Meteorological Satellite Application

Meteorological satellites, also called Weather satellite, are mainly used for weather analysis and forecasting, numerical weather prediction, climate monitoring and prediction, ecological and environmental monitoring, especially in the monitoring and warning of severe cyclone and mesoscale severe convective weather, and meteorological satellites can also be used for Earth observation and scientific experimental satellites. The meteorological satellite ground station receiving and processing system (MSGS) can receive in real time, process images and data of geostationary meteorological satellites in real time and output various forms of products.

Ground navigation satellite systems (GNSS) are widely used in meteorological satellite systems. Its basic functions are positioning, navigation and timing. These features are used for military and civilian purposes. The electromagnetic wave emitted by GNSS is used as the transmitting end of the dual radar. The high-precision receiver installed on the platform such as the ground, the aircraft and the low-orbit satellite is used as the receiving end, and the direct signal of the GNSS electromagnetic wave is received through the ground. The receiver on the low-orbit satellite is on the verge In the edge state, the occultation signal that is refracted by the atmosphere is received or scattered through the sea surface. The reflected GNSS signal can invert the total amount of water vapor in the whole atmosphere, the large temperature, the vertical distribution of humidity, the roughness of the sea surface, the waves and wind, the dielectric constant of the landmark and the soil moisture.

Characteristics of meteorological satellites are as follows:

Meteorological satellites have a wide range of observations, many observations, fast observation time, high quality of observation data, and are not limited by natural conditions and geographical conditions. The meteorological information it provides has been widely used in daily meteorological services, environmental monitoring, disaster prevention and mitigation, atmospheric science, oceanography and hydrology.

At present, meteorological satellites have realized the three-dimensional detection of meteorological elements of the Earth’s atmosphere through the selection of satellite-based remote sensing detectors, detection channels, polarization, scanning methods and active and passive remote sensing, as well as satellite attitudes and orbits: atmospheric composition detection , the detection of physical properties of clouds and aerosols in the atmosphere.

Weather satellite is mainly used to monitor the weather and climate of the Earth. There’re two types for this Satellite, one is be polar orbiting, covering the entire Earth asynchronously, or geostationary, located over the equator.

Polar orbiting satellites are low-altitude flying satellites orbiting the Earth in a nearly north-south orbit hundreds of kilometres above the earth. Most of them go through the same place several times a day. Since they travel closer to Earth, only images of limited areas can be taken at a time. However, the resolution of these images is higher than that of geostationary satellites. By contrast, geostationary satellites provide more satellite imagery of the same area on a daily basis.

Geostationary satellites are stationary relative to the Earth, which makes they capture images of the same geographical area on Earth 24 hours a day. Located about 35,800 kilometers above the equator, they take almost half of the world’s photos.

The purposes for Meteorological satellite data as below:

Satellite imagery provides a global view of the distribution of clouds and weather systems whichforms an important source of information, especially in areas where oceans and other weather observations are scarce.
Rainstorm clouds develop and rise to high altitudes, and their cloud top temperatures are relatively low. Infrared satellite images depicting cloud top temperatures can be used to monitor the development of rainstorms.
The characteristic cloud of tropical cyclones are easy to identify on satellite images and can be of great help in tracking their movement and estimating their strength.
Infrared satellite images depict changes in sea surface temperature as long as the area is not obscured by clouds. This information is useful for predicting sea fog and monitoring the development of tropical cyclones.
In addition to displaying cloud images, some satellite images also provide useful information for environmental monitoring, such as the distribution of haze, the location of wildfires, the eruption of volcanic ash and the location of dust storms.

Classification

Meteorological satellites are generally classified into polar orbit meteorological satellites and Stationary orbit meteorological satellite.

Polar orbit meteorological satellite

It is also called the Sun Synchronous Orbiting Meteorological Satellite. Its orbit is between 650 and 1500 kilometers above the Earth. It runs around the north and south poles of the Earth. The operating cycle is about 115 minutes. It can determine the height and type of the cloud and calculate the temperature of the ground and the water surface. Pollution, tides and currents on the sea surface. For the maritime industry, ocean current information is very important and can be used to predict the likelihood of a fire. Observing the snow and ice on the mountain can provide information on river water supply during the year, providing valuable forecasts for flood control and irrigation. The observation of sandstorms by meteorological satellites plays a very important role in human understanding and prediction of this phenomenon.

Stationary orbit meteorological satellite

A geostationary satellite is an artificial earth satellite that orbits a geostationary orbit. Because it is relatively stationary with the ground points, it is called a geostationary satellite. It runs on a circular orbit about 35,790 kilometers above the equator and runs at an angular velocity of 100,856,667°/s. Under the influence of some interfering forces, the orbit changes to the satellite, and orbit correction must be performed frequently. Widely used as meteorological satellites, communication satellites and broadcasting satellites. The period of the geostationary satellite is very precise. The period is large and the satellite is to drift westward. The period is small and the satellite will drift eastward. From the geostationary satellite, 40% of the Earth’s surface can be seen, so that there are three geostationary satellites with a 120-degree angle above the equator, which can cover the whole world, and are commonly used in communications and broadcasting.

Any satellite communication includes originating and terminating ground stations, uplink and downlink lines, and communication satellite transponders. It can be seen that the ground station is an important part of the satellite communication system. The basic role of a ground station is to transmit signals to satellites while receiving signals relayed by other ground stations via satellite.

The ground stations used in various satellite communication systems are diverse, and a typical duplex ground station equipment should include a channel termination subsystem, a high power transmission subsystem, a high sensitivity receiver subsystem, and an antenna feed subsystem. , servo tracking subsystem, power subsystem and monitoring subsystem.

The function of the originating device in the channel termination subsystem is to process the baseband signal and modulate the intermediate frequency (such as 70MHz); the role of the terminating device is opposite to the above process.

The channel terminal equipment can be divided into analog channel terminal equipment and digital channel terminal equipment according to the different processing signals. According to the communication service, it can be divided into channel terminal equipments such as television, telephone and data.

The functions of each unit are as follows: The function of the telephone baseband processing unit is to process the frequency division multiplexed baseband signal sent by the transmitting terminal, that is, perform pre-emphasis, automatic gain control, peak clipping, adding energy spreading signals, and adding pilot signals, etc. The function of the frequency modulator unit is to use the signal output from the baseband processing unit to the intermediate frequency FM signal of 70 MHz; the function of the intermediate frequency amplifying unit is to amplify the intermediate frequency FM signal, and to equalize the amplitude frequency characteristic and the group delay characteristic.

Transmit

In standard ground stations, high-power microwave signals of several hundred watts to more than ten kilowatts need to be transmitted to satellites. In order to achieve multiple-access communication, several carriers are often transmitted simultaneously to other ground stations. Therefore, the ground station should be able to operate with high voltage, high power, wide frequency band and multi-carrier. This system includes an upconverter, an automatic power controller, a transmit wave synthesizer, an exciter, and a high power amplifier.

The intermediate frequency broadband frequency modulated signal sent from the transmitting terminal is converted into a microwave signal by an up-converter (generally using a parametric frequency converter). The local oscillator frequency used by the upconverter is generated by the local oscillator (also called the pump source). The local oscillator generally uses the crystal phase-locked frequency multiplication method to generate a microwave oscillation frequency with a high frequency stability.

The antenna of the ground station is like a cauldron facing the communication satellite. Its diameter is generally 10-30 meters, which consists of the antenna itself, the feeding part, the tracking part and the driving part. It is responsible for monitoring, controlling and periodically testing various equipment in the ground station. Powering all ground station equipment.

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