Abstract

What a weather radar measures are the collective effects of wave scattering and propagation from clouds and/or precipitation containing numerous hydrometeors. Not only do the hydrometeors scatter waves sampled by the radar to yield Doppler radar measurements such as reflectivity, Doppler velocity, and spectrum width, as well as measurements of polarimetric variables such as differential reflectivity, linear depolarization ratio, co-polar correlation coefficient, and cross-polar correlation coefficients, but hydrometeors along the beam also cause attenuation, phase delay, and depolarization of wave propagation. The wave scattering and propagation properties depend on both hydrometeor characteristics and wave properties such as frequency and transmitted wave polarization. It is important to know the wave statistics and how polarimetric radar variables are related to the microphysical and statistical properties of hydrometeors. This chapter deals with wave scattering and propagation in clouds and precipitation. It describes the concepts of scattering models, coherent and incoherent scattering, coherent wave propagation, wave statistics, and polarimetric radar variables.