Geoscience Reference
In-Depth Information
satellites do not measure the same variables, and this type of data needs to be
calibrated and validated by conventional data. With this in mind, the data produced
by satellites are seen as providing information that complements the information
used for the spatial representation of the climate variables. This point will be
explained through the use of examples chosen for the following sections of this
chapter.
3.3. Examples of how geostationary data are used in Brazil
3.3.1.
Geostationary satellites: GOES and Meteosat
Geostationary satellites have been monitoring meteorological activity in most of
the world since 1977 (excluding areas of high altitude). A group of five satellites are
responsible for regularly monitoring meteorological activity on a world scale. The
Meteosat satellites (created by the European Space Agency) monitor activity that
takes place in the Europe-Africa zone. The American GOES satellites monitor
activity that occurs in the America-Atlantic and America-Pacific zones. The
Japanese GMS satellites monitor activity in the Asia-Pacific-Australasia zone, and
the Asia-Indian Ocean zone is monitored by Russian satellites (GOMS), Indian
satellites (INSAT) or Chinese satellites (FY-2). These are geostationary satellites.
The term geostationary is used because the satellites seem to be stationary in
relation to the surface of the Earth. What actually happens is that the satellites move
at the same speed as the Earth, but at an altitude of 36,000 km. Despite having a
spatial resolution of between 5 and 10 km for a long time, as well as recording data
every 30 minutes or every hour for over 10 years now, geostationary satellites have
improved dramatically over the last decade. Since 2002, METEOSAT entered into a
new era, with the launch of MSG. Performance has improved with an increase in
spatial resolution in the visible band (1 km as was the case for the American GOES
satellites in 1994). Performance has also improved thanks to the fact that an image is
captured every 15 minutes and there are new spectral bands that can be used to
produce the images (see Table 3.1).
The high number of images taken makes it possible to record data on a daily
bases (as used for TV news headlines), on a monthly basis, or on a yearly basis.
These images are the key elements to modern weather forecasting because with
these images it is possible to recreate movements that take place in the atmosphere
(or wind field) from the continuous observation of cloud formations. Clouds are the
first elements of the Earth's atmosphere that are observed by satellites. The
International Satellite Cloud Climatology Program (ISCCP) was created in 1983
[SCH 83]. The ISCCP was used to create a global database so that it would be
possibly to study clouds from data that was provided by the geostationary and
orbiting satellites. The data was analyzed on a global scale every 3 hours and at
different resolutions. The resolutions ranged from 30-250 km. Monthly data
analyses are also available. On a local and regional scale, however, several different
research studies have used satellite data to monitor cloud cover [MOU 81]. We will
use the example of Mato Grosso in order to highlight the link that exists between
