ISSN:0048-6604    

DOI:10.1029/RS017i006p01347

年代:1982

数据来源: WILEY

摘要:

This paper summarizes annual and cumulative attenuation data, depolarization data, and associated local rain rate distributions obtained with the COMSTAR family of 19.04‐ and 28.56‐GHz satellite beacons during the years 1977–1981. It discusses the relationships between attenuation and rain rate and between attenuation and depolarization, compares measured data on the joint distribution of attenuation and depolarization, and examines the limitations that propagation effects will impose on future 20/30‐GHz satellite communications

ISSN:0048-6604    

DOI:10.1029/RS017i006p01349

年代:1982

数据来源: WILEY

摘要:

The Dutton‐Dougherty (DD) model for predicting microwave attenuation distribution on an annual basis on earth‐space telecommunications links was first developed at the Institute for Telecommunication Sciences in 1973. The version for making predictions throughout the United States, with year‐to‐year variability allowance, was developed in 1977 and had been essentially unmodified until the present improvement efforts were undertaken. The refinements of the Dutton‐Dougherty model discussed in this paper include an extension of the attenuation distribution prediction range to 0.001% of a year, whereas it had previously extended only to 0.01% of a year. This extension is accomplished in two alternative ways: empirically and analytically. Both extension procedures give nearly identical prediction results. An analysis is conducted of the pertinency of ‘effective path length’ models for evaluating rain attenuation at microwave frequencies to the DD model. It is determined that whereas effective path length methodologies may be useful in their own right, it would be difficult and unwieldy to incorporate this concept into the DD mode

ISSN:0048-6604    

DOI:10.1029/RS017i006p01360

年代:1982

数据来源: WILEY

摘要:

A new model is presented for the calculation of the probability of exceeding specified attenuation values due to rain on single earth‐satellite or terrestrial propagation paths. The model was formulated to explore a prediction procedure that differs significantly from most of the accepted models for attenuation prediction but holds considerable promise for extension to modeling the joint statistics required for space diversity system design, the statistics of interference due to rain scatter at attenuating frequencies, and the duration statistics for attenuation events. The new procedure calculates the probability of occurrence of a convective (volume) cell or widespread debris which could cause the specified value of attenuation. The performance of the new model was evaluated by comparison with observed attenuation statistics and by comparison with the performance of the recently adopted International Radio Consultative Committee (CCIR) model and the earlier global model. The results of the comparison show that the new, two‐component model performs as well as the other models for prediction on earth‐satellite paths. It is the promise of the application of the new model to the unsolved problems of diversity improvement and interference prediction, however, that justifies the consideration of yet another

ISSN:0048-6604    

DOI:10.1029/RS017i006p01371

年代:1982

数据来源: WILEY

摘要:

The context and role of the CCIR is briefly summarized. The recent advances in CCIR Study Group 5 texts, relevant for earth‐space systems, are engineering models of propagational effects. They are briefly described, identifying their associated recommendations and reports and specifying the additional experimental data and theoretical studies require

ISSN:0048-6604    

DOI:10.1029/RS017i006p01389

年代:1982

数据来源: WILEY

摘要:

An empirical model has been generated to estimate diversity gain on earth‐space propagation paths as a function of earth terminal separation distance, link frequency, elevation angle, and angle between the baseline and the path azimuth. This analysis utilized 34 diversity experiments which have been conducted in Canada, England, Japan, and the United States during the past decade. The resulting model reproduces the entire experimental data set with an rms error of 0.73 dB. The separation distance dominates the dependence of the diversity gain. The dependence on link frequency is small but significant. No identifiable dependence on baseline orientation was foun

ISSN:0048-6604    

DOI:10.1029/RS017i006p01393

年代:1982

数据来源: WILEY

摘要:

Both single‐terminal and two‐terminal joint probability rain fade distributions for earth‐satellite paths at 28.56 GHz are derived for Wallops Island, Virginia, by using radar modeling techniques. An array of parallel paths is modeled in the vertical plane which contained the COMSTAR satellite and a terminal receiving the 28.56 GHz COMSTAR beacon. The paths are displaced 1 km apart (8–100 km from the radar) at a fixed elevation angle (θ0= 45°). They pass through the volume whose rain environment has been monitored as radar rain reflectivity levels and stored on magnetic tape. An attenuation at 28.56 GHz and a ground rain rate level is calculated for each path and for each radar scan. Both single and joint terminal conditional fade statistics are derived for an ensemble of such arrays, where the conditioning constant is the long‐term rain rate distribution. The single and joint terminal distributions are calculated by multiplying the conditional fade statistics by the measured long‐term rain rate distribution. As a partial check, the radar‐derived single‐terminal fade distribution at Wallops Island is compared with the directly measured levels obtained over a 3‐year period showing very good agreement. A family of diversity gain curves is calculated from the joint probability distributions corresponding to different probability levels. These are demonstrated to be represented by a single diversity gain function defined as the ‘relative diversity gain.’ The radar‐derived relative diversity gain is compared with those obtained from other investigations as well as with derived autocorrelation function resul

ISSN:0048-6604    

DOI:10.1029/RS017i006p01400

年代:1982

数据来源: WILEY

摘要:

Deep‐space missions and radio navigation satellite operations place high requirements upon the precision of range and Doppler frequency measurements and may be sensitive to even small increases in radio noise. For paths to geostationary satellites and beyond, the excess range delay due to the ionosphere and plasmasphere is proportional to the total electron content along the path and inversely proportional to frequency squared. The delay for a one‐way path is about 8 m for a total electron content of 1018el/m2at a frequency of 2.2 GHz. The one‐way excess range delay due to the dry air of the troposphere on earth‐satellite paths is typically of the order of a few meters and is dependent only on surface pressure for a given elevation angle. The delay due to water vapor, a few tens of centimeters, is responsible for most of the temporal variation in the range delay for clear air. In the navigation of Voyager spacecraft, where two‐way range measurements are made, range is determined with a precision of better than 3 m by the National Aeronautics and Space Administration/Jet Propulsion Laboratory Deep Space Network, made up of stations in Goldstone, California, Madrid, Spain, and Canberra, Australia. System noise temperatures for the Deep Space Network are typically 20–30 K. For such low‐noise systems and for attenuation values up to about 10 dB, the increase in sky noise due to rain and clouds degrades the received signal‐to‐noise ratio more than does the reduction in signal level due to attenuation. Clouds as well as rain contribute significantly to attenuation and sky noise, especially for frequencies greater than 10 GHz. Doppler frequency fluctuations due to the interplanetary plasma can be reduced by using higher frequencies (XorKband rather thanSband, for example), but scintillation of tropospheric origin may then become the principal factor limiting the ability to detect gr

ISSN:0048-6604    

DOI:10.1029/RS017i006p01411

年代:1982

数据来源: WILEY

摘要:

At millimeter wave frequencies the scattering cross section of raindrops becomes comparable to the absorption cross section, and incoherent intensity due to multiple scattering may become significant. This paper presents calculations of the incoherent intensity at 30, 60, 90, and 120 GHz. The scattering and absorption characteristics of the rain are calculated using the Mie solution and the Laws‐Parsons distribution. Incoherent intensities for the horizontal and vertical polarizations are obtained using the equation of transfer and the Stokes parameters. The obliquely incident wave is linearly polarized. The equation of transfer is solved by using the Gauss quadrature formula and the matrix eigenvalue technique. The matrix elements are calculated using the formulations developed by Sekera, and the vertical and horizontal components and their correlations are used in the Stokes parameter representations. The received incoherent intensity depends on the field of view of the receiving antenna. The ratio of the copolarized incoherent intensity to the copolarized coherent intensity is defined as the incoherent copolarized discrimination I‐CPD, and the ratio of the cross‐polarized incoherent intensity to the copolarized coherent intensity is defined as the incoherent cross‐polarized discrimination I‐XPD. These are computed in terms of rain rate, field of view, and copolarized attenuation. It is shown that multiple scattering effects may become significant during heavy rains. Backscattering results are also

ISSN:0048-6604    

DOI:10.1029/RS017i006p01425

年代:1982

数据来源: WILEY

摘要:

Satellite‐to‐earth rain attenuation at 11.7 GHz was measured at Waltham, Massachusetts (42.4°N, 71.3°W; elevation angle 24°), utilizing the Communications Technology Satellite (CTS) beacon signal. This paper summarizes 29 months of measurements by presenting attenuation and rain rate distributions, fade duration distributions, fading rate distributions, and statistical relationships between attenuation and rain rate. For a two‐year statistical base, rain attenuation exceeded 9.7 dB for 0.01% of the time and 2.0 dB for 0.1% of

ISSN:0048-6604    

DOI:10.1029/RS017i006p01435

年代:1982

数据来源: WILEY