What is weather radar?

Basic profile

A radar specially used for atmospheric detection. Belonging to active microwave atmospheric remote sensing equipment. The high-altitude wind radar used with radiosonde is only a special equipment for positioning displacement balloons, and it is generally not considered as such radar. Meteorological radar is one of the main detection tools for early warning and forecasting small-scale weather systems (such as typhoons and rainstorm clouds).

Conventional radar equipment generally consists of directional antenna, transmitter, receiver, antenna controller, display and camera equipment, computer and image transmission.

Weather radar uses a wide range of radio wavelengths, from 1 cm to 1000 cm. They are usually divided into different bands to represent the main functions of radar. 1, 3, 5, 10 and? What is the wavelength of 20 cm? K-band (wavelength 0.75 ~ 2.4 cm) and x-band (wavelength? 2.4 ~ 3.75cm), C-band (wavelength 3.75 ~ 7.5cm), S-band (wavelength 7.5 ~ 15cm) and? L-band (wavelength 15 ~ 30cm), and the wavelength ranges of UHF and VHF radars are 10 ~ 100cm and100cm respectively. The performance of radar in detecting atmospheric targets is closely related to its working wavelength. Considering the scattering and absorption of radio waves by cloud and rain particles, various bands have only a certain scope of application. K-band radar is often used to detect clouds that do not produce precipitation, while X-band radar, C-band radar and S-band radar are used to detect precipitation. Among them, S-band radar is most suitable for detecting rainstorm and hail, and ultra-high frequency and ultra-high frequency radar with high sensitivity can detect the clear sky flow field in troposphere-stratosphere-middle layer.

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).

Species classification

Any radar without Doppler performance is called incoherent radar or conventional weather radar, and radar with Doppler performance is called coherent radar or Doppler radar. The main weather radars are:

①? Cloud radar. It is a radar used to detect the height, thickness and physical characteristics of clouds without precipitation. Its common wavelength is 1.25 cm or 0.86 cm. ?

②? Weather radar. It is a radar used to detect the occurrence, development and movement of precipitation, and to warn and track the precipitation weather system. ?

③? Circularly polarized radar. Generally, weather radar emits horizontally polarized waves or vertically polarized waves, while circularly polarized radar emits circularly polarized waves. When radar emits circularly polarized waves, the echo of spherical raindrops will be circularly polarized waves rotating in the opposite direction, while non-spherical large particles (such as hail) will depolarize the circularly polarized waves. Based on the echo characteristics of non-spherical hail depolarization, circular polarization radar can be used to identify whether there is hail in the storm. ?

④? Fm continuous wave radar. It is a radar for detecting the boundary layer atmosphere. It has extremely high range resolution and sensitivity, and is mainly used to measure the fluctuation, wind and turbulence of the clear atmosphere in the boundary layer (see atmospheric boundary layer). ?

⑤? Meteorological Doppler radar. A radar that uses Doppler effect to measure the radial velocity of cloud and precipitation particles relative to the radar. ?

⑥? VHF and UHF Doppler radar. A radar for detecting horizontal wind profile, vertical airflow profile, atmospheric turbulence parameters, atmospheric stable stratification and atmospheric fluctuation in a clear atmosphere with a height of 1 ~ 100 km by using the inhomogeneous structure of refractive index in troposphere and stratosphere and the scattering of free electrons in the middle atmosphere. ?

The radars studied and tested include dual-wavelength radar and airborne Doppler radar. Since 1970s, the new development of synthetic aperture radar (SAR), that is, replacing a large antenna composed of many stationary small antennas with a moving small antenna, will surely accelerate the development of airborne Doppler radar in the future. Airborne Doppler radar has strong maneuverability and can obtain high-resolution Doppler velocity distribution map of convective storm.

You can find the vicinity of dangerous weather at the first time and take preventive measures in time.