Recent advances in the measurement of precipitation by radar

The phase is important for predicting attenuation on communication links. For meteorological and hydrological application, the rainfall rate at the ground (R in mm/hr) is estimated using an empirical relationship of the form: Z=200 R^1.6 An ice sphere has a value of Z which is 7 dB less than the same size liquid water sphere; when a low density ice particle starts to melt it reflects microwaves like a giant raindrop and Z may 10 dB higher than for the equivalent raindrop. Values of R from equation 1 are prone to error, due to, for example: variation in the raindrop size distribution, the enhanced return from melting snowflakes (`the bright band´), overshooting of the low level precipitation at large ranges, the presence of large hailstones and ground clutter, and the spurious returns due to anomalous propagation. The author considers how polarisation parameters can be used to provide additional information on the types of precipitation present. The survey concentrates on the parameters derived from radiation linearly polarised in the horizontal and vertical directions