Evaluation of phase ambiguity problem due to sampling time when measuring refractivity with precipitation radar

As first proposed by Fabry (1997), the precipitation radar signal reflected from ground targets can be used in same way to measure the local water vapour content and this could be useful for convective system prediction. More recently Parent-du-Châtelet and Boudjabi (2008) proposed a new formulation to estimate the refractivity measurement ability of magnetron radars, for which the frequency variation is a problem. These methods are based on phase difference estimations which can be corrupted by aliasing problems due to time or space undersampling, depending on weather phenomena space or time scales.

In this paper we present first results obtained by a simulation study from Trappes in-situ (P T U) data measured every minute during 4 years(2005-2008). From these data, we compute refractive index time series, and we deduce simulated radar phase time series for different sampling time, and which correspond to major climatic events (heavy rain, thunderstorm, ..). As a conclusion, we give the radar sampling time acceptable to avoid phase aliasing problems during such events. We also propose a similar method, based on high space resolution numerical weather prediction model, to estimate space sampling problems expected when measuring refractivity for extreme events.