Advanced microwave radiometry: refining Sun-Tracking technique for atmospheric attenuation retrieval and sun brightness temperature estimation

Sun-Tracking (ST) is a novel ground-based microwave radiometric technique that allows the retrieval of the slant-path atmospheric attenuation in all-weather conditions as well as the estimation of the Sun brightness temperature. This work proposes a refinement procedure of the ST technique based on taking into account the Sun's angular size variability throughout the year. We have obtained a reduction up to more than 50% of the standard deviation of the estimated Sun's brightness temperature. On the other hand, we have demonstrated that the approximation of a constant value for the Sun's angular size, that strongly limits the precision of the Sun brightness temperature estimation, is acceptable for the ST-based attenuation retrieval algorithm. The study is performed exploiting a three-years dataset of ST measurements collected in Rome NY between 2015 and 2018 at 23.8 (K-band), 31.4 (Ka-band), 72.5 (V-band), and 82.5 (W-band) GHz.