ2) found to change with atmospheric stability, whereas they inversely decrease under unstable conditions, approximately constant at neutral cases, and increase under stable conditions. Values of (C2µ) on average appears to be lower during the rainy and foggy weather cases compared to those of clear sky.

9

Study on self-repairing and non-diffraction of Airy beams in slant atmospheric turbulence

Li Y.-Q., Wang L.-G.

Optica Applicata

|

2018

|

Vol. 48, nr 3

435--447

EN

The Airy beams propagation in atmospheric turbulence along a slant path was simulated numerically, based on the split-step Fourier method. Also, the self-repairing and non-diffraction characteristics of Airy beams were investigated and compared with beams propagation on a horizontal path. The effects of parameters including zenith angle, propagation distance, radii of Gaussian aperture and turbulence intensity on the two characteristics of beams were revealed. Additionally, the two characteristics of the Airy beam were compared with those of a Bessel–Gauss beam. The results showed that the two beams obscured by Gaussian apertures can be repaired after propagating some distance along a slant path. However, the non-diffraction characteristic of an Airy beam was stronger than that of a Bessel–Gauss beam and the amplitude attenuation rate of the Bessel–Gauss beam was greater than that of the Airy beam in the process of self-repairing. Results obtained can provide a theoretical basis for an outdoor experiment as well as theoretical guidance for various practical applications including laser communications, laser warning systems, and remote sensing.

10

Dynamic evolution of mixed circular edge-screw dislocations

Gao P., Li J., Cheng K., Duan M.

Optica Applicata

|

2017

|

Vol. 47, nr 3

471--481

EN

Based on the extended Huygens–Fresnel principle, the analytical expressions for the cross-spectral density function of mixed circular edge-screw dislocations beams propagating through atmospheric turbulence have been derived, and used to study the dynamic evolution of mixed circular edge-screw dislocations in free space and atmospheric turbulence. It is shown that the radius of circular edge dislocations increases with increasing propagation distance, and both the positions of the optical vortex and the center of circular edge dislocations are located at the point (0, 0) when mixed circular edge-screw dislocations propagate in free space. When mixed circular edge-screw dislocations propagate in the atmospheric turbulence, the position of optical vortices varies with increasing propagation distance, the circular edge dislocation evolves into a pair of optical vortices with the opposite topological charge ±1, and the pair of optical vortices will annihilate as soon as the propagation distance becomes large enough.

11

Characterization of sub-channel based Málaga atmospheric optical links with real β parameter

López-González F. J., Jurado-Navas A., Garrido-Balsells J. M., Castillo-Vázquez M., Puerta-Notario A.

Optica Applicata

|

2017

|

Vol. 47, nr 4

545--556

EN

A generalization of the Málaga atmospheric optical communications links treated as a finite number of generalized-K distributed sub-channels is analyzed in terms of outage probability and outage rate when its β parameter belongs to the set of real numbers. To the best of the author’s knowledge, this is the first time that β ∈ ℜ is considered. The new analytical expressions derived in this paper lead to a new physical and more realistic interpretation of atmospheric optical links, especially in terms of performance.

12

Optimal threshold detection for Málaga turbulent optical links

Jurado-Navas A., Garrido-Balsells J. M., Castillo-Vázquez M., Puerta-Notario A., Monroy I. T., Olmos J. J. V.

Optica Applicata

|

2016

|

Vol. 46, nr 4

577--595

EN

A new and generalized statistical model, called Málaga distribution (M distribution), has been derived recently to characterize the irradiance fluctuations of an unbounded optical wave front propagating through a turbulent medium under all irradiance fluctuation conditions. As great advantages associated to that model, we can indicate that it is written in a simple tractable closed-form expression and that it is able to unify most of the proposed statistical models for free-space optical communications derived until now in the scientific literature. Based on that Málaga model, we have analyzed in this paper the role of the detection threshold in a free-space optical system employing an on-off keying modulation technique and involved in different scenarios, and taking into account the extinction ratio associated to the employed laser. First we have derived some analytical expressions for the lower-bound performance of the free-space optical system with the light intensity fading induced by turbulence obtained when the additive white Gaussian noise is not present in the system. Then, we have analyzed the optimal threshold in the system and how it changes when atmospheric conditions vary. Finally, a closed form expression for the bit error rate of that system is derived.

13

Dynamic evolution and classification of coherent vortices in atmospheric turbulence

Zeng J., Li J.

Optica Applicata

|

2015

|

Vol. 45, nr 3

299--308

EN

Based on the extended Huygens–Fresnel principle, the analytical expressions for the cross-spectral density function of partially coherent sine-Gaussian vortex beams and partially coherent sine-Gaussian non-vortex beams propagating through free space and atmospheric turbulence are derived, and used to study the dynamic evolution behavior of coherent vortices in free space and atmospheric turbulence. According to the creation, the coherent vortices are grouped into three classes: the first is their inherent coherent vortices of the vortex beam, the second is created by the vortex beam itself during transmission process in free space, and the third is created by the atmospheric turbulence inducing the vortex beam.

14

Performance analysis of bit error rate for free space optical communication with tip-tilt compensation based on gamma-gamma distribution

Wu H., Yan H., Li X.

Optica Applicata

|

2009

|

Vol. 39, nr 3

533-545

EN

In this paper, the gamma - gamma probability distribution is used to model turbulent channels. The bit error rate (BER) performance of free space optical (FSO) communication systems employing on-off keying (OOK) or subcarrier binary phase-shift keying (BPSK) modulation format is derived. A tip-tilt adaptive optics system is also incorporated with a FSO system using the above modulation formats. The tip-tilt compensation can alleviate effects of atmospheric turbulence and thereby improve the BER performance. The improvement is different for different turbulence strengths and modulation formats. In addition, the BER performance of communication systems employing subcarrier BPSK modulation is much better than that of compatible systems employing OOK modulation with or without tip-tilt compensation.

15

Coherence characterization of partially coherent flat-topped beam propagating through atmospheric turbulence

Kashani F. D., Alavinejad M., Ghafary B.

Optica Applicata

|

2009

|

Vol. 39, nr 2

429-440

EN

We study the change in the degree of coherence of a partially coherent flat-topped (PCFT) beam propagating through atmospheric turbulence. It is shown analytically that with a fixed set of source parameters and under a particular atmospheric turbulence model, a PCFT beam propagating through atmospheric turbulence reaches its maximum value of coherence after propagating a particular distance, and the effective width of the spectral degree of coherence also has its maximum value. This phenomenon is independent of the turbulence model used. We also study the effects of beam width values, the structure constant of turbulent media and the degree of coherence on effective width of spectral degree of coherence. The results are illustrated by numerically calculated curves.

16

Sensitivity of a bomb to wind turbulence

Żyluk A.

Journal of Theoretical and Applied Mechanics

|

2009

|

Vol. 47 nr 4

815-828

EN

This paper presents results of numerical investigations into the bomb release in a turbulent wind field. Short descriptions of mathematical models of both the bomb dynamics and the stochastic wind are shown. The effect of parameters of the turbulent wind field on a random distribution of points of the impact is investigated.

PL

W pracy przedstawiono wyniki numerycznej symulacji wpływu turbulencji wiatru na zrzut bomby. Praca zawiera opis matematyczny dynamiki lotu bomby oraz stochastycznego pola wiatru. Badano zależność pomiędzy parametrami turbulencji i punktem upadku bomby.

17

Influence of atmospheric turbulence on bomb release

Kowaleczko G., Żyluk A.

Journal of Theoretical and Applied Mechanics

|

2009

|

Vol. 47 nr 1

69-90

EN

A model of the bomb release dynamics is presented in the paper, and how it is influenced by a wind field. The applied way of describing this field is discussed with account taken of its stochastic nature. Exemplary results of a numerical simulation of bombing are submitted and concluded.

PL

W pracy przedstawiono model dynamiki zrzutu bomby. Pokazano wpływ pola wiatru na szybowanie bomby. Strukturę wiatru opisano, uwzględniając jego stochastyczny charakter. Pokazano wyniki symulacji numerycznej zrzutu oraz poddano je analizie.

18

Propagation properties of partially coherent beams through turbulent media with coherent modes representation

Alavinejad M., Ashiri F., Ghafary B.

Optica Applicata

|

2008

|

Vol. 38, nr 3

549-558

EN

The partially coherent beams propagating through turbulent atmosphere have been studied in the past using coherent mode representation. In this research, the propagation of any modes of Hermite-Gaussian beam in a turbulent atmosphere is investigated and analytical formula for the average intensity of these beams is derived. The power in bucket (PIB) for any modes is also examined. The number of modes which exist in a partially coherent beam with known degree of global coherence (ratio of correlation length and the waist width of the Gaussian-Schell model (GSM) beam) is determined and the PIB for partially coherent beams is investigated using coherent mode representation.

19

Stable-boundary-layer regimes from the perspective of the low-level jet

Banta R.

Acta Geophysica

|

2008

|

Vol. 56, no. 1

58-87

EN

This paper reviews results from two field studies of the nocturnal stable atmospheric boundary layer (SBL) over the Great Plains of the United States. Data from a scanning remote-sensing system, a High-Resolution Doppler Lidar (HRDL), provided measurements of mean and turbulent wind components at high spatial and temporal resolution through the lowest 500-1000 m of the atmosphere. This data set has allowed the characteristics of the low-level jet (LLJ) maximum (speed, height, direction) to be documented through entire nights. LLJs form after sunset and pro-duce strong shear in the layer below the LLJ maximum or nose, which is a source of turbulence and mixing in the SBL. Simultaneous HRDL measurements of turbulence quantities related to turbulence kinetic energy (TKE) has allowed the turbulence in the subjet layer to be related to LLJ properties. Turbulence structure was found to be a function of the bulk stability of the subjet layer. For the strong-LLJ (> 15 m s-1), weakly stable cases the strength of the turbulence is proportional to the strength of the LLJ. For these cases with nearly continuous turbulence in the subjet layer, low-level jet scaling, in which lengths are scaled by the LLJ height and velocity variables are scaled by the LLJ speed, was found to be appropriate. For the weak-wind (< 5 m s-1 in the lowest 200 m), very stable boundary layer (vSBL), the boundary layer was found to be very shallow (sometimes < 10 m deep), and turbulent fluxes between the earth's surface and the atmosphere were found to be essentially shut down. For more intermediate wind speeds and stabilities, the SBL shows varying degrees of intermittency due to various mechanisms, including shear-instability and other gravity waves, density currents, and other mesoscale disturbances.

20

A comparative aerodynamic analysis of two different cable-stayed bridges in Poland

Flaga K., Podgórski J., Błazik-Borowa E., Bosak G., Bęc J.

Archives of Civil Engineering

|

2005

|

Vol. 51, nr 2

155-178

EN

The paper deals with aerodynamic analysis of the two longest cable-stayed bridges in Poland. This analysis comprises: modal analysis, estimation of stresses generated by static wind action, analysis of vibrations excited by atmospheric turbulence and feedbacks, determination of bridge vibrations generated by vortex excitation, calculation of stresses produced by dynamic wind action. The dynamic structure response has been calculated using the quasi-steady method, which allows analysis of just a few representative mode shapes, with the result precision acceptable in the engineering practice. Finally, both bridges have been found safe and resistant to the dynamic wind action, however the Warsaw bridge is more susceptible to the aerodynamic actions, especially its deck.

PL

Przedmiotem pracy jest analiza aerodynamiczna dwóch najdłuższych mostów podwieszanych w Polsce. Analiza obejmuje: analizę drgań własnych konstrukcji, oszacowanie naprężeń wywoływanych statecznym działaniem wiatru, analizę drgań wzbudzanych turbulencją atmosferyczną przy występowaniu sprzężeń aerodynamicznych, okreslenie drgań mostów pod wpływem wzbudzenia wirowego, obliczenie naprężeń wywołanych dynamicznym działaniem wiatru. Odpowiedź dynamiczna konstrukcji na działanie wiatru została obliczona przy wykorzystaniu teorii quasi-ustalonej, bazując na metodzie superpozycji modalnej uwzględniającej kilka reprezentatywnych postaci drgań własnych, co prowadzi do wystarczającej dokładności w praktyce inżynierskiej. Ostatecznie, obydwa mosty uznano za bezpieczne i odporne na dynamiczne działanie wiatru, przy czym most w Warszawie jest bardziej podatny na wpływy aerodynamiczne, zwłaszcza jego pomost.