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After a review of the physical/mathematical definitions of anisotropy and canting angle, parameters currently used for describing the depolarization of electromagnetic waves due to hydrometeors, we present some specific algorithms to retrieve these parameters from measurements of the atmospheric polarization transfer matrix, based on data collected during the Italsat propagation experiment at 50 GHz in a slant path with elevation angle 37.7^\circ. The data analysis, conducted after applying particular “ad hoc” procedures and severe editing, allowed to separate in many cases the ice- from the rain-effects, both in single events and statistically. We also present mathematical models derived from the observed behavior of the descriptive parameters, hopefully applicable also in different conditions. [ABSTRACT FROM AUTHOR]

Ground-based microwave radiometer (MWR) observations of downwelling brightness temperature (TB) are commonly used to estimate atmospheric attenuation at relative transparent channels for radio propagation and telecommunication purposes. The atmospheric attenuation is derived from TB by inverting the radiative transfer equation with a priori knowledge of the mean radiating temperature (TMR). TMR is usually estimated by either time-variant site climatology (e.g., monthly average computed from atmospheric thermodynamical profiles) or condition-variant estimation from surface meteorological sensors. However, information on TMR may also be extracted directly from MWR measurements at channels other than those used to estimate atmospheric attenuation. This paper proposes a novel approach to estimate TMR in clear and cloudy sky from independent MWR profiler measurements. A linear regression algorithm is trained with a simulated dataset obtained by processing 1 year of radiosonde observations of atmospheric thermodynamic profiles. The algorithm is trained to estimate TMR at K- and V–W-band frequencies (22–31 and 72–82 GHz , respectively) from independent MWR observations at the V band (54–58 GHz). The retrieval coefficients are then applied to a 1-year dataset of real V-band observations, and the estimated TMR at the K and V–W band is compared with estimates from nearly colocated and simultaneous radiosondes. The proposed method provides TMR estimates in better agreement with radiosondes than a traditional method, with 32 %–38 % improvement depending on frequency. This maps into an expected improvement in atmospheric attenuation of 10 %–20 % for K-band channels and ∼30 % for V–W-band channels. [ABSTRACT FROM AUTHOR]

Ground-based microwave radiometer (MWR) observations of downwelling brightness temperature (푇퐵) are commonly used to estimate the atmospheric attenuation at relative transparent channels for radiopropagation and telecommunication purposes. The atmospheric attenuation is derived from 푇퐵 by inverting the radiative transfer equation with a priori knowledge of the mean radiating temperature (푇푀푅). 푇푀푅 is usually estimated by either time-variant site climatology (e.g., monthly average computed from atmospheric thermodynamical profiles) or condition-variant estimation from surface meteorological sensors. However, information on 푇푀푅 may also be extracted directly from MWR measurements at other channels than those used to estimate atmospheric attenuation. This paper proposes a novel approach to estimate &#119879 푀푅 in clear and cloudy sky from independent MWR profiler measurements. A linear regression algorithm is trained with a simulated dataset obtained by processing one year of radiosonde observations of atmospheric thermodynamic profiles. The algorithm is trained to estimate 푇푀푅 at K-, and V/W-band frequencies (22-31 and 72-82 GHz, respectively) from independent MWR observations at V-band (54-58 GHz). The retrieval coefficients are then applied to a one-year dataset of real V-band observations, and the estimated 푇푀푅 at K- and V/W-band are compared with estimates from nearly collocated and simultaneous radiosondes. The proposed method provides 푇푀푅 estimates in better agreement with radiosondes than a traditional method, with 32-38% improvement depending on frequency. This maps into an expected improvement in atmospheric attenuation of 10-20% for K-band and ~30% for V/W-band channels. [ABSTRACT FROM AUTHOR]

A detailed analysis of 1-year, long-term experimental measurements of signal enhancement at a terrestrial link between two cities in the Czech Republic is presented with respect to an interference and frequency coordination analysis based on recommendation ITU-R P.452-14. Three different models for terrain diffraction are considered to demonstrate a significant influence on signal enhancement predictions. The impact of radiometeorological parameters, serving as inputs for recommendation ITU-R P.452-14, was addressed by utilizing available ITU-R and ERA-Interim maps, or, their locally obtained values. Monthly and seasonal variations are discussed in addition to the 1-year signal enhancement statistics. [ABSTRACT FROM PUBLISHER]

Atmospheric refractivity and its vertical gradient affect electromagnetic wave propagation in the atmosphere. Consequently, their statistics are needed for propagation predictions. New world maps of refractivity and its vertical gradient statistics are derived from a global, long-term dataset of meteorological quantities as given by ERA-Interim reanalysis. The derived maps provide long-term statistics obtained from 33 years of meteorological data with a one-degree spatial resolution on a latitude/longitude mesh. A processing method is described and examples of the derived maps are shown. The consistency of the new maps is checked by comparing world maps provided by ITU-R. Accuracy is tested by comparing refractivity statistics obtained from high-quality local measurements using radiosonde and tower measurements. New global maps demonstrate enhanced statistical stability, spatial resolution, and accuracy. [ABSTRACT FROM PUBLISHER]

In response to the current need for a reliable interference and frequency coordination analysis, especially within the ground segment of satellite systems, atmospheric refraction and terrain diffraction phenomena play a key role from a radiowave propagation point of view. While it is convenient to use an ITU-R model for the case of the atmospheric refraction, several different types of models for terrain diffraction are identified in the literature. On the other hand, only a limited amount of experimental data is globally available to address their performance. This is why we carried out own short-term terrain diffraction measurements at the frequencies from L- to Q-band. During the trials, truck-mounted access platforms reaching up to 46 m above ground level were used and terrain profiles with path lengths from 7 km up to 50 km for various combinations of transmitter and receiver heights were addressed. Based on the obtained experimental dataset, the performance of the delta-Bullington and Deygout models, currently recommended by the ITU-R for the purposes of interference analysis, and the terrain diffraction models based on the UTD and parabolic equation approach has been addressed in terms of the testing variable defined in this paper. [ABSTRACT FROM PUBLISHER]

In a suggested radio propagation experiment using a deep space antenna, accurate calibration of the propagation delay through the Earth's atmosphere is essential. One or two microwave radiometers can be used for this purpose. Differences in precise locations of the radiometer(s) and antenna to be calibrated leave a residual wet path delay value. We computed the Allan Standard Deviation (ASD) of this residual, as well as the one resulting from different pointing positions in the plane of the sky, by simulations. Pointing offsets, e.g., to avoid solar radiation into the radiometer beam, lead in general to an increased ASD. However, for many observation geometries a deliberate pointing offset can compensate for the location differences. In the case studied we found a reduction of the ASD with up to 45% compared to the ASD obtained for a zero pointing offset. The size of the calculated ASD depends strongly on the model parameters used, e.g., the turbulence strength parameter Cn^2, which has a significant natural variation over a year. [ABSTRACT FROM PUBLISHER]

Radiometric measurements could provide continuous information about atmospheric conditions. In this paper, a sky status indicator (SSI) is proposed as a real-time recognition criterion for the detection, in particular, of the presence of rain events along the propagation path. The computation of the SSI is based on ground-based brightness temperature measurements, at 23.8 and 31.4 GHz, collected in Cabauw, Netherlands, in 2009 by the ESA Atmospheric Propagation and Profiling System (ATPROP) multichannel radiometer. A validation analysis is carried out between simulated data, which are computed by applying the radiative transfer equation to a database of radiosonde profiles collected in De Bilt, Netherlands, by the Royal Netherlands Meteorological Institute, and two data sets of radiometric observations at two elevation angles (\theta equal to 90^\circ and \theta equal to 69.6^\circ). The analysis based on SSI probability distribution functions has allowed for calculation of the boundary threshold values that are able to discriminate the status of the sky. Furthermore, performances of the SSI were validated against rainfall measurements collected at the ground by a rain gauge located near the ESA ATPROP multichannel radiometer. [ABSTRACT FROM AUTHOR]

A physically-based parametric model (PPM) to predict the sky-noise temperature in all weather conditions is proposed. The proposed prediction model is based on the non-linear regression fit of numerical simulations derived from the sky-noise eddington radiative-transfer model (SNEM) in an absorbing and scattering medium such as gaseous, cloudy and rainy atmosphere. The PPM prediction method, dependent on measured path attenuation, beacon frequency, and antenna-pointing elevation angle, describes the statistical behavior of the atmospheric mean radiative temperature, which in its turn relates sky-noise temperature to slant-path attenuation. PPM validity ranges from X- to W- band and from 10^\circ to 90^\circ in terms of elevation angle. A comparison of the estimated PPM radio-propagation variables with corresponding ITALSAT satellite data, collected at the Spino d'Adda receiving station (Italy), is also carried out and discussed. The PPM prediction technique provides a root-mean-square retrieval error generally less than 8 K for all frequencies. Results show an improvement with respect to the current International Telecommunication Union (ITU) recommendations, especially at Q- and V-band and above, where the atmospheric multiple scattering effects cannot be disregarded. [ABSTRACT FROM PUBLISHER]

Reconfigurable on-board antenna systems are a potential solution to mitigate the effect of atmospheric fades in broadband SatCom. The on-board power is dynamically shared among the users according to the time and space-varying meteorological conditions in the service area by tuning the antenna radiation pattern. An efficient algorithm of dynamic on-board power allocation is presented here. Preliminary results show the superiority of the adaptive technique over a state-of-the-art fixed antenna system in terms of on-board power reduction to achieve a given service availability target. [ABSTRACT FROM AUTHOR]

The objective of this study, named AWARDS (Advanced microWAve Radiometers in Deep space Stations), is the preliminary design of a transmission Media Calibration System (MCS) to be located at an ESA Deep Space Antenna (DSA) site. The crucial aspect is the capability to accurately retrieve the tropospheric path delay along the line-of-sight of the deep space probe in order to allow precise tropospheric calibration of deep space observables (range and range-rate) with particular reference to the BepiColombo spacecraft and its primary DSA at Cebreros (ES). The study focuses on two main aspects which lead to the preliminary design of the Mercury Orbiter Radioscience Experiment (MORE) MCS: the characterization of current microwave radiometers (MWRs) available at ESA/ESTEC and the atmospheric fluctuation effects on the MCS error budget, in terms of the Allan standard deviation (ASD). In the course of the study, further critical aspects have been identified (effects of Sun contamination, effects of ground noise emission), and mitigation strategies have been proposed. The final outcome is a preliminary design of the MWR (and the entire MCS) to be deployed at the ESA/ESTRACK (ESA Tracking station network) sites and being compliant with MORE requirements. [ABSTRACT FROM AUTHOR]

The control of the radiation of a telecommunication multispot satellite antenna is discussed in which the power can be flexibly routed towards the various spots so as to contrast at best the time variant atmospheric attenuation while keeping at minimum the number of users which do not receive enough signal level. The antenna control is exerted by applying a particular strategy based on the knowledge of the distribution of the weather conditions all over the served region as derived by standard sources like the European Centre for Medium Range Weather Forecasting (ECMWF) or the Meteosat. The paper describes the principles of two types of optimizations: a fixed one based on climatological long term data, which acts as reference, and an adaptive one based on quasi instantaneous pictures that represent the weather situation across the served region. After an explanation of the basic principles of the optimizations, the paper gives an example of application that, despite the brevity of the trial period we are now able to present, indicates an excellent effectiveness of the system which, in the period observed, allows a reduction of the number of non-served users of the two orders of magnitude in the case of low-margin systems (approximately 2-3 dBs over free space) and a still conspicuous advantage (a reduction of a factor about 5) for greater available margins (approximately 6-7 dBs). [ABSTRACT FROM AUTHOR]

An improved version of the exponential cell (EXCELL) rain attenuation model is presented here. Analogously to the original one, it predicts attenuation through a cellular representation of precipitation, but, in addition, is able to discriminate between stratiform and convective rain by means of an embedded algorithm. Accordingly, two separate physical rain heights, derived from the ERA-15 database, are used to calculate stratiform and convective rain attenuation and, when considering stratiform precipitation, the melting layer contribution to attenuation is added. Eventually, the predicted cumulative distribution function (CDF) of excess attenuation is the combination of the contributions due to stratiform and convective precipitation types. Some input parameters of the prediction model, such as those defining the melting layer process or the rain plateau embedding rain cells, can be modified in order to account for the local meteorological characteristics. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]