Exploiting Tropospheric Measurements From Sun-Tracking Radiometer for Radiopropagation Models at Centimeter and Millimeter Wave

The objective of this paper is to characterize the atmospheric radiometeorological parameters (optical thickness and brightness temperature) at centimeter and millimeter waves. To this aim, we have exploited two radiative transfer models (RTMs): a three-dimensional model (3D-RTM), driven by numerical weather forecasts, and a stochastic one-dimensional (1-D) model (1D-RTM), fed by a synthetic clouds dataset. We have compared the radiative transfer simulations with measurements from two ground-based microwave radiometers: a profiler and a Sun-tracking radiometer. The peculiarity of the latter is the capacity of simultaneously measuring atmospheric optical thickness and brightness temperature in all-weather conditions and at variable elevation angles. The comparisons between simulations and measurements provide satisfactory results that assess the reliability of the 3D-RTM with some biases, in terms of brightness temperature, that should be investigated. 3D-RTM turns out to be able to successfully reproduce correlations between brightness temperature and optical thickness and correlations among the different frequency channels. This confirms the potential of the combined use of weather forecast models and physically-based RTMs. On the other hand, 1D-RTM reveals to be able to reproduce frequency-channel correlation trends, but additional climatological set-up are needed to make the model exploitable for the computation of statistics of atmospheric optical thickness. These comparisons also highlight some possible calibration errors in the Sun-tracking radiometer that must be fixed. Finally, we have exploited measurements from the Sun-tracking radiometer to develop a model to retrieve the probability of atmospheric optical thickness conditioned to a given elevation angle.