Measured variances of Zdr, phidp, and rhohv from simultaneous H and V transmissions

Zdr, phidp, and rhohv need to be measured at `zero lag', namely as if the H and V polarizations were transmitted simultaneously. However, the quantities have traditionally been determined by alternately transmitting H and V signals on successive pulses. The alternating pulse measurements are substantially affected by the pulse-to-pulse Doppler effects, which increase both the variance and the complexity of the measurements. Because the depolarization effects are often small, it is important that the variances be minimized. In this paper we present measurements of the variance of the dual-polarization quantities determined from simultaneous H and V transmissions, which are unaffected by the Doppler effects. The measured values are compared with the fundamental results for the variances of phase and correlation measurements and are found to have the fundamental variances as their lower bound. The receiving system used to obtain the measurements employed constant-phase amplitude limiters to achieve the required dynamic range; the consequent loss of amplitude information resulted in the variances having the fundamental values only as their lower bound. Fully linear `digital IF' receiving techniques will not have this restriction and the observed variances should more often reach their fundamental values.