How does the weather radar work?

The weather radar emits pulsed radio waves into space through a highly directional antenna, and interacts with the atmosphere during the propagation. For example, the water vapor condensate in the atmosphere (clouds, fog, precipitation) scatters and absorbs radar waves; The depolarization caused by the scattering of circularly polarized waves by non-spherical particles, the uneven structure of air refractive index of radio waves and the scattering of incident waves by ionized media formed by lightning discharge stabilizes the partial reflection of incident waves by stratified atmosphere; And the Doppler effect of the motion of the scattering target in the scatterer on the incident wave.

Weather radar echo can not only determine the macroscopic characteristics of the detection target, such as spatial position, shape, scale, movement and development, but also determine various physical characteristics of the target according to the amplitude, phase, frequency and polarization of the echo signal, such as water content in the cloud, precipitation intensity, wind field, vertical airflow speed, atmospheric turbulence, precipitation particle spectrum, cloud and precipitation particle phase state, lightning and so on. In addition, the vertical gradient of refractive index can be obtained from the vertical distribution of troposphere temperature and humidity by using the law that the refractive index changes with height caused by the change of troposphere temperature and humidity, and the detection distance of radar can be predicted by analyzing the propagation conditions of radio waves, or the stratification of atmospheric temperature and humidity can be inferred from the abnormal phenomenon of radar detection distance (such as superrefraction phenomenon).