Rain Height Research Articles

Rain height variability in the Tropics

Most prediction methods relating to propagation in rain and other hydrometeors take into consideration the height of the melting layer in order to separate the effects of rain from ice. Here, we present the annual variability of this height, from five years' of data from the precipitation radar on board the Tropical Rainfall Measurement Mission (TRMM) satellite. The variability is derived for latitudes ranging from −30° to +30°, and compared with the corresponding freezing heights derived from the ECMWF reanalysis data. The two sets of heights show a strong variation with latitude, with the tropics showing the narrowest distribution. Their differences also show a latitude dependence, and indicate that the melting layer thickness is more variable for the subtropics. The implications are examined with reference to hydrometeor scatter interference. The recommended global standard prediction procedure for this mode of interference is evaluated using the variable distribution of the melting layer heights and their effects are examined in terms of the overall interference signal levels at 11 GHz and 30 GHz. When compared with the results using the fixed distribution specified in the current recommendation, small but significant differences at the 0.01 time percentages are observed, particularly for the 30 GHz case. The evaluation of an enhanced version of the procedure shows that significant differences can be observed even at 11 GHz, thus demonstrating the need to use a latitude-dependent rain height variability for the full evaluation of rain scatter interference levels.

A New Formula for the Prediction of the Site Diversity Improvement Factor

Site diversity is considered as an effective technique to mitigate fading due to rain in satellite communication networks. This paper reviews a site diversity prediction model incorporating the recently released ITU‐R recommendations, which provide detailed statistics for the rain rate and the rain height. The results obtained are compared against experimental data with excellent results. A new prediction model for the site diversity improvement factor is proposed.

Rain height in relation to 0�C isotherm height for satellite communication over the Indian Subcontinent

¶The 0 °C isotherm height, a parameter needed for the estimation of attenuation of microwave and millimetre wave for earth-space communication, has been estimated for different stations spread over India. The variations of 0 °C isotherm height for different seasons over these stations are presented. Attenuations of radio wave due to rain at frequencies 10 GHz and above have also been estimated for few stations using the 0 °C isotherm height so derived. The results are useful for radio systems designers.

Interference analysis applied to a double site diversity Earth‐space system: Rain height effects and simple regression‐derived formulas

Site diversity is considered to be an effective technique to overcome potential large rain fade margins in satellite communication links. In addition, because of the expected orbital and frequency congestion, the aggravation of the signal leakage from an adjacent Earth‐space system operating at the same frequency due to potential differential rain attenuation will be considered as a dominant source of interference. In this paper, an existing method to predict the differential rain attenuation statistics with respect to a double‐diversity system is properly modified after assuming a more realistic model for the rain height. Some simple regression‐derived formulas appropriate for use by the system designer and concerning both existing and proposed analysis are also presented. Further, the difference between existing results and the ones deduced from the use of the modified procedure for various availabilities and frequencies is examined, and some useful conclusions are derived.

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.

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 aRb 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%.

Oceanic Rain Column Height Derived from SSM/I

Abstract The climatology of oceanic rain column height derived from 12 years (July 1987–June 1999) of Special Sensor Microwave Imager (SSM/I) data is presented. The estimation procedure is based on a technique developed by Wilheit et al. In the annual mean, the SSM/I-derived oceanic rain height shows a maximum of about 4.7 km in the Tropics and decreases toward the high latitudes to less than 3.5 km at 50°. Interannual variations exhibit seasonal dependency and show maxima of about 200–300 m in the oceanic dry zones and in the midlatitude storm track regions. The rain heights estimated from the morning passes of the SSM/I are lower than those computed from the afternoon passes by about 60 m in the Tropics but are higher north of 40°N. This small difference cannot change the conclusion about the morning maximum in rain rate. The nonsystematic error increases with decreasing rain column height and is estimated to be about 120 m for rain heights of 4–5 km and 200 m at 3.5 km. Comparison with the height of th...

Rain height information from TRMM precipitationradar

Measurements from the precipitation radar on-board the TRMM satellite have been analysed to obtain the latitude dependence of the annual mean rain height during stratiform precipitation. The results are in good agreement with a simple set of formulas used for propagation predictions. Supporting evidence is obtained from two ground-based radars.

Effective rain height statistics for slant pathattenuation prediction in Singapore

The statistical features of effective rain height have been studied based on an analysis of radiosonde data and S-band Doppler radar and Ku-band radiometric measurements. The results from radar and radiosonde measurements are compared with the ITU-R recommendations. A discussion of the exceedence probability statistics of rain height is also presented based on a radiometric data analysis.

Melting layer studies in Singapore: Experimental results from an S-band Doppler polarisation-diversity radar

The heights of melting layer bottom and top (i.e., rain height and melting thickness) have been derived from the vertical profiles of radar parameters of S-band radar measurements in Singapore. Results have also been compared with the 0°C height measured from the radiosonde data. Aspects of height associated with peak radar reflectivity, linear depolarisation ratio and Doppler velocity in the melting layer are discussed.

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 γ -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.

Some results on 0 °C isotherm height over three stations in tropical India

Some results on rain height in relation to 0 °C isotherm height over three stations located in different geographical regions of tropical India at different latitudes are presented in this paper. The seasonal variation in rain height has been found to be appreciable over the stations located in the central plains (Nagpur) and the Kashmir region (Srinagar), while the seasonal variation is not significant over the station located on the south-west coast (Cochin). The distribution of 0 °C isotherm height over the different stations is also discussed on the basis of local weather conditions. The variation in ground temperature over Nagpur and Srinagar during the year is large, while the variation over Cochin is not significant. © 1998 John Wiley & Sons, Ltd.

Letter: A predictive analysis of differential attenuation on adjacent satellite paths including rain height effects

AbstractInterference between adjacent Earth‐space paths can be caused by propagation effects due to differential rain attenuation. In the present paper, a modification of an existing method to predict the rain differential attenuation statistics is proposed. The modified method takes into account a more complicated but realistic model for the description of the rain height. The present results are compared with the available simulation data for the differential attenuation over pairs of paths in the Montreal area. The difference between the existing predictive results and the deduced ones after use of the modified procedure, for various geographic latitudes and climatic zones, is also examined.

Rain measurement with SIR-C/X-SAR

Rain measurement is needed over many parts of the world: oceans and less-developed areas without ground-based radars and extensive rain-gauge networks. The presence of several synthetic-aperture radars (SARs) imaging the Earth suggests that these may be used to get an idea of the rainfall in the needed areas. An experiment was conducted using SIR-C/X-SAR that flew in 1994 to determine how well we can measure rain with such systems. The experiment reported here involved measurements over the southwest Pacific Ocean and the Amazon rain forest. In the former case, a method was developed to measure the rain rate using the strength of the backscatter from rain. In the latter, we used estimates of the attenuation through the rain. Backscatter methods suffer from lack of knowledge of the appropriate ZR relations. In addition, for SARs one must estimate independently the rain height and turbulent velocity. Furthermore, some method must provide information on the back-ground “clutter” from the surface. Other problems arise in dealing with attenuation through the rain cell. Here we found reasonable rain rates from 10 mm/h to 200 mm/h in convective cells over the ocean. Without correction of the C-band calibration, an unreasonable peak rain rate of 375 m/s appeared, but we believe a correction is necessary. We present results in terms of two ZR relations and both with and without correction for C-band calibration. Some discrepancies between C-band and X-band measurements remain to be explained. The attenuation method can be used where obvious rain shadows occur, as over the Amazon. Here the difference between echo in the shadow and in the unshadowed background can be used to estimate rain from the attenuation. Fewer assumptions are needed for this method than for the backscatter method, and results appear more consistent between C-band and X-band. Rates from 77 mm/h to 128 mm/h were measured in storm cells. The results show that spaceborne SARs can measure rain, but the accuracy of the measurements is unknown. Accurate absolute calibration is necessary for the backscatter method, as well as sound estimates of surface clutter, storm height, and turbulent velocities. Further study is needed, particularly for the backscatter method.

A Modified Analysis for the Prediction of Multiple-Site Diversity Performance in Earth-Space Communication Including Rain Height Effects

Site diversity is considered to be an effective technique to overcome severe rain attenuation in satellite communication links. In the present paper, a modification of an existing method to predict the improvement in using dual/triple site diversity techniques is proposed. The modified method assumes a more complicated but realistic model for the description of the rain height. The present results are compared with a representative set of available experimental data taken from operated links. The difference between the existing predictive results and the deduced ones after use of the modified procedure, for various geographic latitudes and climatic zones, is also examined.

Results of a two year radiometric measurement programme in New Zealand

Annual and cumulated two year statistics of rainfall rate, sky noise temperature and attenuation are presented, derived from two years radiometric measurements at 11.6 GHz in New Zealand. Total attenuation statistics are well predicted by both the ITU-R method and the PARC model when a rain height of ~2.3 km is used. The ITU-R's ‘K’ zone rainfall rate profile accurately represents the two year cumulative rain statistics.

A modified interference analysis between a satellite path and an adjacent terrestrial microwave system, including rain height effects

The main propagation effect on interference between a satellite system and an adjacent microwave terrestrial path is the differential rain attenuation. In the present paper, a modification of an existing method for the prediction of the differential rain attenuation is proposed. The modified model takes into account more realistic considerations for the rain height. The results of the predictive procedure are compared with the unique available set of experimental data taken from Yokosuka, Japan. The perturbation of the existing predictive results, due to the employment of the modified procedure, for various geographic latitudes and climatic zones, is finally examined.

Interference due to hydrometeor scatter on satellite communication links

A brief review of hydrometeor scatter interference is given, focusing on recent improvements to International Radio Consultative committee (CCIR) texts on interference between terrestrial and earth stations, and research to effect possible future improvements. The following improvements are suggested: smaller reflectivity factor slope above the 'rain height' coupled with a revised empirical constant in the transmission loss equations; inclusion of melting layer scatter; improved rain height model; improved horizontal structure model for precipitation cells; consideration of correlation between the wanted and unwanted signals; and consideration of a range of terrestrial elevation angles in coordination.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Prediction of rain attenuation in slant paths in equatorial areas: application of two layer rain model

The Letter reports the performance of the two layer rain model at three equatorial sites in Brazil (Belem, Manaus and Rio), for which (relatively) long term (two years for each experiment) attenuation at 12GHz and concurrent rain rate distributions have become recently available in the CCIR data bank of slant path attenuation. The prediction is excellent for Belem and Manaus, and good for Rio. The results may suggest that the CCIR rain height at latitudes around 23° is too high and that the CCIR rain zones near the equator are too coarse.

Prediction of attenuation due to rain: Characteristics of the 0°C isotherm in temperate and tropical climates

AbstractA detailed investigation of the vertical structure of rain and of the characteristics of the 0°C isotherm height in both rainy and non‐rainy conditions has been carried out in connection with the prediction of rain attenuation on Earth‐satellite links. Radiosonde data have been analysed for eight and nine locations in the southern and northern hemispheres, respectively. The temporal, latitudinal variations and the relationship between the 0°C isotherm height and ground meteorological parameters such as rainfall, temperature and relative humidity, are reported. The equivalent rain height measured along the Earth‐satellite link is compared with the heights obtained from meteorological data.