Traditional astronomical observation is carried out on the ground by the observatory with various instruments. Because most of the electromagnetic radiation emitted by celestial bodies is blocked by the earth's atmosphere, only a small part can reach the ground, so the universe that can be observed with optical telescopes or radio telescopes on the ground is only a small and incomplete part, and it is impossible to fully understand the true face of the universe.
The artificial earth satellite is an astronomical satellite, and its appearance has made a revolutionary leap in astronomical observation, because it fly at a height of several hundred meters to several Qian Qian meter outside that earth's atmosphere, and can observe space in the whole band without being blocked by the atmosphere. The appearance of astronomical satellites has promoted the formation of a new discipline-space astronomy, which is an effective means for human beings to further explore and understand the universe.
Astronomical satellites are equipped with various detection instruments, which have their own characteristics compared with other satellites.
High pointing accuracy. Because the astronomical satellite wants to find the celestial object to be observed in the vast space, the observation instruments and equipment must always point at this celestial body, which requires the astronomical satellite to have extremely accurate pointing accuracy and attitude control accuracy. Therefore, astronomical satellites generally point to the sun or stars as reference objects.
High structural requirements. Because of the high pointing accuracy, the requirements for satellite structure are also very strict. It is necessary to ensure the high assembly accuracy and stability of satellite structure, especially the minimum deformation when heated, so as to ensure the pointing accuracy.
The observation instrument is very complicated. Astronomical satellites are equipped with high-precision observation instruments and equipment, such as infrared, ultraviolet, X-ray and visible light telescopes. They are not only complicated in structure and difficult to manufacture, but also need to work reliably at ultra-low temperature, so complex refrigeration measures should be taken. In addition, the observation data of astronomical satellites are huge, so it is necessary to use the computer on the satellite for data processing and operational control.
Various astronomical satellites have been developed. According to different observation targets, it can be divided into two categories: solar observation satellites that mainly observe the sun and non-solar exploration astronomical satellites that mainly detect celestial bodies outside the solar system. The first astronomical satellite in the world is the "Solar Radiation Monitoring Satellite" launched by the United States in 1960, which mainly detects the ultraviolet rays and X-rays of the sun. The "orbiting solar observatory" launched by the United States from 1962 to observe the sun is also a solar observation satellite. The Solar and Heliospheric Observatory (SOHO) launched in Europe in recent years has made many new achievements in observing the sun.
Many non-solar astronomical satellites have been launched, such as Hubble Space Telescope and Chandra X-ray Telescope, and are currently flying in orbit. Their main tasks are to detect the emission sources of ultraviolet rays, X-rays and gamma rays in the universe, determine their direction, intensity and radiation spectrum characteristics, and detect stars, nebulae, interstellar matter, the Milky Way and celestial bodies outside the Milky Way.
According to the main observation bands of scientific instruments loaded on astronomical satellites, astronomical satellites can be divided into infrared astronomical satellites, ultraviolet astronomical satellites, X-ray astronomical satellites and gamma-ray astronomical satellites. They all have special purposes to detect different radiation characteristics. For example, the "orbital observatory" launched by the United States in 1968 and 1972 was the earliest astronomical satellite devoted to ultraviolet observation; The "Small Astronomical Satellite" launched by 1970 is an astronomical satellite specially used for detecting X-rays. Since the 1990s, the United States began to implement the "big observation plan", that is, launching four large astronomical satellites, which can carry out full-band observation. At present, three space telescopes have been launched, namely Hubble Space Telescope, Compton γ -ray Observatory and Chandra X-ray Space Telescope, and the infrared space telescope will be launched soon. They are the most advanced astronomical satellites and have made great achievements. For example, through the Hubble space telescope, human understanding of the size and age of the universe has been greatly enhanced; It is proved that there are supermassive black holes in the center of some cosmic galaxies; The exploration of "primitive galaxies" in the early days of the birth of the universe made it possible for astronomers to track the history of the development of the universe; It clearly shows the environment in which quasars, the brightest celestial bodies in the Milky Way, exist. It is found that oxygen exists in the atmosphere of Europa and Ganymede. The first image of an extrasolar planet was captured. Compton γ -ray Observatory has expanded the observation range of cosmic rays by 300 times. It once observed the cloud of antimatter particles ejected by the Milky Way, which caused a sensation in the astronomical world. The Chandra X-ray Space Telescope found that there are about 7,000 X-ray sources in the universe.
At present, many astronomical satellites with various purposes have been launched in the world. With the continuous development of astronomical exploration, there will be more and more advanced astronomical satellites.
Scientific satellite
Scientific exploration satellite is a satellite used to explore the physical environment in space. It carries all kinds of instruments, crosses the atmosphere and outer space, and collects all kinds of information from space, which makes people have a deeper understanding of the universe and provides very valuable information for human beings to enter and use space. Most of the satellites initially launched by countries all over the world are such satellites or technical test satellites.
The first satellite launched by the United States, Explorer, was a scientific exploration satellite. Later, the explorer developed into a series of scientific satellites, mainly used to detect the earth's atmosphere and ionosphere. Measuring the earth's high-altitude magnetic field; Measuring solar radiation and solar wind; Explore interstellar space, etc. Explorers are mostly small satellites, but their shapes and structures are quite different. Due to the different space areas of exploration, their orbits are high and low, far and near, and there are also great differences.
Electronic satellites are a series of scientific satellites in the former Soviet Union. It is equipped with high-sensitivity and low-sensitivity magnetometers, low-energy particle analyzers, proton detectors, solar X-ray counters and instruments for studying the composition of cosmic radiation. The main task of this series of satellites is to study the particles entering the radiation belt inside and outside the earth and related space physical phenomena.
China's "Practice" series of satellites are both technical experimental satellites and scientific exploration satellites. The "Shi Jian 1" satellite is equipped with infrared horizon and solar goniometer, and a large amount of environmental data has been obtained. "Practice II" and "2 A" and "2 B" are three satellites launched at the same time by a rocket. Among them, the shape of "Practice II" is an octahedral prism, and its task is to detect the space environment and test new technologies such as directional attitude control and large-capacity data storage of solar array.
Astronomical satellite is also a kind of scientific satellite, which specializes in scientific observation of various celestial bodies and other space substances. Astronomical satellites operate in orbits hundreds of kilometers or higher from the ground. Because there is no atmosphere to stop them, the instruments on board can receive electromagnetic radiation of various bands from other celestial bodies and can better observe space.
The orbits of astronomical satellites are mostly circular or nearly circular, with a height of several hundred kilometers, but generally not less than 400 kilometers. This is because the celestial bodies outside the solar system are far away from the earth, and increasing the orbital height can not shorten the distance between them and improve the observation ability; When the orbit is too low, the atmospheric density increases, making it difficult for satellites to operate for a long time.
Radio relay satellite
An artificial earth satellite of a radio communication relay station. Communication satellites reflect or forward radio signals to realize communication between satellite communication earth stations or between earth stations and spacecraft. Communication satellite is the space part of various satellite communication systems or satellite broadcasting systems. A geostationary communication satellite can cover about 40% of the earth's surface, so that any communication station on the ground, at sea and in the air can communicate with each other at the same time. Three geostationary communication satellites distributed at equal intervals over the equator can achieve global communication except for parts of the poles.
1958 65438 February, the United States launched the world's first experimental communication satellite. 1963, the United States and Japan made the first trans-Pacific TV transmission through the "relay 1" satellite. China launched a geostationary orbit test communication satellite on April 8, 1984. Communication satellites are divided into stationary communication satellites and non-stationary communication satellites according to their orbits; According to different service areas, it can be divided into international communication satellites and regional communication satellites or domestic communication satellites; According to the purpose, it can be divided into special communication satellites and multi-purpose communication satellites. The former is such as TV broadcasting satellite, military communication satellite, maritime communication satellite, tracking and data relay satellite, while the latter is such as military-civilian communication satellite and multi-purpose satellite with communication, meteorology and broadcasting functions.
As a radio communication relay station. A communication satellite, like an international messenger, collects all kinds of "letters" from the ground and then "delivers" them to users in another place. Because it "stands" at an altitude of 36,000 kilometers, its "delivery" coverage is particularly large, and a satellite can be responsible for the communication of the earth's surface13. If three communication satellites are evenly placed in the geostationary orbit, except the north and south poles, global communication can be realized. When a satellite receives a weak radio signal from a ground station, it will automatically turn it into a high-power signal, and then send it to another ground station, or to another communication satellite, and then to a ground station on the other side of the earth. In this way, we received a signal from far away.
Communication satellites generally adopt geostationary orbit, which is located at 35786 kilometers above the equator of the earth. In this orbit, the satellite rotates around the earth from west to east at a speed of 3075 m/s, and the time for one round of the earth is 23 hours, 56 minutes and 4 seconds, which is exactly the same as the time for the earth to rotate once. Therefore, from the ground, the satellite image hangs motionless in the sky, which makes the work of the ground receiving station much more convenient. The antenna of the receiving station can be fixed on the satellite and communicate day and night without interruption, so that the signal is intermittent during communication. Now, communication satellites undertake all intercontinental communication services and TV transmission.
Communication satellite is one of the earliest and most widely used satellites in the world, and many countries have launched communication satellites.
1On April 6, 965, the United States successfully launched the world's first practical geostationary orbit communication satellite: "Intelsat 1". So far, this type of satellite has developed to the eighth generation, and each generation has improved in volume, weight, technology, communication ability and satellite life.
The communication satellite of the former Soviet Union was named Lightning. Including "lightning 1, 2, 3" and so on. Because of the vast territory of the former Soviet Union, most lightning satellites are not in geostationary orbit, but in an elliptical orbit with a large eccentricity.
China's first geostationary communication satellite was launched on April 8, 1984, named "Dongfanghong II". So far, five satellites have been successfully launched. These satellites have successively undertaken radio and television signal transmission and long-distance communication, and played a great role in national economic construction.
meteorological satellite
Meteorological satellite originated from reconnaissance satellite, which is a kind of satellite specially used to observe the earth and atmosphere. 1 April 19601day, the United States launched the world's first meteorological satellite, taking the lead in introducing space science and technology into the field of meteorological science. It provides the United States with worldwide meteorological information. The former Soviet Union applied meteorological satellites earlier, and its first practical meteorological satellite was launched in June 1966.
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 to the predetermined orbit, the camera of its TV camera system opens the shutter at regular intervals to obtain the image of the earth's atmospheric clouds. 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 the memory is not used, the satellite can immediately transmit the radio signal to the ground. 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 meteorological photos of the whole western hemisphere to the ground day and night with high resolution. 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 an altitude 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 nearly polar circular orbit with an inclination of 99 degrees and a height of 920 kilometers, the orbital plane rotates 1 degree every day along the earth's rotation direction, which is just in synchronization with the sun's irradiation direction, because the earth revolves around the sun, or an orbit with the same rotation direction and period as the earth's revolution direction is called a sun-synchronous orbit. 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 degrees, 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, while broadcasting "weather forecast" every day, colorful satellite cloud pictures are also displayed, 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 constantly monitor the changes of severe 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 degrees north and south latitude and 70 degrees east longitude, are provided by the United States, the former Soviet Union, ESA and Japan each provide 1 satellite, and two polar orbiting meteorological satellites are launched to make up for the defect that five geostationary meteorological satellites cannot cover the polar regions of the earth, one provided by the United States and the other by the Soviet Union. 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.
Ocean satellite
Most of the earth's surface where human beings live is ocean, accounting for 7 1% of the total surface area of the earth. It is changeable and has a great influence on human activities. A deep understanding of the ocean has always been an urgent desire of scientists. However, the observation conditions in the ocean are much more difficult than those on land, and the classical oceanographic observation method using ship measurement has great limitations, which seriously hinders the observation of marine phenomena, especially ocean dynamics. Only by continuous and real-time observation of the changeable state of the ocean can human beings grasp the dynamic data of the ocean in time, understand the ocean and develop and utilize it.
Marine satellite is equipped with optical imaging equipment and microwave equipment, which can detect marine electromagnetic radiation and its reflection and scattering characteristics on the sea surface in different States. It can not only measure the image of the sea surface, but also obtain data such as sea temperature, sea surface wind speed, wind direction, sea surface wave height, ocean current and sea surface appearance.
According to the characteristics of satellite orbit, ocean satellites can provide large-scale or even global ocean data in a short time, thus becoming the most powerful tool for observing oceanography, especially ocean dynamics. Ocean satellites can also predict the atmospheric circulation of the ocean, roughly monitor and predict the dynamic phenomena on the ocean surface, and improve the accuracy of global weather forecast and global geoid.
Marine satellites are generally equipped with five kinds of remote sensors, namely radar altimeter, microwave scatterometer, synthetic aperture radar, microwave radiometer, visible light and infrared radiometer. The radar altimeter has two functions: one is to measure the distance from the satellite to the sea surface under the satellite and provide data for measuring the ocean horizon. The ranging accuracy can reach10 cm; The second is to measure the sea surface roughness, so as to obtain the wave height information in the range of 1 ~ 20m, and the accuracy is 10% of the wave height. Tsunamis caused by submarine earthquakes spread rapidly, often causing great disasters to ships on shore and at sea. Radar altimeter can measure the height and distribution of tsunami waves, determine the direction of tsunami propagation, and give early warning to the attacked areas.
Synthetic Aperture Radar (SAR) can obtain ocean images, and extract ocean waveforms and ocean dynamics features from them. The radar can emit seawater wave images with the wavelength of 50 ~ 1000 meters. This imaging radar wave can pass through clouds, rain or shine, and can work day and night. It can provide high-resolution images of wave patterns, mineral deposits and other similar features near the coastline, and measure their areas. You can also draw the pollution range such as ice sheet and oil pollution. It can also identify fish schools and map ocean currents with a resolution of 25 meters.
Microwave wind scatterometer is also an active radar and a long pulse radar. It can measure the wind field in any direction in the world, and the wind speed measurement range is 3 ~ 25m/s. The ground coverage of the scatterometer is a symmetrical broadband, about 235km from both sides of the next point of the satellite.
Microwave radiometer is a scanning multi-frequency passive microwave remote sensor, which can sense the intensity of microwave radiation on the ocean surface or the brightness temperature of microwave radiation on the surface. Brightness temperature is a function of material emissivity, electrolytic characteristics and roughness. This microwave radiometer can detect the amplitude of sea surface wind with wind speed greater than 50 m/s; It can detect the surface temperature of seawater within the range of 2 ~35 degrees Celsius; Measure the sea ice distribution within the range of10 ~15km; Measure water vapor in the atmosphere, coastal characteristics, etc. The antenna of scanning microwave radiometer scans from the range of 35 degrees vertical to the ground of the satellite, which is equivalent to the ground coverage of about 1000 km centered on a point below the satellite. Microwave radiometer provides important atmospheric correction data for scatterometer and radar altimeter.
Scanning visible and infrared radiometer is an auxiliary measuring equipment, which provides visible and thermal infrared images of marine coastal and atmospheric characteristics and helps to identify ocean currents, storms, marine ice, clouds and islands. It uses 360-degree scanning to monitor the wide coverage area of 1800 km under the satellite.
The material benefits created by ocean satellites to mankind are enormous. It can provide real-time or near-real-time data of environmental conditions, making the engineering design of marine and coastal life protection, coastal construction, ship design and manufacturing, fishery and offshore operation more reasonable and economical.
Resource satellite
A satellite used to investigate and study the natural resources of the earth. It can "see through" the stratum, find underground treasures, historical sites and stratum structure that people can't see with the naked eye, survey crops, forests, oceans, air and other resources, and predict various serious natural disasters.
The resource satellite uses multi-spectral remote sensing equipment on board to obtain multi-band electromagnetic wave information radiated or reflected by ground objects, and then sends these information to the ground station. Because the reflection of each object in different spectral bands is different, after receiving the satellite signal, the ground station will process and interpret the information according to the spectral characteristics of various substances, so as to obtain detailed information such as the characteristics, distribution and status of various resources, so that people can avoid the hard work of running around and investigating on the spot.
Resource satellites are divided into two categories: one is land resource satellites, and the other is marine resource satellites. Land resources satellites are mainly used for land surveys, and marine resources satellites are mainly used for finding marine resources.
Generally, a resource satellite runs in a sun-synchronous orbit, which can make the orbital plane of the satellite rotate 1 degree along the earth's rotation direction every day, which is basically equal to the distance of the earth's revolution around the sun every day of about 1 degree. This not only enables the satellite to observe any place on the earth, but also enables the satellite to fly to a certain area at the same time every day, thus realizing the regular survey of the sky.
The world's first land resources satellite was launched by the United States on July 23, 1972, and was named "Landsat 1". It adopts a nearly circular sun-synchronous orbit, 920 kilometers high from the earth, and orbits the earth 14 times a day. The camera equipment on the satellite continuously shoots the earth's surface, and each image can cover nearly 20,000 square kilometers, which is 140 times that of aerial photography.
The world's first marine resources satellite was also launched by the United States in June 1978, and was named "Ocean Satellite 1". It is equipped with all kinds of telemetry equipment, which can observe the characteristics of seawater, draw routes, find fish schools, and measure waves and sea breeze in all kinds of weather.
Television direct broadcast satellite
Television direct broadcast satellite, also called broadcasting satellite, is a special communication satellite, which is mainly used for television broadcasting. This is a TV broadcast forwarding system, which consists of a broadcast repeater, a transceiver antenna and a security system. This is a space broadcasting transmitting station operating in geostationary orbit.
The way of broadcasting TV images and sound signals directly to the public through broadcasting satellites is called satellite broadcasting. Satellite broadcasting is realized by satellite broadcasting system, which consists of broadcasting satellite, ground receiving network, uplink station and sounding station.
The TV direct broadcast satellite adopts three-axis satellite measurement and control technology, which has high accuracy of orientation to the ground, and is equipped with folding large-area solar panels, with high emission power and wide coverage area. Through the satellite broadcasting system, as long as a small antenna and other equipment are installed on the TV, you can receive the live TV broadcast without the need for TV relay. Therefore, live TV broadcast provides great convenience for TV education, medical activities and cultural and sports life. Movies can also be broadcast through this satellite. For example, the satellite film company first transmits the image of the film to the rented satellite channel by radio, and then transmits it to the ground by satellite. If a cinema on the ground wants to show a movie from a satellite film company, it must buy a "relay cipher" from the company and install it on its own receiving equipment, so that it can play the movie on its own big screen.
The application of TV direct broadcast satellite is of great benefit to individual family users. Especially compared with terrestrial TV, it has great advantages. First of all, it covers a wide area, which can solve the problem that it is difficult to build ground relay stations in remote areas, mountainous areas and islands in some countries and cover local TV. Now with live TV, retail investors living in remote mountainous areas can install a small antenna on TV, and through TV, they can see the world like a big city. Secondly, terrestrial TV stations and networks often relay TV to distant places many times, which seriously affects the broadcasting quality. However, satellite live TV broadcasts few links, and usually adopts FM mode, so the reception quality is better.
earth observing satellite
It turns out that in thousands of years of production activities and life practice, we humans have gradually realized the great influence that the earth has brought to mankind. On the one hand, the earth, as a place where human beings thrive, unreservedly provides various conditions and materials for human survival and production activities, such as mineral resources, food crops, forests and grasslands, aquatic resources and so on. On the other hand, the earth has also brought huge and sometimes devastating disasters to human beings, such as floods, volcanic eruptions, earthquakes and diseases and pests of crops and forests and grasslands.
According to incomplete statistics, the annual losses caused by various natural disasters in the world are as high as hundreds of billions of dollars. In the United States, due to crop diseases, the annual loss is about $3.7 billion, while the loss of pests is $3.8 billion. China is also a country with frequent disasters, whether it is floods or earthquakes, there are considerable losses every year.
Humans have also found that although we live on the earth, due to our own limitations and the limitations of scientific and technological development, we do not fully understand the mystery of the earth itself. We just study the earth on the earth. As the poet said, "We don't know the true face of Lushan Mountain, we only live on this mountain". Therefore, we must seek a new method, that is, to study and explore the earth outside it, so as to better develop and utilize it. Earth observation satellite is our ideal tool, which can help us really understand the earth.
So, what are the advantages of Earth observation satellites? Characteristics of Earth Observation Satellites
(1) Come on. Earth observation satellites are generally launched into low orbit, and the time for such satellites to fly around the earth is about 90 minutes, that is, 1? Around the earth in 5 hours, the information obtained is very timely.
(2) see wide. Generally, the orbits of earth observation satellites are elliptical orbits with large inclination angles, even polar orbits passing through the north and south poles, so they can be reached everywhere on the earth. Moreover, a satellite can cover tens of millions of square kilometers of ground area, and can carry out a very extensive survey of the earth, especially in those areas where human beings can't reach, which shows its advantages.
(3) A large amount of information. There are various observation means and equipment on the earth observation satellite, which can comprehensively detect all kinds of information on the earth.
Take photography as an example. A photo can contain a variety of rich contents, including forests, mountains and oceans, as well as farmland, highways, cities, villages, airports and shipping ports, which can be said to be all-encompassing.
In this way, different professional departments can extract different professional contents from it, and there is no need to send another satellite for agricultural exploration and another satellite for mineral exploration, which greatly improves efficiency, saves funds and realizes the comprehensive utilization of information.
In addition, it can not only observe the visible part of the surface, but also observe the invisible part, such as detecting a certain depth range below the surface.
Application fields of Earth observation satellites
The information obtained by earth observation satellites is very rich and can be applied to all fields of national economy. Let's take China as an example to talk about its main applications:
(1) Wan Li has a panoramic view.
The so-called national territory refers to all the land, territorial sea and continental shelf within the sovereignty of a country. Including the integration of above-ground, underground and air resources. China has a vast territory and rich products, with a land area of 9.6 million square kilometers and a continental shelf of10.3 million square kilometers, which is rich in various resources and needs to be developed and utilized urgently. In the past 40 years, the ecological environment in China has changed obviously. On the one hand, with the development of urban and rural construction, agriculture and fishery, the expansion of cultivated land has brought prosperity and development. On the other hand, in some places, blindly destroying forests to expand fields and reclaiming land from lakes have aggravated ecological deterioration, accelerated soil erosion and caused the trend of increasing natural disasters. If we use the traditional census method, we will encounter many difficulties. Especially some ancient alpine forests and desert swamps are difficult for people to reach. Is a place that can be reached. Relying on traditional manual measurement is slow and costly. How much time and manpower does such a big country need? Earth observation satellites have the characteristics of fast flight speed and large field of view, and can conduct an all-round and large-scale investigation of China and obtain all kinds of useful information. This will provide a basis for rational development and utilization of land.