THIS
PLANET EARTH: THE VISION AND MAJESTY OF
NASA’S REMOTE SENSING LEGACY
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SeaWiFS:
Remote Views of a Living Planet
EARTH’S
CHECK-UP
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If
the Earth had a heartbeat, its pulse has just been taken.
Using three years of continuous data from an orbiting instrument
called SeaWiFS, NASA scientists have amassed a first look
at how carbon moves through the biosphere. Carbon is one of
the most essential elements for life, and experts say that
this research is a major step in the effort to monitor overall
planetary health, from climate change to the rhythms of life
in oceans and on land.
COLORFUL
SHADOWS: INFERRING CARBON’S CYCLE
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By
monitoring the color of reflected light via satellite, scientists
can determine how successfully plant life is photosynthesizing.
A measurement of photosynthesis is essentially a measurement
of successful growth, and growth means successful use of ambient
carbon.
Until
now, scientists have only had a continuous record of photosynthesis
on land. But following three years of continual data collected
by the SeaWiFS instrument, NASA has gathered the first record
of photosynthetic productivity in the oceans. The process
begins with a measurement of surface chlorophyll concentration.
Chlorophyll
is the material that allows plant cells to convert sunlight
into energy, thus enabling them to grow. It’s a green substance,
and thus a good indicator of overall plant health: robust
forests and lush lawns and vibrant phytoplankton blooms appear
green. By measuring chlorophyll concentration, scientists
can determine the health and growth of plants in a given area.
By extension, healthy color signatures indicate the successful
use of carbon, the fundamental building block for life. In
other words, lots of green indicates lots of chlorophyll;
lots of chlorophyll implies healthy photosynthesis; strong
photosynthesis indicates growth, and growth indicates successful
use of carbon.
Over
the past twenty years, researchers have amassed a repository
of chlorophyll concentration data about the land. That measurement
is called NDVI, for the Normalized Difference Vegetation Index.
But chlorophyll concentration measurements regarding the ocean
have remained elusive.
This
release from the SeaWiFS research team marks the first continuous
record of surface chlorophyll concentration in the ocean.
The power of these three years of collected data can be summed
up by a single word: continuity. By taking three years of
continuous data as a whole, experts have been able to map
trends and anomalies in the global circulation of carbon to
a degree of detail than has never been done before. It is
a baseline measurement to by which all future measurements
will be compared.
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Looking
at the Future with Advanced Tools
LANDSAT:
Continuing a Legacy of Earth Observation
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Landsat
7 is the latest in a series of satellites. From an altitude
of 438 miles (730 kilometers), Landsat 7 can see surface features
as small as 15 meters, providing world-wide land resource
information for a diverse range of uses.
The
only scientific instrument onboard the satellite is the Enhanced
Thematic Mapper Plus, a passive sensor that measure reflected
solar radiation (light) from the surface of the Earth. Landsat
7’s ETM+ is a refinement of previous Landsat Thematic Mapper
systems.
Landsat
7 is part of a global research effort NASA calls the Earth
Science Enterprise, which seeks to acquire a long term understanding
of the changes to our planet. The satellite roared into orbit
aboard a Boeing Delta II rocket on April 15, 1999 from Vandenberg
Air Force Base in California. NASA officially called the first
Landsat satellite the Earth Resources Technology Satellite,
or ERTS-1, on July 23, 1972. Since then the program has continued
to pave the way in research and data acquisition techniques
about the surface of our planet.
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TERRA:
FLAGSHIP OF THE EARTH OBSERVING SYSTEM
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On
December 18, 1999 NASA launched Terra, paving the way for
a new era in orbiting Earth science tools. It’s a multi-national
orbiting research platform managed at NASA’s Goddard Space
Flight Center. By synchronizing a sophisticated suite of sensors
and instruments, Terra will help researchers pursue some of
the grandest and most complex questions about the nature of
our home planet, including cutting edge research into climate
change.
The
satellite can simultaneously study clouds, water vapor, aerosol
particles, trace gases, terrestrial and ocean properties,
and systemic interactions on a planetary scale. In the following
sections we take a closer look the five scientific instruments
that comprise the Terra platform.
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THE
MODIS INSTRUMENT
(MODerate
resolution Imaging Spectroradiometer)
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In
science, color is more than simply a characteristic. It’s
information. As described by the instrument’s acronym, Modis
collects images of the Earth’s surface, reading the various
spectra (or color) of reflected radiation from different points
on the globe . Primary investigative pursuits for Modis include
the study of surface temperature (including fire detection),
ocean sediment and phytoplankton concentrations, vegetation
maps, pollution, snow cover, and more.
Data
from Modis will be available to individual users around the
world on a continual basis via X band satellite downlink.
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The
ASTER INSTRUMENT:
(Advanced
Spaceborne Thermal Emission and Reflection Radiometer)
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The
Aster instrument is a collaborative effort between NASA and
the Japanese Ministry of International Trade and Industry.
It’s designed primarily to collect data based on the reflection
and absorption of heat on the planet below. From its ability
to generate stereoscopic images, Aster can create digital
elevation maps. It is also the instrument on Terra with the
highest spatial resolution; in other words, it’s capable of
observing the smallest area in the greatest detail.
Aster
and its sibling instrument Mopitt each require higher levels
of cooling than the other instruments on board. A unique heat
pumping capillary system designed at the Goddard Space Flight
Center in Greenbelt, Maryland, will be employed for the first
time to do the job.
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THE
MOPITT INSTRUMENT
(Measurements
of Pollution in the Troposphere)
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Of
the five Terra instruments, Mopitt looks at the largest geographic
sample area at one time. Its main purpose is to measure carbon
monoxide and methane levels in the lower atmosphere, called
the troposphere. Various sources of these gases include pollution
from industrial zones, herds of cattle, decomposition of biomass
in swamps, and others. By studying where atmospheric gasses
are concentrated, how they circulate through the atmosphere,
and how they form, scientists hope to gain a more complete
picture about how atmospheric pollution interacts and affects
the environment.
Mopitt
and its sibling instrument Aster each require higher levels
of cooling than the other instruments on board. A unique heat
pumping capillary system designed at the Goddard Space Flight
Center in Greenbelt, Maryland, will be employed for the first
time to do the job.
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THE
MISR INSTRUMENT
(Multi-angle
Spectroradiometer)
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MISR
is similar to MODIS in that it, too, looks at color. But MISR
is unique. Instead of looking either straight down or toward
the edge of the planet like other instruments, a series of
nine cameras, each pointed at a different angle, looks at
a the same slice of the Earth below from a different perspective
as the instrument passes overhead. Further, the cameras make
their observations in four different wavelengths of light:
blue, green, red, and near-infrared. The purpose of such a
detailed analysis is to determine both how sunlight behaves
and interacts as it passes through Earth’s environment. Further,
Misr’s sophisticated sensors can also monitor long term trends
in pollution and naturally generated aerosols, cloud heights,
and distribution of land surface cover.
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THE
CERES INSTRUMENT
(Clouds
and the Earth’s Radiant Energy System)
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Ceres
looks at clouds. More specifically, Ceres studies the radiation
balance on Earth--how much heat is absorbed and reflected
in different areas. By looking at how different cloud formations
absorb or reflect various amounts of energy, scientists can
develop new predictive models about weather systems and how
the Earth maintains its delicate balance in temperature.
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COLORS
BEYOND COMPARE: EARTH IMAGING WITH EO-1
EO-1:
A VIEW FROM ABOVE
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The
hexagonal satellite called EO-1 carries a suite of instruments
designed to test new technologies while also conducting valuable
research about our home planet. Flying almost 438 miles above
the Earth, the satellite’s scientific hardware can deliver
some of the data collection capabilities previously possible
only from satellites far larger and more complex. Fully outfitted,
EO-1 weighed nearly 1166 pounds at launch. NASA launched it
on a Delta 7320-10 rocket from Vandenberg AFB in California.
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SeaWiFS:
Big Returns from a Small Package
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SeaWiFS
(Sea-Viewing Wide Field of View Sensor) is the scientific
portion of the OrbView-2 satellite, orbiting The Earth at
an altitude of 423 miles (705 kilometers). By providing a
regular picture of the planet's color, SeaWiFS helps researchers
learn about the state of the world's interconnected ecosystems.
OrbView-2 blasted into space on August 1, 1997 lifted by an
extended Pegasus rocket. SeaWiFS is considered a low cost
mission, many orders of magnitude less expensive than other
Earth observing instruments. In scientific terms, however,
this little instrument has proved to be one of the space agency’s
star performers, it’s highly focused mission parameters netting
huge scientific returns for researchers studying a wide variety
of questions.
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