Radio Refractivity Research Articles

Studies on radio duct occurrence and properties

It is necessary to clarify radio duct properties in order to estimate propagation characteristics for radio system design. In this paper, radio duct properties are statistically analyzed using aerological data observed at six typical stations in Japan over seven years, and meteorological data observed near the ground by a balloon or tower. Radio refractivity gradient statistics are then compared with duct occurrence probability and fading occurrence probability. Consequently, it was possible to evaluate quantitatively a probability of duct occurrence using refractivity statistics. Certain properties of the radio duct were also quantitatively obtained.

Radio refractivity over Bay of Bengal during monsoon season from Monex-79 data

From the upper air data recorded by the Russian research vessels and the Indian ships in the Bay of Bengal during July 1979 under Monex-79 programme, the radio refractive indices (RRI) valid for surface, 850, 700 and 500 mb were calculated. The time and space variations have been discussed. The comparison of RRI values from observations at a coastal station and from a ship in the mid seas at the same latitude is interesting.

A Study of the Diurnal and Seasonal Variations of Ducting Conditions at Poona Upto a Height of 33.5M

The paper discusses the vertical gradient of refractivity from the meteorological observations available at Poona near the ground and on the tower 33.5 m. The mean gradient of dry, wet and total refractivity have been computed for each hour for the different months from the data available for the years 1948–1961. The periods at which ducting conditions occur during the day and the factors contributing towards the same have been discussed. It is observed that the dry refractivity gradient due to the temperature inversion alone does not result in ducting conditions, but the wet refractivity gradient due to the onset of sea breeze causes the same. The total gradient due to the temperature inversion and the moisture gradient result in longer duration of ducting. An attempt has been made to estimate the approximate height up to which the ducting may extend from the available data. It is found to be of the order of about 250 m which seems to be reasonable when compared with the estimates made from other considerations. The present study is an important step forward pending collection of meteorological observations at different heights with tethered balloon to study the Radio Refractivity profile.

Radio refractivity over equator and south Arabian Sea from Monex-1979 data

Surface and radiosonde observations collected by Russian ships during May and June of Monex-1979 experiment have been analysed and radio refractive indices were calculated for levels upto 500 mb. Typical vertical profiles for different location over sea and for equator have been arrived at. Tim and space variation of the Radio Refractive Index (RRI) over equator have been investigated around the time of onset of monsoon.
 
 An increase in RRI values was brought about around 18 May between 850 and 700 mb levels as observed by Russian ships in south Arabian Sea. This shows a change in moisture character of the airmass due to monsoon arrival and this hints that the influx of moisture is mainly in the mid-troposphere rather that at surface level. There does not seems to be any diurnal variations in RRI either at surface or at higher levels.

Oblique‐incidence sporadic‐E propagation and its ionospheric attenuation

This paper describes an improved method for the calculation of sporadic‐E signal strength which was mainly developed through the work of the Interim Working Party 6/8 of the CCIR. In this method, the effect of atmospheric radio refraction on the sporadic‐E propagation path and of antenna height gain are given major consideration. Empirical formulas of sporadic‐E attenuation are also presented for use in computer calculation. Finally, some examples are shown for comparing the values predicted by using this method with measured ones. This study is believed to be applicable to the lower VHF band and upper HF band (e.g., 10 to 150 MHz).

Utilisation of radiosonde data in propagation research

A computer program is presented for the calculation of the spatial distribution of radio refractivity and potential refractive modulus using data obtained from radiosonde ascents.

Diurnal Variation of Radio Refractivity over India for Altitudes upto 3 km

Path loss trials indicate a high correlation between signal strength and radio refractivity at surface and aloft. Detailed studies have therefore been carried out in temperate latitudes to estimate diurnal variations of radio-refractivity and to assess their effects on tropospheric communications and radar ranges. Similar studies could not be attempted in the tropics due to lack of upper air data. Radio-sonde ascents are made in India only twice a day and twelve hourly data are not adequate for analysis of diurnal variation. However in 1960–1961, radio-sonde ascents were arranged at six hourly intervals at New Delhi, Calcutta, Bombay and Madras in four representative months July, October, January and April. Based on these data, six hourly refractive indices from surface to about 3 km have been compiled and diurnal variations of radio refractivity analysed. In view of their importance to system engineers, diurnal variations of the effective earth's radius factor (k) and radio horizon at these four places h...

The influence of Sea breeze circulation on surface radio refractivity and tropospheric signal strength at Bombay

The influence of Sea breeze circulation on surface radio refractivity and tropospheric signal strength at Bombay

Simultaneous measurements of radio refractivity and multipath fading on 2 July 1975 at 11, 19 and 36 GHz on a 7.5 km path

A change of about 20 N-units in radio refractivity between 30 and 40 m above the ground is reported, together with simultaneous radio-propagation measurements at 11, 19 and 36 GHz. Abnoraml radio-propagation effects, e.g. divergence and multipath, are discussed, using examples from the refractivity and propagation measurements.

Radio Refractive Index Variations over Arabian Sea during MONEX 1973

During the period June 1973 to July 1973, meteorological observations using radio sondes from ships under Indo-Soviet collaboration called the MONEX (Monsoon Experiments) were conducted over Arabian Sea roughly along the latitudes 11°N and 16°N respectively. These observations were used to study the vertical distribution of radio refractive index structure up to 3 kilometers over the region during the active and the weak monsoon seasons.It is found that the super-refracting conditions are more favourable over the north-western Arabian sea during active as well as weak monsoon period.

Radio-climatology of the sea areas adjoining the Indian sub-continent

Based on the climatological data. provided by the International Indian Ocean Expedition (1959-1965), radio-climatology of the Sea areas adjoining the Indian sub-continent has, been worked out ill this paper. Monthly and seasonal mean values of radio refractivity are given for the sea level, 850 mb and 700 mb levels. Vertical gradients of radio refractivity are also presented.

Variation of surface radio-refractivity at New Delhi

Studies carried out in temperate latitudes indicate that a significant relation exists between the signal strength of microwave communication systems and the variations in surface radio refractivity (Ns). With the expansion of microwave communication and television in India, communication engineers are vitally concerned in finding the extent of Variation in Ns in the country. To this end, Ns values for four representative months have been calculated In respect of New Delhi, (Safdarjung) based on ten years monthly mean data for six synoptic hours. A comparison with corresponding Ns values at New Delhi {Palam} has also been made to bring out the Importance of proper site selection. The most significant feature of the analysis is the year round diurnal range of 20 N Units or less accompanied by a strong seasonal range of about 70 N units in surface radio-refractivity. An attempt has been made to relate these changes with climatological features and to assess their likely effect on signal strength.

A Note on the FM-CW radar as a remote probe of the pacific trade-wind inversion

A vertically pointed FM-CW radar was used to monitor the Pacific Trade-Wind Inversion in the Hawaiian Islands during the summer of 1971. An instrumented aircraft was used forin situ measurements of radio refractivity and temperature. The correspondence between the position of the radar returns and the aircraft data was excellent. The strong returns seen by the radar were due chiefly to the strong lapse of humidity across the inversion. The radar indicated that over the island of Lanai the trade-wind inversion was highly variable both in position and intensity. At times the layer would move from above 2 km to less than 1 km in the space of five minutes associated with strong mechanical turbulence. Its thickness would change rapidly from tens of meters to hundreds of meters. Wave-like structure induced by the mountains on the east side were observed by the radar. Our analysis indicates that interpretation ofin situ aircraft measurements may be greatly aided by using the FM-CW radar as a guide.

Radio climatology of Gauhati

An attempt has been made to study the pattern of radio refractivity of air over Gauhati from the surface to the 700.mb level. It is noticed that the variations in the surface values of refractivity do not reflect and are not correlated with the changes in the, ertioal profile of refractivity. Fluctuations in refractivity are not always the highest at the surface, stoadily decreasing upwards. Ideas about models of refractivity derived from studies in the temperate countries need to be modified before they can find application in tropical countries like India. The occurrence of super-refraction and S11b.refraction in the layers near the ground over Gauhati has been studied and the frequency distributions of the values of vertical gradients of refractivity have been worked out.

Anticipated Super‐Refraction Over India, Based on the Climatology of the Vertical Structure of Radio Refractivity

From the monthly average values of radiorefractivity near the ground surface and at the 850‐mb level (approximately 5000 ft above sea level), values of refractive index gradient have been computed between ground surface and 5000 ft above sea level for the 12 Indian radiosonde stations. These values of N gradients have been examined to estimate super‐refraction of radio waves in the lower troposphere over India. Maps showing isopleths of refractive index gradient over the country during different seasons are also presented.

Astronomical refraction at millimeter wavelengths

Measurements of the difference between radio and optical astronomical refraction at \lambda=8.6, 4.3, 3.1 , and 2.2 mm are described. The measurement technique utilized solar limb crossing times observed with a 16-foot radio telescope. Results show the expected dependence upon atmospheric water vapor below \lambda= 3 mm, but radio refraction tends to approach optical refraction at the shortest wavelength.

Radio Refractive Index over India and Their Climatic Classification for Microwave Propagation

The climatology of refractivity has assumed great importance due to large increase in the use of many kinds of microwave radar and communication systems. The refractivity of the air on the surface (Ns) computed from the pressure, temperature and humidity over 230 stations in India and also from over neighbouring countries and adjacent seas has been studied in this paper. Since refractivity at the surface varies with height, and cannot therefore be used to draw isogonals, the most suitable factor to reduce these values to the sea level has been obtained from the mean radiosonde data of 12 stations over India.The charts showing the surface refractivity (03 GMT) and their values reduced to sea level have been drawn for January and it is shown that with the former the isogonals followed the contour of the land, while it is very much simplified when reduced to sea level. Charts have been drawn for each month of the year showing the sea level refractivity, as also the annual mean, the highest and the lowest mon...

Variation of Radio Refractivity with Height above Ground

In Vilnius, the daily and the seasonal variations of the radio refractivity values have been computed at the Earth surface in the years 2005-2010 and at the heights up to 1.2 km in November 2010. The International Telecommunications Union - Radiocommunications Sector (ITU-R) model was used for calculation of the radio refractive index according to the peculiarities of climatic conditions of Lithuania. As a result of obtained data analysis, the days with more variable meteorological parameters have been chosen for more detailed investigation. The radio refractivity gradient has been computed at the heights starting from the Earth surface up to 1.2 km above the ground, using the meteorological data measured at those heights. The variation of radio refractivity and its gradient are influenced by the changes in air's humidity and temperature in most part. Ill. 7, bibl. 17, tabl. 1 (in English; abstracts in English and Lithuanian).http://dx.doi.org/10.5755/j01.eee.111.5.349

Radio ray refraction in the lowest three Kilometers over India – Climatological aspects

Seasonal variation of refraction at, 0,10 and 52.4 mr angles of elevation over inland and coastal stations of India has been studied. An examination has been made whether refraction could be used as 80 parameter for airmass identification for Indian stations during different seasons. Statistical regression method has been utilized to compute values of constants for predicting values of radio refraction from the surface values of radio refractive Index.

Spectral Interdependence of the Radio Refractivity and Water Vapor in the Atmosphere

Continuous measurements of temperature, water vapor, and radio refractivity were taken over several days at a height of 11 meters above ground over the high plains of Colorado. A spectral analysis indicates that temperature fluctuations contribute little to radio refractivity fluctuations, which are primarily caused by variations in water vapor density over a wide range of spectral frequencies.