RAINFALL MEASUREMENT BY RADAR - A REVIEW

Several measuring methods using various properties of radar signals to estimate rainfall rate R are reviewed. These methods are based on measurements of the radar reflectivity factor Z at one or two polarizations, on measurements of attenuation A or on a combination of these two quantities. When only one radar observable is measured, R is computed from analytical relations of R-Z or A-Z type, ignoring the spatiotemporal variations of the raindrop size distribution N(D), where D is the drop diameter. If N(D) can be approximated by a two parameter equation, R can be estimated from the determination of N(D), using measurements of two radar observables. Some of these methods are notably improved if the radar data are combined with rain gauge network measurements at the ground. The mean volume rainfall and the areally averaged rain rate can be estimated from the area-time integral and fractional area methods.