The first Clouds and the Earth's Radiant Energy System (CERES) instrument launched in 1997. Before that, the job was done by the Earth Radiation Budget Experiment (ERBE) beginning in 1984.

For 27 years without a break, the instruments collectively have returned a vast amount of data about the solar energy reflected and absorbed by Earth, the heat the planet emits, and the role of clouds in that process.

"Like wine, CERES gets better with time," said Norman Loeb, CERES principal investigator at NASA's Langley Research Center in Hampton, Va.

Amassing a long record of data is important because CERES monitors minute changes in Earth's energy budget -- the balance between incoming and outgoing energy -- that can lead to serious longer-term consequences, such as polar ice melting and rising sea levels, said Loeb.

How It Works

Scientists are studying the planetary energy balance that results from these interactions primarily because Earth's atmosphere is influenced by the buildup of human-released carbon dioxide and other greenhouse gases.

"Clouds both reflect sunlight and block energy from radiating to space," Loeb said. "Which of these two dominates depends upon the properties of clouds, such as their amount, thickness and height."

"As the Earth undergoes changes in its climate, cloud properties may change in ways that may amplify or offset climate change. Understanding the influence of clouds on the energy budget is therefore a critical climate problem."

The four other CERES instruments are in orbit aboard NASA's Aqua and Terra satellites. The instruments use a radiometer to measure the power of electromagnetic radiation being transmitted in the atmosphere.

All the radiometers on the CERES instruments are essentially the same, are well calibrated and produce comparable data -- and that's critical, said Mark Folkman, director of sensor products for Northrop Grumman Aerospace Systems, which made CERES.

"Because scientists need to measure minute changes in the Earth's radiance over decades, CERES provides the absolute radiometric accuracy that is essential to monitoring the temperature of our planet," he said.

"If the instrument calibration were to change over these long timeframes, scientists might draw the wrong conclusions about the Earth's environment," Folkman added. "For more than 25 years, CERES has generated the accurate, long-term measurements that are essential to providing a true picture of the Earth's radiation balance, a critical element of the climate system."

Overall Mission

This fall, the climate-monitoring torch is being passed to NASA's NPP, a satellite carrying the fifth edition of CERES. The spacecraft, carrying four other Earth-observing instruments, is scheduled for launch into a polar orbit Oct. 25 from Vandenberg Air Force Base in California on a Boeing Delta II-7920-10 launch vehicle.

The five-instrument suite will collect and distribute remotely sensed land, ocean, and atmospheric data to the meteorological and global climate change communities. It will provide atmospheric and sea surface temperatures, humidity sounding, land and ocean biological productivity, cloud and aerosol properties, total/profile ozone measurements, and monitor changes in Earth's radiation budget.

NASA's Goddard Space Flight Center manages the NPP mission on behalf of the Earth Science Division of the Science Mission Directorate at NASA Headquarters, Washington. NASA Langley manages the CERES mission. The TRW Space & Electronics Group in Redondo Beach, Calif., now owned by Northrop Grumman Aerospace Systems, built all of the CERES instruments.

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