Rain attenuation measurements over New Delhi with a microwave radiometer at 11 GHz

Rain attenuation measurements over New Delhi carried out with a microwave radiometer installed at the National Physical Laboratory (NPL), New Delhi and operating on 11 GHz for a period of more than three years are presented. For 0.01 percent of time for the period June 1977-April 1978, the attenuation exceeded for the monsoon period is 14.0 dB whereas for the whole year, it exceeds 10.4 dB. During the winter for the same percentage of time, the attenuation exceeded 1.5 dB, whereas for March-April it exceeds 0.5 dB. For the period May 1978-June 1980, it is observed that for 0.01 percent of time the attenuation for the whole year exceeds 9.0 dB. During the winter for the same percentage of time, the attenuation exceeds 1.4 dB whereas for March-April it exceeds 0.4 dB. A comparison of attenuation over New Delhi and those reported elsewhere are discussed. Yearly and worst month time ratio over New Delhi are given also as the values reported for the European region. Comparison of the attenuation distribution and the rate of surface rainfall measured with a rapid-response rain gauge are also given. The comparison shows that for the monsoon period and for 0.01 percent of time, the attenuation value exceeded for 14 dB corresponds to the surface rainfall rate of 140 mm/h. For the monsoon of 1978, 1979, comparison shows that for 0.1 percent of time, the attenuation value exceeded for 9.0 dB corresponds to the surface rainfall rate of 90 mm/h. Variation of attenuation and effective path length for various rainfall rates and elevation angles are also given.     

Attenuation/rain-rate relationships on terrestrial microwave links in the frequency range 10?40 GHz

Attenuations of radio transmissions at 10.7, 19.4 and 36.05 GHz by rain on a 7.5 km path have been compared on a statistical basis with attenuations derived from rainfall rates, measured simultaneously along the path, using the empirical relationship ? = ?R?, where ? is the attenuation coefficient in dB km?1, R is the rainfall rate in mm h?1 and ? and ? are parameters dependent on polarisation and frequency.     

Modified rain attenuation model for tropical regions for Ku‐Band signals

Attenuation measurement on Ku‐ band satellite signal in a tropical site, Fiji is presented. Rain‐attenuation prediction by ITU‐R and the Crane Global models showed noticeable deviation to the measured values. Unlike the monotonic decrease predicted by these models, exceedance of rain‐rate and attenuation in Fiji and other tropical regions showed the presence of breakpoints. For Suva, the breakpoint in rain‐rate and attenuation were at 58 mm/h and 9.4 dB with exceedances of 0.009 and 0.018%, respectively. Modifications to the ITU‐R model are proposed in this paper, for adopting it in the tropics. These modifications are based on the properties that in the tropics (i) the accumulation time factor at the breakpoints is an invariant (ii) for elevation angles <60° and at high rain rates multiple rain cells intersect the slant path. The attenuation exceedance is predicted by two expressions similar to the ITU‐R model, one for rain‐rates lower than the breakpoint rain‐rate and the other above it. The modified prediction model show remarkable agreement with the measured Ku‐band attenuation in seven tropical sites. Copyright © 2006 John Wiley & Sons, Ltd.     

Rain attenuation at 15 and 35 GHz

In order to satisfy future earth-to-space communications needs, new regions of the electromagnetic spectrum must be exploited. A program to determine the feasibility of using millimeter waves for this application has been conducted at Air Force Cambridge Research Laboratories (AFCRL) for approximately 6 years and it has been shown that at frequencies of 15 GHz (lambda = 2.0cm) and 35 GHz (lambda = 8.6mm) atmospheric attenuation is relatively low except for conditions of heavy clouds and precipitation. A portable radiometric system designed to measure attenuation at 15 and 35 GHz under conditions of precipitation was constructed and located in Hilo, Hawaii, a region where it rains frequently thus making it possible to conduct many attenuation measurements for varying rainfall rates. Attenuation was determined from both extinction and emission measurements as a function of zenith angle and rain rate. On the basis of the results that were obtained, it is concluded that for orographic rain up to rates of 50 mm/h in Hawaii: 1) attenuations up to approximately 10 dB can be calculated quite accurately from an emission measurement; 2) zenith attenuations are well correlated with rain rate and can be estimated from the regression lines which have been obtained; 3) attenuations at angles off zenith are not as well correlated with rain rate and thus the values obtained from the regression lines are only approximate; 4) attenuations at 15 and 35 GHz are well correlated.     

Effect of Atmospheric Parameters on Satellite Link

The rainfall path attenuation measured at Universiti Sains Malaysia (USM) for 4 years (January 02 to January 06) is presented. The data obtained are useful to investigate the impairment due to rainfall attenuation in satellite links operating in tropical and equatorial climates. It shows that the logarithmic function with ground rain rate deviates at very high rain rate. A rainfall rate of 130 mm/h causes the rainfall attenuation threshold (> 20 dB) to be exceeded. Maximum exceedences for rain rate and attenuation were observed during the wet months. The cumulative distributions of attenuation derived from the measured data are presented and compared with those obtained with existing prediction methods.     

Attenuation in melting snow on microwave- and millimetre-wave terrestrial radio links

The scattering properties of melting snow on microwave and millimetre-wave terrestrial radio links are predicted using a new model for melting which includes coalescence. Attenuation, differential attenuation and differential phase are calculated for a horizontal path, with results at 36.25 GHz presented. Peak specific attenuation in the range 8?13 dB/km is expected for underspread rain with 10?15 mm/h rain rates.     

Measurements of rainfall attenuation at 8 and 15 GHz

Measurements of attenuation at frequencies of 8 and 15 GHz, and their correlation with rainfall rate, along a 15.78 km path near Ottawa, are described. Empirical expressions which relate the observed attenuation to the measured rainfall rate are derived and compared with similar expressions obtained on the basis of earlier theoretical studies of the problem. It is concluded that while the theoretical predictions of attenuation in rain are reasonably satisfactory, at least for rains observed at Ottawa, there is a definite tendency for observed attenuations at low rainfall rates to be somewhat higher than the expected values. The cumulative distribution of rainfall attenuation over a six-month period is compared with the attenuation predicted on the basis of average rainfall data obtained during the last five years. Although the agreement between observation and prediction, using the theoretical relation between rainfall rate and attenuation, is good for path attenuations greater than 2 dB, it can be greatly improved if the empirical expression relating rainfall rate to attenuation is used.     

Measurement of rain-induced zenith-path attenuation using 19.9 GHz radiometer at Amritsar (India)

The paper presents the results of 19.9 GHz radiometric propagation studies conducted over a period of one year at Amritsar, for determining rain-induced zenith path attenuation. The zenith path attenuation has been determined by the measurements of sky noise temperature received by the radiometer. The results obtained from the experiment are presented in the form of annual cumulative distributions of rain rate, sky noise temperature, and zenith path attenuation together with worst-month statistics. The rainfall rate cumulative distribution as predicted by ITU-R for our geographical location is lower than the actually measured rainfall rate cumulative distribution. The cumulative distribution of zenith path attenuation predicted by using ITU-R model overestimates the measured cumulative distribution of zenith path attenuation.     

雨衰减的解析近似

本文对Ｌａｗｓ－Ｐａｒｓｏｎｓ和广州雨滴尺寸分布雨衰减和降雨经之间的指数关系中的ａ和ｂ值＾「１」「２」进行了分析和解析回归，给出其与频率的解析近似关系，利用其计算的雨衰减和数值计算结果有很好的一致性。     

Rain-induced attenuation for Ku-band satellite communications in the west coast of Peninsular Malaysia, Penang

Accurate rainfall rate is important for predicting rain attenuation over a satellite link. Raindrops are able to take in, spread out, and change the polarization of satellite signals that pass through the atmosphere of the earth, especially in equatorial regions like Malaysia where heavy rainfall normally occurs. Satellite communications system network operating at Ku-Band will experience rain fade due to absorption and scattering of signal. This paper aims to discuss the range of effects of rain on the transmission of electromagnetic signal and to determine the significance of rainfall rate in the prediction of rain attenuation based on measurements carried out in the northern region of Peninsular Malaysia (Penang). At 0.01% of time, 140?mm/h and 22?dB of rain rate and attenuation were observed, respectively.     

Frequency dependence of rain attenuation measurements at microwave frequencies

The values of attenuation versus frequency for 10 mm/h, 25 mm/h, and 40 mm/h rain rates for frequencies of 11, 18, and 22.2 GHz are presented. On the basis of these observations the attenuation at frequencies below 10 GHz and above 22.2 GHz have been obtained. The values obtained at various frequencies show an agreement with those calculated on the basis of Oguchi's work. Comparison of the above values in dB/km (assuming a path length of 2.5 km) have been made and they show an agreement with International Radio Consultative Committee (CCIR) values. Also cumulative distributions of attenuation at various frequencies have been given taking 11 GHz results as the reference point.     

Rain fades on low elevation angle Earth-satellite paths:comparative assessment of the Austin, Texas, 11.2 GHz experiment

Only a few years of rain attenuation data for Earth-space paths are available for low elevation angle paths, and these show a consistent tendency by the CCIR fade prediction model to underpredict rain fades. The authors contribute to the database four years of 11.2 GHz measurements, taken on a 5.8° elevation path in Austin, Texas, USA and assess higher than predicted fade results with respect to earlier measurements and the CCIR model. At the fiducial 0.01 percent of time, the rain fall rate was 73 mm/h and the attenuation exceeded the 25 dB measurement fade margin. It is found that the monthly variability of rain fall rates and decibel fades follows a normal distribution. Durations of rainfall and fades are classified into events, episodes, interevent gaps (longer than 4.2 h), and interepisode gaps (shorter than 4.2 h). Rainfall interevent gaps and event durations, as well as fade event, episode, and gap durations are log-normally distributed     

A two-year measurement of rainfall attenuation of CW microwaves inSingapore

The authors present two-year statistics on the rainfall attenuation of 21.225 GHz vertically polarized CW microwave signals in Singapore. The CCIR recommendation is found to underestimate the microwave specific attenuation (dB/km) per path average rain rate (mm/h) as well as the accumulated time of attenuation exceeding preset levels. A negative exponential raindrop size distribution based on spherical droplets is constructed from the measured data     

Melting layer attenuation at 28.6 GHz from simultaneous comstar beacon and polarisation diversity radar data

Attenuation data at 28.6 GHz obtained from measurements of the Comstar beacon show that, for moderate rain, slant path attenuation may significantly exceed that calculated from simultaneous radar reflectivity measurements. Polarisation diversity radar data were used for positive identification of the rain and the melting layer, and for estimating the rain attenuation along the path. These results indicate that the melting layer attenuation is significant.     

Propagation observations at 3.2 millimeters

A millimeter-wave system for the transmission and reception of television signals has been constructed. The propagation path is 450 meters above sea level at the transmitter and traverses an 18.95-km path to the receiver, which is at an elevation of 39 meters atop a two-story building in El Segundo, Calif. The elevation angle is 1.17 degrees when corrected for curvature and refraction. Received picture quality and tropospheric scintillation and attenuation for various weather conditions are discussed. Tropospheric attenuation ranged from about 13 dB on a typical day to approximately 36 dB when moderate rainfall (∼4 mm/hr) occurred over much of the 18.95-km path. Tropospheric turbulence effects were almost nonexistent on days of heavy fog but reached peak-to-peak magnitudes of 20 dB or more in received signal fluctuations on dry, windy days. High quality television and voice reception were obtained over this link even during light to moderate rainfall periods (∼3 mm/hr). A transmitter output of approximately 100 mW, 0.61-m parabolas at each end of the link, and a receiver noise figure of 25 dB were the main system characteristics. Tropospheric attenuation measurements are in close agreement with values calculated from modified versions of the Van Vleck expressions for attenuation due to oxygen and water vapor. The average of measured tropospheric attenuation rates was approximately 0.7 dB/km for July 1965.     

Rainfall attenuation at 36 GHz and 55 GHz

Simultaneous rainfall measurements at 36 GHz and 55 GHz on a common 4.1 km path show, under the conditions of these experiments, that the attenuation due to rainfall lies between the attenuation values predicted by the lognormal and the Best rain drop size distributions.     

Microwave attenuation at 35.8 GHz due to rainfall

A short double-pass microwave link at 35.8 GHz has been used, with four rapid-response rain gauges, to measure excess attenuation from rain as a function of mean rainfall rate along the path. The results are in good agreement with theoretical predictions.     

The influence of heavy rainfall on attenuation at 18.5 and 30.9 GHz

Percent-of-time distributions of rain-induced fades obtained on a 6.4-km path in New Jersey operating at a frequency of 18.5 GHz are discussed for the period of 1968-1969; data obtained at 30.9 GHz on a 1.9-km path for the same period are also discussed. The attenuation distributions are compared with attenuations calculated from the distributions of average rain rates on the paths. With these data, it is found that distributions of attenuation can be predicted from the path-average rain-rate distributions for a given sample period. Detailed rain-rate and attenuation measurements at 18.5 GHz on the 6.4-km path are presented for the most intense storm observed in a three year recording period. Point rain rates in excess of 250 mm/h and path-average rates exceeding 180 mm/h were observed; the attenuation exceeded the 50-dB dynamic measuring range of the equipment for more than seven minutes.     

Absorption and scintillation effects at 3 mm wavelength on a short line-of-sight radio link

Measurements on a path 150m long, with narrow-beam transmitting and receiving antennas 2m above the ground at one end of the path, and a reflecting plate at the other end, at the same height, have shown attenuation in rain to be about 17dB/km and 8dB/km for rainfall rates of 48mm/h and 7mm/h, respectively. Amplitude variations of up to ±0.4dB can occur in a time interval of the order of 1s during sunny, humid conditions in summer.     

Performance Estimation for 15-GHz Microwave Links as a Function of Rain Attenuation

In this concise paper we present a method to estimate the performance of wide-band 15-GHz microwave line-of-sight communication links as a function of precipitation statistics, given specific fade margins derived from equipment and path parameters. The method is based on the use of theoretical or measured rain attenuation rates, statistics of surface point rainfall rates, and relations between point and path-average rainfall rates derived from measurements in Florida. Results in terms of total path attenuation or maximum usable path lengths for given performance criteria can vary widely depending on the data base used; they are particularly sensitive to the attenuation rate model used and to the rain climate. As a practical matter, the analysis shows that path lengths up to about 30 km for line-line-of-sight links (with adequate terrain clearance) may be usable in climates characterized by moderate rainfall amounts (such as central Europe) even if relatively pessimistic assumptions are made regarding rain attenuation rates.