Every day, above our planet, five Earth-observing satellites rush along like trains on the same "track," flying minutes, and sometimes seconds, behind one another. They carry more than 15 scientific instruments in total, looking at many different aspects of our home planet. Called the Afternoon Constellation, or A-Train, these satellites work as a united, powerful tool for advancing our understanding of Earth's surface and atmosphere.
The train is about to get longer.
"The A-Train constellation is an ideal measurement system for us," said
OCO-2 will fly along the same path as
OCO-2 measures carbon dioxide by observing its effect on sunlight. Sunlight is made up of waves of many lengths, or frequencies, some visible and others invisible. As sunlight passes through the atmosphere, carbon dioxide and other molecules absorb specific frequencies in the spectrum of light, leaving dark, narrow gaps in the spectrum. The more light that has been absorbed in a certain column of air, the more carbon dioxide is present there. In some cases, this may suggest that Earth's surface beneath that air contains a source of carbon dioxide, like a large industrial city. Less carbon dioxide implies a "sink," which absorbs carbon dioxide, like a thick forest during the growing season.
The OCO-2 spacecraft carries a single instrument composed of three spectrometers that measure different regions of the spectrum of light. One of these spectrometers observes the spectrum of molecular oxygen, referred to as the A-band spectrum. This is important because molecular oxygen is a relatively constant fraction of the atmosphere and can be used as a reference for measurements of other atmospheric gases, such as carbon dioxide. In addition to being critical for calibrating the carbon dioxide concentrations, it also tells scientists how much sunlight is absorbed or reflected by the aerosols and clouds, features that
"If we combine the A-band spectrometer's measurements with information on aerosols and clouds from
"To check OCO-2's accuracy, we can compare it to CloudSat and
Winker noted, "From OCO-2's point of view,
The A-Train's other satellites support OCO-2's work, too. MODIS (Moderate Resolution Imaging Spectroradiometer), an instrument on the Aqua satellite, tracks cloud cover. AIRS (Atmospheric Infrared Sounder), another Aqua instrument, measures air temperature and the amount of water content in the atmosphere. To accurately measure carbon dioxide, scientists must know all those details.
"We have the platforms that can tell us about water vapor and temperature, as well as clouds from the CloudSat satellite, the
For more information about OCO-2, visit these sites:
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