Correlation Coefficient - ρHV
This is the correlation of the time series of the H and V returns. If a radar bin contains particles of constant shape, Zh/Zv, is constant in a series of pulses and there is no variance which appears as 1 on a ρHV display. With mixed particles, Zh/Zv is not constant and ρHV shows variances less than 1.
It is a measure of the variety of particle shapes and fall modes and is also independent of calibration, attenuation, and particle concentration. ρHV displays are problematic if reflectivities are less than 20 dB.