ABSTRACT
For decades, the weather radar has played an important role in quantitative precipitation estimation (QPE). The radar has the advantage of large coverage and short data-updating intervals. As a result, it has been widely used by the international meteorological/hydrological community. There are numerous weather radar networks in the world. The common methods for polarimetric radar–rain estimation are based on empirical relations or raindrop size distribution (DSD) retrievals. This chapter focuses on the basis of radar measurements associated with the DSD and rain physics. When radar is used to measure precipitation, what it measures are compositive back-scattering signals from hydrometeors within a radar resolution volume. Each particle contributes to the total signal received by the radar, depending on its size, shape, orientation, composition, location, and other factors such as temperature, radar frequency, antenna pattern, and scanning. While a radar wave is incident on hydrometeors, its energy is either scattered or absorbed by the hydrometers.
