Satellite Missions
NOAA-20
What impact do clouds have on Earth’s climate? This is one of the most pressing scientific questions of our time. One way NASA is working to answer that question, among others, is by launching the latest in a long line of successful spaceflight instruments, CERES FM6. The instrument measures reflected sunlight and thermal radiation emitted by the Earth.
CERES FM6, or Clouds and Earth’s Radiant Energy System Flight Model 6, is a three-channel radiometer that measures both solar-reflected and Earth-emitted radiation from the top of the atmosphere to the Earth’s surface. CERES measures radiances in three broadband channels: a shortwave channel, a longwave channel, and a total channel.
There are currently six CERES instruments on satellites orbiting Earth and taking data. CERES is a key component of the Earth Observing System (EOS), Suomi National Polar-orbiting Partnership (S-NPP) observatory, and NOAA-20 observatories. The first CERES instrument flew on the Tropical Rainfall Measuring Mission (TRMM) in 1997. The instruments were launched on EOS Terra in 1999, Aqua in 2002, Soumi NPP in 2011 and most recently on NOAA-20 in 2017.
CERES helps provide measurements of the spatial and temporal distribution of Earth’s Radiation Budget (ERB) components. This further develops understanding of the links between the ERB and the proprieties of atmosphere and surface that define it.
Earth’s climate system tries to balance radiant energy from the Sun that reaches the Earth with the energy that is emitted from Earth back to space. Measurements from CERES help scientists understand the links between the Earth’s incoming and outgoing energy and the properties of the atmosphere that affect that energy.
The observations from CERES FM6 help measure the effect of clouds on the energy balance, which strongly influences both weather and climate. CERES allows scientists to validate models that calculate the effect of clouds in driving planetary heating or cooling. CERES’ global observations provide data for improving seasonal climate forecasts, including cloud and radiative aspects of large-scale climate events like El Niño and La Niña.
CERES also determines cloud properties including the amount, height, thickness, particle size and phase of clouds using simultaneous measurements by other Earth Observing System (EOS), and Joint Polar Satellite System (JPSS) instruments such as the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Visible Infrared Imaging Radiometric Suite (VIIRS). Analyses using CERES data, build upon the foundation laid by previous missions such as NASA Langley’s Earth Radiation Budget Experiment (ERBE), leading to a better understanding of the role of clouds and the energy cycle in global climate change. These measurements are critical for understanding cloud-radiation climate change and improving the prediction of global warming using climate models.
CERES data can also be used for assessing the radiative effects and climatic impact of natural disasters like volcanic eruptions, major floods and droughts. The long-term data will provide a basis for scientific understanding of cloud and climate feedback that determines climate variations and trends.
The CERES instruments were built by TRW in Redondo Beach, California (now Northrop Grumman Aerospace Systems) and managed by NASA’s Langley Research Center in Hampton, Virginia. The international CERES science team includes scientists from NASA, NOAA, U.S. universities, France, and Belgium. The team blends expertise and guides the definition of the CERES instrument and science studies.
NOAA-20 Operations
The NOAA-20 spacecraft, carrying the CERES instrument (FM-6), was launched from Vandenberg AFB, CA on November 18, 2017. It extends the measurement series initiated with Earth Observing System (EOS) Terra, Aqua, and Suomi-NPP missions.
FM-6 Operations
For information on JPSS Mission: JPSS Mission
NOAA-20 Pictures
NPP
CERES is a key component of Earth Observing System (EOS) and Suomi National Polar-orbiting Partnership (S-NPP) observatory. The first CERES instrument (PFM) flew on TRMM, four instruments are currently operating on the EOS Terra (FM1 and FM2) and Aqua (FM3 and FM4) platforms, and FM5 was launched on the S-NPP platform on October 28, 2011. CERES measures radiances in three broadband channels: a shortwave channel (0.3 — 5 µm), a total channel (0.3 — 200 µm), and an infrared window channel (8 — 12 µm).
The last data processed from the PFM instrument aboard TRMM was March 2000; no additional data are expected. Until June 2005, one instrument on each EOS platform operated in a fixed azimuth scanning mode and the other operated in a rotating azimuth scanning mode; now all are typically operating in the fixed azimuth scanning mode. The S-NPP platform carries the FM5 instrument, which operates in the fixed azimuth scanning mode though it can operate in a rotating azimuth scanning mode.
CERES climate data records involve an unprecedented level of data fusion: CERES measurements are combined with imager data (e.g., MODIS on Terra and Aqua, VIIRS on S-NPP), 4-D weather assimilation data, microwave sea-ice observations, and measurements from five geostationary satellites to produce climate-quality radiative fluxes at the top-of-atmosphere, within the atmosphere and at the surface, together with the associated cloud and aerosol properties.
CERES is a Principal Investigator instrument provided by NASA and managed by NASA’s Langley Research Center (LaRC) in Hampton, Virginia. The instrument was built by TRW in Redondo Beach, California. The CERES Team Leader is Norman Loeb.
NPP Operations
The S-NPP spacecraft, carrying the CERES instrument (FM-5), was launched from Vandenberg AFB, CA on October 28, 2011. It extends the measurement series initiated with Earth Observing System (EOS) Terra and Aqua missions.
FM-5 Operations
For information on S-NPP Mission: S-NPP Mission
NPP Quick-Look Results
These pictures show examples of the first measurements that the CERES instrument on the S-NPP satellite have made. We use data products such as these to validate the accuracy of our Earth energy estimates. As we gain confidence in the proper operation of the instrument and the data interpretation algorithms, the science data products will be archived at the Atmospheric Science Data Center.
Contributions to these pages are welcome.
We are pleased to announce that the CERES FM-5 main and MAM covers have opened successfully. Earth viewing science observations began January 26, 2012 at 17:09:13 GMT. All instrument operations are nominal. The attached files are our the First Light images (full 24-h period of data collection). Read NASA’s featured article here.
This image is from the first test scans of Langley’s Clouds and the Earth’s Radiant Energy System (CERES) instrument aboard a NASA Earth-observing satellite launched October 28, 2011 from Vandenberg Air Force Base in California. The CERES instrument targeted the Baltimore-Washington area as the satellite it is aboard passed over the region in the course of its polar orbit. The scans are to make sure planning tools and orbital predictions are accurate. The scans are used for field missions and for ground truth validation purposes. Read the entire article here.
NPP Pictures
Aqua
Aqua carries two CERES instruments, the fourth and fifth CERES to fly in space. The first CERES was launched in November 1997 on board the Tropical Rainfall Measuring Mission (TRMM). satellite, and the next two CERES were launched in December 1999 on Terra. The TRMM and Terra CERES have obtained levels of accuracy never before achieved for comprehensive Earth radiation-budget measurements. All the CERES instruments have the capability of operating in either of two scanning modes: fixed azimuth plane scanning, where the scan lines are perpendicular to the path of the satellite, and rotating azimuth plane scanning, where the scan lines are at wide range of angles with respect to the satellite’s path. The paired CERES on Terra and on Aqua provide both of those missions with the possibility of coincident fixed azimuth plane scanning from one CERES and rotating azimuth plane scanning from the other CERES, enhancing the quality of the final products.
CERES is a Principal Investigator instrument provided by NASA and managed by NASA’s Langley Research Center (LaRC) in Hampton, Virginia. The instrument was built by TRW in Redondo Beach, California.
Aqua Operations
The Aqua spacecraft, carrying two CERES instruments (FM-3 and FM-4), was launched from Vandenberg AFB, CA on May 4, 2002 at 09:55 Universal Time. The links below will list key operations for the two CERES instruments on Aqua, beginning at launch.
FM-3 Operations | FM-4 Operations
Aqua Quick-Look Results
NASA’s latest Earth Observing System satellite – Aqua – is dedicated to advancing our understanding of Earth’s water cycle.Launched on May 4, 2002, Aqua has successfully completed its checkout period and is fully operational. Using multiple instruments,Aqua data and images are crucial toward improving our knowledge of global climate change.
The clouds and the Earth’s Radiant Energy System (CERES) instrument is one of six on board the Aqua satellite. CERES detects the amount ofoutgoing heat and reflected sunlight leaving the planet. A detailed understanding of how clouds affect the energy balance is essential forbetter climate change predictions.
These Aqua images show CERES measurements over the United States and the Gulf of Mexico from October 1, 2002. Visible are Hurricane Liliat the center of the image and tropical storm Kyle located to the upper right. Lili developed into a major category 4 hurricane and madeland fall over the coast of Louisiana two days later. Both of these tropical cloud systems have a tendency to cool the Earth by reflectinga large amount of sunlight (white and green areas in the left image) back to space. At the same time, these tropical cloud systems havecountering tendency to warm the Earth by reducing the amount of outgoing heat lost to space (blue and white areas in the right image).Without these tropical cloud systems, the Earth would lose a large amount of heat to space as seen by the surrounding clear-sky regions (red and yellow areas in the right image). The key to unlocking the mysteries of climate and climate changes is understanding the Earth’sdelicate energy balance between reflected sunlight and outgoing heat, and how this balance is affected by the presence of different cloud systems.
Aqua is part of NASA’s Earth Science Enterprise, a long-term research effort dedicated to understanding and protecting our home planet.Through the study of Earth, NASA will help provide sound science to policy and economic decision makers so as to better life here, whiledeveloping the technologies needed to explore the universe and search for life beyond our home planet.
NASA TV VIDEO-FILE FOR JULY 29, 2002
ITEM 1 – AQUA/CERES Instrument First Light Images Over the U.S. – GSFC
NASA’s latest Earth Observing System (EOS) satellite, Aqua, is dedicated to advancing our understanding of Earth’s water cycle. Launched on May 4, Aqua has successfully completed its checkout period and is fully operational. Using multiple instruments, Aqua data and images are crucial toward improving our knowledge of global climate change.
The Clouds and the Earth’s Radiant Energy System (CERES) instrument is one of six on board the Aqua satellite. CERES detects the amount of outgoing heat and reflected sunlight leaving the planet. A detailed understanding of how clouds affect the energy balance is essential for better climate change predictions.
These Aqua images show CERES measurements over the United States from June 22, 2002. Clear ocean regions, shown in dark blue on the left image, reflect the least amount of sunlight back to space. Clear land areas, shown in lighter blue, reflect more solar energy. Clouds and snow-covered surfaces, shown in white and green, reflect the greatest amounts of sunlight back to space. Clear warm regions, shown in yellow over much of the western U.S. on the right image, emit the most heat. High, cold clouds, shown in blue and white, significantly reduce the amount of heat lost to space.
Aqua is part of NASA’s Earth Science Enterprise, a long-term research effort dedicated to understanding and protecting our home planet. Through the study of Earth, NASA will help to provide sound science to policy and economic decision makers so as to better life here, while developing the technologies needed to explore the universe and search for life beyond our home planet.
These images represent the first 24 hours of high-rate science data collection from the 2 CERES instruments on Aqua. The sensor scan head remained stowed, staring at internal instrument structure which provides a stable source so characteristic noise patterns of the sensors may be quantified. CERES collects 660 samples (abscissa) in a data packet, representing a 6.6 second packet length, the ordinate represents raw digital output of the sensors. A single count is equivalent to roughly 0.5 W/m2 TOA flux. Globally averaged Outgoing Longwave Radiation and reflected Solar radiation values are typically 240 W/m2 and 100 W/m2 respectively. Patterns in the data are correlated with onboard microprocessor activities. There is no measurable difference from identical measurements made during ground calibrations prior to launch.
Aqua Pictures
Terra
CERES consists of two broadband scanning radiometers that measure the Earth’s radiation balance and provide cloud property estimates to assess their role in radiative fluxes from the surface to the top of the atmosphere.
CERES is a broadband scanning thermistor bolometer package with extremely high radiometric measurement precision and accuracy. The Terra Mission spacecraft carries two identical instruments: one operates in a cross-track scan mode and the other in a biaxial scan mode. The CERES Terra cross-track scanning data greatly extends the CERES data from the Tropical Rainfall Measuring Mission (TRMM) to achieve complete global measurements by adding mid-latitude and polar observations. TRMM data is restricted by its orbit to roughly cover 40S to 40N. Terra crosstrack data also adds observations at different times of day than TRMM (and later Aqua) in order to increase the accuracy of measuring the large diurnal cycle of the radiation fields from day to night.
Finally, the CERES Terra biaxial scan mode provides new observations of the angular radiation fields in order to greatly improve the accuracy of the final fluxes of solar and thermal energy used to derive the Earth’s radiation balance.
Each CERES instrument has three channels–a short-wave channel for measuring reflected sunlight, a longwave channel for measuring Earth-emitted thermal radiation in the 8-12 µm “window” region, and a total channel for total radiation. Onboard calibration hardware includes a solar diffuser, a tungsten lamp system with a stability monitor, and a pair of blackbody sources. Cold space and internal calibration looks are performed during each normal Earth scan.
CERES is a Principal Investigator instrument provided by NASA and managed by NASA’s Langley Research Center (LaRC) in Hampton, Virginia. The instrument was built by TRW in Redondo Beach, California. The CERES Team Leader is Norman Loeb. More information may be obtained on the CERES Home Page.
Terra Operations
The Terra spacecraft, carrying two CERES instruments (FM-1 and FM-2), was launched from Vandenberg AFB, CA on December 18, 1999 at 18:57 Universal Time. Terra, originally designated as EOS-AM, is the flagship for the Earth Observing System (EOS). The links below list key operations for the two CERES instruments on Terra, beginning at launch.
FM-1 Operations | FM-2 Operations
For information on Terra Mission: Terra Mission
Terra Quick-Look Results
These pictures show examples of the first measurements that the CERES instruments on the Terra satellite have made. We use data products such as these to validate the accuracy of our Earth energy estimates. As we gain confidence in the proper operation of the instrument and the data interpretation algorithms, the science data products will be archived at the
Atmospheric Science Data Center.
Contributions to these pages are welcome.
This image shows reflected solar radiance emerging from the top of the atmosphere, as measured by the CERES Flight Model 1 (FM1) instrument on the Terra spacecraft. These preliminary (unvalidated) data show twenty four hours of measurements covering the entire Earth from North Pole to South Pole. Reflected solar radiance (or brightness) is a quantity describing how much light energy is moving in a particular direction, in this case the direction between a position on the Earth and the Terra spacecraft. Terra is moving from north to south in the individual orbital swaths that are sometimes visible on close examination of this image. Swath-related features appear most noticeable over the Eastern Pacific, which is just west of South America. There are four features spaced between the left edge of the image and South America that are probably related to the geometry of the scan pattern, where the east side of each swath is being observed at about 11:45 a.m., local solar time, while the west side of each swath is observed at about 9:45 a.m. Where there are no clouds over the oceans, this image is very dark — as we can easily see in the Carribbean or the Indian Ocean between Saudia Arabia and the Indian subcontinent. Where the ocean part of the image is lighter, there are clouds reflecting sunlight back to the CERES instrument. The tropical oceans near the Equator show intense thunderstorms. These are particularly visible between Africa and Australia, where the storms form part of the Intertropical Convergence Zone (ITCZ). Air ascends in the ITCZ and descends on the midlatitudes, where it makes it harder to form clouds. Further away from the Equator, we can see large storms, such as the cold front west of the Appalachians and the storm over the Northwest Pacific Coast of the United States. The southern oceans show particularly striking patterns associated with huge storm systems circling the Antarctic continent. Land reflects more sunlight than the oceans do. The Sahara Desert, in the center of this image, is one of the most reflective large land targets in the world, along with the Saudi Arabian Peninsula. Other land areas of the Earth are darker — with the rain forests of South America and Africa being almost as dark as the oceans. In this image, the rain forests are covered by clouds, so these naturally dark regions do reflect a large amount of sunlight. While this image is a beautiful reminder of the relationship between clouds and radiation, much work remains to be done in quantifying the uncertainty in the measurements. Other instruments on Terra will also contribute to determining the properties of the clouds, the state of the vegetation on the land, and the mixture of biological and chemical activities in the oceans.
This image shows the reflected solar flux emerging from the top of the atmosphere. The data are taken from an entire day of observations from the CERES Flight Model 1 (FM1) instrument on the Terra spacecraft. The quantity plotted is “reflected solar flux,” which not only involves instrument calibration and geolocation, but also removes the angular dependence of the upwelling radiance field. Thus, these data are Level 2 data, which means that CERES has been able to get a reasonable “engineering” calculation of derived physical fields within a few days of opening its covers. The data shown come from Saturday, February 26, 2000, the first full day of FM1 scanning. The latitude where the Sun is overhead is slightly below eight degrees south of this day. The upper portion of the globe, from about 80 degrees north to the North Pole, receives no sunlight on this day and reflects none. The CERES instrument sees an entire swath of the Earth from limb-to-limb as the satellite passes from North to South. The short black arcs that are regularly spaced near the Equator mark the edges of the scan swaths. Although the CERES instrument actually covers the Earth from one swath to the next, the image was made without taking the expansion of the instrument field-of-view into account. Just to the left of the center of the image, we can see South America. The North American continent is off to the northwest, where it is obscured by a cold front east of the Appalachians and a storm striking the Northwest Pacific Coast. Africa, particularly the Sahara Desert, and Saudi Arabia are clearly visible to the right of center in this image. The Sahara is obscured to some extent because of clouds. Saudi Arabia is not obscured, so we can see the bright sands of the desert contrast with the dark ocean at the southern edge of the Arabian Peninsula. Most of the patterns visible away from the Equator are large storm systems, where clouds reflect a large fraction of the incident sunlight. To the right of center, we can see much of the Indian subcontinent, although a large and very bright storm over the Himalayas extends to obscure the Pacific coast of China. Between India and Australia (visible just below the Equator on the lower right of the image), we can see a series of large thunderstorms that form the clouds in the Intertropical Convergence Zone (ITCZ). Far to the south, we can also see the high reflectivity of the Antarctic snow and ice emerge from the mixture of the cloudy and clear areas over the Southern Atlantic and Pacific.
Emitted Longwave Flux – 2/26/2000 – This image shows the energy being lost from the Earth and the atmosphere by thermal emission. This process, familiar to most of us as the heat radiated by electric stove elements, involves light with wavelengths invisible to the eye. Again, these data are Level 2 data from Saturday, February 26, 2000. In this image, blue values come from cold scenes with low thermal emission, while red/magenta values come from hot ones with high emission. As we might expect, the colder regions near the poles are blue, while the much warmer tropics are red. Near the center of the image, in red, we can see the Saudi Peninsula standing in contrast with the warm waters of the Indian Ocean, which appear a light shade. The land is hotter than the ocean, as we might expect from having the Sun shining on the Earth under clear skies at about 10:45 a.m. local time. Surprisingly, the Sahara Desert appears to have fairly extensive cloud cover, particularly near the Mediterranean. Along the Equator from the Amazon Basin in South America, across the Atlantic to the Congo Basin, and then over the Indian Ocean, we can see the tops of very high, thunderstorms in the Intertropical Convergence Zone. These appear in the image as very dark blue or black features that we typically associate with huge cirrus anvils. The temperature of the atmosphere declines with altitude, so that the tops of these tropical thunderstorms are actually colder than the surface of the Earth at the wintertime pole. The red/magenta features in this image are primarily clear areas, where we see through to the Earth’s surface without much impediment from clouds. In addition to the Indian Ocean, we might expect central Mexico and a large area of the Western Pacific to be relatively cloud free. The prominent green and blue features away from the Equator are typically large storm systems. Over the United States, we can see a frontal system west of the Appalachians that brought a moderate amount of rain to the Ohio Valley and the Northeast. We can also see a massive storm system depositing rain (and snow) on the Northwest Pacific Coast.
This picture shows Terra and TRMM data as the two satellites cross each other’s path (also see image below). The black dots and red circles represent Terra and TRMM data, respectively. The 70 black dots inside red circles correspond to overlapping Terra and TRMM measurements. To compare their data directly, the two instruments must look at their target from the same viewpoint. The 17 blue dots show the matched Terra and TRMM measurements of radiation emitted by the Earth (LW) while the 7 yellow dots are matched measurements of reflected solar radiation (SW). The difference between Terra and TRMM is on the order of 1% or less, but the variability is large (2.5-5%). To improve the confidence in our comparisons we must collect data from many such overlaps.
On March 3, 2000, the CERES team began joint operations with TRMM and Terra to compare the performance of the instruments on each satellite. This picture shows a comparison on March 4 with the Terra satellite moving north to south and the TRMM satellite moving west to east at nearly the same time. At the orbit crossing point, we rotate the scan plane of CERES FM1 on Terra to match the scan plane of TRMM. This event is over the northern Pacific and shows a bright cloud (in red) at the crossing point. Many such crossings are needed to gain confidence in the accuracy of the measurements.
CERES Terra FM1, 2/29/00, Hour 2, CERES Total Filtered Radiances Upward. Instrument is in the crosstrack, normal-earth scanning configuration. The spacecraft is descending over the Phillipines. Note the overlapping biaxial data from the corresponding FM2 data plot.
CERES Terra FM2, 2/29/00, Hour 2, CERES Total Filtered Radiances Upward. Instrument is in the biaxial, normal- earth scanning configuration. The spacecraft is descending over the Phillipines. Note the overlapping crosstrack data from the corresponding FM1 data plot.
CERES Terra FM2 – 2/27/2000 – CERES Total Filtered Radiances Upwards for Data Range: 01:58:44 – 02:53:57. Instrument is in the crosstrack, normal-earth scanning configuration. The spacecraft is descending over the Phillipines. The sun viewing zenith can be seen by the horizontal line just below the equator and the line runs east to west during this period.
CERES Terra FM1 – 2/26/2000 – CERES Total Filtered Radiances Upwards for Data Range: 01:15:04 – 02:44:57. Instrument is in the crosstrack, normal-earth scanning configuration and the period is within one hour of commencing science operations after the covers were opened. The spacecraft is descending over the Phillipines. The sun viewing zenith can be seen by the horizontal line just below the equator and the line runs east to west during this period.
Terra Pictures
TRMM
The Clouds and the Earth’s Radiant Energy System (CERES) experiment will allow researchers to study the Earth’s atmosphere from space. Measurements from CERES will be used to help us understand the complicated balance between the energy from the Sun which the Earth absorbs either at the surface or in the atmosphere, and the energy which is radiated from the Earth to space. If this balance changes, so will our climate (this is what happened, for example, in the Ice Ages).
In particular, CERES will help us understand how clouds influence the Earth’s energy balance and the role of clouds in regulating our climate. With this increased understanding, scientists will be able to improve long term climate forecasting — not just what the weather will be in the next few days, but will there be long term changes in the coming years: hotter summers, colder winters, and stronger storms — and will be able to investigate on-going natural and human-induced global climate change.
Because characterizing clouds is the biggest unknown in current climate prediction models, the type of measurements that CERES will provide have become one of the top scientific priorities in the U.S. Global Change Research Program.
With the launch of the first CERES instrument in November 1997 on the Tropical Rainfall Measuring Mission, we will begin to obtain this critical information. Additional flights will occur in 1998 and 2000. CERES data will become part of the planetary “health checkup” of the Earth system that will provide a baseline for measuring any future changes in the Earth’s climate system.
TRMM Operations
The Tropical Measuring Mission (TRMM) spacecraft, carrying the first Clouds and the Earth’s Radiant Energy (CERES) instrument, launched from Japan on November 28, 1997 (Thanksgiving Day in the United States). Following is a monthly account of the CERES instrument mission.
PFM Operations
Engineering Checkout Operations (during the first 2 weeks)
The Tropical Measuring Mission (TRMM) spacecraft, carrying the first Clouds and the Earth’s Radiant Energy (CERES) instrument, launched from Japan on November 28, 1997 (Thanksgiving Day in the United States). Following is an account of the first 14 days of the CERES instrument mission:
| Launch through Day 5 | November 27 – December 1, 1997
The instrument was launched with survival power applied and was operated in this mode until day six. All temperatures were noted to be within expected ranges. |
| Day 6 | December 2, 1997
CERES operational power was applied for the first time. The memory patches for the instrument were uploaded and the instrument was allowed to “warm up” before further operations. The instrument sensor temperatures were observed in the expected operational range after approximately 15 minutes. Other temperatures were observed during real time passes and were within the ranges for commencement of operations in approximately three orbits. During the day, the instrument was commanded to uncage the azimuth gimbal brake and move to the crosstrack position. Several default parameters were reset in software and a memory dump was performed. The instrument was placed in the safe mode for the remainder of the day. Key parameters of the instrument were monitored during each pass. It should be noted after application of operational power, the azimuth encoder did not experience the “rollover” that had been seen occasionally during I&T testing. |
| Day 7 | December 3, 1997
This was the first day in which the azimuth gimbal was rotated through the entire range of motion. The instrument was commanded through several sequences which incrementally moved the azimuth gimbal to the operational position (first commanded to the discrete locations and later allowed to scan between locations). The elevation gimbal was also exercised in the various scan profiles which were used during operations. The functionality of the temperature controller for the science sensors was also verified. At the conclusion of testing, the instrument was placed in the crosstrack mode for the remainder of the day. Special NOTE: During the day high resolution gimbal data was taken which, after analysis, showed no increase in friction for the azimuth gimbal operations as compared to prelaunch values. |
| Day 8 | December 4, 1997
The instrument continued to operate primarily in the crosstrack mode. The first internal calibrations were performed in the crosstrack and biaxial modes. All calibration sequences executed as expected. Later analysis of the science data showed the offsets of the shortwave channel matched the offsets measured during ground testing. This is the primary channel calibrated using this sequence. During this day it was observed the telemetry parameter for the main cover sensor number 1 occasionally oscillated and a bad sensor telemetry point was periodically recorded for sensor status. This type of response had been seen in thermal vacuum testing and is normal during periods of heating and cooling of the main cover. These events were correlated to solar events (sunrise, sunset) and the response to the limited conditions were noted for the Flight Operations Team. |
| Day 9 | December 5, 1997
The instrument continued to operate primarily in the crosstrack mode. The solar calibration contamination safe, and hold sequences were functionally verified. All temperatures and voltages continued to be within specification. |
| Day 10 | December 6, 1997
During this day the instrument was operated primarily in the crosstrack mode. During a period of the day the instrument was operated in the biaxial mode and spacecraft stored solar avoidance commanding was verified. This verification occurred during a real time pass. |
| Day 11 | December 7, 1997
The instrument operated in the crosstrack mode commanded entirely by stored spacecraft commands. An internal calibration was performed during the day. |
| Day 12 | December 8, 1997
The instrument was operated in the biaxial mode with all solar avoidance commanding being issued by stored spacecraft commands. |
| Day 13-14 | December 9-10, 1997
The instrument was operated in the crosstrack mode. |
CERES +15V Power Converter Anomaly
Anomaly Summary
The CERES Proto-Flight Model (PFM) instrument aboard the Tropical Rainfall Measuring Mission (TRMM) exceeded a yellow high limit for the Data Acquisition Assembly (DAA) +15 volt measurement on August 18, 1998. Upon review of instrument data it was noted the +15 volt level began increasing on July 31, 1998. The trend for the maximum voltage seen during a 24 hour period has been gradually upward since July 31st with an amplitude peak reaching approximately 16.9 volts on September 1, 1998. Due to overvoltage concerns for electronic parts downstream of the converter, the CERES instrument’s operational power has been removed. LaRC, TRW, and the TRMM Flight Operations Team continue to examine the CERES instrument and spacecraft data for an explanation and resolution to the anomaly.
Status Reports
- Status as of August 28, 1998 – (Bruce A. Wielicki)
We have experienced our first hardware glitch on the otherwise fantastic performance of the CERES instruments. A brief summary of what we know so far is given below courtesy of Jack Cooper and Greg Stover:
- The CERES Proto-Flight Model (PFM) instrument aboard the Tropical Rainfall Measuring Mission (TRMM) exceeded a yellow high limit for the Data Acquisition Assembly (DAA) +15 volt measurement on August 18, 1998. Upon review of instrument data it was noted the +15 volt level began increasing on July 31. The data shows that the +15 volt reading increases cyclically during each orbit with a peak at satellite sunset. The data also shows an enveloping peak that occurs several hours into each operational day. The trend for the enveloping peak has been gradually upward since July 31st with an amplitude peak reaching approximately 16.5 volts. At first the data only indicated that the biaxial and along-track scan modes were susceptible to this cyclic behavior, but recently the increases appear in the cross-track mode as well.
- LaRC, TRW, and the TRMM Flight Operations Team continue to monitor and examine the instrument data for an explanation and resolution to the anomaly. In the interim, a decision has been made to operate the instrument in the cross-track mode only. In this mode the voltage peaks have shown to be lower in amplitude and this mode provides for continued science data collection.
- We will keep you posted as we strive to further understand this anomaly. For now, however, we will leave the CERES instrument in its normal crosstrack scan mode until the anomaly is better characterized and understood.
- Power is Turned Off – dtd 09/01/98 – (Greg Stover)
During the evening Greg Stover, Deputy Manager for CERES Project, was paged by the TRMM FOT with the news that the CERES instrument DAA +15 V had reached a value of 16.5 Volts. This was seen during the real time contact that started at 244:03:36:00 UT. This was the pass during which the SWICS was turned OFF. During the next pass (started at 244:04:25) Greg instructed the TRMM FOT to SAFE the CERES instrument and turn OFF the operational power. At the beginning of the pass the voltage was 16.64 Volts. TRW and LaRC CERES Project Office will examine the latest data and decide what course of action to take. At this time it is not clear as to how we will proceed with the Deep Space Calibration.
- CERES +15V Anomaly Report – dtd 09/02/98 – (Compiled by Greg Stover) – PDF
- CERES Weekly Status Report – dtd 09/29/98 – (Compiled by Leonard Kopia)
PROTO-FLIGHT MODEL CONVERTER TIGER TEAM CONTINUES INVESTIGATION —
- The Tiger Team examining the anomalous operation of the +15 volt converter on the Clouds and the Earth’s Radiant Energy System (CERES) instrument aboard the Tropical Rainfall Measuring Mission (TRMM) continues its investigation. The anomaly exhibits characteristics that can be attributed to several potential causes. Recently, following component testing and further data examination, the team has ruled out two potential causes: radiation damage to the voltage converter components, and, a defective voltage monitor circuit. Additional effort continues to assess potential failure mechanisms of the converter components that may be attributed to mechanical and electrical attachment, premature part degradation, and/or thermal stress effects.
- A high fidelity computerized model of the converter (PSPICE) will be developed to aid in understanding the anomaly. This model will be developed by TRW and will later be enhanced by a separate corporation (STI) which specializes in circuit modeling. Prior to STI’s circuit model development, a non-disclosure agreement with the voltage converter manufacturer will be required and is expected shortly after initiation of the STI task.
- In the interim, activity continues at TRW to determine the upper voltage operational limits on components downstream of the converter, and to ascertain the thermal conditions in the vicinity of the converter. These determinations will assist the Team in making a decision as to the proper conditions for re-powering the instrument to gather additional diagnostic data.
- Status as of October 9, 1998 – (Bruce A. Wielicki)
- The problem is definitely with the voltage converter and not with the voltage measurement (housekeeping data).
- The problem is not caused by radiation damage. Laboratory radiation tests of similar converters have shown that it takes 100 times the radiation exposure that the TRMM spacecraft has seen to cause degradation of the converter.
- The problem was not caused by the CERES instrument design, use, or mounting process at TRW.
- Of roughly 5000 of these military spec parts that the voltage manufacturer has sold, only 1 has come back with a similar problem to our experience on CERES. That part was used in a high temperature environment (>100C) in a commercial aircraft, and showed a problem with bleeding of a silver conductive epoxy during the curing process. The silver epoxy is used to mount an optical coupler that controls the feedback gain of the converter. Normally, this optical coupler can experience degradation in gain of as much as a factor of six without affecting the performance of the converter. The bleeding of the silver epoxy, however, is thought to have decreased the gain the optical coupler by acting as a resistor across two of the couplers leads which should not be in contact. The theory is then that this gain loss still allows the converter to operate normally, but without much margin for any further degradation. If later radiation exposure caused an additional 1 or 2% gain loss of the optical coupler, then this might explain why the converter passed extensive burn in, but later showed the anomaly on the CERES instrument. TRW is working up a detailed theoretical model of the converter physics to test if this type of problem can explain the temperature sensitivity seen in the CERES converter. Expect results in 2-4 weeks. While this is a candidate for the anomaly, we still do not have a mechanism that fits all the observed behavior. This is currently, however, the best candidate and it is being pursued further.
- The sensitivity of the voltage converter to instrument temperature change (variations in orbital heating of the spacecraft and instrument) has remained constant at roughly 0.6V per degree C. What has changed is the minimum temperature Tmin at which the sensitivity begins. Below Tmin, there is no sensitivity of the voltage converter to temperature and it operates normally. From late July to late August the Tmin decreased almost linearly with time until it reached about 17.3C and then stabilized over the last 4 days the instrument ran in August (before we turned it off to investigate). If the converter has indeed stabilized for the long term, then the maximum voltages we will see in the future will be less than 18V, which is not a safety risk to the instrument.
- TRW has tested all 7 of the electrical components downstream of this converter to 30V. The maximum voltage the converter will let through from the spacecraft in the event of total failure is estimated to be 29.4V. At 30V, all 7 of the parts operated nominally, and TRW is readying a complete breadboard for long term testing at 30V to test lifetime at this elevated voltage. This testing will begin next week and will continue indefinitely. Unfortunately, there is no way to do an “accelerated life test” with this type of problem. So it will take 2 months to know if the parts could survive a converter failure for 2 months. This will, however, be a worst case scenario since the actual voltage fed through from the spacecraft will vary from roughly 23 to 29V depending on orbital conditions.
- On October 13 at 8pm EST we will power up the CERES instrument on TRMM. It will slowly warm to operational temperature, and we expect that around 8am on Wed Oct 14, that the temperature will increase to near the 17.3C value of Tmin that we saw in late August. The tiger team has planned a 6-day test sequence of all of CERES operational modes to evaluate the converter condition and whether any further degradation has occurred. This data will be evaluated, and along with the results of the other ongoing studies, a plan will be developed for further instrument operation. We will be able to monitor throughout the 6 day period whether any further instrument degradation occurs with further operation. We should know sometime on Wednesday if it looks good to continue running the instrument. It looks like we should be able to continually monitor the voltage converter sensitivity by using the temperature/voltage relationship: changes in this linear relationship can be directly related to changes in Tmin: Voltage output = 15 + 0.6(T – Tmin). Given values of voltage and T at any time, you can solve for Tmin. This allows a monitoring of Tmin without powering down the instrument to get to temperatures below Tmin.
- If we can convince ourselves using the 29V lifetime tests that we have a high probability of the instrument lasting at least 1 month after any failure of the converter, then I would propose that we continue to operate the instrument in our normal 2 days of crosstrack followed by 1 day of rotating azimuth plane day while we monitor the the voltage converter output for any further degradation. If it remains stable below 18V (no additional risk) or perhaps even below 21V (design is 15V, so small risk) then we continue to operate the instrument routinely. If the voltage converter continues to degrade and appears headed to a rapid failure, then we safe the instrument, and save it for intercalibration with CERES data on EOS-AM. We would run the instrument after the EOS-AM CERES instrument is operational and only for the two or three day periods where the TRMM orbit swath and local time sampling is similar to that of EOS-AM CERES instrument in order to verify intercalibration (this allows optimal time/space/angle matching of the two data sets). This will allow extremely accurate ties of the TRMM data to the EOS-AM and PM data. Once we get sufficient overlap data to tie the relative calibration of EOS-AM and TRMM CERES instruments to one or two tenths of a percent, then we could operate the TRMM instrument continuously for as long as it lasts. Note that the current best RUMORED date for EOS-AM launch is probably Fall, 99, which would be two years after TRMM launch: with roughly 1.5 years of TRMM lifetime remaining before we run out of fuel to boost it in the low orbit altitude of 350 km. The reason that overlap is critical is that the CERES instruments calibration data within the first 8 months appear to be stable to 0.2% or better (all 3 channels). This indicates that rather like solar constant measurements: while you may not know the absolute accuracy to better than 0.5 to 1.0%, you can measure the month to month and year to year changes much more accurately: approaching 0.1 to 0.2%. We still need longer time series to prove this stability with the new CERES instruments, but results so far look like this is the conclusion we will reach with further data.
- We are checking the part lot numbers of the voltage converters in the other 5 CERES instruments on the ground. If movement of the silver conductive epoxy is indeed the problem, then it turns out that this process was changed about a year after the parts lot that was used in the TRMM CERES instrument. The change eliminates the non-conductive epoxy layer because the voltage manufacturer changed suppliers of the optical couplers, and the new optical couplers were lighter and did not need the mechanical support of a non-conductive epoxy layer below the coupler. Potential cost and schedule impacts of changing the voltage converters on the AM, PM, and FOO CERES instruments are being evaluated.
- We have looked at the data and in-orbit calibration data from August and it shows no sensitivity of the CERES radiometric data to the elevated voltage of the converter (it shouldn’t, but this has been confirmed).
- Bottom line: looks very encouraging so far for continued CERES operations throughout the TRMM lifetime, but the acid test will be the results of the 6 days of operation starting October 13. A good target for deciding to restart routine science operations would seem to be to restart routine data collection on Nov. 1 or Dec 1 depending on the results of the 6-day test. Note that if we miss Sept/Oct/Nov data, that we have basically missed one season of climate data. Fortunately the El Niño event was captured by the first 8 months of data.
- Initial Activation and Evaluation Checkout Plan – dtd 10/10/98 – (Prepared by P. Hess and B. Weaver) – PDF
- Instrument Restart Status – dtd 10/13/98 – (Bruce A. Wielicki)
Yesterday at 8pm EST the CERES instrument was powered back up. Greg Stover of the CERES instrument team just called from GSFC where a joint LaRC/GSFC team are monitoring the instrument operations and real-time data as the instrument warms back up to operational temperatures.
- So far the instrument appears to be operating nominally and the DAA +15V volt converter is still holding at its nominal value of 15V. This is now an exciting game of watching the instrument temperature rise and monitoring the response of the converter. Recall from my earlier email that we have found DAA +15 Voltage = 15 + 0.6 (T-Tmin)
- Over the month of August, Tmin dropped from 20.7C to 17.2C, or 3.5C in one month (linear with time). It leveled off near 17.2C the last four days of August. If this trend of 3.5C drop every 4 weeks had continued through Sept into mid-October, then we would predict that Tmin would now have dropped to around 12C.
- The temperature value most closely correlated with the DAA voltage is the MAM baffle temperature. Unfortunately, this temperature is not part of the real-time housekeeping data that we can monitor at GSFC or LaRC: we have to get it off the telemetry data tapes. The GSFC TRMM spacecraft operations group and the LaRC DAAC have done a great job of turning those data around quickly, so we only have about a 6 hour delay in getting the MAM temperature. As of roughly 2am EST the MAM temperature had risen to 11.4C, and was expected from earlier thermal modeling to be near 17C by 9am EST.
- There is an additional temperature that is typically reasonably close to the MAM value, that is reported in the real time data. By 9am this temperature had risen to about 17C and we still had seen no rise in the DAA +15V output voltage. By early this afternoon we should have the actual MAM temperatures and can confirm the relationship.
- So far, it looks like there has been no further degradation of the DAA +15V converter past that seen at the end of August.
- Status as of October 14, 1998 – (Bruce A. Wielicki and Phil Hess)
- The MAM Assembly temperature rose to a peak of about 17.1C. The start of the DAA +15 volt converter’s sensitivity to temperature occurred at about 16.4C. The voltage followed the MAM Assembly temperature above this minimum level with the same sensitivity seen in August data. The current Tmin value is about 0.8C lower than seen at the end of August, and indicates some further degradation of the DAA +15V converter, but only about 14% of the degradation rate seen through most of August. This again indicates that the degradation of the converter has slowed greatly from that experienced in August (roughly a drop of 0.13C per day in Tmin from Aug 3 to Aug 29).
- Tommorrow the instrument will be operated in a higher temperature orientation (greater sunlight incident on the DAA electronics box) and we expect roughly 2C higher temperatures to be reached. Voltages are expected to still be well below our new limit of 18V. Given today’s data and an expected 2C rise in MAM assembly temperatures, we might see maximum voltages of around 16.6V. The instrument is now set to go to safe mode if the voltage exceeds 18V, even during periods when the spacecraft is not in direct communication with the operations center.
- Over the next 6 days the instrument will be operated in a variety of modes designed to isolate the impacts of individual instrument functions (elevation scan motor, azimuth scan motor, SWICS calibration lamp, etc), culminating with the full RAPS scanning mode on day 6 of the test. The tests will include 2 calibration sequences to verify the calibration stability over the last 6 weeks.
- This next 6 days should also help to determine if further degradation in Tmin during instrument operation occurs in Tmin at the rate of 0.13C/day (August) or closer to the 0.02C/day since then.
- The latest quick-look data for the last three orbits have revealed that the DAA+15-volt converter is now starting to show expected variations. Some observations: (provided by Phil Hess)
- The voltage is essentually following the MAM TOT Assy temperature cycle as has occurred prior to the September 1 shutdown.
- The start of the voltage variations (i.e., “lose” regulation) for each of the three orbital temperature peaks occurred as the MAM TOT Assy temperature increased through ~16.5 degrees C. The end of the voltage variation cycle (i.e., “regain” regulation) occur as the temperature drops below ~16.4 degrees C.
- Some approximate peak data values for these three orbits (time is GMT):
Time DAA+15-volt MAM Temperature 13:06 15.09 16.7 14:37 15.37 17.1 16:08 15.39 17.1 - There is a noticable positive “jump” of ~0.1 volts at sunrise (coincident with a “sharp” ECA Radiator Temperature peak). This seems to be in the opposite direction that we’ve seen prior to September shutdown. (There the “jump” was in the negative direction, not the positive direction.) We’ll be looking into this in further detailed, so I wouldn’t want to draw any conclusions about this just yet.
- Based on the MAM data, it would suggest that the diurnal peak has passed. We will know when the next quick-look data arrive.
- Status as of October 15, 1998 – (Bruce A. Wielicki)
Here is the latest after almost 2 days of operation:
- We reached a peak voltage of 16.4V today, similar to the anticipated maximum of 16.6V mentioned yesterday. The relationship of the MAM assembly temperature to the DAA +15V converter voltage is now starting more stringent statistical analysis to assure a consistent analysis method of August and October data, as well as placing confidence limits on the Tlim analysis. Note that yesterday’s reports were based on eyeball analysis of quick-look plots. The MAM Assembly temperature for a given DAA +15V temperature can vary by 0.3C depending on time of day and whether the instrument is heating up or cooling down. This adds some uncertainty to the analysis of Tmin for any short time interval, so this will be studied closely over the next several days. As mentioned earlier, there is also a desire to look for sensitivity to scan motors and the SWICS lamp as power draws on the system.
- CERES Weekly Status Report – dtd 10/16/98 – (Compiled by Leonard Kopia)
PROTO-FLIGHT MODEL CONVERTER TIGER TEAM CONTINUES INVESTIGATION —
- Operational power was restored to the Clouds and the Earth’s Radiant Energy System (CERES) Proto-Flight Model (PFM) instrument aboard the Tropical Rainfall Measuring Mission (TRMM) spacecraft on October 13. A series of specific instrument commands was scheduled over the next six days to obtain temperature and converter voltage information to assess converter operational characteristics. During this time, the converter voltage was observed to rise steadily with temperature, and power was removed at approximately 5:00 AM EDT on October 18, 1998. The TRMM telemetry monitor designed to place CERES in the safe mode (elevation head stowed, azimuth brake applied) and remove operational power was automatically triggered after the Data Acquisition Assembly (DAA) +15 Volt converter exceeded a predefined limit of 18.0 Volts. The 18.0-Volt limit was chosen in order to provide operating margins for components downstream of the voltage converter. This action occurred after approximately 4.5 days of instrument operation This operational time provided valuable data that will be used by the CERES Tiger Team in determining the status of the voltage converter (degradation rates and sensitivity) and will aid in planning for future operations to restore the instrument to a science operations mode.
- An analysis of the internal calibrations conducted on October 17 indicates that the radiometric gains of the three channels have not changed. There is also no indication that there has been any drift in radiometric performance over the first 10 months of mission life.
- CERES Operational Power Removed – dtd 10/18/98 – (Greg Stover)
- Operational power for the Clouds and the Earth’s Radiant Energy System (CERES) Proto-Flight Model (PFM) instrument aboard the Tropical Rainfall Measuring Mission (TRMM) spacecraft was removed at approximately 5:00 AM EDT October 18, 1998. A TRMM telemetry monitor designed to place CERES in the safe mode (elevation head stowed, azimuth brake applied) and remove operational power was triggered after the Data Acquisition Assembly (DAA) +15 Volt converter exceeded a predefined limit of 18.0 Volts. The 18.0-Volt limit was chosen in order to provide operating margins for components downstream of the voltage converter.
- This action occurred after approximately 4.5 days of instrument operations in various modes designed to collect data for engineering assessments. This operational time provided valuable data that will be used by the CERES Tiger Team in determining the status of the voltage converter (degradation rates and sensitivity) and will aid in planning for future operations to restore the instrument to a science operations mode.
- CERES Weekly Status Report – dtd 10/27/98 – (Compiled by Leonard Kopia)
PROTO-FLIGHT MODEL CONVERTER TIGER TEAM CONTINUES INVESTIGATION —
- The Tiger Team investigating the converter anomaly observed on the Clouds and the Earth’s Radiant Energy System (CERES) Proto-Flight Model (PFM) on board the Tropical Rainfall Measuring Mission (TRMM) continues in its attempt to isolate the root cause. Data from the interim turn-on (October 13-18) indicates that the onset of unregulated converter operation occurred at a lower temperature than that which occurred on September 1 (the last powered operation of the instrument). This suggests a degradation has occurred over the time that the instrument was off (approximately 40 days). The instrument will be powered up once again in early November to place the instrument in a protected position to minimize any detrimental effects from passing through the Leonid shower in mid-November. Data from that operational sequence will be used to confirm degradation rates for the converter and provide information for future operational scenarios.
- No specific cause for the converter anomaly has yet been determined but several possibilities are being considered seriously. The strongest possibilities include: deterioration of the feedback opto-coupler, including possible electrical and physical changes of the bonding material used to hold it in place; and, a possible cracked resistor in the gain control loop which has become thermally dependant and is degrading. Other lesser possibilities also exist and are being thoroughly examined for their relevance.
- Status as of October 28, 1998 – (Bruce A. Wielicki)
The Good News:
- As reported earlier, there was only a small degradation of the +15V DAA voltage converter during the 6 weeks the instrument was turned off: roughly September 1 – October 13. If the degradation was due to radiation exposure in space, then that damage should continue independent of the instrument operation, and the small degradation over the 6 weeks would have indicated approach of an asymptotic limit: similar to radiation damage over time of optical components. However, upon restoring operational power, it was observed the degradation continued at a greater rate than when powered off, therefore the asymptotic point for the degradation has not been reached. More information concerning the degradation is given below.
- An internal calibration was performed during October and showed that the calibration of the CERES instrument remains unchanged (at the 0.2% noise level of an individual internal calibration). In analysis of the August and October data we see no evidence of radiometric changes in the instrument at the higher voltage levels of the DAA +15V.
- The instrument operated normally in a wide range of test modes until the orbit geometry increased temperatures and voltage on the DAA +15V to a level of 18V where the instrument automatically went into safe mode and operational power was removed. This automatic turn off of the instrument at a prescribed voltage was a new operation programmed into the TRMM on-orbit computer system and worked as planned. The power down occurred on day 5 of the test period.
- If the voltage converter becomes totally deregulated, then it will pass roughly 23 to 29V (caused by variations in spacecraft bus voltage) to the 7 electronics components supplied by the converter. All of these components are currently under test at 30V. The component thought to be most sensitive, the analog to digital converter has been successfully run at 30V for roughly 4 weeks so far and that test will continue. Two entire sets of the 7 electrical components have also begun a long-term test and have operated successfully at 30V for 1 to 2 weeks. A third set of components may also enter the test if sufficient spare parts at TRW are available. It is not considered meaningful to test electrical components that are not from the same manufacturing lot.
Now the Bad News:
- There is evidence from the 5 day test that the voltage converter may continue to degrade at the rate seen in August when the instrument is operated. Further analysis is needed to tighten up the relationship of voltage to temperature in order to get more accurate determination of the minimum temperature of the converter sensitivity and its time history. Work is also underway to theoretically model the converter physics and simulate the behavior seen so far. If in fact the degradation continues at the August rate for every day of further instrument operation, then the voltage converter may become completely deregulated in roughly 100 days of instrument operation. Total lifetime of the instrument would then depend on how long the 7 electrical components could last at 23-29V instead of the designed 15V. From data so far, there do not appear to be any calibration changes at elevated voltages, so the concern is instrument lifetime and maximizing the science return.
What are the Candidates to Explain the Problem?
- The Tiger team is focusing on two primary candidates:
- migration of conducting silver across an insulating epoxy layer, thereby causing a short in an LED, and
- a cracked resistor that is degrading with thermal cycling.
- Both of these potential problems can affect the voltage converter’s output regulation feedback mechanism. Modeling studies are underway to test which hypothesis better explains the data.
What about the other CERES instruments for EOS-AM and PM?
- The current plan is for the EOS-AM and PM instruments to have the voltage converters replaced. Newer versions of these voltage converters eliminate the insulating epoxy layer, and would eliminate any problems with silver migration. If the problem is a cracked resistor, it is a random part failure, and as such is rare and cannot be predicted. Note that this is only the second of roughly 6000 of these parts to show an anomaly.
What about overlap of the CERES data record with SCARAB and the EOS-AM CERES instruments?
- SCARAB is now starting to get some data on the Russian RESOURC platform in a morning sunsynch orbit. Once they are routinely gathering data, we will pick a period of 1 or 2 days when the TRMM local time of day at the equator nearly matches that of SCARAB (10 am), align the CERES scan plane with the SCARAB scan plane (the orbital inclinations are very different) in order to maximize the intercalibration opportunities with matched time, space, solar zenith, and viewing zenith/azimuth.
- We will make sure that we can get overlap of the TRMM CERES instrument with EOS-AM. What this means for the future operational schedule of the instrument depends on the results of the Tiger team studies, and on the experience with running the 7 electrical components for longer time periods at 30V.
What about the upcoming meteor shower in mid-November?
- The instrument will be placed in the stowed position.
- CERES Weekly Status Report – dtd 11/03/98 – (Compiled by Leonard Kopia)
EFFORT ON CONVERTER ANOMALY DETERMINATION CONTINUES —
- The investigation into the cause of the +15 volt converter anomaly on the Clouds and the Earth’s Radiant Energy System (CERES) Proto-Flight Model (PFM) continues. The overvoltage tests at TRW on the downstream circuit components have been underway for several weeks. To date, no detrimental effects on the components have been observed in this elevated voltage condition. A set of tests is also underway on the converters using external leads which have been connected to specific circuit attachment points. A limited series of tests under varying temperature conditions has been conducted to try and simulate hypothesized failure conditions on the converter but has not duplicated the anomaly as yet. Because components in the converter package are so highly integrated, lead attachment requires great care since there exists a distinct possibility of damaging adjacent connections and components. This fact limits the nature of the tests which can be conducted. Since a definitive cause of the anomaly has not yet been determined, it has been assumed that a latent failure mode exists on all converters, and a plan is in place to replace converters on all instruments. The replacements, which are from a more recent lot date code, contain a manufacturers process change which eliminates one of the more highly suspected, but as yet unverified, causes of the anomaly. A back-up plan is in place should there be delivery problems with the replacement parts for Flight Models 1 and 2. Additional units are on order and will be available at a later date for Flight Models 3 though 5.
- Plans are in process to turn the PFM instrument on again in mid-November to gain additional information on degradation rates from which a better basis of lifetime prediction may be formed.
- CERES PFM Instrument Operations Status – dtd 11/06/98 – Greg Stover
After review of information concerning the Leonid meteor storm composition, and of the analysis provided concerning the storm’s direction with respect to the CERES instrument, a decision has been made to leave the CERES instrument in its current state. At this time, the instrument is at an azimuth position of 216 degrees, the elevation head is stowed, and all operational power is removed.
Furthermore, it has also been concluded it is not necessary to conduct special test sequences for the purposes of collecting additional engineering data. This data will be collected coincident with the periods when the instrument is operated specifically to fulfill science team objectives. Therefore future operations will primarily be scheduled based on science collection periods with consideration for safe instrument operations.
At this time the CERES science team is reviewing the next time when science data will be collected. It is currently anticipated this period of CERES operations will occur in December.
- Status as of December 21, 1998 – (Bruce A. Wielicki)
Here is an update of our current understanding of the impact of the voltage converter anomaly on the CERES instrument on TRMM.
- Ground tests are now through 3 months of testing on the potentially more sensitive A/D converter and are through 2 months of testing on two sets of the 7 components powered by the anomalous converter. All tests are being conducted at 30V, while the expected range of converter output voltage is 23-29V to these parts when the voltage converter completely loses regulation. This indicates that it is unlikely that the higher voltage level will degrade the data or lifetime of the instrument.
- It has been determined from analysis of the August data (initial degradation) and the 5 day test in mid-October, that:
- the calibration and radiometric performance of the CERES instrument is not affected by the higher than normal output voltage of the converter (as expected).
- the voltage output of the converter is expected to continue to degrade with additional operation. The instrument only monitors this converter output voltage up to 20V, while total deregulation implies voltages as high as 29V. From data taken to date, we anticipate crossing the 20V level in roughly 10-30 days of further operation. The length of time depends on whether further degradation takes place linearly in time: which cannot be assured.
- Ground testing has, however, identified a risk to the lifetime of the instrument once the converter has lost the ability to regulate its output voltage. Once in an unregulated state, if voltage input to the converter drops to zero, and then later is restored, the inrush of current into a capacitor in the converter may be sufficient to melt leads: leaving an open circuit, and terminating the life of the CERES instrument. Power has been removed from the CERES instrument once during the TRMM mission, and while the cause of this inadvertent shutdown of the CERES instrument by the spacecraft has since been fixed, it remains true that the default method to “safe” or shutdown the spacecraft is to remove power (voltage) to all of the instruments. The past occurrence of power loss to the CERES instrument was early in the TRMM mission when the spacecraft inadvertently switched to this “safe” mode. Since CERES is a very small part of the TRMM spacecraft power budget, we will request the TRMM project to change the “safe” procedure for future operations such that they switch CERES to a standown mode with minimum power instead of turning the instrument off. In this case, there would be no additional risk to the CERES instrument, even with the voltage regulator in an uncontrolled state. This change would probably require modifying the spacecraft software and the impact/risk is being assessed by the TRMM project. We expect to know more on this critical issue in January.
- We currently plan to turn on the CERES instrument for 2 days in mid-January to perform an intercalibration between CERES and the SCARAB radiation budget instrument on the Russian RESOURC satellite. Starting in mid-November 1998, SCARAB has been collecting 4 days (Mon through Thursday) out of every week of data (limitations at the Russian downlink station) but hopes to increase this to 100% in the future. Therefore, we should have some broadband measurements during the peak of LaNina currently expected for Dec/Jan. La Nina is then predicted to disappear by Summer, 1999. CERES is planning to perform 2-day intercalibrations of CERES/SCARAB every 1-3 months until the CERES EOS-AM instrument is operating, at which time we will turn on the TRMM CERES instrument and leave it running indefinitely. The number of the calibrations done depends on the experience we gain in analyzing the January test, and in the amount of further degradation of the voltage converter compared to instrument test performed in mid-October.
- We plan to replace the voltage converters on the EOS-AM and PM CERES instruments. The suspect optical coupler and its mounting method were both changed in the design of this converter several years ago and the current parts are not susceptible to this potential failure mode.
- The final report of the tiger team is expected late January.
- Given the above scenario, what are some of the CERES science objectives that will not be affected, and which science objectives will be impacted by the probable loss of data from Sept 1998 through Aug 1998?
- No loss of 1998 El Niño tropical data: captured the El Niño peak in Jan through March 1998 as well as the decay through July, 1998.
- No loss of stable calibration/continuity for global change long-term climate record: CERES calibration unaffected by voltage converter degradation and overlap with EOS-AM CERES instruments will establish calibration continuity to ~ 0.1%.
- No loss of optimal multiple satellite data because of delay in EOS-AM launch to summer,1999. Multiple satellite CERES data is more accurate than single satellite data, and is more useful for shorter time scale studies (daily to seasonal scale).
- Reduced accuracy (~ factor of 2) for La Nina tropical data: SCARAB began routine data collection November 16, 1998 and will cover the rest of the gap through EOS-AM. Accuracy reduction is one satellite (SCARAB on RESOURC) versus two satellites (TRMM + RESOURC) for diurnal sampling. Other accuracy issue is whether SCARAB can increase sampling from 4 days out of 7 (ground station limitation).
- Delays by 1 year, the new CERES angular models required to obtain a factor of 3 to 4 improvement in TOA flux accuracy, and therefore delays the expected improved constraints on surface and atmosphere radiative fluxes.
- Lost year of data degrades statistical accuracy of final CERES angular models by sqrt(1/3.5) = 15%. This assumes the VIRS instrument performs nominally through the expected 3.5 year TRMM mission lifetime.
- Lose overlap with two field experiments planned for spring 1998: Nauru99, and INDOEX. Radiation data for these experiments will be provided by SCARAB.
- Note that the scientific impacts listed assume:
- EOS-AM launch by July 30, 1999, CERES TRMM turn on Sept 1, 1999 to match the turn on of the CERES instruments on EOS-AM (30-day outgassing period).
- CERES intercalibration with SCARAB is successful using 1.5 day periods every 23 or 46 days from January through August, 1999.
- TRMM spacecraft can change the spacecraft “safing” procedure to turn the CERES instrument to its reduced power “safe” mode instead of removing power to the CERES instrument.
Graphs
- DAA+15V Output Anomaly Onset on 7/31/98
- DAA+15V Output Anomaly on 8/31/98
- DAA+15V Daily Statistical Trends (7/1/98 to 10/18/98)
- MAM Temperature Threshold where DAA+15V Unregulation Onset Occurs
- DAA+15V, MAM Temperature Data for October Checkout 10/14-18/98
For information on TRMM Mission: TRMM Mission
TRMM Quick-Look Results
These pictures show examples of the first measurements that CERES has made. We use data products such as these to validate the accuracy of our Earth energy estimates. As we gain confidence in the proper operation of the instrument and the data interpretation algorithms, the science data products will be archived at the Atmospheric Science Data Center
Contributions to these pages are welcome.
TRMM Pictures
