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Weather Satellites [ Deutsch Dansk Español Français Italiano Dutch Português ]
  Introduction
  METEOSAT
  METEOSAT Second Generation
  NOAA
Introduction 
  All weather satellites deliver frequently updated data covering large geographical areas. Weather services are dependent upon the satellites' continuous flow of up-to-the-minute images of weather conditions. However, with poor spectral and spatial resolution, the data is generally less suitable for detailed mapping of surface conditions. However, the NOAA has a spatial resolution of 1 km that has been found to be very useful as a large scale resource-mapping system such as for global and regional mapping of vegetation and surface temperature.

 

METEOSAT 
  Five geostationary meteorological satellites have been placed in a ring around the Equator:
  • METEOSAT by the European Space Agency (ESA),
  • GMS by Japan
  • INSAT by India and
  • GOES E and GOES W by USA
Between them they produce updated images every half hour of global weather conditions, except for the polar regions.

METEOSAT rotates on its own axis which is parallel to the axis of the Earth. It rotates 100 times per minute. For each rotation it scans a 5 km wide strip from east to west. The strip is divided into 2500 scanning areas. For each rotation the scanner's mirror is adjusted so that a new strip can be scanned.  


METEOSAT image in channel 1, Dec. 21st 1997 at 12 GMT. Channel 1 covers both the visible and the near infrared range of the spectrum. 		An image showing the entire Earth disk consists of 2500 strips, which are scanned in 25 minutes. After a five-minute pause the next image is started. The continuous stream of data is sent to the control centre at Darmstadt in Germany where the material is processed. The scan is performed using three channels: one visible and near infrared, one medium infrared, and one thermal infrared.

In the visible and near infrared (channel 1), the albedo is measured for various surfaces. Clouds, snow and ice have a strong reflection and are, therefore, seen as light grey. Dry and bare ground or sand is also light, while regions covered with vegetation have a slightly lower albedo and appear darker. Water surfaces have a very low albedo and are therefore dark. In channel 1 images the whitest clouds are the thickest, while thinner cloud formations appear greyish, because the surface of the earth is partially visible. Space is black as the empty space does not reflect light.  

  See the latest image from Meteosat 
 
Surface
Albedo %
Water
5-10
Desert
25-30
Fresh snow
80-90
Old snow
45-70
Green forest
5-10
Green leaves
5-25
Clouds (average)
50-55
Clouds < 150 m thick
25-63
Clouds 150-300 m thick
45-75
Clouds 300-600 m thick
59-84
Sea ice
30-40
Bitumen road
5-10
 
  Albedo values for various types of surface. The value indicates the percentage of sunlight reflected from the surface. 

METEOSAT image in the thermal infrared channel, Dec. 21st 1997 at 12 GMT. 		In the thermal infrared (channel 3) cold surfaces are light and warm surfaces are dark. Like in channel 1 clouds appear as light areas, but there are significant differences. The lightest clouds are the coldest and must consequently be the highest in the atmosphere. Temperature drops with height above the surface of the earth. The darker the cloud formation, the lower it is in the atmosphere. On infrared images it can be difficult to distinguish between low-lying clouds and cloudless areas, because the temperature difference between the cloud and a wet surface on Earth can be quite small. Space is white in these images as it does not radiate thermal infrared energy.  
  See the latest infrared image from METEOSAT 
   

METEOSAT image in the water vapour channel (2), Dec. 21st 1997 at 12 GMT. The light grey tones indicate a high concentration of water vapour in the atmosphere. 		The water vapour channel is special, because it records at a wavelength where the atmosphere is not translucent, because the radiation is nearly 100% absorbed. The radiation received by the satellite in this channel comes from the content of otherwise invisible water vapour in the atmosphere. It is thus possible to analyse the transport of water vapour, which contains large quantities of latent energy. These movements are a significant factor in the distribution of energy throughout the atmosphere. The tropical rain forests assist this process by delivering enormous quantities of water vapour and energy to the temperate zones. The climatic significance of rain forest deforestation and the resultant impact on evaporation has yet to be clarified. 
  See the latest Water vapour image from METEOSAT. 
METEOSAT Second Generation 

Launching of a second generation of METEOSAT satellites wasm launched in 2002.
The opportunity to analyze the atmosphere and its trace gasses will be enhanced.

The first of three MSG spacecraft has been launched in the year 2002.

MSG generates multispectral imagery of the Earth's surface and cloud systems at double the rate (every 15 minutes instead of every half an hour) of the current Meteosat, and for a much larger number of spectral channels (twelve compared to three for Meteosat). There is also a vastly improved geometric resolution (1 km for the high-resolution visible channel and 3 km for the others).

Eight of the channels are in the thermal infrared, providing among other information, permanent data about the temperatures of clouds, land and sea surfaces. Using channels that absorb ozone, water vapour and carbon dioxide, MSG will also allow meteorologists to analyze the characteristics of atmospheric air masses making it possible to reconstruct a three-dimensional view of the atmosphere. The current Meteosat capabilities will be maintained to enable temporal comparisons. 

  The characteristics of MSG can be studied more closely at ESA

 

NOAA 

Denmark seen from NOAA, May 2nd 1990, in its thermal infrared channel. Notice that the image shows surface temperatures of the Earth/water, not air temperatures measured 2 m above the surface (as with conventional meteorological instrumentation).
Source: H. Soegaard, The Geographical Institute, The University of Copenhagen. 		The National Oceanographic and Atmospheric Administration sent the first of a series of NOAA satellites into orbit in 1970. They move in solar synchronous orbits about 850km above the Earth and scan the entire Earth in twenty-four hours.

The latest NOAA satellites are equipped with an Advanced Very High Resolution Radiometer (AVHRR) which scans in five channels. The AVHRR scanner makes it possible to map vegetation and cloud formation and to measure temperature and humidity in the atmosphere and on Earth.

Below is a geometrically rectified segment of a NOAA image in the thermal infrared channel covering Denmark and the south of Sweden.

As the NOAA is equipped with both a visible and a near infrared channel, it can also be used for small-scale mapping of vegetation. The daily transects occur at the same local time making it possible to put together (mosaic) cloudless images based upon several days' sensing.

 

  NOAA AVHRR 
This website gives you more information on the AVHRR sensor (Advanced Very High Resolution Radiometer) on board the NOAA series of satellites.
  NOAA  
This website gives you more information on the satellites of NOAA - use our Search function above to find out more.