Improving the accuracy of near-surface 3-D radar refractivity retrievals

Radar refractivity retrievals provide valuable information of near surface atmospheric moisture, which is related to convective and boundary layer processes. Therefore, accurate refractivity retrievals are critical for quantitative applications, such as data assimilation into numerical weather models and short-term forecasting. But the technique as originally developed makes some crude assumptions about target properties (all aligned at the radar height) and terrain (flat Earth). In this study, we quantify and discuss one of the main unsolved biases of refractivity retrieval associated with the vertical gradient of refractivity (DN/DH) and with target height.

Additional dual-polarization data at multiple elevations are collected to enhance the knowledge of ground targets and to improve the quality of the phase measurement. Based on the point target assumption, a new method is proposed to estimate the DN/DH variation and representative target height using the power return of targets at multiple elevations. Dual-polarization phase at successive elevations is evaluated as a quality index of targets. Therefore, the near-surface 3-D radar refractivity will consist of a more accurate horizontal refractivity map at a given height and of a more reliable DN/DH.