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Media propagation delay and delay-rate induced by the water vapor within the Earth's troposphere represent one of the main error sources for radiometric measurements in deep space. In preparation for the BepiColombo and JUICE missions, the European Space Agency has installed and operates the prototype of a tropospheric delay calibration system (TDCS) at the DSA-3 ground station located in Malargüe, Argentina. An initial characterization of the TDCS performance was realized using two-way Doppler measurements at X-band to perform the orbit determination of the Gaia spacecraft. This work will further characterize the system by analyzing two-way Doppler and range data at X- and Ka-band for 31 tracking passes of the BepiColombo spacecraft, which were recorded between March 2021 and February 2022 during the first two solar conjunction experiments. The performance exceeds the expectations based on the previous analysis, with a reduction of the Doppler noise of 51% on average and up to 73% when using the TDCS measurements in place of standard calibrations based on global navigation satellite system data. Furthermore, the campaign serves as validation of the TDCS operations during superior solar conjunctions, with most of the tracking passes at low elongation now satisfying the Mercury orbiter radioscience experiment requirements on two-way Doppler stability. These results, which are in line with those of similar instruments installed at other Deep Space Network antennas, are obtained using a commercial microwave radiometer with significantly lower installation and maintenance costs.

Media propagation noises are amongst the main error sources of radiometric observables for deep space missions, with fluctuations of the tropospheric excess path length representing a relevant contributor to the Doppler noise budget. Microwave radiometers currently represent the most accurate instruments for the estimation of the tropospheric delay and delay rate along a slant direction. A prototype of a tropospheric delay calibration system (TDCS), using a 14 channel Ka/V band microwave radiometer, has been developed under a European Space Agency contract and installed at the deep space ground station in Malargüe, Argentina, in February 2019. After its commissioning, the TDCS has been involved in an extensive testbed campaign by recording a total of 44 tracking passes of the Gaia spacecraft, which were used to perform an orbit determination analysis. This work presents the first statistical characterization of the end-to-end performance of the TDCS prototype in an operational scenario. The results show that using TDCS-based calibrations instead of the standard GNSS-based calibrations leads to a significant reduction of the residual Doppler noise and instability.

Sun-tracking microwave radiometry (STMW) is a ground-based technique where the Sun is used as a beacon source to infer the atmospheric path attenuation in all-weather conditions. STMW shows an appealing potential for overcoming the difficulties to perform satellite-to-Earth radiopropagation experiments in the unexplored millimeterwave and submillimeter-wave frequency region, especially where experimental data from a beacon receiver are not available. The theoretical framework and the ad hoc procedures and data processing developed in the last 5 years will be presented, together with the estimate of the overall error budget. The application and experimental challenges during long-term deployments, such as the field campaign of the W-band radiometric study (WRad) funded by the European Space Agency (ESA), will be reviewed.

Radio Frequency Interference (RFI) is a growing threat to all Earth Observation (EO) passive microwave missions. Many RFI detection algorithms are used on-board and in the ground segment data processing, but there is no single algorithm that can detect all RFI instances. The best strategy is always to combine several detection methods. This paper presents the results of the new Ground RFI Detection System (GRDS). The GRDS uses a combination of a wide variety of RFI detection algorithms to clean the Earth Observation measurements from RFI. The system is built to be able to scan for RFI for any EO mission. The initial results show the important reduction on RFI in the EO data as measured by the European Center for Mid-Range Weather Forecast (ECMWF) first guess departure statistics.

The modeling of the earth-satellite propagation channel requires experimental data that is usually obtained by monitoring continuous wave (CW) signal sources installed in satellites (beacons). Although there is considerable experience in the development of beacon receivers for geostationary satellites, this is not the case for Medium Earth Orbit (MEO) or Low Earth Orbit (LEO) constellations. The main considerations for the development of propagation receivers for monitoring MEO satellites are addressed in this article. The target constellation is presented with a description of the satellite orbits, characteristics of the beacon payload and the project requirements. The receiver's requirements are then analyzed, starting with the antenna, satellite tracking, beacon detection and propagation data handling.

Sun-tracking microwave (ST-MW) radiometry is a ground-based technique where the Sun is used as a beacon source to infer the atmospheric path attenuation in all-weather conditions. ST-MW radiometry shows an appealing potential for overcoming the difficulties to perform satellite-to-Earth radiopropagation experiments in the unexplored millimeter-wave and submillimeter-wave frequency region, especially where experimental data from beacon receivers are not available. The theoretical framework, the ad hoc procedures and data processing will be presented, together with the estimate of the overall error budget. The applications and challenges during field deployments, such as the recent WRad campaign in Italy based on ST-MW data analysis, funded by ESA and carried out together with AFRL (NY, USA), will be discussed.

Spectral-efficient space communication links are impaired by atmospheric depolarisation caused by rain and ice along the Earth-space path. In this contribution three experiments experiencing three different climatological conditions are compared to assess the underlying mechanisms of depolarisation, in particular to evaluate a possible correlation between depolarisation and ice content.

Ground-based microwave radiometer (MWR) observations of downwelling brightness temperature (TB) are commonly used to estimate the atmospheric attenuation at relative transparent channels for radiopropagation 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 other channels 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 one 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 V-band (54–58 GHz). The retrieval coefficients are then applied to a one-year dataset of real V-band observations, and the estimated TMR at K- and V/W-band are compared with estimates from nearly collocated 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 and ~ 30 % for V/W-band channels.

Radio Frequency Interference (RFI) is a serious constraint affecting the Earth Observation (EO) passive microwave missions whose effect has been increasing. There is no single algorithm that can detect all RFI instances. The best strategy always is to combine several detection methods. This paper presents a new system concept: Ground RFI Detection System (GRDS). The GRDS uses a wide variety of RFI detection algorithm to clean the Earth Observation measurements from RFI. The system architecture is modular and it is built to be able to scan for RFI for any EO mission. The initial assessments reported show the potential for this GRDS system.

The availability of reliable measurements on atmospheric depolarization is fundamental for the improvement of the current Cross Polar Discrimination (XPD) prediction models. In particular, the joint rain attenuation and XPD statistics are foreseen to be the basis in this process. The statistical analysis presented in this contribution for the site of Pomezia (Rome), within the scope of the Italsat experiment, provides the reference information for the development of models at Ka, Q and V bands.

Cross polar discrimination (XPD) is a widespread parameter used to measure the disturbance introduced on electromagnetic signals by the loss of polarisation, when dual polarisation links are employed. Rain precipitations and ice clouds contribute to the increase of XPD in the atmosphere. The current ITU-R Recommendation P.618 links the prediction of the XPD to the excess attenuation probability of a specific site. The statistical analysis of the XPD reported in this contribution is a basic step towards an improved model for next generation dual polarisation links design.

The design phase of an ESA project (MEKaP-MEO Ka-band Propagation) is described. The study, involving Politecnico di Milano, Sapienza Universita di Roma, Instituto de Telecomunicacoes-Aveiro Pole and Thales Alenia SpaceItalia, aims at characterizing the main properties of the atmospheric radio channel of a MEO Ka-band SatCom system. The propagation campaign, lasting at least two years and including four ground receivers, will rely on the MEO O3b Ka-band satellite constellation, which has key characteristics for propagation measurements, such as continuous observation time (at least one satellite is always visible) and global coverage up to mid-latitudes. The experimental data collected during the campaign will be used to test and improve the available propagation models for non-geostationary systems and to extend the experimental database of radio regulatory bodies such as the ITU-R.

In the next generation of satellites, innovative services are intended to be offered by the communications operators. Due to the congestion of the spectrum, the implementation of such services is only possible at high frequency bands. However, at these frequencies, the atmospheric channel has more impact on the propagating signals, compromising the quality-of-service (QoS). In order to study the Earth-space link, several experimental campaigns have been performed below the Q-band with GEO satellites. This paper addresses a new propagation experiment which will permit to extend the understanding of the Earth-space channel up to the W-band and LEO orbits.

The Alphasat Aldo Paraboni Experiment is a radio propagation experiment in the Ka and Q bands started in 2013 with the launch of the Alphasat satellite. It consists of two CW beacons transmitted from the satellite to a large area centered on Europe. Sapienza University, in cooperation with Istituto Superiore delle Comunicazioni (ISCOM) and Fondazione Ugo Bordoni (FUB), joined this experimentation from the very beginning with the installation of two receivers, one for each band. In this article we will show the last technology upgrades made on the Q-band receiver of the Rome AlphaSat receiving station. Particular attention will be put on the custom tracking system based on ephemeris, its realization, specification and performance. A comparison between measured data before and after the installation will be given. At the end we will analyse clear air scintillation data acquired by the upgraded station to prove the quality of the whole system.

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.

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.

Tests using three selected terrain diffraction models, three available experimental datasets and three digital elevation products with different horizontal and vertical resolutions were carried out to assess the role of input terrain profile in diffraction modeling. It is demonstrated that low-resolution terrain maps are not, generally speaking, suitable for terrain diffraction modeling. Further, it is also shown that utilizing digital elevation products with medium spatial resolution results in predictions close to the case when high-resolution terrain maps are considered.

This paper presents an overview of the activities performed by the Agency in the framework of the Alphasat Aldo Paraboni scientific experiment at Ka and Q band. In particular it addresses the technological developments for the equipment of the propagation campaign, the execution of mission related activities, the execution of propagation campaigns, the international cooperation with the group of propagation experimenters and the planning for future activities. The paper is intended to provide the general European background of experimental results published on scientific publications and conferences.

The move towards higher frequency bands like 26GHz or 32GHz for scientific satellite data downlinks calls for the need to better characterise the atmosphere at the sites where ground antennas are located. For this reason ESA is undertaking the deployment of microwave radiometers at its Deep Space station locations. This paper reports the results of the first two years of site characterisation at the ESA Deep Space antenna 2 located in Cebreros, Spain.

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.

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.

This study addresses the sensitivity of the Sky Status Indicator (SSI) with respect to both the radiometer accuracy and location of three stations included in the ground segment of the Alphasat experiment. The SSI aims at detecting the atmospheric conditions along a slant path, exploiting radiometric data at 20/30 GHz. The analysis is performed on synthetic brightness temperatures computed from a database of radiosonde profiles collected in De Bilt (NL), Milano (I), and Roma (I) through forward modelling. The SSI sensitivity to both radiometric resolution and bias error is computed for elevation angles equal to 27.6, 35.5, 40.2, 69.6, and 90°. Robustness of SSI boundary threshold values between clear and cloudy sky conditions is assessed.

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 degrees and theta equal to 69.6 degrees). 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.

The main objective of the ESA ARTES 5.1 Contract 20887/07/NL/LvH "Verification of Propagation Impairment Mitigation Techniques" with Politecnico di Milano as Prime, ONERA and Space Engineering as subcontractors, was to validate the channel models and related input data appropriate for the design, analysis and/or control phase of Propagation Impairments Mitigation Techniques (PIMTs), both for the Broadcasting Satellite Service (BSS) and the Interactive Multimedia Broadband Service (IMMBS). For the BSS scenario, which is the focus of this paper, the On Board Antenna Pattern Reconfiguration (OBAPR) PIMT is investigated, using as channel models the rain field generators able to provide the spatial distribution of rain across the service area on the basis of large-scale meteorological forecasts. Their performance were tested using either radar data or a large dataset of beacon measurements collected in Europe during the OLYMPUS experiment.

This paper presents an overview of the activities performed by the Agency in the framework of the Alphasat Aldo Paraboni scientific experiment at Ka and Q band. In particular it addresses the technological developments for the equipment of the propagation campaign, the execution of mission related activities, the execution of propagation campaigns, the international cooperation with the group of propagation experimenters and the planning for future activities. The paper is intended to provide the general European background of experimental results published on scientific publications and conferences.

In order to study propagation effects for future satellite communication frequencies, the Alphasat Aldo Paraboni payload includes two beacon transmitters at Ka-band (19.701 GHz) and Q-band (39.402 GHz). Among all atmospheric effects, rain has the biggest impact on signal transmission. Often a single statistical relationship (derived from climatic parameters) between rain rate and specific attenuation is used, but it is well known that the variability of the drop size distribution (DSD) for a given rain rate is considerably large and affects the specific attenuation.