Environmental Case Study
Remote Sensing
How do we measure widespread phenomena such as El Niños, climate change, and weather?
Some information can be gathered from ground-based observatories, but these facilities only tell us about
a scattering of isolated points. To detect patterns on a global scale, a more distant view is useful, and that
is why so much environmental science now involves remote sensing.
Remote sensing is a general term for data gathered from satellites, or sometimes by sensors on
airplanes. Just as a camera is a sensor that captures light energy reflected from objects, sensors on
satellites capture energy wavelengths reflected from the earth’s surface, from clouds, or from the
atmosphere. Some satellites detect infrared wavelengths, which indicate warm areas in the oceans, on
ice caps, or on land. Others might detect selected wavelengths of visible light, such as green or blue, or
microwaves, which provide images of cloud cover and precipitation. Our current understanding of the
Antarctic ozone hole comes from satellites that detect near-ultraviolet wavelengths, which are absorbed
by ozone in the atmosphere.
There are now many different satellites orbiting the earth in order to monitor environmental
conditions. Most satellites carry several sensors, each designed to collect specific wavelengths for
specific monitoring purposes. Perhaps the best-known satellites are the Landsat series (currently Landsat
7 is in operation) sent up to capture land cover and vegetation information. Each pixel represents about
30 x 30 m on the ground, so the images are highly detailed. Another important group of satellites, the
Earth Observing System (EOS), collects coarser pictures more frequently—250 to 1,000 m pixel
resolution images taken every day, instead of every two weeks for Landsat. The EOS satellites collect 36
energy bands, from ultraviolet to infrared. Bands are selected to detect land/sea boundaries, differences
in temperature, phytoplankton concentrations, atmospheric water vapor, atmospheric chemistry, and
other characteristics of the earth’s surface and atmosphere. These satellites orbit the earth,
approximately pole to pole. In contrast, there are “geostationary” satellites that are “parked” over the
earth, orbiting with the planet to maintain a constant position over the Pacific or Atlantic Ocean. These
collect data on atmospheric conditions more than once an hour, so they are good for monitoring the
movement of clouds and storm systems.
Figure 15.1 In early 2002, satellite images showed a Rhode Island–sized sectionof the Larsen B ice shelf
on the Antarctic Peninsula disintegrated into shards. Satellite images show 3,250 km2 that collapsed into
the ocean.
Source: National Snow and Ice Data Center/University of Colorado/NOAA.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1
Environmental Case Study
Remote Sensing
There are more than 7,000 satellites orbiting the earth. Most are used for communication—to
reflect radio, telephone, or TV signals. Others are spy satellites collecting highly detailed images of
strategic areas. The closest satellites, including the EOS satellites, are less than 1,000 km above the
earth’s surface. TV satellites and geostationary weather satellites are more than 35 km up. When you
look up at the sky at night, you might see some of the closest satellites, gathering data to give us the “big
picture” of environmental change as they travel across the sky.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
2