Calibration and Validation of the Polarimetric Radio Occultation and Heavy Precipitation experiment Aboard the PAZ Satellite

This manuscript presents the calibration and validation studies for the Radio Occultations and Heavy Precipitation experiment aboard the PAZ satellite. These studies, neces- 5 sary to assess and characterize the noise level and robustness of the differential phase shift () observable of Polarimetric Radio Occultations (PRO), confirm the good performance of the experiment and the capability of this technique in sensing precipitation. It is shown how all the predicted effects that 10 could have an impact into the PRO observables (e.g. effect of metallic structures nearby the antenna, the Faraday Rotation at the ionosphere, signal impurities in the transmission, altered cross polarization isolation, etc.) are effectively calibrated and corrected, and they have a negligible effect into 15 the final observable. The on-orbit calibration, performed using an extensive dataset of free-of-rain and low ionospheric activity observations, is successfully used to correct all the collected observations, which are further validated against independent precipitation observations confirming the sen20 sitivity of the observables to the presence of hydrometeors. The validation results also show how vertically averaged can be used as a proxy for precipitation.