A Study on the Effects of Heavy Precipitation on Single and Dual Polarization Radio Occultation Observations Using Radio-Holographic Method

Atmospheric moisture plays a significant role in the Earth’s weather system. However, characterizing the near-surface moisture structure in extreme precipitation environment is a challenging task since current remote sensing technology - infrared and microwave sounders - cannot sense near the surface in the presence of heavy precipitation. On the contrary, standard Global Positioning System (GPS) radio occultation (RO) can provide high vertical resolution moisture profiles but is not very sensitive to hydrometeors due to its L-band wavelength. However, by adding a dual-orthogonal receive polarization measurement, it is possible to relate the polarimetric phase difference to the asymmetric shape of the hydrometeors along the propagation path. Up to now, the polarimetric RO (PRO) concept has been studied using geometric optics. It is known, however, that ray paths from both polarizations can suffer severe multipath problem in the moist lower troposphere. This research improves the PRO retrieval process using radio-holographic (RH) method to mitigate the multipath effect. The results are validated using the multiple phase screen (MPS) forward modeling method. In addition, the refractivity bias observed in standard single-polarization GPS-RO retrieval with respect to global weather analyses during heavy precipitation is also statistically analyzed using RH method. Our results suggest that this bias is unlikely to be due to the precipitation influenced GPS-RO retrieval.