POLARIMETRIC RADAR AT ATTENUATED WAVELENGTHS AS A HYDROLOGICAL SENSES

A new method for the estimation of the rain rate using a polarimetric radar at attenuated wavelengths is proposed. At attenuated wavelengths , the differential reflectivity fur horizontal and vertical polarizati on, Z(DR), is the addition of a term depending on the drop shape, Z(DR s), and a term depending on the differential attenuation for the two p olarizations, A(DP). The differential attenuation can be: interpreted as an estimation of the integral of the rain rate along the radar beam . The principle of the method is the following: along the radar beam a first estimation of the rain rate R, in each range gate, is calculate d from the single-wavelength radar reflectivity factor Z using the usu al iterative attenuation correction scheme and a combination of a Z-R and an A-R relation, where A is the single polarization attenuation co efficient. This result permits one to obtain an estimation of Z(DRs). The difference between the measured value of Z(DR) and Z(DRs) is a mea sure of A(DP). Then the integral of R along the radar beam, deduced fr om the single polarization reflectivities, is constrained to be equal to the integral of R deduced from A(DP). This constraint is used to ad just iteratively one of the two parameters of the Z-R relation (let cu be this parameter), the other being maintained constant at a mean val ue. The adjusted a enables the calculation of R in each gate. The radi al observed with the radar can be partitioned, and the algorithm appli ed independently to the individual segments with one value of a, compu ted for each segment. The method is independent from the radar calibra tion and from the attenuation by undetected clouds since it is based o n a differential measurement. This algorithm is also usable as a quali tative hail detector, as well as a detector of anomalous propagation. Simulations of these various functions are presented.