What Is Doppler Radar?

Doppler radar, also known as pulse Doppler radar, is a radar that uses the Doppler effect to detect the position and relative speed of a moving target. In 1842, the Austrian physicist J.C. Doppler discovered that when the wave source and the observer have relative motion, the frequency of the wave received by the observer is different from the frequency of the wave source.This phenomenon is called Doppler. The effect. When the wave source and the observer are close to each other, the frequency received is increased; when they are separated from each other, the frequency is decreased. Doppler radar is a pulse radar manufactured using this Doppler effect. Pulse Doppler radar includes range gate circuit, single sideband filter, main beam clutter suppression circuit and detection filter bank, which can better suppress the ground interference. Pulse Doppler radar can be used in airborne early warning, airborne interception, airborne navigation, low-altitude defense, fire control, battlefield reconnaissance, missile guidance, shooting range measurement, satellite tracking and weather detection. ^[1]

Chinese name: Doppler radar
Foreign name: Doppler radar
Principle: Made with Doppler effect

Features: Positioning, speed measurement, ranging
Inverse: Inversely proportional to the frequency of vibration
nickname: Pulse Doppler radar
Application: Military, meteorological survey, etc.

How Doppler radar works

Doppler radar Doppler effect

In 1842, the Austrian physicist J.C. Doppler discovered that when the wave source and the observer have relative motion, the frequency of the wave received by the observer and the frequency of the wave source are different.This phenomenon is called Doppler The effect. When the wave source and the observer are close to each other, the received frequency increases; when the two are away from each other, the frequency decreases. For example, when the wave source moves away from us, the interval between two successive peaks is larger than when they leave the transmitting source, because each subsequent peak must travel a little more than the previous peak to reach We are here. Therefore, the receiving frequency will be lower than the transmitting frequency. At this time, we will feel that the wavelength of the wave emitted from a wave source moving away from us is longer than the wavelength emitted when the wave source is stationary. Similarly, the wavelength of a wave emitted from a source moving towards us is shorter than the wavelength emitted when the wave is at rest. An example of the Doppler effect is the change in the horn of a whistle as a train passes through a station. In astronomy, the movement of spectral lines in the spectrum emitted by celestial bodies can be used to infer the speed at which celestial bodies approach or leave the observer: according to the Doppler effect, the spectral lines emitted by astronomical bodies are shifted to the longer wavelength (that is, red shifted) , Indicating that the celestial body is away from the observer; the spectral line emitted by the celestial body is shifted to the shorter end of the wavelength (ie, purple shift), indicating that the celestial body is coming towards the observer. ^[2]

Doppler radar radar works

The working principle of the Doppler radar can be expressed as follows: When the radar transmits a fixed-frequency pulse wave to scan the air, if it encounters a moving target, the frequency of the echo and the frequency of the transmitted wave are different, which is called the Doppler frequency . According to the size of the Doppler frequency, the radial relative movement speed of the target to the radar can be measured; according to the time difference between the transmitted pulse and the received time, the target distance can be measured. At the same time, the Doppler frequency line of the target is detected by the frequency filtering method, and the spectral line of the interference clutter is filtered, so that the radar can distinguish the target signal from the strong clutter. Therefore, Doppler radar has better anti-clutter interference ability than ordinary radar, and can detect moving targets hidden in the background.

Doppler radar

Doppler radar development process

Pulse Doppler radar was successfully developed and put into use in the 1960s. Since the 1970s, with the development of large-scale integrated circuits and digital processing technology, pulse Doppler radar has been widely used in airborne early warning, navigation, missile guidance, satellite tracking, battlefield reconnaissance, shooting range measurement, weapon fire control and weather. Detection and other aspects have become important military equipment. Early warning aircraft equipped with pulse Doppler radar have become effective military equipment against low-altitude bombers and cruise missiles. For example, airborne fire control systems are primarily pulsed Doppler radars. For example, the APG-68 radar equipped by American fighter aircraft represents the advanced level of airborne pulse Doppler fire control radar. It has 18 working modes, which can search and track targets in the air, on the ground and at sea, and has good anti-jamming performance. When the aircraft is flying at low altitude, it can also guide the aircraft to track terrain fluctuations to avoid collision with the ground. This radar is small in size, light in weight, and highly reliable.

In addition, this radar is also used for meteorological observation. The measurement of signals from conventional weather radars is limited to the intensity of meteorological targets. The Doppler weather radar, in addition to having all the functions of a conventional weather radar, can also provide signals for the atmospheric wind field. By Doppler velocity resolution of meteorological echoes, the distribution of various air turbulences in the atmosphere at different heights can be obtained. The development of Doppler weather radar technology in China started relatively late. In the late 1980s, research and development of Doppler weather radar and trials in meteorological business began. In the 1990s, 714CD and 714SD interpulse coherence have been produced. In 1997, the country's first imported WSR88D new generation Doppler weather radar was settled in Shanghai. In 1999, the WSR-88D was transformed. The first advanced S-band full-coherent pulse Doppler CINRAD / CC 3824. The major improvement of CINRAD / CC is to use the physical Doppler effect to measure the radial motion velocity of precipitation particles, and to infer the wind velocity distribution, wind field structure characteristics, and vertical airflow velocity of precipitation cloud bodies through velocity information. At present, it is the leading ground-based meteorological detection equipment in developed countries such as the United States and Western Europe. Doppler radar is currently the world's most advanced radar system, known as "Super Clairvoyance", with a maximum detection range radius of 460km. Compared with traditional weather radar, Doppler radar can detect the generation and change of convective clouds in the high altitude of 8-12 kilometers, and determine the speed of cloud movement. Its product information reaches 72 kinds, and the accuracy of weather forecast It will be greatly improved than before. A new generation of weather radar network is under construction for the purpose of improving the timeliness and accuracy of catastrophic weather forecasting such as sudden rainstorms, coastal typhoons and heavy rivers in China. By the end of 2010, 126 new-generation weather radar stations had been built in China, accounting for 73% of the 158 planned nationwide plans. It is divided into S and C bands. There are three different types of radars in the S band. (CINRAD / SA, CINRAD / SB, CINRAD / SC) are mainly distributed along the Yangtze River. C-band radars (CINRAD / CC, CINRAD / CB, CINRAD / CD, CINRAD / CCJ) are mainly distributed inland.

Structure of Doppler radar

Airborne pulse Doppler radar is mainly composed of antenna, transmitter, receiver, servo system, digital signal processor, radar data processor and data bus. Airborne pulse Doppler radar usually adopts a coherent system, has extremely high carrier frequency stability and spectral purity, and extremely low antenna side lobes, and adopts advanced digital signal processing technology. Pulse Doppler radar usually adopts higher and multiple repetition frequencies and multiple transmitted signal forms to use algebraic methods in data processors, and can apply filtering theory to further filter target coordinate data in data processors or prediction.

Doppler radar features

One difference between Doppler radar and traditional radar is that its transmitter is always on. This type of

The radar is called a continuous wave or CW radar. The transmitter must be turned on all the time, because unlike the traditional radar, the time between transmission and reception needs to be calculated. The Doppler radar looks for frequency changes. The frequency change does not last long, so the transmitter must always be on.

Doppler radar

Pulse Doppler radar has the following characteristics:

The programmable signal processor is used to increase the processing capacity, speed, and flexibility of the radar signal, and to improve the reusability of the equipment, so that the radar can search while tracking and can change or increase the operating status of the radar. Provide radar with the ability to cope with various interferences and the ability to identify targets beyond line-of-sight;

The programmable grid-controlled traveling wave tube is used to enable the radar to work at different pulse repetition frequencies, with the ability of adaptive waveforms. According to different tactical states, the waveforms of three types of pulse repetition frequencies can be selected. Best performance in various working conditions;

Using Doppler beam sharpening technology to obtain high resolution, which can provide high-resolution map mapping and high-resolution local magnification mapping in air-to-ground applications, and can distinguish dense formations in the air-to-air enemy situation judgment Group goals.

Doppler radar application

Doppler radar military applications

Doppler radar is widely used in airborne early warning, navigation, missile guidance, satellite tracking, battlefield reconnaissance, shooting range measurement, and weapons.

Doppler radar weather detection

Doppler radar is also used in meteorological detection and other occasions. By Doppler velocity resolution of meteorological echoes, the distribution of various air turbulences in the atmosphere at different heights can be obtained, and relevant meteorological information can be obtained.