Cloud Characteristics and Cloud Attenuation in Millimeter Wave and Microwave Frequency Bands for Satellite and Remote Sensing Applications over a Northern Indian Tropical Station

Microwave and millimeter wave frequency bands are in demand for requirement of more channels in radio communication systems. It has also been recognized that microwave and millimeterwave frequency radiometers on board satellites as promising tools for remote sensing.The frequency more than 10 GHz is affected by rain and cloud. Though the effects of rain on radiowave is more than cloud but the occurence of cloud is more than rain. Cloud has been found to occur for weeks together over this part of the world. It is therefore essential to study cloud morphology over different geographical region.In this paper, an attempt has been made to the cloud occurrences over an Indian tropical station, Delhi (28.35°N, 77.12°E) observed during different months and daytime and nighttime. It is seen that low clouds occurrence over Delhi is very significant and particularly during July, August and September. The specific attenuation of radiowave due to clouds at various frequencies 10 GHz, 20 GHz, 50 GHz and 100 GHz has been deduced. The specific attenuation of radio wave due to cloud at 10 GHz varies from 0.0608 dB/km to 0.1190 dB/km while at 100 GHz the specific attenuation varies from 6.8460 dB/km to 11.9810 dB/km     

Rain induced attenuation of millimeter waves radio link in Indian continent

The performance and reliability of millimeter wave radio link is degraded mainly by rain. In the present paper the aspect of rain induced attenuation with respect to raindrop is described. How the microstructure details of rain are necessary for estimating the rain induced attenuation in millimeter wave region are explained on the basis of the rain data for different stations of India.     

The main results of cloud and rain remote sensing by multichannel microwave radiometry

The basic results have been considered for multiwave remote sounding of the troposphere with clouds and rain from ground-based station in the zenith direction. The radio wave scattering by rain drops as well as variation of vapour content in the atmosphere during measurements are taken into account when processing of the experimental data. A separation of the complete attenuation in clouds with rain has been made over three components: due to vapour, cloud and rain. A relation is considered of millimeter and centimeter wave attenuation in clouds with rain between each other and with the rain intensity. A behaviour of the relation of attenuation structural functions is explained. The Diagnostic problems of millimeter wave attenuation are considered.     

Cloud Height, Cloud Temperature and Cloud Attenuation in Microwave and Millimeterwave Frequency Bands over Indian Tropical East Coast

Based on radar RHI (Range height indicator) measurements, cloud height has been deduced during the worst months (July–August) over Kolkata. Such cloud height results have been utilized to estimate cloud temperature. The attenuation of radiowave due to cloud in various probability levels has been determined in millimeter wave and microwave frequency bands. Such results on different probability levels are useful for satellite communication and remote sensing application over the aforesaid station in tropical India.     

Cloud Attenuation in Millimeter Wave and Microwave Frequencies for Satellite Applications over Equatorial Climate

A propagation experiment has been carried out at Penang using the SUPERBIRD-C satellite beacon. Cloud occurrences were observed during different months and it is seen that the low cloud occurrences over Penang is very significant from October to January. The cloud attenuation results that are presented, which include the testing of models, have been obtained from the data gathered over five years. The specific attenuation of radio wave due to clouds at various frequencies 12 GHz, 20 GHz, 75 GHz, 50 GHz and 100 GHz has been estimated whereby the values varies from 0.14 dB/km at 12 GHz to 10.1 dB/km at 100 GHz.     

Effect of cloud on atmospheric ozone formation over Hyderabad (17.27°N, 78.28°E), India

The paper presents the nature of variations of clouds and total ozone over Hyderabad (17.27°N, 78.28°E), India. The low-level cloud over Hyderabad has been noticed to occur for many days and nights, particularly in the months from June to September. The low level cloud occurrences were minimum in winter months. The effect of cloud occurrence on ozone concentration has been critically analyzed and explained. It has been observed that the concentration of ozone increased with the increase of cloud occurrence. The related possible chemical explanation for ozone production processes has been offered.     

Effect of cloud on atmospheric ozone formation over Kolkata (22°34′N, 88°24′E), India

The paper presents the nature of variations of clouds and total ozone over Kolkata (22°34′N, 88°24′E), India. The low-level cloud over Kolkata has been noticed to occur for many days and nights, particularly in the months from June to September. The low level cloud occurrences were minimum in winter months. The effect of cloud occurrence on ozone concentration has been critically analyzed and explained. It has been observed that the concentration of ozone increased with the increase of cloud occurrence. The related possible chemical explanation for ozone production processes has been offered.     

Attenuation of Centimetre, Millimetre and Sub-Millimetre Waves Due to Rain Over Tropical Indian Stations

The results on attenuation of the radio wave due to rain at frequencies lying in the centimetre, millimetre and submillimetre wave bands for different rain rates over three Indian tropical stations are presented in this paper. The study is possible due to the availability of the rainfall rates measured by rapid response rain gauges and rain height over these stations. The results on attenuation were deduced by taking both 0° C isotherm height and effective height. The Stutzman and Dishman model with -value of 0.033 which is found suitable for the estimation of rain attenuation over the Indian stations has been critically examined in comparison with the attenuations deduced from CCIR (presently known as ITU-R) method.     

A New Formula of Specific Rain Attenuation for Use in Prediction Methods

A new formula of specific rain attenuation aR ^b has been studied, the analytic expressions for a and b are regressed as function of operating frequency and polarization of microwave and millimeter wave system, which are based on the values given by International Telecommunication Union-Radio communication. The results of a and b calculated by this formula are in good agreement with that of tabulated by ITU-R for the power-law relationship of specific attenuation for rain for use in prediction methods.     

Rain Height in Relation to 0°C Isotherm Height Over Some Indian Tropical Locations and Rain Attenuation for an Indian South Coastal Station for Microwave and Millimeter Wave Communication Systems

There is a dearth of results on rain height over Indian tropical stations.The results on rain height in relation to 0°C isotherm height over four stations having different latitudes are presented in this paper. Four stations have been chosen in such a way that all have different latitudes and are located in different geographical regions having different local weather conditions. The seaonal variation of rain height in relation to 0°C isotherm height has been found to be appreciable over the station located in Indian east coast and Gujarat region, while seasonal variation is not significant at lower and intermediate probability levels over the stations located in Indian south-east coast and island. The prevailing local weather conditions over different stations also have been discussed. Based on observed rain heights and rain rates, the attenuation of radio wave at different frequencies lying in the range from 10 GHz to 150 GHz for different probability levels over Indian south-east coastal station have been deduced and presented in this paper.     

Rain induced cross polarization at millimeter waves in a Xi''an environment

The rainfall intensity accumulative distribution, raindrop size and canting angle distributions in Xi'an(108.9 E, 34.3 N) have been obtained from data measured over a long period of time. Rain induced crose polarization in this environment has been studied. The crose polarization discrimination, XPD, was compu ted over a frequency range of 19.3 to 300 GHz for non spherical drops. The variations of XPD with frequency, rainfall rate and copolar attenuation, CPA, were investigated. The computational resulte are in good agreement with experimental data. A mathematical relationship was established between the XPD and CPA, raindrop canting angle, which result is in good agreement with experimental data. The cumulative distribution of rain induced cross polarization for eleven years and in month have been ob tained with the cumulative distribution of the rain rate from the data measured from 1975 to 1985. The role of multiple scattering also has been discussed, it is shown that the multiple scattering play an important part in short millimeter wave.     

The Prediction of Rain-Induced Attenuation in MM Wave Band by Rain Medium System Model

While the millimeter radio wave propagates through rainfall, it will be attenuated heavily due to assimilation and scattering of rain. It is imperative to establish a simple and effective model to predict the rain-induced attenuation. In this paper, the rainfall is taken as a random system that can attenuate the radio wave. The transfer function matrix model is selected to be the random system model. Using experiment rain attenuation data at different rain rate, the correlation entropy and residue error of the system is obtained by system identification method. On the basis of correlation entropy and residue error, we can determine the order of the predication system. At last, the predication model that can forecast heavy rain attenuation by small rain attenuation is gotten by applying the least square method. The comparison shows that the discrepancy between the predication result of the obtained model and the experiment rain attenuation data is relatively minor.     

Temperature Effects on Attenuation Due to Rain for Millimeter and Centimeter Waves

Radio wave operating in millimetrewave and microwave frequency bands are adversely affected due to rain. Particularly the attenuation is of immense significance for sensitive remote measurements by satellites using frequencies greater than 10 GHz. Maintenance of an uninterrupted communication link requires a precise knowledge of the attenuation effect due to rain for commissioning right kind of transmitting sources for various purposes required in present day situation. Precise measurement of attenuation at various frequencies will enable us to choose the right frequency, polarization, incident angle and power of the source for different purposes. In this paper we have compared the results of earlier works using aR^b Olsen et al, (1) and the formulation by Moupfouma, (2) on the basis of theoretical analysis for explaining the observed results. Effect of temperature, considered in detail in this communication, has contributed the necessary correction factor of the rain attenuation for explaining the observed results. Theoretical analyses to measure the attenuation of the propagating wave due to temperature variation in the rain path have been presented. Correction factor due to temperature profile (temperature from the ground to the rain height within which the radio wave traces its path) has been incorporated in two models by using the concept of dipole energy changes. The effect of this temperature is noted to be quite significant and incorporates an error to the extent of 7–8%.     

Diurnal and seasonal variations in h’F and foF2 over low (Indian) and mid (Japanese) latitude stations — a comparative study

Using the simultaneous data of ionosonde from a low latitude station, Waltair, India (17.7°N,83.3°E) in the Indian sector and a mid latitude station, Kokubunji, Japan (35.7°N,139.5°E) in the Japanese sector during the high sunspot year of 2001, a comparative study of the variations in the diurnal, seasonal and day to day characteristics of the ionospheric F-region parameters, such as the virtual height of the F-layer (h’F) and the critical frequency of the F₂ layer (foF2), are studied. The effect of geomagnetic activity variations of the F-region parameters over the low and mid latitude stations is also presented.     

Measurements of cloud contribution to rain millimeter wave attenuation by using a radar and radiometers

The measurement technique of cloud contribution to rain attenuation and the equipment consisted of the coherent pulse Doppler radar at wavelength =3.2 cm, the radiometers at=0.4; 0.8 and 1.35 cm and apparatus for signal recording and processing is described. The results of such measurements are given. The Doppler spectrum of the rain backscattered radar signal was used for determination of rain drop size distribution height profile then rain attenuation was calculated and cloud attenuation was determined as the difference between the total attenuation measured by using the radiometers and rain attenuation. The results of this work gave possibility to improve the known rain model of P.Misme for prediction of rain attenuation statistics for Earth-satellite links at millimeter wave.     

Microwave and Millimeter Wave Characteristics and Attenuation of Clouds over some Malaysian Equatorial Stations

Based on radar range height indicator (RHI) measurements, cloud characteristics in relation to radiowave propagation over three locations in different geographical region in western Malaysia have been presented. It is seen that low cloud occurrence over these locations are quite significant. Cloud attenuation and noise temperature can result in serious degradation of telecommunication link performances. This paper presents cloud coverage in different months, 0°C isotherm height and cloud attenuation results at 12 GHz, 20 GHz, 36 GHz, 50 GHz, 70 GHz and 100 GHz over measurement site. The low level cloud over the measurement sites has been found to occur for many days and nights and particularly in the months of April to May and October to December. Such results are useful for satellite communication and remote sensing application in Malaysia.     

Rainfall Dynamics Over Two Indian Tropical Stations for Radio Communication

The influence of rainfall on radio wave propagation at frequencies above 10 GHz is crucial over ground to space radio links, especially in tropical regions because of the high intensity rainfall. This often makes direct-to-home; very small aperture terminal systems operating at these frequencies to be subjected to many fade occurrences due to heavy rain. In addition to annual and worst month’s cumulative statistics, dynamic characteristics of seasonal and diurnal variations, together with average event length and separation over the day are needed to give the detailed insights for system design. This paper presents the characteristics of rain distribution based on 5-year rainfall data over two locations in India. Rain intensities for the average year and the average worst months, and monthly and diurnal dynamic characteristics of rain events were obtained. The resulting rain intensities are also compared with the relevant ITU-R recommendations. These results are useful to estimate signal outages in a year over the region and for proper planning of radio-communication in the location.     

A Model for Millimeter Wave Attenuation by Atmospheric Gases in China Area

The earth's atmosphere plays an important role in microwave remote sensing and millimeter wave propagation. In this paper, we study the measurements of the attenuation due to atmospheric gases have been made in China, put forward a empirical model for the atmospheric attenuation of millimeter wave in China area.     

Rain Attenuation Ratios on Short Microwave and Millimeter Wave Bands Earth-Space Paths

The knowledge of the ratio of rain attenuation at one frequency to that at another on slant paths is useful for the design of satellite-to-Earth communication links and up-link power control systems. It is well known that the rain attenuation is influenced by parameters of precipitation along the slant path such as DSD (raindrop size distribution), raindrop temperature, rainfall rate, and so on. In this paper, based on several DSDs applied to various climate zones, at short microwave and long millimeter wave bands, the attenuation ratios are estimated on Earth-space paths. A comparison of the prediction results with the experiment data in Boston and Kashima areas is carried out. It is shown that the M-P and Weibull DSD applied to rain attenuation ratios estimation are better DSD at higher latitude regions. The Guangzhou DSD applied to rain attenuation ratios prediction is better in tropical and subtropical areas in China. The lognormal DSD may be a appropriate DSD applied to predict rain attenuation ratios in tropical areas at A_down>1dB or R>15mm/h. However, the attenuation ratios predicted by the Guangzhou DSD disagree with by the lognormal DSD, it requires that the DSD applied to predict rain attenuation ratios are further studied in tropical areas.     

Investigation into the Effect of Dielectric Loss on RF Characteristics of Helical SWS

A general theory has been developed to account for the effect of the dielectric loss of discrete rods on the performance characteristics of an actual helical slow wave structure (SWS). The effect of the lossy dielectric rods has been studied on various propagation parameters, namely, phase propagation constant, interaction impedance and attenuation constant at different operating frequency. It is clearly shown that the influence of dielectric loss on RF characteristics is much larger at the millimeter frequency band than that at the microwave frequency band, especially on interaction impedance and attenuation constant. The general theory developed here has been further confirmed by comparing the results with those obtained elsewhere for some special cases.