[1] Long-term statistics of tropospheric attenuation were derived from almost 4 years of measurements made in the south of England using the ITALSAT F1 beacon signals at 49.5, 39.6, and 18.7 GHz; coincident rainfall rate measurements were made at the site of the receiving ground station. A method to remove the nonatmospheric changes of the beacon signals and to establish the reference levels from which to measure the excess and total attenuation has been presented in detail. The accuracy of fade level retrieval is estimated to be $±0.5 dB. A new method for predicting the annual total attenuation statistics has been proposed and validated against our data and data collected in Italy at 18.7, 39.6, and 49.5 GHz. For both locations, the new proposed method gives much better predictions compared with the established International Telecommunication Union recommendation method. A significant monthly and seasonal variation was observed in the attenuation and rainfall statistics and should be taken into consideration when planning the design and use of future slant path systems. We have seen that the attenuation statistics are subject to diurnal variations; however, for the period analyzed, this variation does not seem to follow a particular pattern.Citation: Ventouras, S., and C. L. Wrench (2006), Long-term statistics of tropospheric attenuation from the Ka/U band ITALSAT satellite experiment in the United Kingdom, Radio Sci., 41, RS2007,
The main propagation effect on interference between adjacent Earth‐space paths is differential rain attenuation. In the present paper, a revised method to predict the rain differential attenuation statistics is proposed which is based on a model convective rain cell structure of the rainfall medium and the assumption that the point rainfall statistics follows a lognormal form. Moreover, the revised model analyzes the general problem of differential attenuation taking into account the difference of elevation angles of the slant paths under consideration. The numerical results are referred to the interference problem from an adjacent satellite located in symmetrical geostationary positions in relation to the intended satellite and examine the significance of the difference of elevation angles for various parameters of the problem.
[1] Earth-space radio systems operating at frequencies of 10 GHz and above are badly attenuated by rain, cloud, and atmospheric gases. As the frequencies of operational systems increase, it becomes increasingly uneconomic to compensate for the effects of fading through the use of a fixed fade margin, hence the implementation of fade mitigation techniques (FMT). The spatial and temporal variation of rain provides the justification for the use of site diversity as an FMT. Site diversity employs two or more ground stations receiving the same satellite signal with a separation distance such that the sites encounter intense rainfall at different times, and switching to the site experiencing the least fading improves system performance considerably. Measurements of the 20.7 GHz beacon carried as part of the Global Broadcast Service (GBS) payload on the U.S. Department of Defense satellite UFO-9 have been made at three sites: two are located in the South of England ($8 km apart), and the third receiver was located in Scotland. These beacon measurements have produced long term attenuation exceedance and site diversity gain and improvement statistics. This attenuation time series data can simulate the performance of an Earth-space system using site diversity, indicating the optimum method of implementing this FMT. In this paper, unbalanced site diversity is investigated, as this is a more likely scenario than the balanced site diversity modeled by the ITU-R recommendations. This paper also investigates the implementation of site diversity from a commercial context, including costbenefit analysis and technical feasibility.
ESPAS, the "Near-Earth space data infrastructure for e-science" is a data e-infrastructure facilitating discovery and access to observations, ground-based and space borne, and to model predictions of the near-Earth space environment, a region extending from the Earth's atmosphere up to the outer radiation belts. ESPAS provides access to metadata and/or data from an extended network of data providers distributed globally. The interoperability of the heterogeneous data collections is achieved with the adoption and adaption of the ESPAS data model which is built entirely on ISO 19100 series geographic information standards. The ESPAS data portal manages a vocabulary of Space Physics keywords that can be used to narrow down data searches to observations of specific physical content. Such contenttargeted search is an ESPAS innovation provided in addition to the commonly practiced data selection by time, location, and instrument. The article presents an overview of the architectural design of the ESPAS system, of its data model and ontology, and of interoperable services that allow the discovery, access and download of registered data. Emphasis is given to the standardization, and expandability concepts which represent also the main elements that support the building of long-term sustainability activities of the ESPAS einfrastructure.
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