Clouds and the Earth's Radiant Energy System

Project Description
The Clouds and the Earth s Radiant Energy System (CERES)
experiment is one of the highest priority scientific satellite
instruments developed for EOS. CERES products include both
solar-reflected and Earth-emitted radiation from the top of the
atmosphere to the Earth's surface. Cloud properties are
determined using simultaneous measurements by other EOS
instruments such as the Moderate Resolution Imaging
Spectroradiometer (MODIS). Analyses of the CERES data, which
build upon the foundation laid by previous missions such as the
Earth Radiation Budget Experiment (ERBE), will lead to a better
understanding of the role of clouds and the energy cycle in
global climate change.

CERES instruments were launched aboard the Tropical Rainfall
Measuring Mission (TRMM) in November 1997 and on the EOS Terra
satellite in December 1999. Two additional instruments will fly
on the EOS Aqua spacecraft in 2002. Multiple satellites are
needed to provide adequate temporal sampling since clouds and
radiative fluxes vary throughout the day. The first 24 months
of CERES data collected on both TRMM and Terra demonstrate that
the CERES instruments are substantially improved over the ERBE
instruments. The CERES data show lower noise, improved ties to
the ground calibration in absolute terms, and smaller fields of
view. CERES instrument calibration stability on TRMM and Terra
is typically better than 0.2%, and calibration consistency from
ground to space is better than 0.25%. Onboard calibration
sources provide traceability of the measurements to the
International Temperature Scale of 1990 at the 0.2% level. Such
levels of accuracy have never before been achieved for rad!
iation budget instruments.

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