How the Orbiting Carbon Observatory Works

An artist's concept of the Orbiting Carbon Observatory.
An artist's concept of the Orbiting Carbon Observatory.
Photo courtesy of NASA/JPL

­Every year, humans add more than 8 billion metric tons of carbon dioxide (CO2) into the Earth's atmosphere by burning fossil fuels, clearing and converting land, and practicing slash-and-burn agriculture. The planet itself produces about 300 billion metric tons of CO2 gas each year through natural events like forest fires and decay, but activities such as heating a home or driving a car don't fit in with this natural carbon cycle [source: Klotz]. It is thought that humans have caused a 20 percent increase in CO2 levels in our atmosphere in the last 50 years [source: MarketWatch].

Why should we care how much CO2 is in our atmosphere? The planet naturally absorbs and reflects the sun's heat, maintaining a life-sustaining temperature. When too much CO2 is in the atmosphere, however, the sun's heat becomes trapped, and is unable to escape into space. In turn, it causes the surface of the planet to heat up -- this is known as the greenhouse effect. CO that is released from human activities is considered a driving force behind our planet's climate changes.

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­Currently scientists are able to measure CO2 emissions via the Carbon Dioxide Information Analysis Center, which monitors CO2 levels from a network of ground instruments. Additionally, NASA has a CO2 detector on the Aqua satellite, which measures greenhouse gases present within 3 to 6 miles (5 to 10 kilometers) of the Earth's surface. From these measurements, scientists know that about 40 to 50 percent of the CO2 resulting from human activity stays in the atmosphere -- they theorize that our oceans and foliage absorb the rest, but without additional data, it remains unknown [source: MarketWatch].

­Scientists now have a new tool in their arsenal against climate change: the Orbiting Carbon Observatory (OCO). We know that once CO2 is released into the atmosphere, it lasts on average for about 300 years, although 20 percent lingers on for 10,000 years or more [source: Klotz]. But with the OCO orbiting the Earth, we'll now have a map of CO2­ in the atmosphere that will help track and monitor the greenhouse gas. Let's find out more about how the OCO works and what scientists are able to do with the data.

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The Orbiting Carbon Observatory will be the first satellite in the A-Train.
The Orbiting Carbon Observatory will be the first satellite in the A-Train.
Photo courtesy of ­NASA

­In early 2009, the Orbiting Carbon Observatory (OCO) was launched into space on a Taurus rocket at Vandenberg Air Force Base in California. The OCO is a satellite built by Orbital Sciences Corporation for NASA, and its mission is part of NASA's Earth System Science Pathfinder (ESSP) program.

The OCO is a climate observation instrument that joins a group of satellites from the United States, Canada and Europe known as NASA's Earth Observing System Afternoon Constellation or A-Train: Aqua, Cloudsat, Calipso, Parasol, Aura and soon Glory. The A-Train is a constellation of satellites that cross the equator in succession every day just after noon. This group of satellites specializes in monitoring climate and carries instruments used to observe climate change -- specifically how water systems, atmospheric chemistry, clouds, aerosols and solar radiation interact and affect the climate.

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The OCO leads the A-Train. It's the first instrument designed to collect space-based measurements of ­Earth's carbon cycle, and its mission is to pinpoint the exact distribution of CO2 around the globe. The OCO maps CO2 sources and sinks -- the places where CO2 is released and absorbed -- on a repeat 16-day cycle during the project's two-year span.

While pre-OCO data laid the groundwork for understanding carbon emissions, it's always helpful to have more detail. Where are the most problematic sources of CO2? Where is the greenhouse gas really being absorbed? Such measurements will complete crucial missing pieces of the climate puzzle for scientists: How much CO2­ is in the atmosphere, where is it precisely and how much is being recycled by the planet and where? These maps could even put an end to countries pointing fingers at one another regarding greenhouse gas output. Predicting emissions outputs will no longer be a guess.

The Orbiting Carbon Observatory is displayed in late 2008 after blankets and edge tape were applied.
The Orbiting Carbon Observatory is displayed in late 2008 after blankets and edge tape were applied.
Photo courtesy of ­NASA/Robert Hargreaves Jr., VAFB

So how will the Orbiting Carbon Observatory work? The observatory is solar powered. It's made of honeycomb panels equipped with solar cells; an onboard computer ensures that the satellite is always facing the sun to charge its battery. The whole system requires about the same amount of power as nine household light bulbs [source: NASA] The computer, along with a GPS system, flies the satellite, manages the measurement tools and communicates with ground st­ations to receive commands and transmit data back to Earth.

The satellite weighs about 1,170 pounds (530 kilograms) and flies in a sun synchronous 438-mile (705-kilometer) high orbit, inclined 98.2 degrees to the equator. This means the OCO travels in the A-Train constellation on a fixed path over the same part of the Earth at the same time every day. Taking measurements at the same time every time is important in this mission because CO2 levels can vary based on time of the day and season. By maintaining t­his path, the satellite is able to observe and record carbon across the surface of the planet once every 16 days. The data is then translated into monthly maps of atmospheric CO2 based on 621-square-mile (1,609-square-kilometer) surface areas.

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To measure and map carbon, the OCO is equipped with three high-resolution grating spectrometers, instruments that measure wavelengths of sunlight reflected off Earth in the presence of CO2 and molecular oxygen (O2. These instruments are able to identify carbon sources to an accuracy of 0.3 to 0.5 percent and within areas as small as 1 square mile (3 square kilometers) [source: Klotz].

Scientists monitor the annual mean growth rate of CO2­ as a way to understand how the planet's carbon budget has changed since the beginning of the industrial revolution. Recently, atmospheric CO2 has increased from 2.0 parts per million (ppm) between the years 2000 and 2007 to 2.2 ppm in 2007. From data collected by the instruments on board the OCO, scientists will have access to carbon concentration levels able to show variations of CO2 less than 1 ppm from the total atmospheric CO2­ concentrations, which increased to a massive 383 ppm in 2007 [source: Bruno].

­The onboard computer transmits all stored data to a gathering station in Alaska, where it's then sent to NASA's Goddard Space Flight Center for processing. We'll learn about the data and analysis next.

The modeling system used to analyze OCO data is similar to the kind used to predict weather patterns.
The modeling system used to analyze OCO data is similar to the kind used to predict weather patterns.
­AP Photo/Salina Journal, Tom Dorsey

­Scientists analyzing data from the OCO are located at numerous institutions but most of the analysis happens at NASA's Jet Propulsion Laboratory at the California Institute of Technology, which leads the OCO mission.

The maps of carbon collected by the observatory detail what gas types and concentrations are in the atmosphere. The information is then analyzed using global atmospheric chemical transport models for the locations of sources and sinks and their seasonal variance -- a modeling system similar to the kind used to predict weather patterns. Scientists translate this information about CO2 levels and distribution to better understand Earth's carbon cycle (human-generated and naturally occurring) and to forecast climate changes and estimate the effect on the planet.

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With the data from the observatory, scientists will be able to explore numerous other studies: They'll get an in-depth look at the ocean carbon exchange, the way atmospheric gases mix across hemispheres, the way weather affects the exchange of CO2­ between different regions and the way fossil fuel plumes move across North America, Europe and Asia.

The data is also checked for accuracy, a process called ground truthing. The OCO project team works with scientists at the National Oceanic and Atmospheric Administration (NOAA) to be sure that the forests, land masses, water and gases detected by the instruments are there in reality. Ground measurements are compared with OCO measurements. But one of the most exciting methods for ground truthing will come with the launch of the $100-million White Knight Two, a high-altitude aircraft designed to fly up to 50,000 feet (80,500 kilometers), and the SpaceShipTwo, which will detach from the White Knight Two in flight and fly more than 60 miles (100 kilometers) above Earth. In comparison, large passenger planes fly at only about 7.5 miles (12 kilometers). Once ­it's ready to fly, the White Knight Two is scheduled to carry OCO-supporting experiments.

Learn more about NASA, satellites and global warming on the next page.

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