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MultiEXCELL, a new rainfall model oriented to the analysis of radio propagation impairments which was developed on the basis of a comprehensive rain field database collected by the weather radar sited in Spino d’Adda (Italy), is presented. Single rain cells are modeled by an analytical exponential profile which best represents real single-peaked rain structures. The rain cells’ probability of occurrence is analytically derived from the local rainfall statistics. The spatial features of the rain field at mid- and large-scale are investigated through their natural aggregative process. The clusters (aggregates) of cells are studied in terms of distance between individual cells, of number of cells per aggregate and of distance between aggregates. Finally, the fractional area covered by rain, which the rainfall spatial correlation strongly depends on, is derived from radar data through the comparison with the same quantity provided by global long-term numerical weather products. The MultiEXCELL procedure for the generation of spatially correlated synthetic rain fields is duly presented and the model’s accurateness is preliminary assessed against the available radar dataset. Although MultiEXCELL is mainly oriented to propagation related applications, its cellular approach may reveal useful also in hydrology, for the prediction/management of water resources, and in meteorology, for the nowcasting of the temporal evolution of rain structures

The Mediterranean region is frequently struck by severe rainfall events causing numerous casualties and several million euros of damages every year. Thus, improving the forecast accuracy is a fundamental goal to limit social and economic damages. Numerical Weather Prediction (NWP) models are currently able to produce forecasts at the km scale grid spacing but unreliable surface information and a poor knowledge of the initial state of the atmosphere may produce inaccurate simulations of weather phenomena. The STEAM (SaTellite Earth observation for Atmospheric Modelling) project aims to investigate whether Sentinel satellites constellation weather observation data, in combination with Global Navigation Satellite System (GNSS) observations, can be used to better understand and predict with a higher spatio-temporal resolution the atmospheric phenomena resulting in severe weather events. Two heavy rainfall events that occurred in Italy in the autumn of 2017 are studied—a localized and short-lived event and a long-lived one. By assimilating a wide range of Sentinel and GNSS observations in a state-of-the-art NWP model, it is found that the forecasts benefit the most when the model is provided with information on the wind field and/or the water vapor content.

INTRODUCTIONCurrent high-throughput satellite (HTS) systems for broadbanddistributed user access are designed following two main concepts: C The use of Ka band radio frequency (RF) links both for the forward and for the return link; this choice is due to the congestion of lower frequency bands and to the relatively large bandwidth available in the Ka band. Moreover, the RF technology in the Ka band is mature [1], [2].C The use of multispot coverage: this technique is largely applied to increase the system throughput through frequency reuse and system reconfigurability [2], [3].HTS systems are dimensioned to support an aggregated total capacity (considering both forward and return links) of a tenth of a gigabit per second over a coverage area as large as Europe, with a single spot capacity of hundreds of megabits per second [3].As a matter of fact, HTSs still offer much less bandwidth per user with respect to the terrestrial broadband networks. To achieve very high throughput towards "terabit connectivity," bandwidth efficient modulation schemes have to be used [4], [5]. However, because there is a trade-off between bandwidth efficiency and power efficiency in modulation schemes, high bandwidth efficiency requires more transmission power that is a limited resource in satellite systems.Therefore, an important breakthrough is needed in terms of bandwidth availability. The Q/V band (40-50 GHz) seems to offer very promising perspectives, being unused for commercial systems and offering a large part of the spectrum allocated for satellite services [1]. In this frame, the medium-term HTS system architecture is based on the use of a Ka-band user link to maintain the user terminal compatibility with the current system and a Q/V band feeder link [4]- [7].This solution is particularly attractive for the following reasons:C The Q/V band spectrum allocated for fixed satellite service is very large, about 5 GHz of near-continuous bandwidth both for uplink and downlink.C The whole Ka-band spectrum (that is currently allocated both for feeder and user links of the HTS systems) will be available for user link, increasing the bandwidth allocated to the user segment. This will require a rethinking of International Telecommunication Union frequency allocation and a strong frequency coordination activity.It is well-known that the atmospheric propagation impairments at extremely high frequency (EHF) bands (30-300 GHz) are severe, not only when rain events occur but also in the presence of clouds. The EHF electromagnetic radiation that propagates through the atmosphere is subject to absorption, scattering, depolarization, and fast fluctuations of amplitude and phase (scintillation) that have to be carefully investigated. Moreover, some mitigation techniques have to be analyzed and properly tuned to realize an efficient transmission. To counteract rain fading effects, high static link margins can be considered to ensure a minimum service outage duration. However, setting large link margins is in contrast with technology limitations of s...

A large database of radiosoundings, brightness temperatures, and satellite beacon data was used to verify the ability of radiometers in estimating the attenuation in nonprecipitating conditions at millimeter wavelengths. The mass absorption models proposed by Liebe and Rosenkranz have been used coupled with the Helsinki University of Technology (TKK) cloud-detection model to derive coefficients for the calculation of the attenuation due to integrated water vapor and liquid water contents. Comparison of predicted and measured attenuation cumulative distribution functions in the 20-50-GHz band confirms radiometers as a unique tool for retrieving attenuation in nonrainy condition and shows the very good performance of the TKK model for propagation applications.

This contribution investigates rain attenuation in Kuala Lumpur, Malaysia, by exploiting local Drop Size Distribution (DSD) measurements. Coefficients for the well- established power law model relating rain rate and specific attenuation are derived for frequencies in the Ku, Ka and Q/V bands based on three years of disdrometer data. We analyze the diurnal variation of rainfall rate for four time intervals, and, moreover, we present statistics of rain attenuation for slant path Earth-space links estimated by means of a new model (Stratiform-Convective SST) which combines the advantages of the Dual-Layer Synthetic Storm Technique (SST) and of the SC EXCELL model. The predicted statistics are in good agreement with those obtained from beacon measurements (MEASAT-1 satellite at 12 GHz). Finally, the diurnal variation of the slant path rain attenuation is presented to provide system operators and radio communication engineers with useful information on the Quality of Service (QoS) that can be achieved during a typical day on an Earth-space link

HF CARRIERS are these days becoming very attractive to satellite-communication (SatCom) system operators because they offer wide bandwidth for the provision of advanced multimedia and interactive services. Above 10 GHz, the atmosphere has a definite impact on Earth-space links and, while rainfall always represents the prevalent impairment affecting radio waves [1], the contribution of suspended liquid water becomes significant at frequencies above 20 GHz and in low elevation links, not only in terms of specific attenuation, but also for the high occurrence probability of clouds (40%-80% of the yearly time in Europe). Even more, at optical wavelengths, which, in principle, would enable Earth-space communication systems with extremely high data rates, the presence of clouds along the path is the limiting factor because Manuscript

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