Humidity remains in the atmosphere even on bright days. Water of all three states can be found naturally in the atmosphere: liquid (rain, fog, and clouds), solid (snowflakes, ice crystals), and gas (water vapour). Water in any state is an obstacle in the link of the electromagnetic wave. When the wave passes through the water particles, a part of its energy is absorbed and a part is scattered. Therefore the electromagnetic wave is attenuated. Prediction of the influence of these factors is very important in radio system design. Attenuation due to rain, fog, and clouds can lead to the perturbations of the wireless, mobile, satellite and other communications. Another problem is the refractive index of the atmosphere, which affects the curvature of the electromagnetic wave path and gives some insight into the fading phenomenon. The anomalous electromagnetic wave propagation can cause disturbances to radar work, because variation of the refractive index of the atmosphere can induce loss of radar coverage. Accurate prediction of losses due to these factors can ensure a reliability of the radio system, decrease an equipment cost, furthermore, the radio systems can become less injurious to health of people. When there are no possibilities to gather data for calculations of the specific attenuation due to rain, clouds and fog, and atmospheric refractive index, the values recommended by the International Communication Union’s Radiocommunication sector (ITU-R) can be used. But the recommended values are not always exact. In design of the radio links, the most desirable operating frequencies are below 10 GHz, because in such cases atmospheric absorption and rainfall loss may generally be neglected (Freeman, 2007). However, in most countries, the frequency-band below 10 GHz is highly congested. In addition, high frequencies provide larger bandwidth, narrower beam width, good resolution and smaller component size (Bhattacharyya et al., 2000). Therefore, the operating frequencies of 10 GHz and above are often used in design of radio systems. The higher the operating frequency, the greater attenuation due to hydrometeors (rain, cloud, fog, snow, and etc.) is observed (Tamosiūnaitė et al., 2010a). In (Ishimaru, 1978), it was mentioned that the electromagnetic wave attenuation due to snow is less than attenuation due to rain, and that the attenuation due to dry snow may be neglected

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Atmospheric Attenuation due to Humidity

There are many issues that affect to WLAN connections (walls, vegetation, rain, objects in the Fresnel zone, etc.). Network designers and telecommunication practitioners must take them into account when they are planning wireless connections between devices. Some studies have demonstrated the implication of the atmospheric variables in the frequency attenuation and in the line of sight of the waves. But, to the extend of our knowledge, there is not any work published that relates the atmospheric variables with the datalink layer parameters of the WLANs. We must take into account that the datalink layer allows us to measure quite more parameters than the physical layer. After a review of the published related works, first, we will show the atmospheric variables measured during two months, and, then we will show the datalink layer parameters that we have been able to measure during those months. Finally, we will discuss the implications of the atmospheric variables in the measured parameters and we will estimate the laws followed by our measurements.

How the Atmospheric Variables Affect to the WLAN Datalink Layer Parameters

Queueing theory approach to rain fade analysis at microwave and millimeter bands in tropical Africa.

The prediction of the electromagnetic wave (EW) power losses is a very important step in the design of radio systems. It is epecially important for high operating frequencies. Accurate prediction of losses can ensure a reliability of the radio system, decrease in equipment cost, and maybe the system can become less injurious to health of people. Rainfall is one of the factors causing the attenuation of the electromagnetic waves while they are propagating through the atmosphere. In this paper, difficulties in prediction of electromagnetic waves attenuation due to rain are analyzed. According to the climatic peculiarities of Lithuania, appropriate model for calculation of electromagnetic waves attenuation due to rain (rain attenuation) was chosen. Applying this model a large quantity of precipitation data was computed and the specific rain attenuation considering the peculiarities of localities of Lithuania was determined. Citations: Milda Tamooisnaito, Milda Tamooisnieno, Alytis Gruodis, Stasys Tamooisnas. Prediction of electromagnetic wave attenuation due to water in atmosphere. 1. Attenuation due to rain - Innovative Infotechnologies for Science, Business and Education, ISSN 2029-1035 - 2(9) 2010 - Pp. 3-10.

Prediction of electromagnetic wave attenuation due to water in atmosphere. 1. Attenuation due to rain

Climate change and urbanization have affected a increase of peak discharge and water pollution etc. In a view of these aspects, the LID(Low Impact Development) technology has been highlighted as one of adjustable control measures to mimic predevelopment hydrologic condition. Many LID technologies have developed, but there is a lack of studies with verification of LID technology efficiency. Therefore this study developed a rainfall-runoff simulator could be possible to verify LID technology efficiency. Using this simulator, this study has experimented the rainfall verification through the rainfall distribution experiment and the experiment to show the relation between inflow and effective rainfall in order to sprinkle the equal rainfall in each unit bed. As a result, the study defined the relation between allowable discharge range and RPM by nozzle types and verified the hydrologic cycle such as the relation between infiltration rate, surface runoff and subsurface runoff at pervious area and impervious area through the rainfall-runoff experiment.

Lid 기술의 효율성 검증을 위한 강우-유출 모의장치 개발 및 검증실험에 관한 연구

This paper describes a technique for modelling of rain drop size distributions at Calcutta in terms of negative exponential function, from the measurements of rain rate and attenuation over a dual wavelength LOS link at millimeter and optical frequencies. The DSD model obtained is then used to determine the attenuation at 94 GHz, for comparison with experimentally obtained attenuation at 94 GHz. This is also compared with the attenuation calculated by considering other experimentally obtained DSD models. The best fit negative exponential distribution function (modified M-P model) is presented along with some other experimentally obtained and reference models.

Marina Dan

Papers

Modelling of Drop Size Distribution of Rain from Rain Rate and Attenuation Measurements at Millimeter and Optical Wavelengths