GeoCarb: A New View of Carbon Over the Americas
A new NASA Earth satellite mission may transform our understanding of the global carbon cycle by mapping key carbon gases from a new vantage point: geostationary orbit.
A
new NASA Earth science mission in the early stages of design may achieve a
transformational advance in our understanding of the global carbon cycle by
mapping concentrations of key carbon gases from a new vantage point:
geostationary orbit. Satellites in geostationary orbit travel at the same speed
as Earth's rotation, allowing them to remain over the same place on Earth's
surface at all times.The
Geostationary Carbon Observatory (GeoCarb), targeted for launch in the early
2020s, will build on the success of NASA's Orbiting Carbon Observatory-2
(OCO-2) mission by placing a similar instrument on a commercial SES-Government
Solutions communications satellite flying in geostationary orbit. Its longitude
will allow "wall-to-wall" observations over the Americas between 50 degrees
North and South latitude -- from the southern tip of Hudson Bay to the southern
tip of South America. Perched 22,236 miles (35,800 kilometers) above the
Americas, GeoCarb will collect 10 million daily observations of the
concentrations of carbon dioxide, methane, carbon monoxide and solar-induced
fluorescence (SIF) at a spatial resolution of about 3 to 6 miles (5 to 10
kilometers).The
abundance and distribution of carbon-bearing gases in the atmosphere are
determined by both the exchange of carbon between Earth's land areas, oceans
and the atmosphere, and their transport by prevailing winds. These exchanges
are best understood by making frequent, densely spaced observations. While
satellites in sun-synchronous, polar low-Earth orbits like OCO-2 provide global
coverage, they have long revisit times, large gaps in coverage, and always look
at the landscape at the same time of day. Because weather affects ecosystems on
timescales of days to weeks, polar orbiting satellites may miss these changes
and how they interconnect with the activities of living organisms --
information that is crucial to developing better models of Earth system
processes."GeoCarb
will complement measurements by OCO-2 and other low-Earth orbiting satellites
by filling in data gaps in both time and space," said Principal Investigator
Berrien Moore of the University of Oklahoma in Norman. "It will be more of a
regional mapping mission than a global sampling mission."Moore
said that just as geostationary weather satellites can sit and stare at storms
and map them, GeoCarb will let us see how different weather patterns influence
carbon dioxide and methane concentrations. "That's the power a geostationary
orbit brings," he said. "Data from OCO-2 have already shown that large-scale
weather patterns such as El
Niño and La Niña affect the large-scale pattern of atmospheric
carbon dioxide concentrations, and that's extremely important."GeoCarb
will address a number of unanswered questions in carbon cycle science, with a focus
on the Americas. For example, to what extent does the Amazonia basin remove
carbon dioxide from the atmosphere and store it in forests, and are methane
emission estimates over the continental United States underestimated?GeoCarb
will also be the first U.S. satellite to measure methane near Earth's surface,
information that will be useful for the energy industry. Methane leakage from
natural gas production costs U.S. industry $5 billion to $10 billion a year.Like
OCO-2, GeoCarb's oxygen spectral band, which is needed to convert abundances of
carbon gases to concentrations, will also measure SIF. This faint glow, emitted
by the chlorophyll molecules in the leaves of plants, is an indicator that
photosynthesis -- the process by which plants convert sunlight into chemical
energy and capture carbon from the atmosphere -- is occurring. GeoCarb will
make daily, near wall-to-wall measurements of SIF under all weather conditions,
allowing scientists and others to track the effects of drought on photosynthesis
in forests, crops and grasslands.GeoCarb
stands on the foundation set by OCO-2, which was built by NASA's Jet Propulsion
Laboratory in Pasadena, California. Like OCO-2, GeoCarb uses a grating
spectrometer, but adds a fourth spectral band to measure carbon monoxide and
methane. It will use the same detector technology, algorithms and calibration
techniques as OCO-2."We
would never be able to do GeoCarb without OCO-2," said Moore. "In designing our
instrument we said, let's do OCO, but in geostationary orbit. We're building on
JPL's work in designing and building OCO-2 and processing its data. In fact,
many members of our science team are also working on the OCO-2 mission."The
GeoCarb instrument views reflected light from Earth through a narrow slit. When
the slit is projected onto Earth's surface, it sees an area measuring about
1,740 miles (2,800 kilometers) from north to south and about 3.7 miles (6
kilometers) from east to west. In comparison, OCO-2's swath is about 6.2 miles
(10 kilometers) wide. GeoCarb stares at that area for about 4-1/2 seconds, then
the slit is moved half a slit width -- 1.9 miles, or 3 kilometers -- to the
west, allowing for double sampling. With this technique, GeoCarb can scan the
entire continental United States in about 2-1/4 hours, and from Brazil to South
America's West Coast in about 2-3/4 hours. It is not designed to observe the
oceans, as reflectivity over the oceans is too low to provide useful data.GeoCarb's
exact orbital slot will be assigned by SES-Government Solutions. A slot farther
to the west will favor U.S. observations over South America, and vice versa for
a slot farther to the east. In the future, Moore says two to three more
GeoCarb-like instruments placed in geostationary orbit at different longitudes
could provide near-global coverage of Earth's terrestrial landscape outside of
the poles.Moore
says GeoCarb and TEMPO, another NASA atmospheric chemistry/air quality mission
currently in development, are serving as pathfinders for geostationary,
commercially-hosted NASA Earth-observing missions. "If we can work out the
legal and practical day-to-day issues, I can see these missions changing the
face of Earth science from space. You don't have to pay for a separate
spacecraft or launcher. You're essentially buying condo space on a spacecraft
and paying for data downlink. The future here is very exciting."Updated on January 24, 2018 at 1:20 p.m. PT to correct the latitude range over which GeoCarb will make observations.