False-Color Image of Earth Highlights Plant Growth
On Aug. 3, 2004, NASA’s Mercury Surface, Space Environment, Geochemistry, and
Ranging (MESSENGER) spacecraft began a seven-year journey, spiraling through the
inner solar system to Mercury. One year after launch, the spacecraft zipped
around Earth, getting an orbit correction from Earth’s gravity and getting a
chance to test its instruments by observing its home planet.
This image is a view of South America and portions of North America and
Africa from the Mercury Dual Imaging System’s wide-angle camera aboard
MESSENGER. The wide-angle camera records light at eleven different wavelengths,
including visible and infrared light. Combining blue, red, and green light
results in a true-color image from the observations. The image substitutes
infrared light for blue light in the three-band combination. The resulting image
is crisper than the natural color version because our atmosphere scatters blue
light. Infrared light, however, passes through the atmosphere with relatively
little scattering and allows a clearer view. That wavelength substitution makes
plants appear red. Why? Plants reflect near-infrared light more strongly than
either red or green, and in this band combination, near-infrared is assigned to
look red.
Apart from getting a clearer image, the substitution reveals more information
than natural color. Healthy plants reflect more near-infrared light than
stressed plants, so bright red indicates dense, growing foliage. For this
reason, biologists and ecologists occasionally use infrared cameras to
photograph forests.
Image Credit: NASA/Johns Hopkins University Applied Physics
Laboratory/Carnegie Institution of Washington
Caption: Holli Riebeek
Caption: Holli Riebeek
Guillermo Gonzalo Sánchez Achutegui
ayabaca@gmail.com
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