Retrieving the 3-D Tropospheric Wet Refractivity Field From a Standalone Ground-Based GNSS Station With A Priori Information: Theory and Simulation

Sensing water vapor contents in the troposphere with ground-based Global Navigation Satellite System (GNSS) stations has been widely studied and related to extreme weather events and climate changes over the years. Usually, GNSS tomography is the tool of choice to retrieve the 3-D water vapor field. However, a dense GNSS network is required, which means that the GNSS tomography is not applicable everywhere, e.g., in island countries, where only one/a few GNSS stations are available. In this work, we propose a new method to retrieve the 3-D wet refractivity field from the data collected at a standalone ground-based GNSS station. Using 3-D Zernike functions to model the turbulent component of the wet refractivity field and the corresponding perturbations in slant wet delays (SWDs), a typical Radon inverse problem is obtained. Two kinds of a priori information, namely, the spatial covariance of the SWDs and a Kaula-like rule, respectively, are proposed and introduced to regularize this ill-posed inverse problem. The proposed method is validated with a simulation experiment. The simulation results indicate its usefulness for retrieving the 3-D wet refractivity field overhead a single GNSS station with the appropriate a priori information.