On Backscatter Differential Phase from Precipitation

Backscatter differential phase δ is significant if scatterers are oriented and in the resonance regime. Nonetheless, there are causes that can produce apparent backscatter differential phase. The following three are exposed. 1) Observations by polarimetric radar operating in the simultaneous mode of transmitting Horizontally (H) and Vertically (V), (SHV)polarized EM waves. 2) Incomplete beam filling along propagation paths. 3) Three body scattering involving ground directly under the observation volume in a hailstorm. Examples of 1) are shown from randomly oriented hydrometeors in the melting layer at vertical incidence. Examples of 2) are from literature and of 3) are from actual observations. Complicating interpretation of δ is that in nature more than one of the causes can be present. Moreover, δ due to coupling in the SHV mode depends on the transmitted differential phase, β. For that and other applications we demonstrate measurement of β.