Evaluating the sensitivity of GNSS-PRO to different microphysical assumptions

The Polarimetric Radio Occultation (PRO) technique involves tracking signals emitted by navigation satellites (GPS, Galileo, Beidou…) from a Low Earth Orbit (LEO) satellite as it rises or sets behind the Earth’s limb. This method extends the capabilities of the standard Radio Occultation (RO) technique by employing two orthogonal linear polarizations—horizontal (H) and vertical (V)—thereby providing relevant information about atmospheric hydrometeors. Furthermore, the traditional RO products (vertical profiles of thermodynamic variables) are simultaneously measured, becoming the first technique to provide both type of observations.

This technique has been under testing since 2018 aboard the Spanish PAZ satellite, a mission that successfully demonstrated the GNSS-PRO concept. Moreover, since 2023, it has been implemented on three Spire global commercial CubeSats and one PlanetiQ satellite. The polarimetric capability of PRO enables to retrieve the observable called differential phase shift, defined as the difference between the phase delays associated with the horizontal and vertical polarizations. Intense precipitation events, characterized by non-spherically symmetric hydrometeors, exhibit a positive differential phase shift when these observations pass through such phenomena, showing sensitivity to microphysical properties related to these events.

The primary hypothesis, that PRO is sensitive to oblate raindrops, has already been validated. Unexpectedly, the technique also demonstrated sensitivity to frozen hydrometeors, further expanding its potential applications. The validation of PRO has been successfully achieved through comparisons with both two-dimensional datasets, such as IMERG-GPM products, and three-dimensional datasets, including observations from NEXRAD polarimetric radars.

Current analyses focus on evaluating the sensitivity of PRO to various microphysical parameterizations obtained from the Weather Research and Forecasting (WRF) model. Additionally, its sensitivity to specific particle habits is being examined using the Atmospheric Radiative Transfer Simulator (ARTS) database. The study is centered on Atmospheric Rivers (AR) to investigate how variations in microphysical parameterizations influence the ability of PRO to detect and characterize hydrometeors. Preliminary results indicate that some specific parameterizations and particle habits better compare to PRO actual observations. These findings aim to enhance our understanding of the processes associated with extreme weather systems and advance the application of PRO in atmospheric science.