The effects of heavy precipitation on Polarimetric Radio Occultation (PRO) bending angle observations

Following the successful launch of the Spanish PAZmission the proof of concept experiment “RadioOccultation and Heavy Precipitation with PAZ (ROHP-PAZ)” started operating in May 2018.The ROHP-PAZ observations demonstrated that precise measurements of the phase differencebetween horizontal and vertical polarizations from GNSS L-band signals are sensitive to orientedhydrometeors along the ray paths. While this differential phase shift measurement on the timedomain has proven very useful, the regular RO intermediate products from different polarizedchannels, such as bending angle and phase retrievals on the domain of impact parameter, have neverbeen exploited. In this research, we studied the characteristics of polarimetric phase and bendingangle difference retrieved by the radio-holographic (RH) method to mitigate atmospheric multipatheffect and to explore their use in data assimilation. To validate RH approach in polarimetricretrievals, we performed end-to-end simulations where the hydrometeors are modeled by theeffective refractivity with different horizontal extents. The simulation results show that the strongprecipitation (>15mm/hr) with 40 km horizontal extent can be detected with the retrieved bendingangle shift. The calibration process on the impact parameter domain has also been developedto extract the differential phase and bending angle shift. Statistics from the actual PAZ data alsosuggests that the retrieved RH polarimetric phase shift is approximately proportional to the rain-rateat a ratio of 0.02 `rad/(mm/hr).