Multiyear assessment of ground-based Sun-tracking microwave radiometric observations in Rome, NY (USA) at millimeter and sub-millimeter wavelengths

Ground-based Sun-tracking microwave radiometric observations allow to exploit the Sun radiation as a signal source, similarly to beacon experiments. Antenna noise temperature measurements are performed by alternately pointing toward-the-Sun and off-the-Sun while tracking the Sun along the diurnal ecliptic. The Sun-Tracking microwave observations are twofold: on one hand, they provide means to estimate the Sun brightness temperature during purely clear-air conditions and, on the other hand, retrieve the atmospheric path attenuation in nearly all-weather conditions, by profiting of the known Sun brightness temperature estimates. In this paper, measurements at K-and Ka-band are analyzed, as well as observations in the marginally explored millimeter-wave frequency region at V-and W-band. A multi-year dataset was assessed, ranging from 2015 until 2018, collected by a Sun-tracking multifrequency radiometer located in Rome, NY (USA). Expanded considerations on Sun brightness temperature trends are reported, together with long-term estimates of the all-weather atmospheric path attenuation. These are then compared with well-established microwave radiometry retrieval methods to test the accuracy of the estimations.