Fog Attenuation Research Articles

Optical Signal Attenuation through Smog in Controlled Laboratory Conditions

Free-space optical (FSO) communication is a line-of-sight (LOS) communication technology that uses light, typically lasers, to transmit data through the atmosphere. FSO can provide high data transfer rates, but factors like weather conditions can affect its performance. Like fog, smog also degrades the availability and reliability of FSO links, as the particulate matter (PM) present in smog scatters the light beam, causing perceptible attenuation. In this paper, we have investigated the attenuation of an optical signal under laboratory-controlled smog conditions, using both theoretical and experimental approaches. A 6 m long acrylic chamber is used to contain artificial smog and measure the optical attenuation through it. The experimental result shows that smog attenuation is approximately 1.705 times more than fog attenuation. The findings of this study offer valuable insights into the effects of smog on optical links and can contribute to the development and optimization of these systems in regions with high levels of smog.

Attenuation Characterization of Terahertz Waves in Foggy and Rainy Conditions at 0.1–1 THz Frequencies

Investigating the absorption and scattering effects of atmospheric particles, i.e., raindrops and fog droplets, is required to establish a comprehensive and accurate channel model. However, for long-distance communication in outdoor scenarios, research on the propagation characterization of fog and rain attenuation in the terahertz (THz) band is insufficient. In this study, fog and rain attenuation characterization with different conditions are characterized. First, fog attenuation at different temperatures and diverse visibility is explored using Rayleigh approximation theory and Mie theory. The results demonstrate that visibility and frequency have a stronger effect than temperature on fog attenuation. Then, rain attenuation as a function of rainfall rate is theoretically determined using Mie theory and the Joss, M-P, and Weibull distribution. The results show that rainfall rate and frequency have greater impact than raindrop distribution on rain attenuation. There are large differences in rainfall attenuation under diverse distributions. Accurate fog and rainfall attenuation information can be used to better estimate path loss and the link budget for terahertz communication in outdoor scenarios.

Smart Channel Modelling for Cloud and Fog Attenuation Using ML for Designing of 6G Networks at D and G Bands

Smart Channel Modelling for Cloud and Fog Attenuation Using ML for Designing of 6G Networks at D and G Bands

Atmospheric Turbulence and Fog Attenuation Effects in Controlled Environment FSO Communication Links

Free-space optical (FSO) communication can be seen as a promising technology for point-to-point and back-hauling links in the next generation wireless networks (5G and beyond) where cell size may shrink to a few hundred meters. In this work, we have experimentally investigated the laser beam propagation for FSO link under atmospheric turbulence and fog conditions. A controlled atmospheric environment chamber is designed to perform experiments under varying channel conditions. For fog attenuation, we have proposed an empirical model as a function of visibility against the measured average values, for visibility range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0\leq V \leq1000$ </tex-math></inline-formula> m. For atmospheric turbulence, we report the measured values of the refractive index structure parameter <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C_{n}^{2}$ </tex-math></inline-formula> . The measured <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C_{n}^{2}$ </tex-math></inline-formula> is used to calculate the atmospheric coherence width along the propagation distance. This work would help in the design optimization of practical FSO links under adverse conditions like fog and atmospheric turbulence.

Atmospheric Effects on Satellite–Ground Free Space Uplink and Downlink Optical Transmissions

Free space optical (FSO) communications have the potential to be one of the most essential technologies for solving the high-bandwidth demands of communications between satellites and ground stations. In this study, we examine the impact of the atmosphere on satellite–ground FSO uplink and downlink communications. To consider diverse atmospheric conditions on both uplink and downlink, we derive FSO channel elements such as the fog attenuation coefficient, refractive index parameter, coherence length, turbulence model, and angle-of-arrival fluctuation. Unlike conventional work, we provide FSO channel analysis based on variations in the Fried parameter, zenith angle, scintillation index, and Rytov variance. Using simulation results from the optical settings, we examine the influence on channel performance of conditions such as atmospheric attenuation and intensity fluctuation. Based on this examination, we determine that 1550 nm is the preferred wavelength for both uplink and downlink FSO channels to mitigate the impact of turbulence and that larger receiver apertures lessen angle-of-arrival changes.

Relating atmospheric aerosol amounts to blue to red ratio and grayscale contrast fluctuations using digitalization of routine webcam photographs taken in the urban environment of Vienna

Visibility and visual contrast depend on several factors such as aerosol concentration, fog attenuation and humidity, viewing direction relative to the sun as well as trace gas amounts. Usually, visibility is determined by observers or by measurement devices such as visiometers. Only few studies reported on the relationship between visibility and aerosol concentration using digital cameras. In the present study, we develop and test new algorithms for the determination of the amount of aerosols by using digital photography. Two years of routine webcam recordings are used for this study. The digital images are taken at the meteorological measurement platform, which is situated on the roof of a university campus building and overlooking the city of Vienna. The photographs are automatically taken as part of Multi AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements, which are continuously performed during daytime at different azimuthal and elevation angles. Two new algorithms for estimating aerosol amounts by quantifying digital images taken on cloud-free days are introduced within the scope of the present study: (1) the ratio of the blue to red (B/R) RGB channels within a vertical pixel line and (2) the grayscale contrast fluctuations (GCF) within a horizontal pixel line. Vertical B/R and horizontal GCF are compared against ground-based aerosol optical depth (AOD) and in-situ particulate matter (PM) < 10 μm (PM10) measurements. Interestingly, the comparisons show promising results for specific azimuthal directions and during certain daytime periods, e.g. for constellations when the sun is to the side or directly behind the camera. In terms of coefficients of determination (R2), B/R correlates best with AOD during summer, while GCF shows better performance in winter. R2 values of up to 0.86 and 0.73 are found between horizontal line GCF and in-situ PM10 and between vertical line B/R and AOD, respectively. For a better interpretation of the correlations, simultaneous measurements of relative humidity (RH) are included in the analyses.

Investigation of link due to atmospheric turbulence in free space optical communication for optical wireless terrestrial networks

Abstract In recent years, wireless communication systems have exploded in popularity. Optical wireless technology is an excellent alternative to RF wireless, but it has high capacity, data speed, frequency, and license-free spectrum, and it is simple to implement. Optical wireless communication sends data through air using optical beams. Atmospheric turbulence degrades the functioning of free-breathing space photosensitive interaction methods by causing interruptions due to weather conditions like fog, smoke, and different pollutants. In this paper, free-space optical communications using snow and fog attenuations and Numerical Weather Prediction (NWP) method is used to determine the turbulence due to the atmosphere. This method improves the data transmission during unfavorable weather conditions by changing the various parameters like receiver aperture size, the wavelength of the transmitter, etc. Furthermore it shows that decrease in air quality and instability are the double significant causes, that can degrade general usage routine, especially when it’s foggy or raining heavily. The result shows that the aperture size and wavelength should be changed as per the weather condition.

Tropospheric attenuation prediction for future millimeter wave terrestrial systems: Estimating statistics and extremes.

SummaryTropospheric attenuations can be significant in the millimeter wave (mmWave) frequency bands; hence, accurate prediction modeling of tropospheric attenuation is important for reliable mmWave communication. Several models have been established by the International Telecommunication Union (ITU), yet estimation accuracy is limited due to the large spatial scales used for model input parameters. In this paper, we address this and apply local precipitation data to analyze tropospheric attenuation statistics and compare to results when using ITU regional input rain data. Specifically, tropospheric attenuation is predicted via simulations using the ITU method at 30, 60, and 90 GHz in four distinct geographic locations with different climate types. From our simulations, we gather statistics for annual average rain attenuation, worst month rain attenuation, and rain attenuation per decade. Our results indicate that when using local measured rain data, for 1 km link distance, mean rain event attenuation increases from 0.5 to 2 dB. Local rain data yield larger attenuations at essentially all percentages of time not exceeded (essentially corresponding to all probability values): for example, for 0.1% of time not exceeded, in Columbia, SC, rain attenuation for 30 GHz frequency increases to 9 dB with local rain data, compared to 5 dB with ITU's regional data, corresponding to rain rates of 38.2 and 17.5 mm/h, respectively; at the same probability and location, the 90 GHz attenuation increases by 10 dB, from 10 to 20 dB when local rain data are used. Fog attenuations are also appreciable, reaching 8 dB for the 90 GHz frequency. Moreover, for the example locations, peak rain attenuations have increased at a rate of approximately 2 dB/decade over the past 50 years. Our results indicate that actual tropospheric attenuations may be substantially larger than that predicted by the ITU model when using regional rain rate data.

Self-consistent non-linear physics based predictive model for the computation of THz-signal attenuation in fog with varying visibility in tropical climatic zone

Self-consistent non-linear physics based predictive model for the computation of THz-signal attenuation in fog with varying visibility in tropical climatic zone

Terahertz Window Frequency Signal Attenuation and Dispersion Characteristics in Tropical Climate Zone: An Experimentally Validated Reliability Analysis

The propagation of electromagnetic signals through atmosphere is affected by absorptive and dispersive processes present therein. The resulting attenuation increases in adverse weather conditions. The loss of signal power due to scattering of electromagnetic waves in free space, is one of the most common hazards in ultrafast wireless communication systems. The scattering of signal is caused by the suspended atmospheric hydrometeors. Moreover, due to the humidity of the atmosphere, the defocusing of the electromagnetic beam, known as scintillation, may occur. In this paper, the authors, for the first time, have presented a comprehensive analysis of terahertz (THz) signal attenuation along with scintillation effect, in fog-laden atmosphere of Indian subcontinent under tropical climatic belt. The frequency-dependent properties of the signal attenuation have been analysed using an indigenously developed Non Linear Terahertz Attenuation Model (NLTAM)simulator. Moreover, the difference between single and multiple scattering effects of THz signal has also been presented here. The nature of THz signal attenuation spectra in foggy atmosphere, agrees closely with experimental findings, for near THz or IR signal transmission in fog-based aerosols weather scenario in both tropical and non-tropical regions. The experimental study at MMW regime was carried out through radiometric measurement of fog attenuation at Kolkata (22 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sup> N, tropical region) and the results are compared with the NLTAM model data for reliability verification. The signal attenuation is found to be <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim \,\,16\times 10^{5}$ </tex-math></inline-formula> dB/Km around 2.0 THz frequency. By incorporating parametric variations in the present simulator, the authors have estimated the reliable range of THz signal energy, coming out of atmospheric fog-layer. The authors have developed a separate reliability model to address this aspect of study. To initiate a comparative analysis on the prediction of attenuation of THz wave for different types of scattering mechanisms, especially in foggy atmosphere, under tropical climatic region, a novel technique has been developed and reported by the authors for the first time.

Fog attenuation penalty analysis in terrestrial optical wireless communication-modified duo-binary return-to-zero system with various receiver pointing errors

In metropolitan communication infrastructures a revolutionary technique is emerge known as terrestrial optical wireless communication (OWC), which makes a high-rise building connection is possible. Even with this solution, there are many other problems like the influence of haze and fog in the propagation channel which obstruct and scatter OWC propagation light and consequently led to a big attenuation, due to propagate in temporal, angular and spatial of the light signal. Not to mention the minimum visibility that discourages the implementation of the pointing errors (PE) and tracking system. This present work aims to analyze the interrelation between multiple scattering (dense fog, heavy fog, light fog, heavy haze and light haze) and receiver PE under modified duo-binary return-to-zero (MDRZ) system. We found that PE caused by beam swag is the main controlling factor and industriously minimize the link margin, signal-to-noise ratio (SNR), and raise the bit error rate (BER) when there is an increasing the turbulence strength and the track length. We recommended to guarantee transmitter– receiver alignment by installing a variable field of view (FOV) receiver (a tracking system) to overcome the scattering impact of the fog that make render urban laser communication effective in the presence of PE.

Performance evaluation and fog attenuation modelling of FSO link for hilly regions of India

Performance evaluation and fog attenuation modelling of FSO link for hilly regions of India

Microphysics and Optical Attenuation in Fog: Observations from Two Coastal Sites

A total of 15 fog events from two field campaigns are investigated: the High Energy Laser in Fog (HELFOG) project (central California) and the Toward Improving Coastal Fog Prediction (C-FOG) project (Ferryland Newfoundland). Nearly identical sensors were used in both projects to sample fog droplet-size spectra, wind, turbulence, and thermodynamic properties near the surface. Concurrent measurements of visibility were made by the present weather detector in both experiments, with the addition of a two-ended transmissometer in the HELFOG campaign. The analyses focused first on contrasting the observed fog microphysics and the associated thermodynamics from fog events in the two locations. The optical attenuation by fog was investigated using three methods: (1) derived from Mie theory using the measured droplet-size distribution, (2) parametrized as a function of fog liquid water content, and (3) parametrized in terms of total fog droplet number concentration. The consistency of these methods was investigated. The HELFOG data result in an empirical relationship between the meteorological range and liquid water content. Validation of such relationship is problematic using the C-FOG data due to the presence of rain and other factors. The parametrization with droplet number concentration only does not provide a robust visibility calculation since it cannot represent the effects of droplet size on visibility. Finally, a preliminary analysis of the mixed fog/rain case is presented to illustrate the nature of the problem to promote future research.

Experimental performance evaluation of weak turbulence channel models for FSO links

Outdoor wireless communication is subject to several outdoor environment conditions. Among them, atmospheric turbulence which happens on a daily basis, introduces signal fading and degrades the system performance. Many channel models have been proposed in the literature to model the turbulence fading in free space optic (FSO) communication systems. In this work, we aim to evaluate the performance of some key proposed channel models for FSO systems under weak turbulence condition. First, an outdoor experimental setup is utilized to measure the turbulence fading and build a dataset. The setup is all-optical, which gives us the advantage of isolating the solar radiation noise during measurements. Second, the obtained dataset is used to investigate the performance of five key FSO channel models claimed to perform well under weak turbulence conditions. The results show that for very weak turbulence with scintillation index (SI) <10−3, four models that claim to work well under such condition failed to fit the dataset. For weak turbulence with SI>10−3, all the models fit the dataset except I-K model. Third, we exploited the obtained dataset to propose a new empirical channel model that has good performance under weak turbulence conditions. Using this model, we studied the outage probability of FSO system under the joint effect of weak turbulence and fog attenuation.

Performance of Opportunistic Receiver Beam Selection in Multiaperture OWC Systems Over Foggy Channels

The atmospheric foggy condition is a major bottleneck for the deployment of optical wireless communication (OWC) systems in outdoor environments. Although the attenuation coefficient in the foggy channel follows the simple Gamma distribution, the distribution of its channel state is quite complicated similar to the well-studied Gamma–Gamma turbulence channel. Furthermore, existing literature suggested schemes that require feedback of the channel state information (CSI) to improve the outage performance of the OWC system under foggy conditions. In this article, we study the average signal-to-noise ratio (SNR), ergodic rate, and energy consumption performance of OWC systems under foggy conditions. First, we show that a single-aperture OWC system suffers significantly from the fog attenuation by deriving analytical expressions on the ergodic rate and energy consumption. Then, we consider a multiaperture OWC system equipped with an opportunistic receiver beam selection (RBS) scheme. The RBS scheme is based on the simple selection combining diversity algorithm, which does not require the knowledge of CSI. We analyze the proposed scheme by deriving computable bounds on the average SNR, ergodic rate, and energy consumption using system parameters and show the performance improvement of the RBS scheme comparing the single-aperture system. We demonstrate the performance of the considered scheme and validate derived expressions using computer simulations.

Fog and rain attenuation characterization and performance of terrestrial free space optical communication in Akure, Nigeria

Reliable broadband communication requires secure high data rate and bandwidth links. With the observedincrease in broadband users, known communication systems such as RF and microwave links cannot promise suchrequirements due to link interference and low bandwidth. A current communication system that promises suchrequirements and more is Free Space Optical (FSO) communication. This system basically involves the transmissionof signal-modulated optical radiation from a transmitter to a receiver through the atmosphere or outer space. However,location-variant atmospheric channel degrades the performance of an FSO system under severe atmosphericconditions, thus necessitating local atmospheric attenuation studies.This paper presents the characterization of both fog- and rain-induced attenuation and the performance ofan FSO system in a terrestrial terrain at Akure, Nigeria. One-year archived visibility data and in-situ measured 1-minute integration time rain rate data obtained from Nigerian Meteorological Agency (NIMET) and the Departmentof Physics, Federal University of Technology, Akure were used to compute the fog- and rain-induced specificattenuations using Kruse model and Carboneur model respectively. The performance of the FSO system is analyzedthrough link margin by using the parameters of a commercial optical transceiver, Terescope 5000.

Fog and Rain Attenuation Characterization and Performance of Terrestrial Free Space Optical Communication in Akure, Nigeria

Reliable broadband communication requires secure high data rate and bandwidth links. With the observed increase in broadband users, known communication systems such as RF and microwave links cannot promise such requirements due to link interference and low bandwidth. A current communication system that promises such requirements and more is Free Space Optical (FSO) communication. This system basically involves the transmission of signal-modulated optical radiation from a transmitter to a receiver through the atmosphere or outer space. However, location-variant atmospheric channel degrades the performance of an FSO system under severe atmospheric conditions, thus necessitating local atmospheric attenuation studies. This paper presents the characterization of both fog- and rain-induced attenuation and the performance of an FSO system in a terrestrial terrain at Akure, Nigeria. One-year archived visibility data and in-situ measured 1-minute integration time rain rate data obtained from Nigerian Meteorological Agency (NIMET) and the Department of Physics, Federal University of Technology, Akure were used to compute the fog- and rain-induced specific attenuations using Kruse model and Carboneur model respectively. The performance of the FSO system is analyzed through link margin by using the parameters of a commercial optical transceiver, Terescope 5000.

Critical Events of Fog Attenuation Using Visibility Data in Lahore, Pakistan.

Free-space optics (FSO) communication system is mature, unique and promising technology which is used in various countries to meet high data rate demand and last mile connectivity. FSO link has a capacity to be utilized as a primary communication links by replacing RF communication systems because of its advantages of unregulated bandwidth, broader spectrum of frequency at low power consumption. Now a days researchers has great interest in this technology because of several features and benefits of larger bandwidth, less power consumption, low installations cost, simple to install, no congestion in spectrum, secure and reliable communication without issues of right of way. In free space optical communication, environment layer is used for signal transmission which can be effected from severe weather conditions like smog, dust, smoke, rain and fog etc. In all these severe weather environments, winter fog is one of the main problem because of it offers high optical attenuation on communication link. In this investigation the entire winter season has been observed. There are four fog events which attenuate the optical signal most. Optical attenuation is estimated using three famous fog prediction models like Al Naboulsi, Kim and at wavelengths of 850nm, 1350nm, and 1550 nm.

Performance Evaluation of G2T FSO Link Under Various Weather Conditions

FSO technology has attracted a lot of popularity for a variety of applied telecommunication fields. It presents a wide range of advantages that place it in the frontier of high data rates applications, last mile problem and bottleneck issues. It has been preferred for its ease of deployment without fiber cables, no extra tariff fees, cost-effectiveness, and efficiency. FSO excels in performance when compared to contemporary RF technology. On the other hand, there is an increased demand for alternative rail communications solutions. In order to deliver a safer, reliable and fast internet access. In this paper, performance evaluation of a ground-to-train Free Space Optical link communication (G2T FSO) was performed. The system was simulated at 2.5 Gb/s link under several weather conditions. Receiver and geometrical loss were included as well. Furthermore, performance was evaluated in terms of received power, Q factor, BER and eye diagram. Substantial vulnerability to severe fog attenuation was found. Although the system was able to operate with acceptable eye height with min BER of 10-38.

Statistical modeling of optical attenuation measurements in continental fog conditions

Free-space optics is an innovative technology that uses atmosphere as a propagation medium to provide higher data rates. These links are heavily affected by atmospheric channel mainly because of fog and clouds that act to scatter and even block the modulated beam of light from reaching the receiver end, hence imposing severe attenuation. A comprehensive statistical study of the fog effects and deep physical understanding of the fog phenomena are very important for suggesting improvements (reliability and efficiency) in such communication systems. In this regard, 6-months real-time measured fog attenuation data are considered and statistically investigated. A detailed statistical analysis related to each fog event for that period is presented; the best probability density functions are selected on the basis of Akaike information criterion, while the estimates of unknown parameters are computed by maximum likelihood estimation technique. The results show that most fog attenuation events follow normal mixture distribution and some follow the Weibull distribution.