Colorado State University, NOAA Help Scientists See Earth at Night for First Time with Satellite

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Researchers at the NOAA Cooperative Institute for Research in the Atmosphere at Colorado State University (CIRA) have advanced scientists’ ability to see nighttime satellite images of Earth to a level of detail never before possible.

For the first time, NASA, NOAA and CIRA scientists unveiled new nighttime lights capability of a NASA/NOAA satellite on Wednesday at the American Geophysical Union annual meeting in San Francisco.

“This is a significant find in collaboration with our partners and could help scientists around the world with this knowledge that a combination of starlight and the upper atmosphere’s own subtle glow can help satellites see Earth’s clouds on moonless nights,” said Steve Miller, research scientist and deputy director at CSU’s Cooperative Institute for Research in the Atmosphere, known as CIRA. “Through coordination with the Naval Research Laboratory in Monterey, we have developed a couple tools to help make quantitative use of these unique nighttime moonlight measurements.”

During the daytime, ultraviolet light from the sun bombards Earth’s upper atmosphere and breaks apart gaseous molecules and atoms. During the nighttime, these molecules and atoms recombine, emitting faint visible light in the process.

This “air glow” combined with starlight illuminates clouds at night, and by using a new and improved satellite instrument, scientists can take advantage of this signal for the first time from space, according to scientists at CIRA, NOAA, Northrop Grumman and the U.S. Department of Defense who published a paper on the topic in September.

Miller and his research team captured the data from a new advanced weather-and-climate monitoring satellite. The satellite, a joint venture between NASA and NOAA, is called the Suomi National Polar-orbiting Partnership, or Suomi NPP, and carries five advanced instruments at an orbit about 512 miles above the earth.

This new ability to see clouds at night could have significant implications for weather and climate observations for forecasters and research scientists alike.

"This development is exciting and impressive," said Mary Kicza, assistant administrator for NOAA’s Satellite and Information Service. "This could be especially useful to our meteorologists in areas like Alaska, where the winter months have long periods of darkness."

Among these sensors is the Visible/Infrared Imager/Radiometer Suite (VIIRS), which includes a “day-night band” that is sensitive to extremely low levels of light. Researchers at CIRA perform many instrument check-out activities for the NPP mission.

“The day-night band is a new capability for NOAA users,” said Mitch Goldberg, program scientist at NOAA Joint Polar Satellite System (JPSS) Office. “We are very encouraged by this remarkable discovery by the CIRA scientists.”

The scientists were applying methods to reduce “noise” in the day-night band measurements, when they found that the instrument was sensitive enough to see clouds and other objects in what would appear to the human eye as complete darkness. The new capability will be useful for improving our views of very low clouds and features such as sea ice at night, potentially benefiting travel and commerce.

“Most weather satellites aren’t even sensitive enough to see the lights from a large city like Denver, much less the reflected moonlight, which is nearly a million times fainter than sunlight. These air glow/starlight sources are 100-1,000 times fainter still,” Miller said. “Instead of using visible light, nighttime observations are typically relegated to infrared (heat) measurements, where near-surface features (such as fog) can blend into their surroundings because they have nearly the same temperature.”

In addition to the clouds, Miller said that sensitivity of the day-night band to direct emissions from air glow allows the sensor to see waves moving through the upper atmosphere, forced by thunderstorms below – which appear like ripples in a pond atop some of the stronger storms.

CIRA was established as an interdisciplinary partnership between the National Oceanic and Atmospheric Administration (NOAA) and CSU in 1980 to accelerate the transition of cutting edge atmospheric science research into the hands of operational users for societal benefit. CIRA researchers on a daily basis translate data collected by globally distributed satellites and output from computers to a scientific and practical understanding that allows researchers to better define and predict changes to weather and climate.