NASA’s new space detective looking for carbon sinks

This newest space detective will provide the first global picture of the human and natural sources of carbon dioxide and the places where this important greenhouse gas is stored. Such information will improve global carbon cycle models as well as forecasts of atmospheric carbon dioxide levels and of how our climate may change in the future.

“NASA’s Orbiting Carbon Observatory satellite will work as a detective from space, measuring the distribution of carbon dioxide thousands of times daily as it orbits the planet, providing 296151main_2-516the data to create very precise carbon dioxide maps that will help us confirm the whereabouts, nature and efficiency of the sinks absorbing the 30 percent of carbon dioxide that disappears each year from the atmosphere,” said Steve Wofsy, a professor of atmospheric and environmental chemistry at Harvard University in Cambridge, Mass., and a co-investigator for the mission. The Orbiting Carbon Observatory will measure carbon in the air, from Earth’s surface to the top of the atmosphere.

“The future behavior of carbon dioxide sinks is one of the most uncertain things in predicting climate in the 21st century,” said Denning. “Mapping today’s sinks will allow us to measure how much of the carbon budget is controlled by carbon dioxide intake from ocean mixing, versus carbon dioxide fertilization, versus forest re-growth, etc. If we can determine that current land sinks are dominated by carbon dioxide fertilization, it would buy us more time to develop alternative energy and other mitigation measures.”

Carbon, a chemical element forms the chemical backbone for all of life. Carbon dioxide, is the basic “molecule” of the carbon cycle. It is “inhaled” by sinks to fuel photosynthesis in plant life. It is “exhaled” by natural sources when plant life dies or burns, and through human activities like the burning of fossil fuels, crops and forests.

If we think of Earth as “breathing,” the balance between photosynthesis, or “inhaling,” and respiration, or “exhaling,” was about equal until humans began mining and burning large amounts of fossilized organic matter like coal, oil and natural gas a couple of hundred years ago.

Until about 1990, most scientists believed land was primarily a source of carbon dioxide to the atmosphere because forests are continuously being destroyed by human activities like deforestation in tropical areas, urban and suburban development, and land clearing for farming.

“The amazing truth is that on a global scale, photosynthesis is greater than decomposition and has been for decades,” said Denning. “… plant life is growing faster than it’s dying. This means land is a net sink for carbon dioxide, rather than a net source.”

Denning outlined the six different ways carbon dioxide sinks can develop on land:

— Carbon dioxide fertilization, usually from land areas, carbon dioxide in the air stimulates photosynthesis to produce a temporary jump in the growth rates of plant life.

— Agricultural abandonment occurs where once-deforested land formerly used as family farms is abandoned, allowing forests to re-grow into terrestrial carbon dioxide sinks.

— Forest fire suppression, the aggressive extinguishing of forest fires that has led to preservation of more wooded areas than existed 100 years ago, saves trees that pull carbon dioxide from the air for growth.

— Woody encroachment occurs when cattle graze on grass but leave behind carbon dioxide-absorbing woody shrubs that accumulate over land ranges throughout the western U.S. and elsewhere.

— Boreal, or northern, warming takes place in northern latitude forests that are experiencing longer frost-free growing seasons due to global warming, allowing more woody growth and more absorption of carbon dioxide.

— Lastly, carbon dioxide sinks are created when nitrogen in agricultural fertilizer or nitrogen oxide from car emissions dissolves into clouds, spreads for hundreds of miles on vegetation with rainfall, and acts in tandem with carbon dioxide fertilization to accelerate plant growth.”1.

“The future behavior of carbon dioxide sinks is one of the most uncertain things in predicting climate in the 21st century,” said Denning. “Mapping today’s sinks will allow us to measure how much of the carbon budget is controlled by carbon dioxide intake from ocean mixing, versus carbon dioxide fertilization, versus forest re-growth, etc. If we can determine that current land sinks are dominated by carbon dioxide fertilization, it would buy us more time to develop alternative energy and other mitigation measures.”

Orbiting Carbon Observatory

The Orbiting Carbon Observatory’s single science instrument consists of three parallel, high-resolution spectrometers, integrated into a common structure and fed by a common telescope. The spectrometers will make simultaneous measurements of the carbon dioxide and molecular oxygen absorption of sunlight reflected off the same location on Earth’s surface when viewed in the near-infrared part of the electromagnetic spectrum, invisible to the human eye.

As sunlight passes through Earth’s atmosphere and is reflected from Earth’s surface, molecules of atmospheric gases absorb very specific colors of light. If the light is divided into a rainbow of colors, called a “spectrum,” the specific colors absorbed by each gas appear as dark lines. Different gases absorb different colors, so the pattern of absorption lines provides a telltale spectral “fingerprint” for that molecule. The Orbiting Carbon Observatory’s spectrometers have been designed to detect these molecular fingerprints.

Each of the three spectrometers is tuned to measure the absorption in a specific range of colors. Each of these ranges includes dozens of dark absorption lines produced by either carbon dioxide or molecular oxygen. The amount of light absorbed in each spectral line increases with the number of molecules along the optical path. assembly that ensures all three spectrometer channels view the same scene. A beam splitter selects specific ranges of colors of light to be analyzed by each spectrometer, which is then refocused on a narrow slit that for the entrance to each spectrometer.

The Orbiting Carbon Observatory spectrometers measure the fraction of the light absorbed in each of these lines with very high precision. This information is then analyzed to determine the number of molecules along the path between the top of the atmosphere and the surface.

If the amount of carbon dioxide varies from place to place, the amount of absorption will also vary. The Orbiting Carbon Observatory’s instrument records an image of the spectrum produced by each spectrometer three times every second as the satellite flies over the surface at more than four miles per second. This information is then transmitted to the ground, where carbon dioxide concentrations are retrieved in four separate footprints for each image collected. These spatially varying carbon dioxide concentration estimates are then analyzed using global transport models, like those used for weather prediction, to infer the locations of carbon dioxide sources and sinks.

This assembly ensures all three spectrometer channels view the same scene. A beam splitter 296386main_instrument-2264selects specific ranges of colors of light to be analyzed by each spectrometer, which is then refocused on a narrow slit that forms the entrance to each spectrometer.

Once light passes through the spectrometer slits, it is aligned, and then divided into its component colors by a diffraction grating. This is similar to the way light shined through a prism creates a rainbow.

The light is then re-focused by a camera lens onto each spectrometer’s focal plane array–image sensing devices designed to detect very fine differences in the intensity of the light within its spectrometer’s spectral range. There, it forms a two-dimensional image of a spectrum and is recorded.

The instrument measures the absorption of reflected sunlight by carbon dioxide in two color ranges. The first absorbs carbon dioxide relatively weakly, but is most sensitive to the concentration of carbon dioxide near Earth’s surface. The second absorbs carbon dioxide more strongly, and provides a totally independent measure of carbon dioxide in the atmosphere. That color range provides critical information about the pathway the light has taken and can detect clouds, aerosols and variations in atmospheric pressure and humidity, all of which can interfere with accurate measurements of carbon dioxide.

The third range of colors, within the molecular oxygen A-band, is used to measure how much molecular oxygen is present in the light’s pathway. To accurately derive the atmospheric concentration of carbon dioxide using instrument data, scientists first need to compare them to measurements of a second atmospheric gas. Because the concentration of molecular oxygen is constant, well-known and uniformly distributed throughout the atmosphere, it provides an excellent reference measurement. The molecular oxygen A-band spectra can also assess the effects of clouds, aerosols and the atmospheric pressure at Earth’s surface.

The observatory will continuously collect 12 soundings per second while over Earth’s sunlit hemisphere. At this rate, the instrument will gather between 33,500 and 35,500 individual measurements over a narrow ground track each orbit.

The surface footprint of each measurement is about 1 square mile (just under 3 square kilometers). Over the course of each 16-day ground repeat cycle, it will collect about 8,000,000 measurements, with orbit tracks separated by less than 1.5 degrees longitude (100 miles or 170 kilometers) at the equator. With so many measurements of this size and density, high-quality soundings, even in regions with clouds, aerosols and variations in topography is possible.

Resources:

Excerpts and Image courtesy of  Nasa.gov

The Mystery of the Missing Sinks nasa.gov/mission_pages/oco/main/index.html January 23. 2009

The Orbiting Carbon Observatory And The Mystery Of The Missing Sinks – Pasadena CA (JPL) January 28, 2009. Spacemart OrbitingCarbonObservatoryAndTheMysteryOfTheMissingSinks

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1 Comment

  1. January 31, 2009 at 9:31 am

    […] Carbon, a chemical element forms the chemical backbone for all of life . Carbon dioxide, is the basic “molecule” of the carbon cycle. It is “inhaled” by sinks to fuel photosynthesis in plant life . It is “exhaled” by natural sources when …$anchor_text[$anchor_choice] […]


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