Main equipment of Doppler weather radar

Under the trigger of the trigger pulse, the modem generates a modulation pulse. The modulation pulse has two characteristics:

(1) has a fixed pulse width (also called pulse duration), which can be expressed in microseconds or pulse space distance h. Pulse width directly affects the detection range and range resolution, that is, the size of radar blind area. Narrow pulse width is used to detect near targets, and wide pulse width is used to increase the intensity of echo signals when detecting far targets. The pulse width of weather radar is generally 0. 1-4 microseconds, which is different for different radar detection purposes.

(2) The modulation pulse provides an appropriate video waveform with sufficient amplitude, so that the next transmitter can work normally. Under the action of modulation pulse, the transmitter generates short and powerful UHF oscillation, which is transmitted into space through the antenna, that is, detection pulse. The main technical parameters of transmitter are wavelength (or oscillation frequency f) and pulse transmission power.

(1) wavelength: The common wavelength of meteorological radar is centimeter wave, which is divided into four bands: K-band radar is used to detect non-precipitation clouds, and X-band, C-band and S-band radar is used to detect precipitation.

(2) Pulse transmission power: refers to the peak power actually transmitted by the antenna. If the loss of waveguide and antenna is ignored, the pulse transmission power is almost equal to the peak power output by the transmitter. (1) Beam width: The antenna of weather radar has strong directivity, and its radiated power is concentrated in the direction indicated by the beam. The relative distribution curve of energy flow density is called antenna pattern, and the length of the connecting line between each point on the curve and the coordinate origin represents the relative energy flow density in this direction. The lobe with the highest energy flow density in the total direction is called the main lobe, and the energy flow density in the side and the opposite direction is much smaller, which is called the side lobe and the tail lobe respectively. On the antenna pattern, the included angle between two half-power points is called beam width. The smaller the beam width, the higher the direction angle resolution and the higher the detection accuracy. The beam width of weather radar is usually less than 2 degrees, and that of Doppler radar is generally less than 1 degree. The beam width depends on the diameter of parabolic reflector and the working wavelength of radar.

(2) Antenna gain: Under the same radiation power condition, the ratio of the energy flow density of directional antenna in the beam direction to the energy flow density of antenna uniformly radiated in all directions is called antenna gain, which is expressed by G, and there is a certain relationship between antenna gain and antenna beam width. The antenna gain is expressed in decibels (dB): dB = 10 log (energy flow density of directional antenna)/(energy flow density of omnidirectional uniform divergent antenna). Receiver: receiving the echo signal of the target, amplifying it and sending it to the display for display. Echo signals are often weak, and the receiver must have the ability to receive weak signals, which is called sensitivity. Sensitivity is expressed by minimum resolvability. When the echo signal can just be distinguished from the noise signal, it is the echo power.

Show:

Plane position indicator (1) is the most commonly used display in weather radar. On this display, on the one hand, the electron beam scans radially from the center of the screen at the same speed at the pulse repetition frequency; On the other hand, the radial scanning rotates around the vertical axis synchronously with the antenna through the antenna transmitting device. When an echo signal enters, the scanning line lights up at the corresponding distance and azimuth, thus displaying the echo, and its brightness depends on the intensity of the echo signal. Recently, video integrated processors have been used to display echo signals in different shades or colors according to different intensities. Once the radar antenna is scanned, the distribution and echo intensity of the targets around the station are displayed on the screen.

(2) Range-altitude display (RHI) is also the most commonly used display in weather radar. Used to display vertical section, the ordinate is height and the abscissa is horizontal distance. The height coordinates are enlarged and the displayed echo is elongated in the vertical direction.