which can also track how fast the precipitation falls. Radar can outline the structure of a
storm and in doing so estimate the possibility that it will produce severe weather.
Figure 16.41: Radar view of a line of thunderstorms. ( 8 )Weather satelliteshave been increasingly important sources of weather data since the first
one was launched in 1952. Weather satellites are the best way to monitor large scale systems,
like storms. Satellites can also monitor the spread of ash from a volcanic eruption, smoke
from fires, and pollution. They are able to record long-term changes, such as the amount of
ice cover over the Arctic Ocean in September each year.
Weather satellites may observe all energy from all wavelengths in the electromagnetic spec-
trum. Most important are the visible light and infrared (heat) frequencies. Visible light
images record images the way we would see them, including storms, clouds, fires, and smog.
Infrared images measure heat. These images can record clouds, water and land tempera-
tures, and features of the ocean, such as ocean currents. Weather patterns like the El Niño
are monitored in infrared images of the equatorial Pacific Ocean.
Two types of weather satellites are geostationary and polar orbiting (Figure16.42). Geo-
stationary satellites orbit the Earth at the same rate that the Earth rotates; therefore, they
remain fixed in a single location above the equator at an altitude of about 36,000 km (22,000
miles). This allows them to constantly monitor the hemisphere where they are located. A
geostationary satellite positioned to monitor the United States will have a constant view
of the mainland, plus the Pacific and Atlantic Oceans, as it looks for hurricanes and other
potential hazards.
Polar orbiting satellites orbit much lower in the atmosphere, at about 850 km (530 miles)
in altitude. They are not stationary but continuously orbit making loops around the poles,
passing over the same point at around the same time twice each day. Since these satellites