Correlation Coefficient

Correlation Coefficient (| _hv(0)|)
The Correlation Coefficient describes the similarities in the backscatter characteristics of the horizontally and vertically polarized echoes.

For meteorological echoes, |

_hv(0)| is typically greater than 0.7.

Hail: Typically 0.90 to 0.95. Can be above 0.95 for a uniform field of small, dry, hail. Can fall significantly below 0.90 in large, wet hail (Mie regime).
Rain: Typically above 0.95, except when drops are mixed with hail or partially frozen. Can be above 0.99.
Drizzle/very light rain: Typically below 0.90, due to low signal-to-noise ratio.
Ice pellets/graupel: Typically greater than 0.95, but significantly lower in mixed phase regions (as is often observed)
Snow: Generally above 0.95, except potentially much lower in wet snow.
Bright band: Typically 0.90 to 0.95 due to mix of hydrometeor types.

_hv(0)| significantly below 1 indicates regions where the horizontal and vertical backscattering fields are not proportional.

_hv(0)| significantly below 1 may indicate regions where the particles are re-orienting, or changing in number.

_hv(0)| significantly below 1 may indicate regions where there is a mixture of hydrometeor types, size, fall eccentricities, and/or shape.

_hv(0)| may drop to 0.5 or lower in regions of Resonant scattering (e.g., very large hail).

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