Satellite
imagery
CSAG uses data received from the first of the new generation
of Meteosat satellites, known as Meteosat Second Generation (MSG),
that was launched in August 2002 from the Kourou launch site in French
Guiana.
The satellite (known as MSG-1 or Meteosat-8 and pictured below) is
in geostationary orbit around the equator.
Satellites in a
geostationary orbit are at 36000 km altitude and travel in such a
way that they follow the Earth's rotation, thus they always "see"
the same part of the Earth's disc. The nominal position of the MSG
satellites will be
centered over the Equator and the
Greenwich Meridian allowing permanent monitoring of Europe,
Africa and the Atlantic Ocean, with the exclusion of only the most
northerly and southerly regions of the globe.
Instrumentation on board MSG-1 observes the earth with a repeat cycle
of 15 minutes in 12 spectral bands (or channels). Eight
of the channels are in the thermal infrared spectrum, providing amongst
other information, data about the temperatures of clouds,
land and sea surfaces. Using channels that absorb ozone, water vapour
and carbon dioxide, MSG allows meteorologists to analyze the
characteristics of atmospheric air masses making it possible to
reconstruct a three-dimensional view of the atmosphere. Images
presented on the CSAG website are from channels 2, 6 and 9 (with
wavelengths of 0.81, 7.35 and 10.80 micrometers) and measure the
visible, water vapour and infra-red spectral bands respectively.
The repeat cycle of 15 minutes means every 15 minutes we have 12 new
images of the observed disc. The ground
resolution is 3 km at nadir which means so we also have very high
spatial resolution data. The availability of such high spatial and
temporal resolution satellite data is unprecedented and allows us to
monitor
weather systems in great detail.
In addition to the MSG-1 satellite, the project covers the introduction
of three more satellites (MSG-2, MSG-3, MSG-4) with the planned launch
of MSG-2 being for late 2005. Each satellite has a life span of about
seven years and the project should provide a service until about 2018.
Some weather features to
look
for
on the satellite photo
1. In the visible range:
- Cold fronts and general cloud structure.
- InterTropical Convergence Zone (ITCZ).
- Cloud bands and thunderstorms over the South African interior.
- Tropical cyclones near Madagascar.
- Affects of the south-easter on the west coast.
- Sun angle and night approaching.
2. In the infra-red range:
- As for visible, but is also possible at night!
- Regions of hot (blacker) and cold (whiter), contrast desert with
coastal and forested regions.
3. In the water vapour range (shows distribution of water vapour in the
atmosphere):
- Synoptic systems as mentioned above
- Moisture sources and moisture trajectories
- If you have a good enough computer and bandwidth, you can save a
days imagery of the full disc and make a beautiful animation.