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This study presents, for the first time ever, occulting signals of the Global Navigation Satellite Systems (GNSSs) acquired at two polarizations from a Low Earth Orbiter, and it shows that they sense heavy precipitation. The data sets are obtained from early stages of the Radio Occultation and Heavy Precipitation experiment aboard the PAZ satellite, launched in February 2018 and activated in May 2018. Preliminary calibration algorithms are applied to remove other systematic effects, and the resulting vertical profiles of polarimetric phase shift observations are compared to precipitation information from other missions. The analysis of the data shows consistency between Radio Occultation and Heavy Precipitation experiment aboard the PAZ satellite polarimetric phase shift measurements and presence of hydrometeors, with strong signatures from heavy precipitation. The polarimetric measurements also capture vertical features consistent with the vertical structures of precipitation.

Plain Language Summary When the satellites of the navigation systems (like GPS) set below the horizon, their signals can be used to measure temperature, pressure, and humidity of the atmosphere at different altitudes (an observation called radio occultation). For the first time, a satellite has collected these setting GPS signals at two polarizations, that is, separating two different orientations of the electromagnetic field (horizontal and vertical with respect to the receiving antenna). It is the Radio Occultation and Heavy Precipitation experiment aboard PAZ satellite, launched in February 2018 and activated in May 2018. Previous theoretical studies have shown that intense rain crossing the path of the GPS signals would introduce a delay of the horizontal component with respect to the vertical one. This study shows the analysis of the polarimetric delays, and it confirms that they are related to the presence of rain, in particular intense precipitation. The measurement of polarimetric delays at different altitudes is consistent with the presence of rain structures at different heights. No other technique captures profiles of both thermodynamics and hydrometeor content in intense rain phenomena, and therefore, the Radio Occultation and Heavy Precipitation experiment aboard the PAZ satellite data could provide a new tool to understand extreme precipitation, with potential to improve its difficult prediction.