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en:lesson04 [2021/04/05 11:28] (current)
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 ====== Satellite image analysis ====== ====== Satellite image analysis ======
  
-===== Weather ​satellite orbits =====+===== Meteorological ​satellite orbits =====
  
 {{:​04image001.png?​600|}} {{:​04image001.png?​600|}}
    
-Weather ​satellites, as a rule, are launched either ​into a sun-synchronous orbitor into a geostationary one. +Meteorological ​satellites are usually ​launched ​into either a sun-synchronous orbit or a geostationary one. A geostationary orbit is an orbit based on which satellite ​orbits ​the Earth for exactly one day. Thus, it turns out that the satellite ​is set over the same point on the equator. The distance from the Earth'​s surface to the geostationary orbit is about 35,800 km. Applying this height ​the satellite can check about 1/3 of the Earth'​s ​entire surface. ​The following meteorological satellites ​are located ​on this orbit: GOMS (Russia), GOES-15 (USA), Meteosat 10 (EU). 
-A geostationary orbit is an orbit in which the satellite’s period of revolution around ​the earth is exactly one day. Thus, it turns out that the satellite, as it were, hangs over the same point at the equator. The distance from the Earth'​s surface to the geostationary orbit is about 35,800 km. From such a height, a satellite can view about 1/3 of the entire surface ​of the EarthMeteosatellites ​are located ​in this orbit: GOMS (Russia), GOES-15 (USA), Meteosat 10 (EU). +
-A sun-synchronous orbit is an orbit in which a satellite passes over any point on the earth’s surface at approximately the same local solar time. Thus, the angle of illumination of the earth'​s surface will be approximately the same at all passages of the satellite. Such constant lighting conditions are very suitable for weather satellites. To achieve such characteristics,​ the parameters of the orbit are selected so that the orbit precesses eastward by 360 degrees per year (approximately 1 degree per day), compensating for the Earth'​s rotation around the Sun. Meteosatellites are located in this orbit: Meteor-M 2 (Russia), NOAA 15, 18, 19 (USA). +
-Meteosatellites located in a sun-synchronous orbit do not immediately capture the entire surface of the Earth, they scan the image on one line and transmit it at a frequency of about 137 MHz in analog format (APT). Special computer programs collect ready-made images from these lines. +
-=====Photo resolution=====+
  
-The resolution of images ​obtained ​from satellites series ​NOAA is 4 km per pixel. The image is made up of two IR channels, ​using geometric correction of perspective distortions. ​Thus, we get a certain average idea of the real temperature at a specific ​point on the surface.+A sun-synchronous orbit is an orbit in which a satellite passes over any point on the Earth'​s surface at approximately the same local solar time value. Thus, the angle of illumination of the Earth'​s surface will be approximately the same during all passages of the satellite. Such constant illumination conditions are very suitable for weather satellites. In order to achieve desired characteristics,​ the orbit parameters are chosen in a way when the orbit precesses eastward by 360 degrees per year (approximately 1 degree per day), compensating for the Earth'​s rotation around the Sun. The following meteorological satellites are located on this orbit: Meteor-M 2 (Russia), NOAA 15, 18, 19 (USA). Meteorological satellites provided in the sun-synchronous orbit do not capture the entire surface of the Earth at once, rather scanning the image in the mode "one line at a time" and transmitting it at a frequency of about 137 MHz using the analog format (APT). Special computer software connects all ready images based on this data. 
 + 
 +===== Image resolution ​===== 
 + 
 +Resolution ​of images ​received ​from NOAA series satellites ​is equal to 4 km per pixel. The image is composed ​of two IR channels, ​applying ​geometric correction of perspective distortions. ​In such a way, we get a kind of averaged representation ​of the real temperature at a particular ​point of the surface.
  
 {{:​04image003.png?​600|}} {{:​04image003.png?​600|}}
  
    
-Since our planet ​has the shape of a ball, the pixels located in the center of the image have a size of 4 km by 4 km, and the pixels located ​at the edges of the image have an elongated ​shape - 4 km by 8 km or even 4 km by 12 km.+Since our planet ​is shaped like a ball, all pixels located in the center of an image are equal to 4 km by 4 km, while pixels located ​on edges of the image turn to be elongated, reaching the value 4 km by 8 km or even 4 km by 12 km.
  
 {{:​04image005.png?​600|}} {{:​04image005.png?​600|}}
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 ===== Infrared radiation ===== ===== Infrared radiation =====
  
-Weather ​satellites ​photograph ​the surface in the visible range and in the infrared (IR) range. +Meteorological ​satellites ​take photos of the surface in the visible range and in the infrared (IR) range. Infrared radiation is not visible to the human eye rather being detected by the satellite'​s ​camera. Infrared radiation is also called "​thermal"​ since infrared radiation ​taken from heated objects is perceived by the human skin as sensation of heat.
-Infrared radiation is not visible to the human eye, but is detected by satellite camera. Infrared radiation is also called "​thermal ​radiation"since infrared radiation from heated objects is perceived by human skin as sensation of heat.+
  
-{{:04image007.jpg?600|}}+{{:en:infrared.png?400|}}
    
 +
 The infrared range is divided into several subranges. The infrared range is divided into several subranges.
  
-Near IR+Near infrared range: wavelength λ = 0.74-2.5 microns
  
-   * frequency ν (nude) - up to 4 · 1014 Hz +Middle infrared range: ​wavelength λ = 2.5-50 microns
-   * wavelength λ (lambda) ​from 730 nm+
  
-Mid IR +Far infrared range: ​wavelength λ = 50-2000 microns
-  +
-   * frequency ν - up to 6 · 1013 Hz +
-   * wavelength λ - from 5 microns+
  
-Far IR 
- 
-   * frequency ν - up to 1013 Hz 
-   * wavelength λ - from 30 microns 
  
  
-===== Atmospheric ​effect ​=====+===== Atmospheric ​influence ​=====
  
-The Earths surface and clouds absorb visible and invisible radiation from the Sun and re-emit most of the energy ​in the form of infrared radiation back into the atmosphere. Some substances in the atmosphere, mainly water droplets and water vaporabsorb this infrared radiation and re-emit it in all directions, including back to Earth. Thus, the greenhouse effect keeps the atmosphere and surface ​in a warmer ​state than if there was no water vapor in the atmosphere. +The Earth's surface and clouds absorb visible and invisible radiation from the Sun and re-radiate ​most of the energy ​as infrared radiation back into the atmosphere. Some substances ​contained ​in the atmosphere, mainly ​water droplets and water vapor absorb this infrared radiation and re-radiate ​it in all directions, including back to the Earth. Thus, the greenhouse effect keeps the atmosphere and surface warmer than if there were no water vapor in the atmosphere.  
-Sunlight ​illuminating the Earth is partially absorbed by the atmosphere, surface and cloudsand is partially reflected from the surface, clouds and aerosols. A satellite camera receives this radiation and forms an image in the visible range. In the infrared range, the satellite’s camera also receives radiation from the surface, clouds and the atmosphere. ​Moreover, ​surface radiation is partially absorbed by the atmosphere.+ 
 +The sunlight ​illuminating the Earth is partially absorbed by the atmosphere, surface and clouds and is partially reflected from the surface, cloudsand aerosols. A satellite camera receives this radiation and forms an image in the visible range. In case of the infrared range, the satellite camera also receives radiation ​data from the surface, clouds and atmosphere. ​It is necessary to consider that surface radiation is partially absorbed by the atmosphere.
  
 {{:​04image009.png?​600|}} ​ {{:​04image009.png?​600|}} ​
  
- +As a result of interactions with the atmosphere, the intensity of solar radiation at the Earth'​s ​surface ​is reduced by more than half compared to its value in the upper layers of the atmosphere.
-As a result of interactions with the atmosphere, the intensity of solar radiation at the surface ​of the Earth in comparison with its value in the upper layers of the atmosphere ​decreases by more than half.+
  
 {{:​en:​image_34.png?​300|}} {{:​en:​image_34.png?​300|}}
    
-Solar radiation ​coming to the surface of the Earth is not completely ​absorbed by it. Part of the radiation ​is reflected by the surface, and only the upper layer of the earth's surface ​is involved in the reflectionin which radiation is absorbed and converted. Such layer includes the entire ​grass and vegetative ​mass of the forest, the first tens of meters of clear water and decimeters of muddy water, as well as decimeters of snow, a few centimeters of sand and a fraction ​of millimeters of dark soil. The reflectivity of the Earth'​s surface depends on the kind of bodies, their physical properties, color and condition. The ratio of reflected radiation to the total radiation ​of the Sun and the atmosphere is called albedo. Albedo values ​​​are most often expressed as percentage. The albedo of the earth's surface varies ​widelyThis is due to the type of landscape zonesand in temperate and high latitudes ​also with the change of seasonsSo, in the central parts of the polar regions ​the reflectivity is great and varies little in the annual course: in Antarctica ​about 85%, in the central Arctic - about 80%. In July, decrease ​in the albedo in the Arctic (up to 65%) is associated ​with more intense ​melting ​of snow than in December in Antarctica. +Solar radiation ​arriving at the Earth's surface ​is not fully absorbed by it. Parts of the radiation ​spectrum are reflected by the surface, and only the upper layer of the Earth's surface, ​where radiation is absorbed and transformed,​ is involved in the reflection process. Such layer includes ​all the grass and plant (green) ​mass of forests, the first tens of meters of transparent ​and decimeters of turbid ​water, as well as decimeters of snow, centimeters of sand and fractions ​of millimeters of dark soils. The reflectivity of the Earth'​s surface depends on the type of its bodies, their physical properties, color and condition. ​ 
-Average albedo values ​​​for various ​types of land surface (in%):+ 
 +The ratio of reflected radiation to the total radiation ​taken from the Sun and atmosphere is called ​"albedo". Albedo values are most commonly ​expressed as the percentage. The albedo of the Earth's surface varies ​within a wide rangeIt is connected with a type of landscape zones and in case of temperate and high latitudes ​with seasonal changesThusreflectivity is large and changes little in the annual course ​in the central parts of the polar regions: in Antarctica ​it is about 85 %, in the central Arctic - about 80 %. In July, the decrease ​of albedo in the Arctic ​region ​(up to 65 %) is connected ​with more intensive snow melting in comparison with December in Antarctica. Average albedo values ​determined ​for different ​types of the land surface (in %):
  
 {{:​en:​image_36.png?​600|}} {{:​en:​image_36.png?​600|}}
    
-The albedo of the water surface is on average ​smaller ​than most natural land surfaces and depends on the angle of incidence of the rays, on the height of the Sun, the ratio of direct and scattered radiationand the waves of the sea surface. ​With the position of the Sun at the zenith ​of the calm sea albedo ​for direct radiation ​is 2%With a decrease in the height of the Sunthe albedo ​increases. With great ocean turmoil, ​when foam and lamb are formed, the sea albedo increases. +The albedo ​value of the water surface is less in average than most natural land surfaces and depends on the angle of incidence of rays, height of the Sun, ratio of direct and scattered radiation and sea surface ​excitement levelsWhen the Sun is at its zeniththe albedo value of calm sea is 2% for direct radiation. ​The albedo increases as the height of the Sun decreases. The albedo value of the sea increases when waves are very rough and have a foamy form. The following ​similes ​show that some objects are better ​to be detected ​in the infrared spectrum. For example, thin clouds.
- +
-The following ​sims show that some objects are better ​visible ​in the IR range. +
-For example, thin clouds.+
  
 {{:​04image014.png?​600|}} {{:​04image014.png?​600|}}
    
-Some objects, on the contrary, ​are better ​visible ​in the visible range.+Some objects are better ​seen in the visible range, on the contrary.
  
 {{:​04image015.png?​600|}} {{:​04image015.png?​600|}}
-In infrared ​photographs, white color corresponds to colder ​areasand black color is warmer. The clouds in these images ​are whitenot because they are white, but because they are cold.+ 
 +In case of infrared ​picturesthe white color corresponds to cooler ​areas and black - to warmer ​areas. The clouds ​shown in these pictures ​are white not because they are white, but because they are cold.
  
 {{:​04image018.png?​400|}} {{:​04image018.png?​400|}}
    
-The cloud temperature can determine the height of the clouds, ​because ​the higher the clouds, the colder they are.+The cloud temperature can determine the height of the clouds, ​since the higher ​are the clouds, the colder they are.
  
 {{:​en:​image_37.png?​400|}} {{:​en:​image_37.png?​400|}}
    
-The range of infrared radiation with wavelength of 10 microns. +An infrared radiation ​range with the wavelength of 10 microns. The wavelength ​range of the Earth strongest radiation with little absorption and over-radiation (atmospheric window).
-The wave range of the Earth’s strongest radiation with little absorption and re-radiation (atmospheric window).+
  
 {{:​04image020.png?​400|}} {{:​04image020.png?​400|}}
    
-The range of infrared ​radiation with wavelength of 6.2 microns. +Infrared ​radiation ​range with the wavelength of 6.2 microns. Wavelength range with significant water vapor absorption (water vapor channel)
-Wavelength range with significant water vapor absorption (Water vapor channel)+
  
 {{:​04image022.png?​400|}} {{:​04image022.png?​400|}}
    
-The range of infrared ​radiation with wavelength of 3.9 μm. +Infrared ​radiation ​range with the wavelength of 3.9 micronsThe data on solar radiation and Earth radiation ​is transmitted simultaneouslyThe instrument allows ​visualization of low clouds and fog at night.
-It transmits information simultaneously about solar radiation and Earth radiation. ​Allows ​visualization of low clouds and fog at night.+
  
 {{:​04image024.png?​400|}} {{:​04image024.png?​400|}}
    
-Also, the IR range allows ​you to see various warm objects - cities, and forest fires. +The IR range also allows ​users to consider ​various warm objects - cities, and forest fires. Moscow.
-Moscow ​city.+
  
 {{:​04image026.png?​400|}} {{:​04image026.png?​400|}}
   ​   ​
-Wildfire ​on the island of Kalimantan. +A forest fire on the island of Kalimantan. ​Only smoke can be seen in the visible range.
-In the visible range, only smoke is visible.+
  
 {{:​04image027.png?​400|}} {{:​04image027.png?​400|}}
    
-In the IR range of 10 microns, too, only smoke.+The smoke is also seen in the infrared ​range of 10 microns.
  
 {{:​04image028.png?​400|}} {{:​04image028.png?​400|}}
    
-In the IR range of 4 μm, fires are clearly visible.+Fire hotspots ​are clearly visible ​in the 4 microns infrared range.
  
 {{:​04image029.png?​400|}} {{:​04image029.png?​400|}}
  
-In order to see the fog at night, the method of subtracting infrared signals is usedFrom a signal with wavelength of 4 μm, a signal with wavelength of 10 μm is subtracted.+The method of subtraction of IR signals is used in order to see fog at night. ​signal with the wavelength of 4 microns is subtracted from the signal with the wavelength of 10 microns.
  
 {{:​en:​image_38.png?​400|}} {{:​en:​image_38.png?​400|}}
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-==== When creating the lesson the following materials were used: ====+==== Materials ​used to provide this information are taken from: ====
  
 Japan Meteorological Agency. www.jma.go.jp Japan Meteorological Agency. www.jma.go.jp
en/lesson04.1585141419.txt.gz · Last modified: 2020/03/25 16:03 by 127.0.0.1