Sun-Tracking Microwave Radiometry: All-Weather Estimation of Atmospheric Path Attenuation at $Ka$ -, $V$ -, and $W$ -Band

Sun-tracking (ST) microwave radiometry is a ground-based technique where the Sun is used as a beacon source. The atmospheric antenna noise temperature is measured by alternately pointing toward-the-Sun and off-the-Sun according to a beam switching strategy. By properly developing an ad hoc processing algorithm, we can estimate the atmospheric path attenuation in all-weather conditions. A theoretical framework is proposed to describe the ST radiometric measurements and to evaluate the overall error budget. Two different techniques, based, respectively, on elevation-scanning Langley method and on surface meteorological data method, are proposed and compared to estimate the clear-air reference. Application to available ST radiometric measurements at Ka-, V-, and W-band in Rome (NY, USA) is shown and discussed together with the test of new physically based prediction models for all-weather path attenuation estimation up to about 30 dB at V- and W-band from multichannel microwave radiometric data. Results show an appealing potential of this overall approach in order to overcome the difficulties to perform satellite-to-earth radiopropagation experiments in the unexplored millimeterwave and submillimeter-wave frequency region, especially where experimental data from beacon receivers are not available.