Clouds and the Earth's Radiant Energy System (CERES) is

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...

climatological experiment from

Earth orbit Earth orbits the Sun at an average distance of 149.60 million km (92.96 million mi) in a counterclockwise direction as viewed from above the Northern Hemisphere. One complete orbit takes days (1 sidereal year), during which time Earth ...

. The CERES are scientific satellite instruments, part of the 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, atmosphere, and oceans ...

(EOS), designed to measure both solar-reflected and Earth-emitted radiation from the top of the

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...

(TOA) to the Earth's surface. Cloud properties are determined using simultaneous measurements by other EOS instruments such as the

Moderate Resolution Imaging Spectroradiometer The Moderate Resolution Imaging Spectroradiometer (MODIS) is a satellite-based sensor used for earth and climate measurements. There are two MODIS sensors in Earth orbit: one on board the Terra (satellite), Terra (Earth Observing System, ...

(MODIS). Results from the CERES and other NASA missions, such as the

Earth Radiation Budget Experiment The Earth Radiation Budget Satellite (ERBS) is a NASA scientific research satellite within NASA's ERBE (Earth Radiation Budget Experiment) Research Program - a three-satellite mission, designed to investigate the Earth radiation budget. It also ...

(ERBE), could enable nearer to real-time tracking of

Earth's energy imbalance Earth's energy budget accounts for 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 consideration, but m ...

and better understanding of the role of clouds in global

climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...

Scientific goals

CERES experiment has four main objectives: * Continuation of the ERBE record of radiative fluxes at the top of the atmosphere (TOA) for

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'', while ''precision'' is how close the measurements are to each oth ...

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 that are 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 microwave w ...

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

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

Tropical Rainfall Measuring Mission The Tropical Rainfall Measuring Mission (TRMM) was a joint space mission between NASA and JAXA designed to monitor and study tropical rainfall. The term refers to both the mission itself and the satellite that the mission used to collect data. ...

(TRMM) in November 1997 from

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

. However, this instrument failed to operate after 8 months due to an on-board circuit failure.

CERES on the EOS and JPSS mission satellites

An additional six CERES instruments were launched on the

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 States ...

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 Sat ...

in November 2017. With the failure of the PFM on TRMM and the 2005 loss of the SW channel of FM4 on Aqua, there are five of the CERES Flight Modules that are fully operational as of 2017.

Radiation Budget Instruments

The measurements of the CERES instruments was to be furthered by the

Radiation Budget Instrument The Radiation Budget Instrument (RBI) is a scanning radiometer capable of measuring Earth's reflected sunlight and emitted thermal radiation. The project was cancelled on January 26, 2018; NASA cited technical, cost, and schedule issues and the im ...

(RBI) to be launched on

-2 (JPSS-2) in 2021, JPSS-3 in 2026, and JPSS-4 in 2031. The project was cancelled on January 26, 2018;

cited technical, cost, and schedule issues and the impact of anticipated RBI cost growth on other programs.

Operating modes

CERES operates in three scanning modes: across the satellite

ground track A ground track or ground trace is the path on the surface of a planet directly below an aircraft's or satellite's trajectory. In the case of satellites, it is also known as a suborbital track, and is the vertical projection of the satellite's or ...

(cross-track), along the direction of the satellite ground track (along-track), and in a Rotating Azimuth Plane (RAP). In RAP mode, the

radiometers 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 microwave wa ...

scan in elevation as they rotate in

azimuth An azimuth (; from ar, اَلسُّمُوت, as-sumūt, the directions) is an angular measurement in a spherical coordinate system. More specifically, it is the horizontal angle from a cardinal direction, most commonly north. Mathematicall ...

, 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 ...

measurement 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 scienti ...

and

Aqua Aqua is the Latin word for water. It is used in many words which relate to water, such as aquatic life. In English, it may also refer to: Arts * Aqua (color), a greenish-blue color Business * Aqua (skyscraper), an 82-story residential skysc ...

satellites one of 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

anisotropy Anisotropy () is the property of a material which allows it to change or assume different properties in different directions, as opposed to isotropy. It can be defined as a difference, when measured along different axes, in a material's physic ...

of the viewed scene, and allow TOA radiative flux retrieval with enhanced precision.

Calibration methods

Ground absolute calibration

For a climate data record (CDR) mission like CERES, accuracy is of high importance and achieved for pure infrared nighttime measurements by use of 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 solar portion of the Total telescope, which have no direct un-broken chain to SI traceability. This is because CERES solar responses were measured on ground using lamps whose output energy were estimated by a cryo-cavity reference detector, which used a silver Cassegrain telescope identical to CERES devices to match the satellite instrument field of view. The reflectivity of this telescope built and used since the mid-1990s was never actually measured, 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%, simply 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 diameter of the footprint) is 10 km for CERES on TRMM, and 20 km for CERES on

and

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 know ...

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 such 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 name "black body" is given because it absorbs all colors of light. A black body ...

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

spectroradiometer A spectroradiometer is a light measurement tool that is able to measure both the wavelength and amplitude of the light emitted from a light source. Spectrometers discriminate the wavelength based on the position the light hits at the detector array ...

s (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.

References

External links

NASA CERES official siteCERES Data ProductsTerra satellite, NASA EOS flagshipAqua satallite, NASA EOSVISIBLE EARTH, catalog of CERES images
{{Space-based meteorological observation NASA programs Articles containing video clips Atmospheric sounding satellite sensors