Horizontal, vertical, and enhanced reflectivities (Z_H, Z_V, Z_HV)

In the case of amplitude (power) measurements, the power returned to the radar can be related either to the particles diameter in the horizontal plane or vertical plane. When expressing this power through the radar equation, these become horizontal reflectivity (Z_H), and vertical reflectivity (Z_V).

Z_H and Z_V are typically calculated using an autocorrelation power estimator, or by performing a cross-correlation of the signal with itself.

The autocorrelation technique finds periodic signals buried within noise. A special case is to perform the cross-correlation of the horizontal power to the vertical power. This becomes enhanced reflectivity (Z_HV) and can be shown to have greater ability to weak signals in the presence of noise, compared to Z_H or Z_V alone.

All power estimators are sensitive to intervening attenuation from precipitation, requiring a data correction for quantitative use with C- or X-band radars.