Radiometric Performance of the CERES Earth Radiation Budget Climate Record Sensors on the EOS Aqua and Terra Spacecraft through April 2007

Kory J. Priestley NASA Langley Research Center, Hampton, Virginia

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G. Louis Smith National Institute for Aerospace, Hampton, Virginia

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Susan Thomas Science Systems and Applications, Inc., Hampton, Virginia

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Denise Cooper Science Systems and Applications, Inc., Hampton, Virginia

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Robert B. Lee III National Institute for Aerospace, Hampton, Virginia

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Dale Walikainen Science Systems and Applications, Inc., Hampton, Virginia

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Phillip Hess Science Systems and Applications, Inc., Hampton, Virginia

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Z. Peter Szewczyk Science Systems and Applications, Inc., Hampton, Virginia

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Robert Wilson Science Systems and Applications, Inc., Hampton, Virginia

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Abstract

The Clouds and the Earth’s Radiant Energy System (CERES) flight models 1 through 4 instruments were launched aboard NASA’s Earth Observing System (EOS) Terra and Aqua spacecraft into 705-km sun-synchronous orbits with 10:30 p.m. and 1:30 a.m. local time equatorial crossing times. With these instruments CERES provides state-of-the-art observations and products related to the earth’s radiation budget at the top of the atmosphere (TOA). The archived CERES science data products consist of geolocated and calibrated instantaneous filtered and unfiltered radiances through temporally and spatially averaged TOA, surface, and atmospheric fluxes. CERES-filtered radiance measurements cover three spectral bands: shortwave (0.3–5 μm), total (0.3>100 μm), and an atmospheric window channel (8–12 μm).

CERES climate data products realize a factor of 2–4 improvement in calibration accuracy and stability over the previotus Earth Radiation Budget Experiment (ERBE) products. To achieve this improvement there are three editions of data products. Edition 1 generates data products using gain coefficients derived from ground calibrations. After a minimum of four months, the calibration data are examined to remove drifts in the calibration. The data are then reprocessed to produce the edition 2 data products. These products are available for science investigations for which an accuracy of 2% is sufficient. Also, a validation protocol is applied to these products to find problems and develop solutions, after which edition 3 data products will be computed, for which the objectives are calibration stability of better than 0.2% and calibration traceability from ground to flight of 0.25%. This paper reports the status of the radiometric accuracy and stability of the CERES edition 2 instrument data products through April 2007.

Corresponding author address: G. Louis Smith, Mail Stop 420, Langley Research Center, Hampton, VA 23681. Email: g.l.smith@larc.nasa.gov

Abstract

The Clouds and the Earth’s Radiant Energy System (CERES) flight models 1 through 4 instruments were launched aboard NASA’s Earth Observing System (EOS) Terra and Aqua spacecraft into 705-km sun-synchronous orbits with 10:30 p.m. and 1:30 a.m. local time equatorial crossing times. With these instruments CERES provides state-of-the-art observations and products related to the earth’s radiation budget at the top of the atmosphere (TOA). The archived CERES science data products consist of geolocated and calibrated instantaneous filtered and unfiltered radiances through temporally and spatially averaged TOA, surface, and atmospheric fluxes. CERES-filtered radiance measurements cover three spectral bands: shortwave (0.3–5 μm), total (0.3>100 μm), and an atmospheric window channel (8–12 μm).

CERES climate data products realize a factor of 2–4 improvement in calibration accuracy and stability over the previotus Earth Radiation Budget Experiment (ERBE) products. To achieve this improvement there are three editions of data products. Edition 1 generates data products using gain coefficients derived from ground calibrations. After a minimum of four months, the calibration data are examined to remove drifts in the calibration. The data are then reprocessed to produce the edition 2 data products. These products are available for science investigations for which an accuracy of 2% is sufficient. Also, a validation protocol is applied to these products to find problems and develop solutions, after which edition 3 data products will be computed, for which the objectives are calibration stability of better than 0.2% and calibration traceability from ground to flight of 0.25%. This paper reports the status of the radiometric accuracy and stability of the CERES edition 2 instrument data products through April 2007.

Corresponding author address: G. Louis Smith, Mail Stop 420, Langley Research Center, Hampton, VA 23681. Email: g.l.smith@larc.nasa.gov

1. Introduction

Our climate is dominated by the radiation from the sun that is absorbed by the earth–atmosphere system, together with dynamic interactions with the atmosphere, land, ocean, and cryosphere. The resulting heat is emitted as longwave radiation after creating atmospheric and oceanic currents, all of which are coupled with the temperature distribution across the planet (Ramanathan 1987). To investigate these processes, it is necessary to measure the absolute values and spatial and temporal variability of radiation absorbed and emitted by the earth–atmosphere system (Hartmann et al. 1986; Ramanathan et al. 1989). The changes of the absorbed solar radiation and the emitted longwave radiation fluxes with climate variations are on the order of a few W m−2 sr−1, so these radiation measurements must be quite accurate. The Clouds and Earth’s Radiant Energy System (CERES) project has the objective of measuring the solar reflected radiation (i.e., the solar irradiance that is not absorbed by the earth) to 1% accuracy and the earth’s emitted radiation to 0.5% accuracy (Wielicki et al. 1995, 1996). To attain and maintain this accuracy of radiometry, the instrument must be calibrated on the ground and repeatedly calibrated in flight. The CERES instrument was designed as an evolutionary improvement (Barkstrom 1990) of the Earth Radiation Budget Experiment (ERBE; Barkstrom and Smith 1986) with instrument errors were reduced by a factor of 2 (Wielicki et al. 1996). To a large degree this was achieved by improvements in the radiation calibration facility and the ground calibration techniques (Lee et al. 1996, 1998). Also, in-flight calibration and validation methods have been refined and extended (Priestley et al. 2007).

To produce accurate radiation fluxes, it was also necessary to reduce the errors resulting from the computation of the instantaneous fluxes at the “top of the atmosphere” (TOA) and monthly average values for 1° regions. The CERES instrument measures radiances, from which fluxes at TOA are computed by using bidirectional reflectance distribution functions (BRDFs) to account for the anisotropy of the reflected solar radiation and limb-darkening functions to account for variation of earth-emitted radiation with a zenith angle of the exiting radiance. One objective of CERES was to make radiance measurements over a full range of view of zenith angles, solar zenith angles, and the relative solar azimuth between the incoming and outgoing radiances, from which improved BRDFs have been developed. The Terra and Aqua spacecraft each carry two CERES instruments: one to scan cross-track to map the radiation fields geographically and the other to obtain measurements in all directions so as to develop BRDFs (Smith et al. 2004). Finally, the solar reflected and earth emitted radiation fields vary with time of day and from day to day, so time sampling is a major consideration for accurate BRDF determination. Harrison et al. (1991, 1983) demonstrated that CERES instruments are required on multiple spacecraft (i.e., Terra and Aqua) in order to provide four measurements each day for each region of the earth (Barkstrom et al. 2001).

Because of the high level of accuracy required for climate-quality radiation budget data, three editions of CERES data products are planned. This three-edition procedure provides a flow of recent earth radiation budget data to the science community, which culminates in climate-quality data products. Edition 1 generates “ERBE-like” data products, whereby the measurements are processed to produce instantaneous and monthly mean fluxes using the ERBE algorithms. After a minimum of four months, the calibration data are examined 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 level 1 algorithms to give the edition 2 data 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 artifacts in the edition 2 data that cannot be seen in shorter periods. For example, the difference between the fluxes measured by the flight models 1 and 2 (FM-1 and FM-2) at nadir has an annual cycle, which is tentatively attributed to the change of the sun’s orientation relative to the spacecraft with the seasons. Also, variations of the spectral responses of the channels are found by comparing measurements from the three channels of each instrument when observing deep convective clouds. These spectral changes must then be characterized. An extensive validation protocol is being applied in order to develop solutions, after which edition 3 data products will be generated with improved accuracies (Priestley et al. 2007).

The purpose of this paper is to report the results of edition 2 calibration for the CERES instruments aboard the Terra and Aqua spacecraft as of April 2007. The CERES instrument and the calibration procedures are described, after which the calibration results are presented for these instruments.

2. CERES instrument

The CERES scanning radiometer has three channels—a shortwave, a total, and a window channel—each consisting of a telescope and a thermistor/bolometer detector, as Fig. 1 shows. The shortwave channel has a quartz filter to pass 0.2–5-μm radiation, the window channel has an 8–12-μm filter, and the total channel has no filter. Figure 2 shows the nominal spectral responses of the three channels. The radiometers are mounted on a beam that rotates about a horizontal axis. The beam can rotate so that the radiometers view the internal calibration module (ICM) inside the scan head (Lee et al. 1996) and the mirror attenuated mosaic (MAM; Lee et al. 1992). This assembly of the beam, ICM, and MAM rotates on a vertical axis to scan in azimuth. The CERES instrument can be programmed to rotate in azimuth to provide measurements for developing BRDFs and also to perform a variety of research tasks (Szewczyk and Priestley 2003, 2004).

The internal calibration module has two blackbodies, one for measuring the gain of the total channel in the longwave part of its spectral response and one for the 8–12-μm window channel. The temperature of each blackbody is determined by a platinum-resistance thermocouple, so that the internal blackbodies (IBBs) are absolute calibration sources. The ICM also has a shortwave internal calibration source (SWICS), which is a tungsten lamp and optics, for measuring the gain of the shortwave channel. The output of the lamp is monitored by a silicon photodiode. Lee et al. (1993) demonstrated that the ICM worked very well for the ERBE instruments; thus, the design was upgraded based on the ERBE experience and used for the CERES instrument. Figure 3 shows the design of the CERES ICM, which consists of a shortwave incandescent calibration source (SWICS) and two internal blackbodies, one for the total channel and one for the longwave window channel.

3. Ground calibration of CERES

An extensive ground calibration program (Lee et al. 1996, 1997, 1998) was carried out in vacuum in the radiometric calibration facility, which was built for the calibration of CERES by TRW, the prime contractor for the CERES instruments. Figure 4 shows the layout of the radiometric calibration facility. The facility provided an absolute calibration in terms of the International Temperature Scale of 1990 (ITS-90) and the Stefan–Boltzmann law.

A narrow field-of-view blackbody (NFBB; Lee et al. 1998) was built using platinum-resistance thermocouples (PRTs), made and calibrated by Rosemont, Inc., to the ITS-90 standard. The longwave response of the total channel and the 8–12-μm window channel were calibrated directly by use of the NFBB. These channels then looked at the blackbodies of the internal calibration module, which also used PRTs calibrated in accordance with ITS-90, to make measurements for reference in orbit.

A shortwave reference source was used to calibrate the shortwave channel and the shortwave response of the total channel. The shortwave reference source was calibrated by use of a (helium-cooled) cryogenic active cavity radiometer (ACR), which was calibrated in turn by use of the NFBB, so that the cryogenic active cavity radiometer served as a transfer radiometer. The shortwave channel was calibrated by use of the shortwave reference source, and then the shortwave channel measured its response to the SWICS, thereby establishing the calibration of the SWICS. This measurement provided a basis for monitoring the stability of the shortwave channel and the SWICS. Figure 5 shows the traceability of the calibrations of the CERES channels to the ITS-90 standard.

4. In-flight calibration results

The Terra spacecraft was placed into orbit on 18 December 1999 and achieved its specified sun-synchronous orbit in January 2000. The orbit has an inclination of 81° retrograde and an altitude of 705 km. It crosses the equator at 2230 h for the ascending node (northbound). After a month in orbit, to provide adequate time for the spacecraft and all instruments to outgas, the contamination covers were opened on 25 February 2000 and the CERES FM-1 and FM-2 instruments began operating (Priestley et al. 2000; Lee et al. 2000; Smith et al. 2004). During this time, the detectors also changed because of prolonged exposure to the vacuum environment. When the instrument begins operation, there is an initial change in the gain of the channels from that measured on the ground. These new calibrations are used for the edition 2 data processing. The FM-1 and FM-2 instruments have each operated for over seven years in orbit.

The Aqua spacecraft with the CERES flight models 3 and 4 was placed into orbit in May 2002. Its orbit, like that of Terra, is sun-synchronous with an inclination of 81° retrograde and an altitude of 705 km, but its ascending node is at 1330 h. The CERES instruments aboard Aqua began operating in June 2002. The FM-3 has operated well for the five years since then. The FM-4 operated until March 2005, at which time the shortwave channel failed. The nearly three years of operation of FM-4 exceeded the requirement that it work for two years. For FM-3 and FM-4 the change of calibration from ground to flight values was applied to edition 1 data processing at the start of the mission.

The primary device for in-flight calibration is the internal calibration module. The shortwave responses of the total channels are calibrated by using observations of deep convective clouds by all three channels of the instruments. Validation checks are then provided by direct comparison of matching pixels and by the tropical mean technique, which will be discussed.

a. Internal calibration module results

The internal calibration module is used up to 3 times each week to check the gains of the three channels of each instrument. Figure 6 shows for each instrument the monthly means of the change of the gain of each channel from the ground calibration in percent. Every four to six months, the gain of each channel to be used for edition 2 data processing is updated based on the internal calibration system results and the three-channel comparison. The gains for edition 2 data processing depend on time after launch and are shown as solid lines in Fig. 6 for the shortwave and window channels and the longwave response of the total channel.

Figure 6a shows that for FM-1 the response of the total channel gain to longwave radiation changed by about 0.1% from the ground calibration to the beginning of operation in space, according to measurements from the internal blackbody. Over a period of seven years in orbit, the gain increased linearly by another 0.5%. The window channel gain changed by 0.5% from its ground calibration value but had some erratic changes of approximately 0.3%. After February 2003 the variation of the window channel gain is very close to that of the total channel. Much of the random variation of the window channel gain can be attributed to the small dynamic range of the window channel. The gain of the shortwave channel as determined by the SWICS decreased by 0.3% when placed into orbit. It changed from this value by less than 0.1% over the 7-yr period of use while in orbit.

Figure 6b presents in-flight results for the calibration of FM-2 using the ICM. At the beginning of the flight, the gain for the longwave response of the total channel was within 0.2% of that measured on the ground. During the first year the sensor response increased to 0.6% above the ground value and over the next six years the gain increased to about 0.9% greater than the ground value. The window channel began flight operations with a gain about 1.2% higher than the ground value and gradually the gain decreased to 1.0% greater than the ground value. The shortwave channel gain began very near its ground value and decreased to about 0.2% less than the ground value during seven years of operation.

Figure 6c shows the results from the ICM for FM-3. The gain of the longwave response of the total channel was the same at the start of the mission as was the ground gain, but it slowly increased by 0.6% over the five years of measurements to date. The window channel gain at the beginning of the mission was the same as for ground calibration, but it soon dropped by 0.4% and thereafter decreased to a level 1% below that from ground testing. At the start of flight operations, the SWICS results showed a decrease of the shortwave channel gain of 3.7% below the gain that had been computed from ground calibration. This change had been seen during spacecraft level calibration testing and was incorporated in the edition 1 data processing. The value gradually increased to 3.2% below the ground value over the next five years of operation.

The in-flight calibration results for FM-4 are shown by Fig. 6d. The ICM results indicate that the gain of the longwave response of the total channel was higher following insertion into orbit by 0.8% than the ground calibration results. This gain increased over a 5-yr period to 1.5% above the ground value (i.e., less than a 1% change in five years). The window channel began with a gain measured as 0.7% above the ground value and hovered at 0.2%, for two years, then increased to 0.8% above the ground value after five years in orbit. The shortwave channel gain as measured by the ICM began in space 2.0% higher than the ground value. This change from the calibration in the Radiation Calibration Facility was also noted during testing at the spacecraft level. Over three years of operation this change increased to 2.9% above the ground value. In March 2005, the temperature control of the thermistor/bolometer detector of the shortwave channel became erratic, causing the loss of the shortwave channel of FM-4.

b. Validation of shortwave responses of total channels

The gains of the shortwave channel and of the shortwave part of the total channel were to be checked by use of the mirror attenuated mosaics. For the protoflight model of CERES, which flew aboard the Tropical Rainfall Measuring Mission (TRMM), the MAMs worked very well. However, for FM-1 though FM-4, the coatings of the MAMs degraded in orbit so that the MAM measurements could not be used. The SWICS measurements of Fig. 6 provide a measure of the slow change of the shortwave channel. Another technique was required to check the shortwave response of the total channel.

To calibrate the shortwave response of the total channel, Priestley et al. (2000) applied a three-channel comparison method that had been used by Green and Avis (1996) for ERBE validation. This method uses the window and shortwave channels to check the shortwave response of the total channel. The longwave part of the measurement of the total channel can be computed as LWtot = Total − Shortwave. The broadband longwave radiance can be computed from the window channel provided the spectral shape is known for the scene, so that LWWn = C1Wn + C2. Any change of the response of the total channel response to shortwave radiance will cause a difference between LWtot and LWWn. Kratz et al. (2002) developed a three-channel comparison method that uses deep convective clouds as calibration targets. These clouds are good for this purpose because water vapor variations create variations in broadband longwave radiance to which the window channel is insensitive and the water vapor above deep convective clouds is small. The difference Δ = LWtot − LWWn is plotted as a function of the shortwave channel measurement for each month. If the changes of total channel response are linear in time, the time history of Δ will be linear.

A plot of the slope of Δ is used to design the modification of the spectral response of the shortwave part of the total channel. The revised spectral response is used to compute the edition 2 daytime longwave radiances. The modified spectral response is then validated by comparing the tropical mean radiances.

Figure 7a shows the slope of Δ for each month for FM-1 and FM-2 expressed as percent per month for edition 1. For FM-1, the total channel response to shortwave radiance changed by −0.008% to 0.005% month−1 during the first two years, after which the slope decreased gradually over the next five years. For edition 1 the slope of the gain of the shortwave response of the FM-2 total channel of the total channel increased from launch to 2004 to 0.05, after which it remained constant. The three-channel comparisons indicate that the shortwave parts of the total channel spectral responses of each of these instruments have changed relative to the longwave portion.

To account for the changes of shortwave response of the total channel, the gain is assumed to be established by the internal blackbody in the longwave response, and the shortwave spectral response of the total channel is multiplied by a factor that is constant over the shortwave spectral response and varying with time. Figure 8 shows the percent change in the shortwave spectral response of the FM-1 and -2 total channels over the 7-yr period to February 2007 that is used in edition 2 data processing.

The slopes of Δ for each month for edition 2 data processing for FM-1 and FM-2 are shown in Fig. 7b (note the change of scale from Fig. 7a). Figure 7b shows that for edition 2 the shortwave responses of the total channels of FM-1 and FM-2 change very little over the 7-yr period of operation. Over the last half of the period, the response decreased by about 0.005% month−1.

Figure 9 shows the change of slope of the shortwave responses of the total channels of FM-3 and FM-4 based on the three-channel comparison for deep convective clouds. For edition 1 of FM-3 measurements the slope is initially −0.016, but increases to +0.012 over the two and a half years from the start of operations aboard Aqua to March 2005. For FM-4 the slope is −0.01 per month at the beginning of mission and increases to +0.006 by March 2005. Figure 10 shows the changes of spectral responses of the total channels of FM-3 and FM-4 that are used to account for the changes of the shortwave response in the edition 2 data products. The three-channel comparisons of the shortwave responses of the total channels with the revised spectral response functions give the results for edition 2 shown in Fig. 9b for FM-3 and FM-4. Although not eliminated, the range of the slope is reduced by a factor of 2.

c. Tropical mean comparison

The tropical mean statistic is defined as the longwave radiance from the earth near nadir averaged over the oceans between 20°S and 20°N for all conditions of cloudiness. Experience with this parameter has shown it to be relatively stable with low temporal variability. The daytime longwave radiance is essentially the difference between the total channel and the shortwave channel radiances. The longwave part of the total channel response is checked by using the internal blackbodies and is the best characterized response. The shortwave channel is characterized by use of the SWICS. This test is important for validating the shortwave response of the total channel, although an error in the shortwave channel would also appear in this test.

For each instrument, the tropical mean is averaged over a month for day and for night. Figure 11a shows the tropical mean from March 2000 through December 2006 for day and night for FM-1, edition 1. Except for two spikes, the tropical mean is 88.5 ± 1 W m−2 sr−1 for both day and night. Figure 11b shows the tropical mean for edition 2. The major effect of the upgrade to edition 2 is to reduce the computed tropical mean by about 0.5 W m−2 sr−1, or 0.5%, and to reduce the trend of Fig. 11a from approximately 1 W m−2 sr−1 to a small fraction of a W m−2 sr−1 over the period 2000–2007.

Figure 12a shows the tropical mean from March 2000 through December 2006 for day and night for FM-2, edition 1. The tropical mean is 88.2 ± 1 W m−2 sr−1 for night, but the day mean has a trend for the first three years, increasing to 90.7 ± 1 W m−2 sr−1, where it stays. Figure 12b shows the tropical mean for edition 2, where the day and night means differ by a fraction of a W m−2 sr−1.

Because FM-1 and FM-2 are on the same spacecraft, the tropical means should be the same for both instruments. The edition 2 tropical mean for FM-2 is more stable than for FM-1, but is a fraction of a W m−2 sr−1 lower. For edition 1 the nighttime results agree very well, but the daytime results differ by 2.2 W m−2 sr−1. This difference is mostly resolved by edition 2, but further improvements are possible by adjusting the shapes of the spectral responses, which is beyond the scope of edition 2.

Figure 13a shows the edition 1 tropical mean longwave radiance for FM-3 from July 2002 through August 2007. At the beginning of the mission, the tropical mean during day is within a fraction of a W m−2 sr−1 of the nighttime value. After January 2003 the difference grows to 1 W m−2 sr−1 and then stabilizes. This difference indicates a change of the shortwave response of the total channel relative to the longwave part. When the shortwave spectral response of the total channel is modified as in Fig. 10a for edition 2 data processing, Fig. 13b shows that the difference between day and night values reduces to a fraction of a W m−2 sr−1.

For FM-4, Fig. 14a shows the tropical mean comparison between night and day measurements of the longwave radiances for edition 1. The difference between the night and day measurements grows from about 0.7 to greater than 1.0 W m−2 sr−1 over a period of time. This change is attributed to exposure to contaminants outgassing from the spacecraft, space, sunlight, and atomic oxygen and the difference of location of the FM-3 and FM-4 on the Aqua spacecraft. Figure 14b shows that when the spectral changes indicated in Fig. 15b are made, the edition 2 radiances agree to a fraction of a W m−2 sr−1.

d. Direct comparison of matched pixels

FM-1 and FM-2 complete a full scan every 6.6 s, so that they each look at nadir within 3.3 s of each other. The location is not the same for each nadir point, but the difference between the two should vanish over a period of averaging. Longwave radiances at night are computed from the total channel alone. Figure 15a shows the difference of nighttime longwave fluxes between the FM-2 and the FM-1 total channels at nadir over the 7-yr data period. For edition 1 FM-2 is less than FM-1 initially by 0.7 W m−2, but the difference decreases over time to 0.4 W m−2. (The average FM-1 flux was 239.6 W m−2.) For edition 2 the difference started with FM-2 less than FM-1 by 0.3 W m−2 and the difference grew until it reached −1 W m−2 after September 2003, where it stayed until the end of the data period under consideration.

Figure 15b shows the difference of nadir values of daytime shortwave fluxes between FM-2 and FM-1. Initially for edition 1 FM-2 is 0.2 W m−2 greater than FM-1 shortwave and then increases to 2.0 W m−2 by October 2001; then the difference deceases until FM-2 is less than FM-1 by 2.4 W m−2 for the last year of the data period. For edition 2, the difference was ±0.3 W m−2 for the first two years, after which FM-2 diminished for two years, becoming 2 W m−2 less than FM-1 by November 2003 and remaining there for the rest of the data period.

The daytime longwave flux is computed from both the total and shortwave channel measurements. Figure 15c shows the differences between the daytime longwave fluxes from FM-2 and FM-1. At the beginning of the flight, the daytime longwave fluxes are very close. After 2.5 years, the difference has increased to 6 W m−2 and remains at that level for the remainder of the time. In edition 2, FM-2 is 1 W m−2 larger than FM-1, but the difference decreases to nearly zero after the first year and is ±0.3 W m−2 for the rest of the flight.

For edition 2 the difference of nighttime fluxes of FM-1 and FM-2 are steady at 0.7 W m−2 after 2003 and the daytime longwave fluxes agree across the data period to a fraction of a W m−2. However, the shortwave fluxes disagree by up to 2 W m−2. A change of shortwave channel gain of either FM-1 or -2 to bring them into agreement will create a disagreement in the daytime longwave flux. Likewise, a change of total channel gain will create disagreement in nighttime longwave fluxes. A possible explanation of this discrepancy is a change of spectral response of one of the total channels.

The comparison of fluxes between FM-1 and FM-2 in Fig. 15 shows that most of the trends seen in edition 1 are removed in the edition 2 product. However, an annual cycle remains. As the solar declination varies during the year, the angle between the sun and the normal to the orbit plane varies. This angle affects the heating of the instrument and the spacecraft, to which some of the annual cycle seen in Fig. 12 is attributed. It is problematic whether one can separate the annual cycle of these instrument artifacts and the annual cycles of insolation and earth radiation.

The nadir pixel values for FM-3 and -4 have been compared in a similar manner for the period from June 2002 through March 2005. Figure 16 shows the difference for nighttime longwave flux, shortwave flux, and daytime longwave flux for editions 1 and 2. The nighttime longwave fluxes agree well within 0.1 W m−2 for both editions 1 and 2, except for June–September 2004, when edition 2 shows a difference that peaks at about 0.15 W m−2. The difference between shortwave fluxes is quite small at the beginning of the period, but for edition 1 increases such that FM-4 is larger than FM-3 by 1.6 W m−2 at the end. For edition 2, the difference only increases to 0.6 W m−2. The daytime longwave flux for edition 1 begins with FM-4 being higher than FM-3 by 0.7 W m−2, but it decreases such that the difference is less than 0.2 W m−2 from September 2002 until January 2004, after which FM-4 is smaller than FM-3 by up to 1.5 W m−2 by March 2005. For edition 2, the daytime longwave flux difference is between 0. and 1.0 W m−2 through the entire period, with FM-4 being larger.

5. Discussion

The stabilities of the various channels of the four CERES instruments aboard the Terra and Aqua spacecraft as demonstrated from the results presented here are summarized in Table 1. The objective of 0.2% yr−1 has been met for the window channel and the nighttime longwave of all four instruments.

Conflicting science requirements have led to three editions of CERES data products. Edition 1 data products are available soon after the measurements are made, using gains that were established on the ground prior to launch. For edition 2 the gains of each channel are adjusted by use of the internal calibration modules. In addition, the shortwave part of the total channel spectral response for each instrument has been modified by a constant factor, without changing the shape.

To resolve the differences found by the various validation checks requires more time than is available for the timely release of edition 2. For edition 2 we use the methods described in this paper to change the gains and to modify the spectral response function of the shortwave response of the total channel. Factors that are not taken into account in edition 2 include changes of the spectral response of the longwave portion of the total channels and the spectral responses of the shortwave channels. The SWICS provides only a single number from which to compute the gain of the shortwave channel. However, the spectral response of the channel is not constant over the bandpass, and measurements of earth scenes depend on these deviations from uniformity. It is not possible to get agreement for all of the checks described here by use only of the gains and the spectral responses of the total channels. Work is ongoing to compute changes in the shapes of the spectral responses in addition to the constant adjustments, after which a number of other validation techniques described by Priestley et al. (2007) will be performed using the edition 2 data. At that point, the spectral responses and other parameters will be upgraded and edition 2 will be produced.

6. Conclusions

CERES scanning radiometers flight models FM-1 and FM-2 were flown on the Terra spacecraft and FM-3 and FM-4 were flown on the Aqua spacecraft to make accurate measurements of the earth’s radiation budget for climate investigations. The instruments each carry an internal calibration module (ICM) for in-flight calibrations of the shortwave and window channels and the longwave portion of the total channel spectral response.

Two editions of data products have been generated. Edition 1 products are based on ground calibrations. After a minimum of six months of data have been acquired, the calibrations are recomputed based on the ICM and other validation checks and edition 2 data products are generated. A third edition is planned that will include all upgrades that are practical. This paper presents in-flight calibration results for editions 1 and 2 for February 2000 through August 2007.

The results from the ICM demonstrate a calibration precision of better than 0.2%. For the flight models 1 and 2 aboard the Terra spacecraft, the calibrations of the three channels of each instrument varied by less than 1% according to the ICM. The tropical mean longwave radiance from the FM-1 is stable to a fraction of a percent for editions 1 and 2. For FM-2, the tropical mean longwave radiance during day varied by 3% over the 7-yr measurement period in edition 1. Changes of the shortwave response of the total channel of up to 3% were made, which brought the tropical mean longwave radiance during day into agreement for edition 2. This adjustment also resulted in FM-1 and -2 radiances at nadir agreeing during daytime to a fraction of a W m−2, but the nighttime longwave differs by 1 W m−2 and the shortwave differs by 2 W m−2.

For flight models FM-3 and FM-4 the ICM showed the calibrations to vary less than 1% over the 5-yr data period analyzed. The tropical mean longwave difference between day and night from FM-3 increased to 1 W m−2 for edition 1. The shortwave response of the total channel was modified to bring the daytime radiances into agreement with nighttime radiances. Similar results were found for FM-4.

Acknowledgments

The authors gratefully acknowledge the support of the CERES Program by the Earth Science Office of NASA and the Sciences Directorate of the Langley Research Center. Also, the contributions of the many people at the Space Division of TRW (now Northrop-Grumman) who designed, built, and tested these instruments must be recognized, in particular Steve Carmen, Tom Evert, Gary Peterson, Arpad Pallai, Peter Jarecke, Mark Folkman, Mark Frink, and Herb Bitting. The outstanding performance of the CERES instruments has been due to the dedication of these people to excellence.

REFERENCES

  • Barkstrom, B. R., 1990: Earth radiation budget measurements: Pre-ERBE, ERBE, and CERES. Long-Term Monitoring of the Earth’s Radiation Budget, B. R. Barkstrom., Ed., International Society for Optical Engineering (SPIE Proceedings, Vol. 1299), 52–60.

    • Search Google Scholar
    • Export Citation
  • Barkstrom, B. R., and Smith G. L. , 1986: The Earth Radiation Budget Experiment: Science and implementation. Rev. Geophys., 24 , 379390.

  • Barkstrom, B. R., Wielicki B. A. , Smith G. L. , Lee R. B. III, Priestley K. J. , Charlock T. P. , and Kratz D. P. , 2001: Validation of CERES/TERRA data. Sensors, Systems, and Next-Generation Satellites IV, H. Fujisada et al., Eds., International Society for Optical Engineering (SPIE Proceedings, Vol. 4169), 17–28.

    • Search Google Scholar
    • Export Citation
  • Green, R. N., and Avis L. M. , 1996: Validation of ERBS scanner radiances. J. Atmos. Oceanic Technol., 13 , 851862.

  • Harrison, E. F., Minnis P. , and Gibson G. G. , 1983: Orbital and cloud cover sampling analyses for multi-satellite Earth radiation budget experiments. J. Spacecr. Rockets, 20 , 491495.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Harrison, E. F., Minnis P. , Gibson G. G. , and Denn F. M. , 1991: Orbital analysis and instrument viewing considerations for the Earth Observing System satellite. Adv. Astronaut. Sci., 76 , 12151228.

    • Search Google Scholar
    • Export Citation
  • Hartmann, D. L., Ramanathan V. , Berroir A. , and Hunt G. E. , 1986: Earth radiation budget data and climate research. Rev. Geophys., 24 , 439468.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Kratz, D. P., Priestley K. J. , and Green R. N. , 2002: Establishing the relationship between the CERES window channel and total channel measured radiances for conditions involving deep convective clouds at night. J. Geophys. Res., 107 , 4245. doi:10.1029/2001JD001170.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lee R. B. III, , Avis L. M. , Gibson M. A. , and Kopia L. P. , 1992: Characterizations of the mirror attenuator mosaic: Solar diffuser plate. Appl. Opt., 31 , 66436652.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lee R. B. III, , Avis L. M. , Gibson M. A. , Thomas S. , and Wilson R. S. , 1993: In-flight evaluations of tungsten calibration lamps using shortwave thermistor bolometers and active cavity radiometers. Metrologia, 30 , 389395.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lee R. B. III, , and Coauthors, 1996: The Clouds and the Earth’s Radiant Energy System (CERES) sensors and preflight calibration plans. J. Atmos. Oceanic Technol., 13 , 300313.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lee R. B. III, , and Coauthors, 1997: Ground calibrations of the Clouds and the Earth’s Radiant Energy System (CERES) Tropical Rainfall Measuring Mission spacecraft thermistor bolometers. Earth Observing Systems II, W. L. Barnes, Ed., International Society for Optical Engineering (SPIE Proceedings, Vol. 3117), 281–293.

    • Search Google Scholar
    • Export Citation
  • Lee R. B. III, , and Coauthors, 1998: Prelaunch calibrations of the Clouds and the Earth’s Radiant Energy System (CERES) Tropical Rainfall Measuring Mission and Earth Observing System morning (EOS-AM1) spacecraft thermistor bolometer sensors. IEEE Trans. Geosci. Remote Sens., 36 , 11731185.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lee R. B. III, , and Coauthors, 1999a: Analyses of on-orbit determinations of the Clouds and the Earth’s Radiant Energy System (CERES) thermistor bolometer sensor zero-radiance offsets. Earth Observing Systems IV, W. L. Barnes, Ed., International Society for Optical Engineering (SPIE Proceedings, Vol. 3750), 482–493.

    • Search Google Scholar
    • Export Citation
  • Lee R. B. III, , Thomas S. , Wilson R. S. , Priestley K. J. , Paden J. , Pandey D. K. , and Al-Hajjah A. , 1999b: Ground through on-orbit transfer of the International Temperature Scale of 1990 (ITS-90): Radiometric scale using the CERES thermistor bolometers and built-in flight calibration systems. Sensors, Systems, and Next-Generation Satellites III, H. Fujisada and J. B. Lurie, Eds., International Society for Optical Engineering (SPIE Proceedings, Vol. 3870), 389–396.

    • Search Google Scholar
    • Export Citation
  • Lee R. B. III, , and Coauthors, 2000: Terra spacecraft CERES flight model 1 and 2 sensor measurement precisions: Ground to flight determinations. Earth Observing Systems V, W. L. Barnes, Ed., International Society for Optical Engineering (SPIE Proceedings, Vol. 4135), 1–12.

    • Search Google Scholar
    • Export Citation
  • Priestley, K. J., and Coauthors, 2000: Post-launch radiometric validation of the Clouds and the Earth’s Radiant Energy System (CERES) Proto-Flight Model on the Tropical Rainfall Measuring Mission (TRMM) spacecraft through 1999. J. Appl. Meteor., 39 , 22492258.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Priestley, K. J., Smith G. L. , Thomas S. , and Matthews G. , 2007: Validation protocol for climate quality CERES measurements. Infrared Spaceborne Remote Sensing and Instrumentation XV, M. Strojnik-Scholl, Ed., International Society for Optical Engineering (SPIE Proceedings, Vol. 6678), 66781I, doi:10.1117/12.735312.

    • Search Google Scholar
    • Export Citation
  • Ramanathan, V., 1987: The role of earth radiation budget studies in climate and general circulation research. J. Geophys. Res., 92 , 40754095.

  • Ramanathan, V., Harrison E. F. , and Barkstrom B. R. , 1989: Climate and the Earth’s radiation budget. Phys. Today, 42 , 2233.

  • Smith, G. L., and Coauthors, 2004: Clouds and Earth Radiant Energy System: An overview. Adv. Space Res., 33 , 11251131.

  • Szewczyk, Z. P., and Priestley K. J. , 2003: CERES instruments special coverage for field campaigns. Proc. ISRSE, Honolulu, Hawaii, NASA. [Available online at http://asd-www.larc.nasa.gov/Instrument/Slide_shows/EPresents_show/PDF_Files/haw03-ppt.pdf].

    • Search Google Scholar
    • Export Citation
  • Szewczyk, Z. P., and Priestley K. J. , 2004: Automated programmable scanning plane orientation of CERES instruments. Proc. AIAA, Reno, Nevada, American Institute of Aeronautics and Astronautics. [Available online at http://asd-www.larc.nasa.gov/Instrument/Slide_shows/EPresents_show/PDF_Files/reno04-paper.pdf].

    • Search Google Scholar
    • Export Citation
  • Wielicki, B. A., Cess R. D. , King M. D. , Randall D. A. , and Harrison E. F. , 1995: Mission to planet earth: Role of clouds and radiation in climate. Bull. Amer. Meteor. Soc., 76 , 21252153.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Wielicki, B. A., Barkstrom B. R. , Harrison E. F. , Lee R. B. III, Smith G. L. , and Cooper J. E. , 1996: Clouds and the Earth’s Radiant Energy System (CERES): An Earth Observing System experiment. Bull. Amer. Meteor. Soc., 77 , 853868.

    • Crossref
    • Search Google Scholar
    • Export Citation

Fig. 1.
Fig. 1.

CERES scanning radiometer.

Citation: Journal of Atmospheric and Oceanic Technology 28, 1; 10.1175/2010JTECHA1521.1

Fig. 2.
Fig. 2.

Spectral responses of CERES channels.

Citation: Journal of Atmospheric and Oceanic Technology 28, 1; 10.1175/2010JTECHA1521.1

Fig. 3.
Fig. 3.

Internal calibration module.

Citation: Journal of Atmospheric and Oceanic Technology 28, 1; 10.1175/2010JTECHA1521.1

Fig. 4.
Fig. 4.

Radiometric calibration facility.

Citation: Journal of Atmospheric and Oceanic Technology 28, 1; 10.1175/2010JTECHA1521.1

Fig. 5.
Fig. 5.

Traceability of CERES calibrations to the International Temperature Scale of 1990.

Citation: Journal of Atmospheric and Oceanic Technology 28, 1; 10.1175/2010JTECHA1521.1

Fig. 6.
Fig. 6.

In-flight results from internal calibration module of each instrument, with lines indicating values used for edition 2 data processing: (a) FM-1 instrument aboard Terra. (b) FM-2 instrument aboard Terra, (c) FM-3 instrument aboard Aqua, and (d) FM-4 instrument aboard Aqua.

Citation: Journal of Atmospheric and Oceanic Technology 28, 1; 10.1175/2010JTECHA1521.1

Fig. 7.
Fig. 7.

Slope of changes of shortwave response of total channel of FM-1 and FM-2 based on applying the three-channel comparison over deep convective clouds for editions (a) 1 and (b) 2.

Citation: Journal of Atmospheric and Oceanic Technology 28, 1; 10.1175/2010JTECHA1521.1

Fig. 8.
Fig. 8.

Shortwave spectral response changes of total channel applied for edition 2 data processing for (a) FM-1 and (b) FM-2 spectral response function.

Citation: Journal of Atmospheric and Oceanic Technology 28, 1; 10.1175/2010JTECHA1521.1

Fig. 9.
Fig. 9.

Slope of the shortwave responses of the total channels of FM-3 and FM-4 based on applying the three-channel comparison for deep convective clouds for editions (a) 1 and (b) 2.

Citation: Journal of Atmospheric and Oceanic Technology 28, 1; 10.1175/2010JTECHA1521.1

Fig. 10.
Fig. 10.

Shortwave spectral response change of the total channel applied to (a) FM-3 and (b) FM-4 for edition 2 data processing.

Citation: Journal of Atmospheric and Oceanic Technology 28, 1; 10.1175/2010JTECHA1521.1

Fig. 11.
Fig. 11.

Tropical mean longwave radiance at nadir for FM-1 during day and night from March 2000 through March 2007 for editions (a) 1 and (b) 2.

Citation: Journal of Atmospheric and Oceanic Technology 28, 1; 10.1175/2010JTECHA1521.1

Fig. 12.
Fig. 12.

Tropical mean longwave radiance at nadir for FM-2 from March 2000 through March 2007 for editions (a) 1 and (b) 2.

Citation: Journal of Atmospheric and Oceanic Technology 28, 1; 10.1175/2010JTECHA1521.1

Fig. 13.
Fig. 13.

Tropical mean longwave radiance at nadir for FM-3 from July 2002 through March 2007 for editions (a) 1 and (b) 2.

Citation: Journal of Atmospheric and Oceanic Technology 28, 1; 10.1175/2010JTECHA1521.1

Fig. 14.
Fig. 14.

Tropical mean longwave radiance at nadir for FM-4 from July 2002 through March 2005 for editions (a) 1 and (b) 2.

Citation: Journal of Atmospheric and Oceanic Technology 28, 1; 10.1175/2010JTECHA1521.1

Fig. 15.
Fig. 15.

Comparison of FM-2 and FM-1 fluxes at nadir from March 2000 through March 2007 for (a) nighttime longwave, (b) daytime shortwave, and (c) daytime longwave.

Citation: Journal of Atmospheric and Oceanic Technology 28, 1; 10.1175/2010JTECHA1521.1

Fig. 16.
Fig. 16.

Comparison of FM-3 and FM-4 fluxes at nadir from July 2002 through March 2005 for (a) nighttime longwave, (b) daytime shortwave, and (c) daytime longwave.

Citation: Journal of Atmospheric and Oceanic Technology 28, 1; 10.1175/2010JTECHA1521.1

Table 1.

Stability of unfiltered radiances for editions 1 and 2. Units are percent per year.

Table 1.
Save
  • Barkstrom, B. R., 1990: Earth radiation budget measurements: Pre-ERBE, ERBE, and CERES. Long-Term Monitoring of the Earth’s Radiation Budget, B. R. Barkstrom., Ed., International Society for Optical Engineering (SPIE Proceedings, Vol. 1299), 52–60.

    • Search Google Scholar
    • Export Citation
  • Barkstrom, B. R., and Smith G. L. , 1986: The Earth Radiation Budget Experiment: Science and implementation. Rev. Geophys., 24 , 379390.

  • Barkstrom, B. R., Wielicki B. A. , Smith G. L. , Lee R. B. III, Priestley K. J. , Charlock T. P. , and Kratz D. P. , 2001: Validation of CERES/TERRA data. Sensors, Systems, and Next-Generation Satellites IV, H. Fujisada et al., Eds., International Society for Optical Engineering (SPIE Proceedings, Vol. 4169), 17–28.

    • Search Google Scholar
    • Export Citation
  • Green, R. N., and Avis L. M. , 1996: Validation of ERBS scanner radiances. J. Atmos. Oceanic Technol., 13 , 851862.

  • Harrison, E. F., Minnis P. , and Gibson G. G. , 1983: Orbital and cloud cover sampling analyses for multi-satellite Earth radiation budget experiments. J. Spacecr. Rockets, 20 , 491495.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Harrison, E. F., Minnis P. , Gibson G. G. , and Denn F. M. , 1991: Orbital analysis and instrument viewing considerations for the Earth Observing System satellite. Adv. Astronaut. Sci., 76 , 12151228.

    • Search Google Scholar
    • Export Citation
  • Hartmann, D. L., Ramanathan V. , Berroir A. , and Hunt G. E. , 1986: Earth radiation budget data and climate research. Rev. Geophys., 24 , 439468.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Kratz, D. P., Priestley K. J. , and Green R. N. , 2002: Establishing the relationship between the CERES window channel and total channel measured radiances for conditions involving deep convective clouds at night. J. Geophys. Res., 107 , 4245. doi:10.1029/2001JD001170.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lee R. B. III, , Avis L. M. , Gibson M. A. , and Kopia L. P. , 1992: Characterizations of the mirror attenuator mosaic: Solar diffuser plate. Appl. Opt., 31 , 66436652.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lee R. B. III, , Avis L. M. , Gibson M. A. , Thomas S. , and Wilson R. S. , 1993: In-flight evaluations of tungsten calibration lamps using shortwave thermistor bolometers and active cavity radiometers. Metrologia, 30 , 389395.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lee R. B. III, , and Coauthors, 1996: The Clouds and the Earth’s Radiant Energy System (CERES) sensors and preflight calibration plans. J. Atmos. Oceanic Technol., 13 , 300313.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lee R. B. III, , and Coauthors, 1997: Ground calibrations of the Clouds and the Earth’s Radiant Energy System (CERES) Tropical Rainfall Measuring Mission spacecraft thermistor bolometers. Earth Observing Systems II, W. L. Barnes, Ed., International Society for Optical Engineering (SPIE Proceedings, Vol. 3117), 281–293.

    • Search Google Scholar
    • Export Citation
  • Lee R. B. III, , and Coauthors, 1998: Prelaunch calibrations of the Clouds and the Earth’s Radiant Energy System (CERES) Tropical Rainfall Measuring Mission and Earth Observing System morning (EOS-AM1) spacecraft thermistor bolometer sensors. IEEE Trans. Geosci. Remote Sens., 36 , 11731185.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lee R. B. III, , and Coauthors, 1999a: Analyses of on-orbit determinations of the Clouds and the Earth’s Radiant Energy System (CERES) thermistor bolometer sensor zero-radiance offsets. Earth Observing Systems IV, W. L. Barnes, Ed., International Society for Optical Engineering (SPIE Proceedings, Vol. 3750), 482–493.

    • Search Google Scholar
    • Export Citation
  • Lee R. B. III, , Thomas S. , Wilson R. S. , Priestley K. J. , Paden J. , Pandey D. K. , and Al-Hajjah A. , 1999b: Ground through on-orbit transfer of the International Temperature Scale of 1990 (ITS-90): Radiometric scale using the CERES thermistor bolometers and built-in flight calibration systems. Sensors, Systems, and Next-Generation Satellites III, H. Fujisada and J. B. Lurie, Eds., International Society for Optical Engineering (SPIE Proceedings, Vol. 3870), 389–396.

    • Search Google Scholar
    • Export Citation
  • Lee R. B. III, , and Coauthors, 2000: Terra spacecraft CERES flight model 1 and 2 sensor measurement precisions: Ground to flight determinations. Earth Observing Systems V, W. L. Barnes, Ed., International Society for Optical Engineering (SPIE Proceedings, Vol. 4135), 1–12.

    • Search Google Scholar
    • Export Citation
  • Priestley, K. J., and Coauthors, 2000: Post-launch radiometric validation of the Clouds and the Earth’s Radiant Energy System (CERES) Proto-Flight Model on the Tropical Rainfall Measuring Mission (TRMM) spacecraft through 1999. J. Appl. Meteor., 39 , 22492258.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Priestley, K. J., Smith G. L. , Thomas S. , and Matthews G. , 2007: Validation protocol for climate quality CERES measurements. Infrared Spaceborne Remote Sensing and Instrumentation XV, M. Strojnik-Scholl, Ed., International Society for Optical Engineering (SPIE Proceedings, Vol. 6678), 66781I, doi:10.1117/12.735312.

    • Search Google Scholar
    • Export Citation
  • Ramanathan, V., 1987: The role of earth radiation budget studies in climate and general circulation research. J. Geophys. Res., 92 , 40754095.

  • Ramanathan, V., Harrison E. F. , and Barkstrom B. R. , 1989: Climate and the Earth’s radiation budget. Phys. Today, 42 , 2233.

  • Smith, G. L., and Coauthors, 2004: Clouds and Earth Radiant Energy System: An overview. Adv. Space Res., 33 , 11251131.

  • Szewczyk, Z. P., and Priestley K. J. , 2003: CERES instruments special coverage for field campaigns. Proc. ISRSE, Honolulu, Hawaii, NASA. [Available online at http://asd-www.larc.nasa.gov/Instrument/Slide_shows/EPresents_show/PDF_Files/haw03-ppt.pdf].

    • Search Google Scholar
    • Export Citation
  • Szewczyk, Z. P., and Priestley K. J. , 2004: Automated programmable scanning plane orientation of CERES instruments. Proc. AIAA, Reno, Nevada, American Institute of Aeronautics and Astronautics. [Available online at http://asd-www.larc.nasa.gov/Instrument/Slide_shows/EPresents_show/PDF_Files/reno04-paper.pdf].

    • Search Google Scholar
    • Export Citation
  • Wielicki, B. A., Cess R. D. , King M. D. , Randall D. A. , and Harrison E. F. , 1995: Mission to planet earth: Role of clouds and radiation in climate. Bull. Amer. Meteor. Soc., 76 , 21252153.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Wielicki, B. A., Barkstrom B. R. , Harrison E. F. , Lee R. B. III, Smith G. L. , and Cooper J. E. , 1996: Clouds and the Earth’s Radiant Energy System (CERES): An Earth Observing System experiment. Bull. Amer. Meteor. Soc., 77 , 853868.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Fig. 1.

    CERES scanning radiometer.

  • Fig. 2.

    Spectral responses of CERES channels.

  • Fig. 3.

    Internal calibration module.

  • Fig. 4.

    Radiometric calibration facility.

  • Fig. 5.

    Traceability of CERES calibrations to the International Temperature Scale of 1990.

  • Fig. 6.

    In-flight results from internal calibration module of each instrument, with lines indicating values used for edition 2 data processing: (a) FM-1 instrument aboard Terra. (b) FM-2 instrument aboard Terra, (c) FM-3 instrument aboard Aqua, and (d) FM-4 instrument aboard Aqua.

  • Fig. 7.

    Slope of changes of shortwave response of total channel of FM-1 and FM-2 based on applying the three-channel comparison over deep convective clouds for editions (a) 1 and (b) 2.

  • Fig. 8.

    Shortwave spectral response changes of total channel applied for edition 2 data processing for (a) FM-1 and (b) FM-2 spectral response function.

  • Fig. 9.

    Slope of the shortwave responses of the total channels of FM-3 and FM-4 based on applying the three-channel comparison for deep convective clouds for editions (a) 1 and (b) 2.

  • Fig. 10.

    Shortwave spectral response change of the total channel applied to (a) FM-3 and (b) FM-4 for edition 2 data processing.

  • Fig. 11.

    Tropical mean longwave radiance at nadir for FM-1 during day and night from March 2000 through March 2007 for editions (a) 1 and (b) 2.

  • Fig. 12.

    Tropical mean longwave radiance at nadir for FM-2 from March 2000 through March 2007 for editions (a) 1 and (b) 2.

  • Fig. 13.

    Tropical mean longwave radiance at nadir for FM-3 from July 2002 through March 2007 for editions (a) 1 and (b) 2.

  • Fig. 14.

    Tropical mean longwave radiance at nadir for FM-4 from July 2002 through March 2005 for editions (a) 1 and (b) 2.

  • Fig. 15.

    Comparison of FM-2 and FM-1 fluxes at nadir from March 2000 through March 2007 for (a) nighttime longwave, (b) daytime shortwave, and (c) daytime longwave.

  • Fig. 16.

    Comparison of FM-3 and FM-4 fluxes at nadir from July 2002 through March 2005 for (a) nighttime longwave, (b) daytime shortwave, and (c) daytime longwave.

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