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Clouds and Earth Radiant Energy System (CERES), a review: Past,
present and future
G.L. Smith
a,⇑
, K.J. Priestley
a
, N.G. Loeb
a
, B.A. Wielicki
a
, T.P. Charlock
a
, P. Minnis
a
,
D.R. Doelling
a
, D.A. Rutan
b
a
MS 420, Langley Research Centre, Hampton, VA 23681, USA
b
Science Systems and Applications, Inc., 1 Enterprise Parkway, Hampton, VA 23666, USA
Received 5 October 2010; received in revised form 22 February 2011; accepted 10 March 2011
Available online 30 March 2011
Abstract
The Clouds and Earth Radiant Energy System (CERES) project’s objectives are to measure the reflected solar radiance (shortwave)
and Earth-emitted (longwave) radiances and from these measurements to compute the shortwave and longwave radiation fluxes at the
top of the atmosphere (TOA) and the surface and radiation divergence within the atmosphere. The fluxes at TOA are to be retrieved to
an accuracy of 2%. Improved bidirectional reflectance distribution functions (BRDFs) have been developed to compute the fluxes at
TOA from the measured radiances with errors reduced from ERBE by a factor of two or more. Instruments aboard the Terra and Aqua
spacecraft provide sampling at four local times. In order to further reduce temporal sampling errors, data are used from the geostation-
ary meteorological satellites to account for changes of scenes between observations by the CERES radiometers.
A validation protocol including in-flight calibrations and comparisons of measurements has reduced the instrument errors to less than
1%. The data are processed through three editions. The first edition provides a timely flow of data to investigators and the third edition
provides data products as accurate as possible with resources available.
A suite of cloud properties retrieved from the MODerate-resolution Imaging Spectroradiometer (MODIS) by the CERES team is
used to identify the cloud properties for each pixel in order to select the BRDF for each pixel so as to compute radiation fluxes from
radiances. Also, the cloud information is used to compute radiation at the surface and through the atmosphere and to facilitate study
of the relationship between clouds and the radiation budget. The data products from CERES include, in addition to the reflected solar
radiation and Earth emitted radiation fluxes at TOA, the upward and downward shortwave and longwave radiation fluxes at the surface
and at various levels in the atmosphere. Also at the surface the photosynthetically active radiation and ultraviolet radiation (total, UVA
and UVB) are computed. The CERES instruments aboard the Terra and Aqua spacecraft have served well past their design life times. A
CERES instrument has been integrated onto the NPP platform and is ready for launch in 2011. Another CERES instrument is being
built for launch in 2014, and plans are being made for a series of follow-on missions.
Ó2011 COSPAR. Published by Elsevier Ltd. All rights reserved.
Keywords: Earth Radiation Budget; CERES; Radiometry; Remote sensing
1. Introduction
The weather and climate system is a heat engine consist-
ing of the atmosphere, oceans, land and cryosphere. The
energy source for this system is sunlight which is absorbed
at low latitudes and the sink is the outgoing longwave radi-
ation (OLR). An understanding of this energy cycle and its
various facets is necessary for comprehending the weather
0273-1177/$36.00 Ó2011 COSPAR. Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.asr.2011.03.009
⇑
Corresponding author.
E-mail addresses: George.l.Smith@nasa.gov (G.L. Smith), Kory.
J.Priestley@nasa.gov (K.J. Priestley), Norman.B.Loeb@nasa.gov (N.G.
Loeb), Bruce.A.Wielicki@nasa.gov (B.A. Wielicki), Thomas.P.Charlock
@nasa.gov (T.P. Charlock), P.Minnis@nasa.gov (P. Minnis), David.
R.Doelling@nasa.gov (D.R. Doelling), David.A.Rutan@nasa.gov (D.A.
Rutan).
www.elsevier.com/locate/asr
Available online at www.sciencedirect.com
Advances in Space Research 48 (2011) 254–263
and climate and its variations (Ramanathan, 1987). The
Earth Radiation Budget Experiment (ERBE) (Barkstrom
and Smith,1986; Barkstrom et al., 1989) provided much
information about the energetics of the system and the
effects of clouds in modulating the energy balance (Rama-
nathan et al., 1989; Harrison et al., 1990). The Clouds and
Earth Radiant Energy System (CERES) project was con-
ceived as a successor to ERBE in order to compile a data
record for the investigation of interannual variations of cli-
mate (Barkstrom, 1990). To determine better these
changes, errors in the data products for the shortwave
and longwave radiation fluxes at the top of the atmosphere
TOA would be reduced by a factor of two. Furthermore,
CERES would also give the radiation fluxes at the surface
and radiation divergence within the atmosphere. Since the
start of CERES, global warming has become a major issue
and the National Research Council (2007) and World
Climate Research Program (2008) emphasized the need
for a highly accurate Earth Radiation Budget Climate
Data Record continuing into the future. This paper reviews
the methods by which the desired accuracies have been
obtained, then describes the data products from CERES
and the special operations of the CERES radiometers to
support atmospheric radiation investigations and compar-
ison of CERES measurements with those from other
instruments.
2. Instrument
Fig. 1 shows the CERES scanning radiometer and Fig. 2
is an exploded view of the instrument. It has three chan-
nels, for measuring the solar radiation reflected by the
Earth, the OLR and the radiance from the Earth in the
8–12 lm window of the atmospheric spectrum. The three
channels are the shortwave channel, 0.2–5 lm for the
reflected solar radiation, a total channel for measuring
radiances 0.2 to beyond 100 lm and an 8–12 lm channel
for the window radiation. From the total channel measure-
ments, nighttime OLR is retrieved and daytime OLR is
computed as the total radiance minus the SW radiance.
Retrieving the radiances requires taking into account the
spectral responses of the channels. Smith et al. (1998) pro-
vide further description of the instrument.
When the sensor module has scanned past the Earth and
space, it looks inside the instrument at the Internal Calibra-
tion Module (ICM). This unit has a ShortWave Incandes-
cent Calibration Source (SWICS) for the shortwave
channel and two black bodies, one for the total channel
and the other for the window channel. In addition to the
ICM is a Mirror Attenuated Mosaic (MAM), which
reflects a fraction of the Sun’s radiance into the total and
shortwave channels for calibration. All of this hardware
is mounted on an azimuthal scan table.
Each instrument is calibrated in the Radiation Calibra-
tion Facility to determine the gain of each channel; the
spectral responses of the channel components are measured
by use of a Fourier Transform Spectrometer. Lee et al.
(1996, 1997) describe the calibration plan and Priestley
et al. (1998) compare ground calibration and early calibra-
tion results for PFM. Barkstrom et al. (2000) and Lee et al.
(2000) present results of the for FM-1 and FM-2 calibra-
tions. Once the instrument begins operating in orbit, the
space environment causes the gains and spectral responses
to change. The ICM and MAM provide information for
adjusting the gains, but there is no on-board device provid-
ing information about the spectral responses.
2.1. Flight missions
The CERES Proto-Flight Model (PFM) flew aboard the
Tropical Rainfall Measuring Mission in November 1997 in
Fig. 1. CERES Scanning Radiometer.
Fig. 2. Exploded view of CERES instrument.
G.L. Smith et al./ Advances in Space Research 48 (2011) 254–263 255
a precessing orbit with inclination of 35°and altitude of
350 km. At this altitude the footprint size of the measure-
ment was nominally 10 km. PFM operated from December
1997 to September 1998, when it was turned off due to
problems with the power supply.
Two CERES instruments, Flight Models 1 and 2, went
into orbit on the Terra spacecraft in December 1999 and
began operating in February 2000. These satellites are at
705 km altitude, so that the footprint is nominally 20 km.
These instruments are still operating as of the time of this
writing, each having yielded a decade of measurements.
In March 2000, PFM was turned on in order to get mea-
surements to compare with FM-1 and FM-2 and operated
until data from PFM became too noisy to be useful,
slightly longer than 1 month (Szewczyk et al., 2002).
Two more CERES instruments, FM-3 and FM-4, were
flown on the Aqua spacecraft in May 2002 and began pro-
viding measurements in June 2002. FM-3 continues to
operate well. FM-4 provided data for over two years, after
which the shortwave channel failed.
2.2. In-orbit calibration and validation
Once in orbit, the CERES instruments are frequently
calibrated using the ICM and the MAM. Lee et al.
(1997) established a validation plan for CERES measure-
ments. Unfortunately, due to problems with the coatings,
the spectral reflectivity of the MAMs of FM-1 through -4
changed so much that the MAMs were useless. As a conse-
quence, the calibration of the shortwave channel relied on
the SWICS, but other techniques were developed to cali-
brate the shortwave portion of the spectral responses of
the total channels. Deep convective clouds were used as
vicarious calibration targets for the shortwave channels
and the results were validated by comparing measurements
of the tropical mean radiation during day and night (Priest-
ley et al., 2007). The presence of two CERES radiometers
on the Terra and Aqua spacecraft permitted additional val-
idation checks as described by Priestley et al. (2003, 2007).
Priestley et al. (2011) discuss the calibration of CERES
flight models 1 through 4 as of 2007.
3. Generation and improvement of data products
The first objective of CERES is to measure OLR radi-
ances to an accuracy of 1% and reflected solar radiances
to 2% (Wielicki et al., 1996). The global mean OLR flux
is approximately 240 W m
2
, so the requirement is
2.4 W m
2
accuracy. Likewise the global mean reflected
flux is 100 W m
2
, thus the requirement for shortwave flux
is 2 W m
2
. These flux requirements are converted to radi-
ance requirements by assuming isotropic radiation, whence
a factor of pi applies. From the measurements (Level 1
data), the shortwave and OLR radiances and fluxes at
TOA are computed (Wielicki et al., 1998). These fluxes
are the Level 2 data products and are averaged over a 1°
quasi-equal area grid system to give instantaneous regional
averages, which in turn are averaged over the day to give
daily averages, whence monthly-means, are computed.
Errors are introduced at each step. There are errors in
the radiance due to measurement errors and the spectral
characterization of its channels. Computation of fluxes at
the TOA requires accounting for the anisotropy of the radi-
ance, which is described by a bidirectional reflectance dis-
tribution function BRDF, which depends on the scene
and is selected by an algorithm. To average the instanta-
neous regional average to get the daily-mean fluxes requires
a knowledge or assumption about the variation of the
fluxes with time between observations. To reduce the errors
in these data products requires reducing the Level 1 (instru-
ment errors), better BRDFs to improve the Level 2 fluxes,
and better characterization of the fluxes at times between
observations to reduce errors incurred in the computation
of Level 3 data products. Each of these steps is reviewed,
then the data products are discussed.
3.1. Bidirectional reflectance distribution functions
The BRDF models used by ERBE to compute fluxes
from radiances were developed by Suttles et al. (1988,
1989). These models are based on 218 days of data from
the Nimbus-7 Earth Radiation Budget (ERB) instrument
(Smith et al., 1977; Jacobowitz et al., 1984). In order to
generate a larger data base for developing an improved
set of BRDFs, CERES scanning radiometers were flown
in pairs aboard the Terra and on the Aqua spacecraft. In
each pair, one instrument scanned cross-track to map the
spatial distribution of radiation fluxes and the other
scanned biaxially to collect data from which bidirectional
reflectance distribution functions (BRDFs) have been
developed by Loeb et al. (2003a, b). The CERES models
were developed for a more extensive set of scenes using
more sophisticated scene identification algorithms. When
the BRDFs are applied to the measured radiances, the
same algorithms are used to identify the scene in the
CERES field of view. The result is used to select the appro-
priate BRDF model. The CERES BRDFs reduce the
errors in computed fluxes by a factor of two or more.
Fig. 3 shows the shortwave BRDF for ice cloud for solar
zenith angle between 60°and 70°; the left panel is for cloud
optical depths sless than 1 and the right panel is for optical
depths greater than 50.
3.2. Clouds and flux computation
The scene identification is based on the underlying sur-
face type and the cloud properties within the CERES foot-
print. Data from high-resolution imagers, the Visible
Infrared Scanner (VIRS) on TRMM and MODIS on Terra
and Aqua, are first analyzed to determine whether each 1
or 2 km resolution pixel is cloudy or clear (Minnis et al.,
2008). Multispectral radiances corresponding to the cloudy
pixels are processed with the system described by Minnis
et al. (2010) to yield cloud phase, temperature, height, s,
256 G.L. Smith et al. / Advances in Space Research 48 (2011) 254–263
and effective particle size among other parameters. The
imager pixels are matched with each CERES scanner foot-
print and convolved with the CERES point spread function
to yield average properties for each footprint. Those prop-
erties along with the surface type are used to select the
appropriate BRDF to convert the CERES radiances to
fluxes. The radiation data are combined with cloud infor-
mation to create the CERES Single Scanner Footprint
SSF product for each pixel. A major purpose of the SSF
data product is for studying the relationships between
clouds and the radiation fields. Also, the SSF fluxes are
gridded and hourly surface flux are computed by use of
parameterizations to create the SFC product. The SSF
information are also compiled into the Clouds and Radia-
tion Swath CRS data product. These CRS data are aver-
aged over 1°boxes and put into hourly files; this data
product is labeled FSW.
3.3. Time averaging
Instruments aboard the Terra and Aqua spacecraft
nominally provide sampling at four local times: 0130,
1030, 1330, and 2230 LT at the Equator. In order to reduce
temporal sampling errors further, data from geostationary
(GEO) meteorological satellites are employed to account
for changes in meteorological conditions between CERES
observations. TOA and surface fluxes and cloud properties
derived every 3 h from narrowband spectral radiances mea-
sured by imagers on five GEOs are used to estimate hourly
fluxes by interpolation in order to compute the daily mean
radiation fields and cloud properties. The 3-hourly results
are retained to provide a measure of the diurnal cycles in
each parameter. The raw GEO flux estimates nearest the
CERES overpass times are first normalized against the cor-
responding CERES fluxes to ensure climate quality fluxes,
free of GEO artifacts and consistent with the CERES
instrument calibration. The interpolations are then per-
formed as described by Young et al. (1998). Regional
monthly fluxes that take onto account the variations
observed by the GEOs differ from those using only the
CERES observations by as much as 20 W m
2
over mari-
time stratus or land afternoon convective regions. The
CERES normalization produces GEO-derived TOA fluxes
that are globally consistent, within 0.1 W m
2
, independent
of the GEO calibrations, even if the GEO calibration is
artificially altered by ±5%, twice the anticipated calibration
error (Keyes et al. 2006). The GEO TOA fluxes normalized
to Terra agree with Aqua CERES flux observations taken
3 h after Terra, as well as with GERB hourly fluxes over
the METEOSAT domain, to within 1% for shortwave
fluxes and within 0.5% for outgoing longwave fluxes for
the bias and with a root-mean-square scatter of 14% for
the shortwave fluxes and 5% for the outgoing longwave
fluxes. Similarly, ground based radiometers have been used
to validate the CERES radiative transfer computed surface
fluxes based on the GEO data (CERES Terra Edition2C/
Aqua Edition2B SYN/AVG/ZAVG Data Quality Sum-
mary).). One set of Edition 2 SYN/AVG/ZAVG products
is based on Terra products interpolated with 3-hourly geo-
stationary data, and another set is based on Aqua with geo-
stationary 3-hourly data. The coming Edition 3 version will
integrate Terra, Aqua and 3-hourly geostationary in one
package, all based on updated coefficients for the broad-
band CERES instruments (see next paragraph). Finally,
the SRBAVG data product is adjusted so that the annual
average global mean radiation budget is balanced except
for a residual of 0.7 W m
2
, to account for heat storage
by the oceans. This energy balanced data product is
denoted EBAF (Energy balanced and filled). A list of the
CERES data products may be found at: http://eos-
web.larc.nasa.gov/project/ceres/table_ceres.html.
3.4. Strategy for improving accuracy of instrument products
Because of the high level of accuracy required for cli-
mate quality radiation budget data, three editions of
Fig. 3. Bidirectional Reflectance Distribution Function for overcast ice clouds. (a) optical depth less than one, (b) optical depth greater than 50.
G.L. Smith et al. / Advances in Space Research 48 (2011) 254–263 257
CERES data products are being produced. This three-edi-
tion procedure provides a flow of recent Earth radiation
budget data to the science community which culminates
in climate-quality data products. For Edition 1 the radi-
ances are computed from the measurements by use of gains
established from ground calibrations. These results are
processed to produce instantaneous and monthly-mean
fluxes using the ERBE algorithms. After a minimum of
4 months, the calibration data are examined in order to
find and quantify any drifts in the calibration over time.
The channel gains are adjusted to account for any changes
during operation in orbit. The data are then reprocessed
with no changes of the spectral responses to give Edition
2 instrument products. These products are used to generate
the Single Satellite Footprint (SSF) product and other
higher level products, which are available for investigations
for which an accuracy of 2% is sufficient.
With a data record of a few years, one may discern arti-
facts in the Edition 2 instrument products that cannot be
seen in shorter periods. For example, changes of the spec-
tral response can be detected and revisions can be com-
puted. An extensive validation protocol is being applied
in order to improve the data products, after which Edition
3 instrument products will be generated for which the
objective is 1% accuracy for shortwave fluxes and 0.5%
for the outgoing longwave fluxes.(Priestley et al., 2007).
3.5. Higher level data products
At the instrument level, data products include the raw
measurements and shortwave, longwave, and 8–12 lm win-
dow radiances together with nadir and azimuth angles and
geolocations. These are included in the Single Scanner
Footprint (SSF) product along with the cloud data, imager
radiances, and meteorological data as well as the TOA
reflected solar, Earth-emitted and window channel fluxes
computed from the radiances and selected BRDFs. Addi-
tionally, the SSF data include estimates of surface long-
wave and shortwave fluxes based on parameterizations.
The SSF data are averaged to produce radiative fluxes over
1°latitude quasi-square regions.
The retrieval of radiation fluxes at the surface and
through the atmosphere is another objective of CERES.
These quantities are computed using cloud as computed
from the analysis of MODIS measurements (for the Terra
and Aqua missions) and meteorological data from the
GEOS-4 Data Assimilation System (Bloom et al. (2005)
so as to be consistent with the TOA measurements from
CERES (Rose et al., 1997). Radiation flux components
for shortwave radiation up and down and longwave radia-
tion up and down are computed at the surface and in the
atmosphere at 500, 200 and 50 hPa (Charlock et al.,
2006). After all parameters have been averaged over a grid
box and then averaged over the day and month, the radia-
tion fluxes are only approximately consistent with the other
parameters. Table 1 lists the CERES data products. These
may be ordered from http://ceres.larc.nasa.gov/order_
data.php.
The higher level data products started with Edition 2
instrument products and changes to the algorithms have
been small. However, in addition to the instrument product
upgrades, the MODIS and GEOS data products have also
been improved during the project, so that the SSF and suc-
ceeding products also are improved.
Fig. 4 is a map of outgoing longwave radiation flux for
July 2000 based on measurements from FM-1 and -2, on
the Terra spacecraft. Fig. 5 is a global map of the monthly
mean longwave convergence between the surface and
500 hPa for March 2005. For the global mean, temperature
and humidity account for over 95% of the cooling by LW
between the surface and 500 hPa. But both “clear sky”
(temperature and humidity) and cloud factors play roughly
equal roles in driving the space-time variance of LW cool-
ing in the lower troposphere. Fig. 6a shows the cloud frac-
tion and Fig. 6b shows the effective heights of the clouds.
The magnitude of the convergence in Fig. 5 is greatest over
the oceanic subsidence regions where the skies are either
mostly cloud free or are covered by warm, low-level clouds,
which enhance LW emission. Deep convection over the
Amazon, the Congo, the maritime continent of Indonesia
and the Philippines produces upper level clouds which sig-
nificantly suppress, rather than enhance, LW cooling
between the surface and 500 hPa. Over high altitude land
areas such as the Himalayas, Tibetan Plateau, Andes,
Greenland, and Antarctica yield the smallest values overall,
because there is less mass (and hence opacity) between the
surface and the 500 hPa (and it is cold there, too).
The total, direct and diffuse parts of photosynthetically
active radiation PAR are also computed (Su et al., 2007).
Fig. 7 is a map of the diffuse part of PAR over the cotermi-
nous United States. Also, total ultraviolet radiation flux,
UVA and UVB are computed at the surface (Su et al.,
2005). Fig. 8 is a map of monthly-mean UV radiation at
the surface over the coterminous U. S. for June 2005.
The effect of clear sky over the Southwest and Southern
Great Plains of the U.S. and the Gulf of Mexico is evident.
4. Special operations
Another application of the CERES scanning radiome-
ters is special operations in which the azimuth of the scan
plane of a CERES instrument is programmed in order to
line up with ground stations or other spacecraft instru-
ments. This capability for operating in a Programmed Azi-
muth Plane (PAP) scan has been used to compare
radiances with those of other spacecraft instruments
(Szewczyk et al., 2004, 2010) and with ground stations
(Smith et al., 2010). One use of this ability has been to
rotate a CERES instrument so as to scan in the same plane
as a second instrument, as was done with a CERES instru-
ment on both the Terra and Aqua spacecraft in order to
compare radiance measurements. These comparisons are
needed in order to assure that any changes in the radiation
258 G.L. Smith et al. / Advances in Space Research 48 (2011) 254–263
budget record due to the change of instruments is under-
stood and quantified and not attributed to a climate shift.
Table 2. lists special operations for comparisons of CERES
measurements with other spacecraft instruments, in partic-
ular ScaRaB (Kandel et al, 1998) and GERB (Harries
et al., 2005). The PAP scan can be used with a ground sta-
tion to get a number of measurements from difference
angles during a single over-flight of the site. Table 3 lists
some applications of PAP scan for investigations at ground
sites.
5. Future missions
The FM-5 CERES instrument has been recalibrated in
the Radiometric Calibration Facility and has been inte-
grated with the NPP spacecraft (Priestley et al., 2009),
which is being prepared for launch in 2011. This spacecraft
also carries the Visible Infrared Imager Radiometer Suite
(VIIRS). CERES will use data from the VIIRS to provide
cloud and scene information as was done with MODIS
data on the Terra and Aqua spacecraft. The orbit of
NPP will cross the Equator north-bound at 13:30 LT at
an altitude of 824 km, so that it is coplanar with the Aqua
spacecraft.
In order to continue the measurement of the Earth’s
radiation budget, the CERES FM-6 is being constructed
(Priestley et al., 2000). A number of flight-qualified parts
for CERES are being used, but some components are no
longer available, so that the design is modified to use new
components. The FM-6 will fly on the JPSS C-1 spacecraft,
Table 1
CERES data products.
Data product Description
Level 1: CERES raw engineering and instantaneous filtered radiances
BDS CERES geo-located and calibrated TOA filtered radiances
Level 2: CERES instantaneous footprint level fluxes and cloud properties
CRS Computed flux profiles from MODIS clouds and aerosols
SSF CERES observed TOA flux, MODIS clouds and aerosols and parameterized surface fluxes
FLASHFlux Near real-time SSF product, not officially calibrated for publication
ES8 CERES observed TOA fluxes using original ERBE algorithms
SSF-SSFM Nadir view CERES-SSF/MODIS/MISR collocated parameters
C3M Nadir view CERES-SSF/MODIS/CALIPSO/CloudSat collocated parameters
Level 3: Spatial and temporally (daily, monthly, etc) averaged fluxes and cloud properties, 1°
SYN1deg CERES observed and GEO-enhanced temporally interpolated TOA fluxes, MODIS/GEO clouds and MODIS aerosols and
associated computed flux profiles for consistent cloud properties
SSF1deg CERES observed temporally interpolated TOA flux, MODIS clouds and aerosols
ISCCP-D2like CERES monthly cloud properties in a similar format to ISCCP
FLASHFlux1deg Near real-time SSF1deg product, not officially calibrated for publication
ES4/ES9 ERES observed TOA fluxes using original ERBE algorithms
Level 4: Consistency between TOA global net flux and ocean heat storage
EBAF CERES TOA fluxes, energy balanced and clear-sky filled
Fig. 4. Longwave flux for July 2000 from measurements of CEERES FM-1 and 2 on Terra spacecraft.
G.L. Smith et al. / Advances in Space Research 48 (2011) 254–263 259
which will have the same orbit as the NPP. Its launch is
scheduled for 2014. The next Earth radiation budget
instrument after CERES FM-6 will require a new design.
This design is expected to rely heavily on the CERES
design, with minor improvements for in-flight calibration.
It is planned that the first instrument of this new design will
fly aboard the JPSS C-3 spacecraft. Fig. 9 shows the time
lines for the CERES instruments and the follow-on design
instruments.
6. Concluding remarks
The Earth Radiation Budget (ERB) instruments which
flew aboard the Nimbus-6 and -7 spacecraft provided the
Fig. 5. Longwave convergence in the atmosphere between the surface and 500 hPa (March 2005, CERES).
Fig. 6. CERES mean (a) cloud fraction and (b) cloud effective height in km from Aqua, March 2003.
260 G.L. Smith et al. / Advances in Space Research 48 (2011) 254–263
first broadband measurements of Earth’s radiation budget.
They gave data from 1975 through 1987. The Earth Radi-
ation Budget Experiment (ERBE) built on the experience
from ERB to produce data from 1985 through 1999. The
CERES project improved on this instrument to measure
the Earth’s radiation budget more accurately for a decade
and these instruments are still operating. There are now
Earth radiation budget data spanning a 35 year period.
These data can be used for process studies as well as for cli-
mate studies. CERES instruments now on spacecraft and
Fig. 7. Diffuse part of Photosynthetically active radiation at surface over coterminous U. S.
Fig. 8. Monthly-mean map of ultraviolet radiation at surface over coterminous U.S, W m
2
.
Table 2
Earth-based special operation campaigns.
Campaign
Valencia Anchor Station, Spain
Chesapeake Light House
Crystal (Deep Convection)
AMMA: special Observing period, 2006: Niamay
Point Barrow, Alaska
Beijing, China
Table 3
Special operations of CERES for space-oriented measurements.
Campaign Purpose
ScaRaB 2 Comparison with CERES Proto-flight model
Terra/Aqua Comparison FM-2 and -3
FM2/GERB1 FM-2 vs. GERB pixel array
True Along Track 08/22, 09/05
G.L. Smith et al. / Advances in Space Research 48 (2011) 254–263 261
in the building phase should give data for another decade,
nearing a half-century of climate data.
Acknowledgements
The authors are grateful to the Science Directorate of
Langley Research Centre and to the Science Mission Direc-
torate of the Earth Science Division of NASA for the sup-
port of the CERES Project. They also acknowledge the
excellent work performed by the people of Northrop-
Grumman Space Technology, under the leadership of
Steve Carman and Tom Evert to achieve the performance
which has been demonstrated by the CERES instruments.
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97 98 99 00 0 1 0 2 0 3 04 05 06 07 0 8 0 9 1 0 11 12 13 14 1 5 1 6 1 7 18 19 20 21
TRMM
Nov-97
Terra
Dec-99
Aqua
May-02
NPP
Jan-11
C1
Jan-13
C3
Jan-18
CERES
PFM
CERES
FM-1,2
CERES
FM-3,4
CERES
FM-5
CER ES
FM-6
CER ES F oll ow-o n
FM-1
Spacecraft:
Sensors:
CY:
Spacecraft I&T
Sensor Fab, Assembly, Test
Initial design studies
Nominal Mission Lifetime
Operational Sensor Lifetime
FM-5
FM-6
CERES Follow-on +
Fig. 9. Time lines of CERES instruments.
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