Yearly, Seasonal and Daily Variations of Radio Refractivity

Abstract

Yearly, seasonal and daily variations of radio refractivity have been analyzed. The method proposed in the recommendation of International Telecommunication Union ITU has been used. The local meteorological data have been used in calculation of radio refractivity. The highest values of the radio refractivity have been observed in Klaipėda (in Seacoast) in the year 2009. In July, the values of the radio refractivity were highest in all localities investigated here and over all the time of the day in the year 2009. In the continental part of Lithuania (in Vilnius and Kaunas), analysis of radio refractivity has been made by using the meteorological data of longer period (starting from April 2005 up to July 2010). Five-year meteorological data collected in February, April, July and October have been used. It was obtained that the values of refractivity in the year 2010 are much higher than ones obtained in all the years of the period investigated here.

Tropospheric effects on L‐band geosynchronous circular SAR imaging

“…Using the reanalysis datasets of NCEP/NCAR (National Centers for Environmental Prediction/ National Center for Atmospheric Research) that can be downloaded free on the website, the meteorological parameters can be obtained and the refractivity can be calculated. The statistical data indicates that the diurnal variation of the refractivity is obvious and periodic [24, 25]. The temperature is the lowest before sunrise and the humidity is high; after sunrise, the air is heated by the Sun, the temperature increases, and the humidity reaches the minimum at about 14:00 p.m.…”

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“…The variations in the vertical profiles of the refractive index and its gradients are responsible for the changes in the trajectory of radio waves in the troposphere. It was noted that occurrence of anomalous propagation is due to deviation of the vertical gradient of refractive index when atmospheric temperature and humidity distributions deviate from the normal / standard radio atmospheric conditions [11,12].…”

“…How far a radio signal will travel within the radio horizon is determined by the distribution of the radio refractivity [16]. Several researchers like Žilinskas et al [12]; Adediji et al [16]; Akpootu and Iliyasu [17]; Agbo [18]; Ayantunji et al [19]; Emmanuel et al [20]; Luhunga et al [21] and Ajileye [22] have carried out studies on radio refractivity for different regions and climates using measured local meteorological data in Nigeria and other parts of the world. The results of their study showed that the local climate has a substantial influence on the radio refractivity and consequently on the transmitted radio signals.…”

Determination of areas for surface refractivity variation analysis over Quebec

“…The knowledge of refractivity variation is important because this variation gives rise to the refraction of radio waves during their propagation through a stratified atmosphere. Such refraction can lead to a significant variation in received power level at the receiver (Ali et al, 2012) (Zilinskas et al, 2012). To obtain reliable communication links, several criteria, such as antenna heights and gains, power levels, path profile, distance, geographical location, atmospheric conditions and properties, etc., must be considered in the design/planning phase.…”