Besides collecting imagery, most environmental
satellites perform additional functions. Some
satellites contain communications packages designed
to receive and relay signals between earth stations and
other satellites and to collect and relay observation
reports from automatic observation sites or buoys.
Some satellites carry search and rescue (SAR) beacon
locators. More advanced satellites carry sophisticated
instruments known as "atmospheric sounders." These
systems use infrared and microwave energy to provide
vertical temperature and moisture profiles of earths
atmosphere from the surface up to 30 miles. They also
evaluate atmospheric stability. In addition, satellites
can be used to measure a variety of other
environmental parameters, such as sea surface
temperature, wave height, snow/ice cover, low-level
wind speed and direction, and ozone distribution.
Although these functions are very important to
meteorology and oceanography, you will not normally
be involved in this type of data collection or data
processing. In this module, we discuss only the
differences in satellites that are important to you in
acquiring satellite imagery.
In the United States, both the U.S. Department of
Commerce and the U.S. Department of Defense
operate meteorological satellite programs. The
National Oceanic and Atmospheric Administration
(NOAA), a division under the Department of
Commerce, operates its satellite programs through the
National Environmental Satellite, Data, and
Information Service (NESDIS). Their primary
meteorological satellite programs are the
Geostationary Operational Environmental Satellite
(GOES), and the Advanced Television InfraRed
Observation Satellite-NOAA (ATN) polar-orbiter
(also called a TIROS-N or NOAA satellite). Both
systems are energized with solar power while in orbit.
The Department of Defense oversees the Defense
Meteorological Satellite Program, usually referred to
as the DMSP.
Geostationary satellites are placed at an altitude
(35,800 km) where their orbital period exactly matches
the rotation of the earth. The satellite sensors scan the
earth in horizontal lines, starting near the North Pole
and working down towards the South Pole.
Geostationary satellites are ideal for making large-
scale, frequent observations of a fixed geographical
area centered on the equator. Thus, they are better
suited to track rapidly moving large-scale disturbances
in the atmosphere, or to look closely at small-scale or
short-duration changes in the atmosphere. However,
their distance from the earth limits the resolution of the
imagery. In addition, these satellites do not "see" the
poles at all, and to achieve global coverage of just the
equatorial regions, a network of 5 to 6 geostationary
satellites is required. Figure 1-5 shows atypical GOES
Figure 1-5.GOES satellite.