What is the great function of meteorological satellites?
Meteorological satellites are usually equipped with television camera system, scanning radiation device, automatic image transmission system and automatic storage device. With these instruments, we can observe the global weather and obtain information such as temperature, humidity, air pressure, density and atmospheric structure.
When the meteorological satellite runs in the predetermined orbit, the camera of its TV camera system opens the shutter at regular intervals to obtain the image of the earth's atmosphere. Then, through the conversion equipment, the satellite converts the image information of the cloud image into electrical signals, which are sent to the storage equipment for automatic storage. Its storage device can accommodate all cloud information from all over the world. When the satellite passes through the ground receiving station, the ground sends instructions to it, and the satellite transmits all information. If no memory is used, satellites can also be transmitted to the ground immediately by radio signals. As long as there is receiving equipment on the ground, real-time photos taken by satellites can be received immediately. Any object has a certain temperature and gives off a certain amount of heat. The scanning radiation device on the satellite measures the thermal radiation of the cloud and obtains the infrared cloud image. Infrared cloud pictures can reflect the temperature of the ground and cloud top. The atmospheric temperature is generally lower than the ground, and the temperatures of clouds at different heights are different, so their thermal radiation is also different. On the satellite infrared cloud picture, the white place is the cold area, which is the middle and high cloud area. Dark places are warm areas, not ground, water or low clouds.
Scanning radiation equipment and TV cameras take pictures in different ways. It scans the earth with a scanning mirror at a fixed speed, and every time it rotates, it gets a long scanning line from one end of the earth to the other. When the satellite keeps moving forward, the scanning lines are connected with each other to form a complete infrared cloud picture.
1974 On May 17, the United States launched its first synchronous meteorological satellite. Compared with other series of meteorological satellites, it covers a large area, can provide a large number of meteorological data in time and transmit high-resolution meteorological photos of the whole western hemisphere to the ground all day. It transmits observation data every half hour, which can be used to deeply understand the process of atmospheric dynamics and energy exchange and improve the accuracy of meteorological forecast. Automatic image devices with more than 500 receiving stations around the world can also receive satellite photos directly.
Although geostationary or synchronous meteorological satellites cover a large area, they cannot cover the north and south poles of the earth. Therefore, countries near the Arctic, like the former Soviet Union, have launched another polar-orbiting meteorological satellite, which is also a sun-synchronous low-orbit meteorological satellite with a height of 700~ 1500 km. This is a meteorological satellite with an orbital inclination of about 90 degrees, flying over the north and south poles of the earth. As we all know, the earth is not a standard sphere, but a slightly inflated flat sphere at the equator. The expanded part has extra attraction to artificial celestial bodies, which can make the orbital plane of the satellite rotate slowly. The rotation speed of the track plane is related to the inclination, height and shape of the track. The smaller the inclination angle, the faster the rotation. A near-polar circular orbit with an inclination of 99 and a height of 920 kilometers is called a sun-synchronous orbit. The orbital plane rotates once a day along the earth's rotation direction, which is just in synchronization with the sun's rotation once a day due to the earth's revolution around the sun, or an orbit with the same rotation direction and period as the earth's revolution direction and period. The advantage of sun-synchronous orbit is that the angle between the orbit plane and the direction of the sun is generally determined. Therefore, meteorological satellites running in sun-synchronous orbit generally pass through the same latitude of the earth at the same time every day; In other words, the sun-synchronous orbit enables meteorological satellites to observe the ground under the same illumination conditions all the time, creating the most suitable illumination conditions for optical sensors. On the other hand, the orbital inclination of polar-orbiting meteorological satellites is about 90, so it is impossible to take advantage of the eastward speed brought by the earth's rotation, which requires the launch vehicle to bear a greater burden. The meteorological satellite Fengyun 1 launched by China is also in sun-synchronous orbit.
Because meteorological satellites can collect high-altitude and ultra-high-altitude meteorological conditions that are difficult to be collected by ground meteorological stations and cannot be obtained by balloons and airplanes, the accuracy and real-time performance of weather forecasting are greatly improved. In TV programs, the weather forecast is broadcast every day, and at the same time, colorful satellite cloud pictures are also broadcast, which are taken from space by meteorological satellites with TV cameras and scanning radiation devices. This daily weather forecast has brought great convenience to everyone and played a great role in agriculture and transportation. Various meteorological satellites operating in space always monitor the changes of disastrous weather such as typhoon, strong storm, rainstorm and drought. They are not limited by geographical conditions, and can obtain meteorological data of sparsely populated areas such as sea surface, polar regions, plateaus, deserts and forests, which can further help monitor harmful weather. With the application of microwave radar in meteorological satellites and the development of atmospheric remote sensing technology and atmospheric science, meteorological satellites have gradually developed from qualitative cloud image detection to quantitative detection of atmospheric temperature, humidity, wind speed, cloud cover, precipitation, sea surface humidity and atmospheric composition, which will play a greater role in improving the accuracy of medium and long-term weather forecast.
In order to better grasp the global weather changes, the World Meteorological Organization organized a global meteorological satellite network and put it into operation. The system consists of five meteorological satellites in geosynchronous orbit and two meteorological satellites in solar synchronous orbit. Five geostationary meteorological satellites, each of which can observe a nearly circular area of 50 N/S and 70 E/E, are provided by the United States, the former Soviet Union, ESA and Japan 1. Two polar orbiting meteorological satellites were launched, which made up for the defect that five geostationary meteorological satellites could not cover the polar regions of the earth. The United States and the Soviet Union provided 1 satellite respectively. This criss-crossing meteorological satellite network can continuously monitor the meteorological changes in any part of the world. All countries in the world can receive the cloud images sent back by satellites for free with simple receiving equipment, thus improving the timeliness and accuracy of weather forecast.
Learning point
satellite cloud picture
We often hear the forecaster mention the word "satellite cloud picture" in the weather forecast. What is a satellite cloud image? The so-called satellite cloud image is the image of cloud cover and surface characteristics observed by meteorological satellites from top to bottom.
Satellite observation of the earth has become an indispensable source of information in today's world. Using satellite cloud images, we can identify different weather systems, determine their positions, estimate their intensity and development trend, and provide important basis for weather analysis and weather forecast. In areas lacking meteorological observation stations such as oceans, deserts and plateaus, the information provided by satellite cloud images makes up for the deficiency of conventional detection data and plays an important role in improving the accuracy of forecasting.