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  • Multispectral Camera Tracks Earth's Atmosphere from Distant Orbit

Photonics.com
Dec 2015
GREENBELT, Md., Dec. 24, 2015 — NASA's Earth Polychromatic Imaging Camera (EPIC), affixed to NOAA's Deep Space Climate Observatory (DSCOVR) about a million miles from Earth, has begun capturing images of the planet's clouds, land surfaces, aerosols and more.

EPIC captures a color image of the sunlit side of Earth at least once every two hours, allowing researchers to track features as the planet rotates in the instrument's field of view.

An image captured by NASA's Earth Polychromatic Imaging Camera (EPIC) showing Australia and part of Asia.
An image captured by NASA's Earth Polychromatic Imaging Camera (EPIC) showing Australia and part of Asia. Courtesy of Alexander Marshak/NASA.

"With EPIC, you see cloud structure from sunrise on the left to sunset on the right," said Jay Herman, EPIC instrument lead investigator at NASA's Goddard Space Flight Center and the University of Maryland, Baltimore County. "It's the only view we have like this where everything is at the exact same instant in time, even though the local times are different."

EPIC takes measurements in visible, UV and near-infrared wavelengths. With the UV channels, researchers can observe dust from the Sahara traveling westward across the Atlantic. While other low-Earth-orbit satellites can pick this up at a fixed local time, EPIC provides a day-long view of the process.

Researchers also can determine the height and location of daytime clouds by comparing EPIC images at two different wavelengths. This measurement is important in calculating Earth's energy balance for climate studies, as well as for tracking weather. For example, hurricanes show up as a high spiral of clouds surrounding a clearly visible eye.

Even a million miles away, EPIC can see the tracks of ships crossing the ocean. Some of the first images from EPIC show the clouds that result from the ships' smoke plumes. Researchers also are analyzing EPIC data to better understand vegetation, aerosols, ozone and other features of Earth and its atmosphere.

DSCOVR was launched in February and, after a four-month journey, reached its orbit around the first Lagrange point, where the matching pull of gravity from the sun and Earth allows the satellite to stay in a relatively stable position between the two bodies. The satellite, a joint mission between NOAA, NASA and the U.S. Air Force, also carries instruments facing the sun that will the study solar wind and its magnetic field.

A second NASA Earth-facing instrument on DSCOVR, the National Institute of Standards and Technology Advanced Radiometer (NISTAR), measures the total amount of solar energy that reflects off Earth, as well as the heat emitted from Earth, said Steven Lorentz, NISTAR instrument lead investigator and president of L-1 Standards and Technology Inc. Because of this, the instrument fills in a missing piece of energy information not observed by other satellites.

Even with less than a year's worth of data collected, the satellite is revealing patterns of energy reflected off Earth, Lorentz said. The instrument picks up fluctuations, with more light reflected from continents and clouds than from oceans.

"Whenever Africa is in view, we get the highest photoreflectance," Lorentz said. "And, even though it's the same planet spinning, the amount of cloudiness varies planetwide every day."

Earth's reflectiveness varies throughout the year, as well. As Antarctica tilts towards the sun in November, NISTAR's signal edges up as the massive ice sheet changes the planet's energy budget. It's a measurement that, over time, could help scientists studying how the reflectance of the sun's energy back into space can impact climate change.

For more information on EPIC, and to view images captured by the instrument, visit epic.gsfc.nasa.gov.


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