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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. Key Points: The Tropospheric Delay Calibration System installed at the Malargüe ground station was operated during the BepiColombo solar conjunctionsThe system calibrations improved the Doppler measurements by 51% on average and up to 73% in optimal conditionsCalibrated two‐way Doppler residuals satisfy the Mercury Orbiter Radioscience Experiment stability 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). Index Terms--Attenuation, rainfall, satellite broadcasting, satellite communication.

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. Index Terms--Attenuation, radio propagation, rainfall effect.

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. Index Terms--Attenuation, radiometry.

Inversion algorithms for ground-based microwave radiometric retrieval of surface rain-rate, integrated cloud parameters, and slant-path attenuation are proposed and tested. The estimation methods are trained by numerical simulations of a radiative transfer model applied to microphysically-consistent precipitating cloud structures, representative of stratiform and convective rainy clouds. The discrete-ordinate method is used to solve the radiative transfer equation for plane-parallel seven-layer structures, including liquid, melted, and ice spherical hydrometeors. Besides ordinary multiple regression, a variance-constrained regression algorithm is developed and applied to synthetic data in order to evaluate its robustness to noise and its potentiality. Selection of optimal frequency sets and polynomial retrieval algorithms for rainfall parameters is carried out and discussed. Ground-based radiometric measurements at 13.0, 23.8, and 31.7 GHz are used for experimentally testing the retrieval algorithms. Comparison with rain-gauge data and rain path-attenuation measurements, derived from the three ITALSAT satellite beacons at 18.7, 39.6, and 49.5 GHz acquired at Pomezia (Rome, Italy), are performed for two selected cases of moderate and intense rainfall during 1998. Results show a fairly good agreement between retrieved and measured rainfall parameters, pointing out possible effects of nonhomogeneous beam filling at low frequencies when observing small convective cells. Index Terms--Atmospheric remote sensing, ground-based microwave radiometry, precipitation retrieval, radiative transfer modeling.

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]