This paper presents the use of a Numerical Weather Prediction model (the WRF US model from NCAR/NCEP) coupled with an electromagnetic module to create rain attenuation time series and statistical results in a tropical region. Simulated results are compared with experimental data collected within a CNES/ONERA sponsored propagation experiment near Kourou, in French Guiana. Both simulated and experimental Complementary Cumulative Distribution Functions of rain attenuation (CCDF) are presented in an annual and monthly basis. Finally, a brief granulometric study is detailed to better understand the impact of the rain drop size distribution (DSD) on the obtained results.

Current spatial resolutions achieved by mesoscale weather forecast models allow them to be used to generate the state of the lowest layers of the atmosphere over areas as small as a few square kilometers which corresponds to the typical size of the tropospheric area crossed by Earth-space links. Furthermore, they allow the evolution of the troposphere to be predicted with a time stamp of five minutes instead of every hour with large-scale weather forecast models which makes them attractive for radio propagation predictions for satellite communication applications. This paper aims at studying the capability of the Weather Research and Forecast (WRF) model coupled with an electromagnetic physical model to reproduce rain attenuation statistics for Earth-space paths at Ka-band. To this purpose, one year of propagation measurements collected at 20 GHz in different places at midlatitudes in Toulouse and Salon de Provence (France), Spino d’Adda (Italy), Aveiro (Portugal), and Madrid (Spain), at high latitudes in Svalbard (Norway) and at low latitudes in Kourou are used to make comparisons between simulations and measurements. Comparisons between the simulated and the experimental annual statistics considered in this paper provide encouraging results, with a similar accuracy as Recommendation ITU-R P.618–13 for midlatitude European locations and with better accuracy for a high latitude area in Svalbard and for an equatorial location in French Guiana.

Frequencies at and above K/Ka band are required for the deployment of (very) high throughput satellites. Yet, radio-links at those frequencies are strongly affected by tropospheric constituents, especially rain. The knowledge of the signal attenuation due to rain comes from dedicated propagation experiments with satellite beacons. Numerical Weather Prediction models could act as an alternative source of rain information, but the validation of their performances against beacon data remains incomplete, notably with respect to the local climatology. This work takes a look at the rain attenuation predicted with the Weather Research and Forecasting (WRF) model 4.0.3 initialized with ERA-5 data, tests nine microphysics schemes, either single-or double-moment, and adapts rigorously the electromagnetic model to their assumed rain drop size distributions. Results are compared over three months in Toulouse, in a temperate region, at both 20.2 and 39.4 GHz, and a strategy is outlined to select the best parametrizations from the error metrics.

Earth-space communications are to make use of higher frequencies, at and above 20 GHz, to offer new services and increased data rates. A consequence is a strong attenuation of the carrier waves by the troposphere, particularly during rain events. The statistical characterization of the rain attenuation on high frequency channels is thus paramount to their link budget. Traditionally this knowledge is obtained via long-term ground measurements of spaceborne beacon signals. Here, simulated results based on Numerical Weather Prediction models are considered as an alternative. A comparison is given based on two years of beacon data at 20 and 40 GHz in Toulouse (France). Four parametrizations of the WRF model's microphysics are tested: the best performances are achieved with the NSSL-2 moment scheme.