C		Clouds and the
E		Earth's
R		Radiant
E		Energy
S		System

CERES consists of two broadband scanning radiometers that will measure the Earth's radiation balance and provide cloud property estimates to assess their role in radiative fluxes from the surface to the top of the atmosphere.

CERES is a broadband scanning thermistor bolometer package with extremely high radiometric measurement precision and accuracy. The Terra spacecraft will carry two identical instruments: one will operate in a cross-track scan mode and the other in a biaxial scan mode. The cross-track mode will essentially continue the measurements of the Earth Radiation Budget Experiment (ERBE) mission as well as the Tropical Rainfall Measuring Mission (TRMM), while the biaxial scan mode will provide new angular flux information that will improve the accuracy of angular models used to derive the Earth's radiation balance.

Each CERES instrument has three channels—a short-wave channel for measuring reflected sunlight, a longwave channel for measuring Earth-emitted thermal radiation in the 8 - 12 µm "window" region, and a total channel for total radiation. Onboard calibration hardware includes a solar diffuser, a tungsten lamp system with a stability monitor, and a pair of blackbody sources. Cold space and internal calibration looks are performed during each normal Earth scan.

Both CERES scanners operate continuously throughout the day and night portions of an orbit. In the cross-track scan mode, calibration occurs biweekly. In the biaxial scan mode, calibration also occurs biweekly, and sun-avoidance short scans occur twice per orbit.

CERES is a Principal Investigator instrument provided by NASA and managed by NASA's Langley Research Center (LaRC) in Hampton, Virginia. The instrument was built by TRW in Redondo Beach, California. The CERES Team Leader is Bruce Barkstrom. More information may be obtained on the CERES Web Page at http://asd-www.larc.nasa.gov/ceres/ASDceres.html.

CERES data will be used to:

• study cloud radiative forcing and feedbacks;
• develop an observational baseline of clear-sky radiative fluxes;
• determine radiant input to atmospheric and oceanic energetics models;
• validate general circulation models; and
• enhance extended-range numerical weather predictions.

CERES Instrument Characteristics
Spectral bands	Shortwave: 0.3-5.0 µm Longwave: 8-12 µm Total: 0.3 to >200 µm
Spatial resolution at nadir	20km
Duty cycle	100%
Data rate	20 kbps (two instruments)
Mass	90 kg (two instruments)
Power	95 W (two instruments)

LONGWAVE CLOUD FORCING 1985-1986 (W/m-2)

SHORTWAVE CLOUD FORCING 1985-1986 (W/m-2)

These global data products were taken by the Earth Radiation Budget Experiment (ERBE)—the heritage instrument for CERES. The data show a one-year average (from 1985-86) of the cloud forcing of incoming solar radiation and outgoing longwave radiation. The colors represent ERBE's measurements in Watts per meter squared (Dennis Hartmann, U. of Washington).

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