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

Evaluation of some rain attenuation prediction models for satellite communication at Ku and Ka bands

This paper presents a new propagation model for evaluating the fading of wireless communication signals in forests. The model considers rainfall and snowfall effects, and allows for the estimation of attenuation at varying frequencies in the VHF/UHF bands that are used by cognitive radios. The structure of the vegetation environment is represented here by five material layers, namely soil, scrubs and small plants under the trees, trunks of trees, foliage of trees, and free space. The model parameters are optimized using the least squares technique. The resulting model is verified by comparison with measured data where acceptable agreement is observed. The average rain rate R0.01% that will probably be exceeded for at most 0.01% of the year is computed using real measured data in Jordan. R0.01% is found to be 22.9 mm/h which agrees with the ITU recommended value of 22 mm/h.

An Optimized Five-Layer Model with Rainfall Effects for Wireless Propagation in Forests

Performance evaluation of some rain rate conversion models for microwave propagation studies

Weather, notably rain, has a negative impact on radio wave propagation between terrestrial and earthspace links at frequencies above 10 GHz. Therefore raininduced attenuation is a significant propagation impact that must be considered when designing satellite communication systems. Analysis of rain attenuation for earth-space links in three locations in Cameroon at V, Ku and Ka bands is investigated using four rain attenuation models: The ITU-R P.618 model, Svjatogor model, GarciaLopez model and Bryant model at 42.5° elevation angles. The major goal is to figure out which rain attenuation prediction models are best for satellite communication in this area. Five years (2013–2017) daily rainfall data obtained from the Tropical Rain Measuring MissionPrecipitation Radar (TRMM-PR) and Global Precipitation Measurement (GPM) mission's Core Observatory were used for this study. The results showed that the ITUR P.618, Garcia-Lopez, and Svjatogor models performed best in this region. Attenuation ranged from 15 dB to 16 at 42.5° elevation angle for time exceedance of 0.01% at Kuband in all the study locations. For the Ka-band, attenuation varied between 32 dB and 38 dB. Signal availability at Ku-band is possible based on predicted rain attenuation values for 0.01 %-time exceedance. At Ka and V-band, the predicted rain attenuation values for 0.01%- time exceedance have shown that availability of signal is impossible, which infers losses of the signal during such rainfall events across the selected locations in Cameroon

/pdf/performance-of-rain-induced-attenuation-prediction-models-2t5cxfxy.pdf

Performance of rain- induced attenuation prediction models for terrestrial link in cameroon

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.

Alytis Gruodis

Papers

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