Clouds And The Earth's Radiant Energy System
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Clouds and the Earth's Radiant Energy System (CERES) is an
NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...
climatological experiment from Earth orbit. The CERES are scientific satellite instruments, part of NASA's
Earth Observing System The Earth Observing System (EOS) is a program of NASA comprising a series of artificial satellite missions and scientific instruments in Earth orbit designed for long-term global observations of the land surface, biosphere, earth's atmosphere, at ...
(EOS), designed to measure solar-reflected and Earth-emitted radiation from the top of the
atmosphere An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...
(TOA) to the Earth's surface. Cloud properties are determined using simultaneous measurements by other EOS instruments such as the Moderate Resolution Imaging Spectroradiometer (MODIS). Results from the CERES and other NASA missions, such as the Earth Radiation Budget Experiment (ERBE), could enable near-real-time tracking of Earth's energy imbalance (EEI) and better understanding of the role of clouds in global
climate change Present-day climate change includes both global warming—the ongoing increase in Global surface temperature, global average temperature—and its wider effects on Earth's climate system. Climate variability and change, Climate change in ...
.


Scientific goals

The CERES experiment has four main objectives: * Continuation of the ERBE record of radiative fluxes at the top of the atmosphere (TOA) for
climate change Present-day climate change includes both global warming—the ongoing increase in Global surface temperature, global average temperature—and its wider effects on Earth's climate system. Climate variability and change, Climate change in ...
analysis. * Doubling the
accuracy Accuracy and precision are two measures of ''observational error''. ''Accuracy'' is how close a given set of measurements (observations or readings) are to their ''true value''. ''Precision'' is how close the measurements are to each other. The ...
of estimates of radiative fluxes at TOA and the Earth's surface. * Provide the first long-term global estimates of the radiative fluxes within the Earth's atmosphere. * Provide cloud property estimates consistent with the radiative fluxes from surface to TOA. Each CERES instrument is a
radiometer A radiometer or roentgenometer is a device for measuring the radiant flux (power) of electromagnetic radiation. Generally, a radiometer is an infrared radiation detector or an ultraviolet detector. Microwave radiometers operate in the micro ...
which has three channels – a shortwave (SW) channel to measure reflected sunlight in 0.2–5 μm region, a channel to measure Earth-emitted thermal radiation in the 8–12 μm "window" or "WN" region, and a Total channel to measure entire spectrum of outgoing Earth's radiation (>0.2 μm). The CERES instrument was based on the successful Earth Radiation Budget Experiment, which used three satellites to provide global energy budget measurements from 1984 to 1993.


Missions


First launch

The first CERES instrument Proto-Flight Module (PFM) was launched aboard the
NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...
Tropical Rainfall Measuring Mission (TRMM) in November 1997 from
Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...
. However, this instrument failed to operate after 8 months due to an onboard circuit failure.


CERES on the EOS and JPSS mission satellites

Six more CERES instruments were launched on the
Earth Observing System The Earth Observing System (EOS) is a program of NASA comprising a series of artificial satellite missions and scientific instruments in Earth orbit designed for long-term global observations of the land surface, biosphere, earth's atmosphere, at ...
and the
Joint Polar Satellite System The Joint Polar Satellite System (JPSS) is the latest generation of U.S. polar-orbiting, non-geosynchronous, environmental satellites. JPSS will provide the global environmental data used in numerical weather prediction models for forecasts, and ...
. The Terra satellite, launched in December 1999, carried two (Flight Module 1 (FM1) and FM2), and the Aqua satellite, launched in May 2002, carried two more (FM3 and FM4). A fifth instrument (FM5) was launched on the
Suomi NPP The Suomi National Polar-orbiting Partnership (Suomi NPP), previously known as the National Polar-orbiting Operational Environmental Satellite System Preparatory Project (NPP) and NPP-Bridge, is a weather satellite operated by the United State ...
satellite in October 2011 and a sixth (FM6) on
NOAA-20 NOAA-20, designated JPSS-1 prior to launch, is the first of the United States National Oceanic and Atmospheric Administration's latest generation of U.S. polar-orbiting, non-geosynchronous, environmental satellites called the Joint Polar Sate ...
in November 2017. With the failure of the PFM on TRMM and the 2005 loss of the SW channel of FM4 on Aqua, five of the CERES Flight Modules are fully operational as of 2017.


Radiation Budget Instruments

The measurements of the CERES instruments were to be furthered by the Radiation Budget Instrument (RBI) to be launched on
Joint Polar Satellite System The Joint Polar Satellite System (JPSS) is the latest generation of U.S. polar-orbiting, non-geosynchronous, environmental satellites. JPSS will provide the global environmental data used in numerical weather prediction models for forecasts, and ...
-2 (JPSS-2) in 2021, JPSS-3 in 2026, and JPSS-4 in 2031. The project was cancelled on January 26, 2018;
NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...
cited technical, cost, and schedule issues and the impact of anticipated RBI cost growth on other programs.


Libera

NASA announced in February 2020 its selection of the Libera instrument to launch on JPSS-3 by the end of 2027. Libera is planned to provide data continuity and updated capabilities. LASP is the lead instrument developer.


Operating modes

CERES operates in three scanning modes: across the satellite
ground track A satellite ground track or satellite ground trace is the path on the surface of a planet directly below a satellite's trajectory. It is also known as a suborbital track or subsatellite track, and is the vertical projection of the satellite's ...
(cross-track), along the direction of the satellite ground track (along-track), and in a Rotating Azimuth Plane (RAP). In RAP mode, the radiometers scan in elevation as they rotate in
azimuth An azimuth (; from ) is the horizontal angle from a cardinal direction, most commonly north, in a local or observer-centric spherical coordinate system. Mathematically, the relative position vector from an observer ( origin) to a point ...
, thus acquiring
radiance In radiometry, radiance is the radiant flux emitted, reflected, transmitted or received by a given surface, per unit solid angle per unit projected area. Radiance is used to characterize diffuse emission and reflection of electromagnetic radiati ...
measurements from a wide range of viewing angles. Until February 2005, on
Terra Terra may often refer to: * Terra (mythology), primeval Roman goddess * An alternate name for planet Earth, as well as the Latin name for the planet Terra may also refer to: Geography Astronomy * Terra (satellite), a multi-national NASA scient ...
and Aqua satellites, one of the CERES instruments scanned in cross-track mode while the other was in RAP or along-track mode. The instrument operating in RAP scanning mode took two days of along-track data every month. However, the multi-angular CERES data allowed to derive new models which account for the
anisotropy Anisotropy () is the structural property of non-uniformity in different directions, as opposed to isotropy. An anisotropic object or pattern has properties that differ according to direction of measurement. For example, many materials exhibit ve ...
of the viewed scene and allow TOA radiative flux retrieval with enhanced precision. All CERES instruments are in
Sun-synchronous orbit A Sun-synchronous orbit (SSO), also called a heliosynchronous orbit, is a nearly polar orbit around a planet, in which the satellite passes over any given point of the planet's surface at the same local mean solar time. More technically, it is ...
. Comparable
geostationary A geostationary orbit, also referred to as a geosynchronous equatorial orbit''Geostationary orbit'' and ''Geosynchronous (equatorial) orbit'' are used somewhat interchangeably in sources. (GEO), is a circular geosynchronous orbit in altitud ...
data between 60°S and 60°N are also applied within "balanced and filled" data products to provide a diurnally complete representation of the radiation budget and to account for cloud changes between CERES observation times.


Calibration methods

The CERES instruments were designed to provide enhanced measurement stability and precision; however, achieving and ensuring absolute
accuracy Accuracy and precision are two measures of ''observational error''. ''Accuracy'' is how close a given set of measurements (observations or readings) are to their ''true value''. ''Precision'' is how close the measurements are to each other. The ...
over time was also known to remain an ongoing challenge. Despite the more advanced capability of CERES to monitor Earth's TOA radiative fluxes globally and with relative accuracy, the only practical way to estimate the absolute magnitude of EEI (as of 2020) is through an inventory of the energy change in the climate system. Consequently, an important constraint within CERES data products has been the anchoring of EEI at one point in time to a value which corresponds to several years of
ARGO In Greek mythology, the ''Argo'' ( ; ) was the ship of Jason and the Argonauts. The ship was built with divine aid, and some ancient sources describe her as the first ship to sail the seas. The ''Argo'' carried the Argonauts on their quest fo ...
data.


Ground absolute calibration

For a climate data record (CDR) mission like CERES, accuracy is highly important and achieved for pure infrared nighttime measurements using a ground laboratory SI traceable blackbody to determine total and WN channel radiometric gains. This, however, was not the case for CERES solar channels such as SW and the solar portion of the Total telescope, which have no direct unbroken chain to SI traceability. This is because CERES solar responses were measured on the ground using lamps whose output energy was estimated by a cryo-cavity reference detector, which used a silver Cassegrain telescope identical to CERES devices to match the satellite instrument's field of view. The reflectivity of this telescope, built and used since the mid-1990s, was never actually measured; it was estimated only based on witness samples (see slide 9 of Priestley et al. (2014)). Such difficulties in ground calibration, combined with suspected on-ground contamination events have resulted in the need to make unexplained ground to flight changes in SW detector gains as big as 8%, to make the ERB data seem somewhat reasonable to climate science (note that CERES currently claims a one sigma SW absolute accuracy of 0.9%).


In-flight calibration

CERES spatial resolution at nadir view (equivalent footprint diameter) is 10 km for CERES on TRMM, and 20 km for CERES on
Terra Terra may often refer to: * Terra (mythology), primeval Roman goddess * An alternate name for planet Earth, as well as the Latin name for the planet Terra may also refer to: Geography Astronomy * Terra (satellite), a multi-national NASA scient ...
and Aqua satellites. Perhaps of greater importance for missions such as CERES is calibration stability, or the ability to track and partition instrumental changes from Earth data so it tracks true climate change with confidence. CERES onboard
calibration In measurement technology and metrology, calibration is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy. Such a standard could be another measurement device of known ...
sources intended to achieve this for channels measuring reflected sunlight include solar diffusers and tungsten lamps. However, the lamps have very little output in the important ultraviolet wavelength region where degradation is greatest, and they have been seen to drift in energy by over 1.4% in ground tests, without a capability to monitor them on-orbit (Priestley et al. (2001)). The solar diffusers have also degraded greatly in orbit, that they have been declared unusable by Priestley et al. (2011). A pair of
black body A black body or blackbody is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. The radiation emitted by a black body in thermal equilibrium with its environment is ...
cavities that can be controlled at different temperatures are used for the Total and WN channels, but these have not been proved stable to better than 0.5%/decade. Cold space observations and internal calibration are performed during normal Earth scans.


Intercalibration

Data is compared between CERES instruments on different mission satellites, as well as compared to scan reference data from accompanying spectroradiometers (e.g., MODIS on Aqua). The planned CLARREO Pathfinder mission aims to provide a state-of-the-art reference standard for several existing EOS instruments, including CERES. A study of annual changes to Earth's energy imbalance (EEI) spanning 2005-2019 showed good agreement between the CERES observation and EEI inferred from in-situ measurements of ocean heat uptake by the Argo float network. A concurrent pair of studies measuring global ocean heat uptake, ice melting, and
sea level rise The sea level has been rising from the end of the last ice age, which was around 20,000 years ago. Between 1901 and 2018, the average sea level rose by , with an increase of per year since the 1970s. This was faster than the sea level had e ...
with a combination of space altimetry and gravimetry suggested similar agreements.


See also

*
Earth's energy budget Earth's energy budget (or Earth's energy balance) is the balance between the energy that Earth receives from the Sun and the energy the Earth loses back into outer space. Smaller energy sources, such as Earth's internal heat, are taken into con ...
* Geostationary Earth Radiation Budget *
Radiometry Radiometry is a set of techniques for measurement, measuring electromagnetic radiation, including visible light. Radiometric techniques in optics characterize the distribution of the radiation's power (physics), power in space, as opposed to phot ...
*
Remote sensing Remote sensing is the acquisition of information about an physical object, object or phenomenon without making physical contact with the object, in contrast to in situ or on-site observation. The term is applied especially to acquiring inform ...


References

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External links


NASA CERES official siteCERES Data ProductsTerra satellite, NASA EOS flagshipAqua satellite, NASA EOSVISIBLE EARTH, catalog of CERES images
NASA programs Articles containing video clips Atmospheric sounding satellite sensors