SAN FRANCISCO — After more than a decade in orbit, the Clouds and the Earth’s Radiant Energy System (CERES), an instrument first launched in 1997, is becoming more useful with each passing year. “Like wine, CERES gets better with time,” said Norman Loeb, CERES principal investigator at NASA’s Langley Research Center in Hampton, Va. “The longer your data record, the more you learn.”
Four CERES instruments are gathering data aboard the NASA Earth-observing system’s Terra and Aqua satellites. While those sensors continue to function well, scientists are eager to send up additional instruments to ensure a continuous data record, Loeb said.
Another CERES instrument has been integrated on a NASA-led mission set for launch in September 2011, the National Polar-orbiting Operational Environ- mental Satellite System (NPOESS) Preparatory Project, known as NPP, said Sean Kelly, CERES program manager for instrument builder Northrop Grumman Aerospace Systems of Redondo Beach, Calif.
The final sensor being built by Northrop Grumman is scheduled for delivery to NASA Langley in 2012, Kelly added. That sensor is expected to fly onboard the National Oceanic and Atmospheric Administration (NOAA) Joint Polar Satellite System (JPSS), a mission that will take on a portion of the climate-monitoring work of NPOESS, a joint civil and military project canceled by the White House in February. No launch date has been announced for the two JPSS spacecraft. However, the first satellite with CERES onboard is expected to be completed in 2015, according to NOAA’s National Environmental Satellite Data and Information Service Web site.
CERES measures solar energy reflected by Earth and Earth’s emitted thermal energy, key elements that make up the Earth’s radiation budget, an important factor in helping scientists understand the complex global climate system.
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Already, scientists have learned about the role clouds play in causing variations in the amount of solar energy reflected and thermal energy emitted from Earth by looking at CERES data in conjunction with measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS), which also flies on both Terra and Aqua. “Coincident observations from CERES and MODIS instruments provided unprecedented data on how variations in the Earth’s radiation budget are associated with variations in cloud properties such as cloud height, thickness and amount,” Loeb said. “With a 10-year record we are starting to see that.”
However, 10 years of data is not enough to give scientists a clear picture of global climate change because of the natural variables. For example, El Niño, a climate pattern associated with changes in Pacific Ocean temperatures, floods and droughts, occurs every three to seven years, causing large fluctuations in cloud and radiation patterns that can mask cloud and radiation changes associated with increasing levels of greenhouse gases. To provide evidence of the ongoing changes in the Earth’s climate, CERES needs to gather data over a much longer period of time, Loeb said.
“For climate measurements, we are talking about measuring a few tenths of a degree changes in Earth over decades,” said Mark Folkman, Northrop Grumman’s director of products and sensing. “To do that, you’ve got to make well-calibrated measurements for multiple decades.”
What’s more, CERES is monitoring extremely small changes in the Earth’s energy budget that, over time, can lead to serious consequences, including ice caps melting and sea levels rising. One particularly useful aspect of CERES is its ability to help evaluate and refine the computer models used to predict the consequences of global climate change. “If we are going to try to have informed policy decisions, let’s make sure those decisions are based on facts,” Loeb said.
CERES and its predecessor, the Earth Radiation Budget Experiment, also built by Northrop Grumman, have provided a record of solar, thermal and reflected radiation stretching back to 1984. If all goes well, the CERES instrument being built for JPSS may continue gathering data for a decade or more, which could carry the program through 2025.
The two CERES sensors launched in 1999 on Terra are providing useful data after more than a decade in orbit, and the two sensors on Aqua, launched in 2002, also continue to function well, Loeb said. The first CERES sensor flew on NASA’s Tropical Rainfall Measurement Mission. That instrument collected data continuously for eight months in 1998 before problems with the instrument’s power converters forced mission planners to use the instrument only sporadically.
Because of the CERES program’s multi-decade, multi-sensor approach, some NASA officials attending a celebration of Terra’s 10-year anniversary in December dubbed the program “infinite CERES.” That’s not entirely accurate, but “it would be great to go on as long as we can,” Loeb said.
He compares CERES and its ongoing data-gathering mission to annual medical checkups performed by doctors. Ongoing checkups give doctors a chance to monitor vital signs and identify problems before they become serious. Similarly, CERES provides a long-standing record of the Earth’s radiation budget, which helps scientists identify changes in the global climate.
Another suite of instruments designed to provide detailed data on Earth’s climate is expected to fly aboard the Climate Absolute Radiance and Refractivity Observatory (CLARREO), a wide-ranging mission recommended by the National Science Foundation’s Decadal Survey. CLARREO, which is expected to launch between 2016 and 2019, is designed to improve the accuracy of climate models by collecting data on atmospheric, land and sea-surface temperature, cloud properties, ocean color, solar irradiance and aerosols. In addition, CLARREO will include onboard calibration to obtain highly accurate data records, Loeb said.
Nevertheless, CLARREO will not replace CERES. The two CLARREO satellites will fly in a polar orbit and will not provide the type of daily, global coverage offered by the CERES instruments carried by Aqua and Terra. “You still need CERES to continue,” Loeb said. “CERES and CLARREO are complementary.”
As Northrop Grumman completes construction of the CERES instrument ordered for the NPOESS program, company engineers are looking for ways to improve the technology for future sensors. Much of the CERES technology was developed during the 1990s, so it is a good time to modernize the instrument, Folkman said.
“In the process of modernizing, we want to be careful that we don’t have any discontinuity in the data record,” he added. “It’s an interesting challenge to improve the measurements, improve the noise performance with new technology, without making a change that causes you to lose your baseline.”
