--Sandra Smalleysesmalley@larc.nasa.gov,
NASA Langley Research Center
On June 11 & 12, a Science Team Meeting for the Stratospheric Aerosol and Gas Experiment (SAGE) III was conducted at Hampton University. The meeting was hosted by the project Principal Investigator (PI), M. Patrick McCormick. The meeting primarily focused on validation planning for SAGE III. Status briefings were also given for the program, project, instrument, mission operations, and software development.
Jack Kaye, NASA Headquarters (HQ) Program Scientist, gave an overview, including broader issues relating to Mission to Planet Earth (MTPE) and the Earth Observing System (EOS). A major focus of his talk was a focused review of MTPE's atmospheric chemistry program that was established as one of two areas of emphasis (along with EOSDIS) for a broader biennial review of MTPE's programs.
The Atmospheric Chemistry Review Panel was chaired by Michael Prather of the University of California at Irvine. SAGE-related panel members included Lamont Poole, head of the Aerosol Research Branch at the NASA Langley Research Center (LaRC), Steven Wofsy of Harvard University, who is a member of the SAGE II and SAGE III Science Teams, and O. Brian Toon of the University of Colorado, who is a member of the SAGE II Science Team. Wofsy also served as a member of the panel for the larger biennial review, in addition to his service as Chair of MTPE's Earth System Science and Applications Advisory Committee. The two questions that the chemistry review panel was asked to address most closely were the current instrument complement and planned architecture for the EOS CHEM satellite mission, and the balance of resources between space-based measurements (and associated ground systems) and research and analysis (R&A) activities.
Among the conclusions of the Atmospheric Chemistry Review Panel of most interest to SAGE were a strong endorsement of the current EOS CHEM instruments and plans for their flight on a single spacecraft; concerns that the funding decline for R&A science be halted and funds preferentially restored to allow for increased scientific activities in the area of atmospheric chemistry; and improved coordination between the EOS project and R&A, especially in the area of calibration/validation for EOS sensors. They also expressed extreme concern about the current manifest plans for SAGE, noting that the next inclined orbit for SAGE was planned for the International Space Station (ISS) in 2002, and that ISS has limitations as a platform due to lost viewing opportunities during Shuttle visits, etc. The panel strongly endorsed exploring the possibility of MTPE's finding an early inclined orbit for the third SAGE III instrument, for which no flight opportunity has yet been identified.
Kaye noted that some 270 proposals had been received at NASA HQ in response to the NASA Research Announcement (NRA) soliciting proposals for EOS calibration and validation. Approximately 40 of these were in the areas of atmospheric chemistry (covering MOPITT and/or SAGE). A panel review for all the proposals was to be held in July. The NRA for Kaye's Atmospheric Chemistry Modeling and Analysis Program (ACMAP) was open, with proposals due August 15; the NRA may be found on the World Wide Web.
Kaye also reported on his activities associated with the Integrated Global Observing Strategy (IGOS) being organized in part under the auspices of the Committee on Earth Observing Satellites (CEOS). Kaye was asked to co-lead an activity on "Long-term continuity of ozone measurements" in conjunction with Chris Readings of the European Space Agency (ESA). A two-page activity description had been prepared this spring, and the group's activity will be kicked off this summer as part of a CEOS Analysis Group meeting in Tokyo, Japan.
The status of the EOS program was briefly summarized by Kaye. He considers it likely that there will be a major change in the EOS program away from the original concept of multiple copies of each instrument to provide 15 years of continuous data. The new paradigm for implementing the second series of EOS missions is to treat the required observations in two groups: Process Understanding Observations and Long-Term Systematic Observations. The intent is to solicit and select the Process Understanding Observations through a mechanism such as that used for the Earth System Science Pathfinder (ESSP) program. NASA intends also to obtain the Long-Term Systematic Observations through open solicitation, but with an emphasis on domestic and international partnerships. In both cases, the emphasis will be on small missions requiring short development cycles of no more than 3 years from the time of selection of each mission.
Shahid Habib, the SAGE III Program Integration Manager (PIM), followed Kaye's discussion with a status report on MTPE. He reiterated that the program is going through a Biennial Review where the focus is placed on a new way of doing business. In other words, future missions will rely on smaller instruments, a faster development process, smaller spacecraft, and a more-efficient project life cycle. The paradigm shift is driven by a more-lean budget, and a need to infuse state-of-the-art technologies. The results of the Biennial Review will establish a new baseline for future missions slated for flight after the year 2000. Another area being evaluated is NASA's involvement in future missions in terms of project management. For example, the ESSP mission may provide some insight as to how effectively a PI-mode program will run with minimal involvement from NASA. In spite of these changes, MTPE as a whole is very healthy and doing well. Habib also provided an overview of the Flight of Opportunity (FOO) status resulting from a series of meetings with the Russian Space Agency (RSA). Three possibilities for the flight of the FOO were identified: 1) a mid-inclination orbit in 1999, 2) a joint SAGE/TOMS/Meteor in Aug 2000 in a 1030 sun-synchronous orbit, and 3) a TBD sun-synchronous orbit after 2000. Habib is also discussing possible flight opportunities with countries other than Russia, including Brazil. In addition to SAGE, Habib is responsible for the TOMS, Chemistry, and New Millennium Earth Orbiting-1 missions.
L. Edward Mauldin, SAGE III Project Manager, presented the SAGE III project status. The tenth Technical Interchange Meeting (TIM) was held in Moscow May 19-23. The Russians are still preparing for an August 1998 launch. The next TIM is scheduled for September and will be critical to ensure convergence of the various elements as the launch date approaches. Mauldin expressed concern with the Ukrainian rocket failure on May 20. Investigations were in progress during the science team meeting and preliminary analysis pointed to a software problem. The contingency plan includes utilization of a military Zenit rocket. Contamination control had been a project concern, but the three facilities in the Ukraine were found to be very clean. Successful execution of a tight spacecraft and instrument development schedule is critical to meet launch in August 1998. Mauldin stated that the project was well within budget but the schedule is tight. As of June, RSA had not signed a Zenit rocket fabrication contract, but money had been appropriated. Mauldin also provided an overview of instrument changes on the Meteor spacecraft.
With respect to the ISS instrument, launch has been delayed to January 2002. An ISS payload TIM was held at Kennedy Space Center (KSC) in May. During this TIM, informal agreements were reached on all major ISS issues except providing power to the Shuttle bay. Mauldin also mentioned that the NASA/ESA Early Utilization Agreement has been signed and the Hexapod is now in phase C/D with a Preliminary Design Review (PDR) planned later this year. The Interface Design Specifications (IDS), which identify all requirements to Ball Aerospace, ISS, and ESA were published. This was critical because Ball will be delivering the instrument prior to baseline of the ISS Interface Control Documents (ICD).
Regarding the FOO mission, Mauldin stated that NASA HQ rejected the SPOT 5 proposal with the French because it ran counter to a no-exchange-of-funds policy between the U.S. and other countries. The fact that the FOO mission had not been identified is a major concern from two aspects: (1) HQ funding issues, and (2) Ball's contract expiration prior to identification of FOO mission requirements.
SAGE is also sponsoring two outreach programs (education and business), which support the outreach goals identified during the latest Gore-Chernomyrdin Commission agreement. Mauldin asked the science team to recommend SAGE III-related experiments for potential use in the educational outreach program with a current target student age of 10-12 years. The SAGE business outreach program links the Hampton Roads business community with the Russian manufacturing community in Istra.
Obie Bradley, SAGE III Instrument Manager, provided the status of the instrument and test schedule. Specifically, Bradley discussed the instrument electronics, pointing system, spectrometer telescope, flight software, and detectors. Many subsystems have been completed and are in testing. Several problems have been identified, including difficulty bonding to the thermal electric coolers and detector problems. The Charge Coupled Device (CCD) detector problems including serial leakage from the parallel registers and from bulk silicon at the segment breaks, and red leakage were identified during testing with the test model spectrometer/telescope. Also, there have been 3 failures due to electrostatic discharge (ESD) to date. Handling methods have been modified to avoid ESD-related damage. Several options are being considered to reduce the leakage effects.
Joe Zawodny, LaRC co-investigator, continued the detector failure discussion with a presentation on science impact. As designed, the CCD cannot meet the 0.02 % out-of-band rejection specification. Ball Aerospace provided data on the serial and parallel leakage. Zawodny compared scattered light to desirable light (wing to core) and found the ratio of "bad" to "good" data to be 1.4% at 850 nm or 50 times specification. At 950 nm the ratio was close to 6%. It was found that you would have to go 100 pixels from line center at 850 nm to reach specifications. At 950 nm it was found to be over 150 pixels. The detector was deemed unacceptable, based on Zawodny's evaluation. A significant amount of light comes from pixels as far away as 150 nm in the 900- to -1000-nm spectral region. Measurements of aerosol at 1020 nm and water vapor are, therefore, interdependent and both must be considered simultaneously in the retrieval. There is also the possibility that species which SAGE III does not measure (such as CO2 and CH4) may also need to be modeled in the data reduction. In response to the question inquiring why this problem cannot be corrected via the algorithm, it was stated that monitoring of the effective spectral band passes could be accomplished on the ground but not in flight. Therefore, the calibration could not be maintained in the long term.
Advanced Camera has also experienced and investigated similar leakage problems since their CCDs were produced on the same wafer as the SAGE III CCDs.
Advanced Camera moved the gold layer from the bottom of the substrate to between the glass and silicon. Their performance improved significantly except at 1 micrometer (where the gold layer may not be thick enough to prevent tunneling). The transparency of silicon in the infrared and the "soda-like" glass on which the detector was mounted were found to be the problem. When the gold was removed from the back of the SAGE detector and re-coated with black, a factor of ten improvement (as determined by Ball Aerospace) was observed, which still did not meet specifications. An additional factor of ten was anticipated from the detector slotting option. Etaloning effects remain a concern. Zawodny speculated that the etaloning effects could be used for cloud detection. The response was that these effects need to be carefully characterized and understood. The impact on lunar occultation was not considered to be at risk because neither the red leak nor the etaloning occurred at wavelengths less than 700 nm. Questions were asked about the impact on solar occultation ozone measurements.
Zawodny developed a revised specification table with extra science channels to measure ozone using differential absorption. The Project Office has been working on a contract incentive to demonstrate/implement the revised table. The red leakage problem is exacerbated if the modified table is not implemented. The possibility of masking all pixels that aren't being used was evaluated but is in conflict with the calibration specification, which is dependent on using Fraunhofer lines. With regard to the GSFC alternate detector solution, dark current may be a potential problem. Detector contingency plans continue to be worked, and the scientific impact will continue to be evaluated as data become available.
Herb Mott, a SAGE Mission Operations Specialist, provided an update on the status of the SAGE III mission operations. The Joint Mission Operations Plan was reviewed during TIM #10, with anticipated signing during the upcoming TIM in September. An extensive review of the detailed command exchange protocol was performed. The Russian GLONASS definitive solution matches the U.S. GPS definitive solution, using simulated data. The U.S. and GLONASS solutions will be compared regularly during the mission for validation. Nominal data exchange occurs between NASA LaRC, Central Aerological Observatory (CAO)/Dolgoprudny, and MCC-M. CAO/Dolgoprudny will now manage the link of the science and raw data exchanges between LaRC/CAO/NPO. The command station memory storage and transmission rates are still open issues.
Mary Osborn gave an overview presentation on the SAGE III science software development, development resources, processing strategy, and data archiving activities. The objective of Phase A was to design and write the software that will produce the SAGE III Level 1B data products (transmission profiles). Phase A software was ready for integration and testing at the Distributed Active Archive Center (DAAC) in late June. During Phase B, retrieval software for producing Level 2 solar and lunar products will be designed and written, and supporting databases (spectroscopy, meteorological, etc.) used in the data processing will be developed. During post-launch activities, instrument calibration (CCD wavelength registration and mirror calibration) will be performed, and the Level 1B and 2 data products will be distributed to the science team via the world wide web. The transmission algorithm, retrieval algorithm, and data production procedures were outlined, and the software development schedule was provided.
The SAGE III Algorithm Theoretical Basis Document (ATBD) panel review was held on March 12-13. McCormick provided a summary of this review process. Chu, the SAGE III associate PI, discussed the critiques. A formal response to the panel critique is being prepared. In general, the SAGE III oral review was a resounding success!
Chip Trepte led a discussion on Meteor/SAGE III validation requirements and correlative measurement plans. The discussion began with a listing of the major validation needs and sampling constraints. Besides acquiring correlative measurements for each science product near the location of SAGE III occultation, the science team identified a need to verify the altitude registration of transmission profiles to <100 m. Further discussion ensued on the need to acquire correlative measurements of known accuracy and precision, sampling representativeness, and completeness for validation. It was recognized that for many of the SAGE products (e.g., aerosol extinction) such an approach was difficult without standard procedures. For these products validation would, instead, be more of an intercomparison activity.
A correlative measurement strategy was outlined that consisted of three components: (1) leveraging upon measurements from on-going ground-based observational activities; (2) intercomparisons with concurrent satellite programs; and (3) use of supplemental airborne measurement campaigns to satisfy additional measurement needs. The first part of the strategy has low risk and takes advantage of operational and international measurement programs, such as the World Meteorological Organization (WMO) and the Network for Detection of Stratospheric Change (NDSC), by coordinating satellite occultation events with these sites. Both the Lauder, NZ, and the arctic NDSC stations were identified as being anchor sites for early validation activities. A number of remote sensing measurements from these locations would provide early feedback on the retrieval products. Mohnen and Trepte will oversee coordination of the WMO ozonesonde network with SAGE activities. Brogniez will help coordinate valuable European balloon activities during the Third European Stratospheric Experiment on Ozone (THESO) campaign (1999) with SAGE III overpasses.
A listing of concurrent satellite missions was also presented that showed more than 5 missions that may be available for intercomparisons. Most of the meeting, however, centered around prioritizing measurement activities and discussing the airborne correlative measurement campaign in the fall of 1998. Because correlative measurements are needed within 90 days of the operation of SAGE III, a strawman airborne mission based from Fairbanks, Alaska, was presented to meet this requirement. For this mission, emphasis is placed on acquiring measurements of stratospheric ozone and aerosol.
Trepte announced that a meeting was scheduled in August for coordinating SAGE III validation with NASA's Upper Atmospheric Research Program. This program manages stratospheric chemistry research with the ER-2 and DC-8. The Program Manager, M. Kurylo, was interested in working together with SAGE and merging measurement objectives into a unified airborne campaign.
Andreas Herber, from the Alfred Wegener Institute (AWI) presented an overview of the validation sites at Svalbard. This site performs NDSC measurements targeting vertical profile and columnar measurements in an effort to gain a better understanding of stratospheric and tropospheric processes. Herber also presented details on a lidar instrument and their high-latitude stratospheric and tropospheric measurement facilities which have been used to measure two different types of polar stratospheric clouds (PSCs) within the past year. AWI has also been successful in intercomparing lidar results with backscatter sondes. Herber described the AWI microwave radiometer instrument developed by the University of Bremen. The microwave radiometer is used for ozone profiles, ClO, and other measurements. Good coincidence was observed in a comparison of microwave measurements to ozone profile measurements in February/March 97 as well as in the February/March comparison between the University of Wyoming and AWI ozonesondes. Details were also provided of the AWI sun photometer. They have been very successful with this instrument due to the extremely stable conditions in Svalbard, which simplifies the calibration process. Herber discussed the AWI star photometer and how it could be used in conjunction with lidar for a better vertical profile as another validation option.
Collette Brogniez, Laboratoire d'OptiqueAtmos-pherique (LOA), France, presented a European Validation proposal. The Europeans are planning a balloon campaign in late summer 1998 from Sweden to support Improved Limb Atmospheric Spectrometer (ILAS), Polar Ozone and Aerosol Measurement III (POAM III), SAGE III, and one in January-March, 1999 from THESEO. The balloons will cover altitudes from 12-30 km.
Nicolai Elansky, co-investigator, Russian Institute of Atmospheric Physics (IAP), presented the Russian validation activities of both the Central Aerological Observatory (CAO) and IAP. Elansky presented a slide of current WMO-Global Atmosphere Watch (GAW) validation stations as well as proposed future sites. Sites at Zhigansk and Yakutsk were used to measure total ozone and NO2. These were the only sites where regular ozonesondes were carried out in the winter and spring. Both sites registered the severe ozone depression above Siberia for March-April 1997. The total content of ozone decreased here up to 40% of the mean values. Measurements of total ozone and vertical profiles of O3 and NO2 are carried out at the Tomsk and Obninsk sites, using the Brewer spectrophotometer and lidars. Vertical profiles of ozone were made using microwave techniques in Nijniy Novgorod and Zvenigorod near Moscow. IAP was specifically responsible for the NO2 network that includes Kislovodsk, Murmansk, Tomsk, Zvenigorod, and Issyk-Kul sites. In September 1997 the NO2 instrument intercomparisons will take place at the Zvenigorod observatory. All Russian instruments will be compared with the reference spectrophotometer from the Lauder observatory. Elansky also presented the carriage-laboratory for atmospheric minor species measurements along the Trans Siberia Railway. Three Russian-German expeditions for gases and aerosol concentration measurements have been made in 1995-1997 between Moscow and Vladivostok. Some important features of O3, NO2, CH4, CO, and other compound distributions over the continent have been obtained. In spring 1997, the first vertical profiles of O3 and NO2 were measured from the carriage-laboratory in the ozone depression area above Siberia. These data show that a carriage-laboratory could be used effectively for SAGE III data validation. IAP is hosting an international conference to intercompare validation instruments in mid September
Volker Mohnen, co-investigator, SUNY Albany, gave a presentation intercomparing SAGE II vs. ozonesondes using the Eulerian intercomparison techniques and found the delta of 20-30 km to be well within specification. The most significant discrepancy occurred below 15 km. The following reasons were cited: (1) air masses associated with the two measurements were not correlated; and (2) ozonesondes are not as effective at these levels. For SAGE III the focus will be on the 8-16 - km range. Mohnen suggested ozone intercomparisons for SAGE III plus Lagrangian intercomparisons in the future for potential vorticity field measurements to enhance coincidence and reduce the meteorological variability. A comparison of SAGE with HALOE has been published in the July issue of JGR.
Mohnen suggested using the WMO-GAW/International Global Atmospheric Chemistry (IGAC)- Global Tropospheric Ozone Network (GLONET) validation approach, stating that the GAW measurements are of known quality. A permanent GAW facility for ozonesonde intercomparison and calibration is being established at Julich, Germany. Lidar is also used for ozonesonde intercomparisons. Discrepancies above 8 km may be corrected with Lagrangian techniques. Globally coordinated quality assurance for ozonesondes in support of SAGE III ozone validation could be based on WMO-GAW and IGAC-GLONET procedures, but would require funding.
Sasano, of the National Institute of Environmental Studies (NIES) Data Handling Facility (DHF) Earth Observing Center (EOC), introduced the planned ILAS activities and stated that data should be available to the public after May 1998. The instrument consists of two spectrometers (one visible and one infrared) and a sun-edge sensor. The instrument is on the ADEOS satellite in a sun-synchronous high-latitude polar orbit and is designed to measure ozone, ozone chemistry-related gases, aerosols, PSCs, and meteorological parameters, including temperature and pressure. The channels range between 6.2 and 11.8 micrometers. Unfortunately, the ADEOS spacecraft ceased operation in early June this year, after successful operation for eight months. The data processing algorithms used a transmission comparison, but plans were underway for a utilization of the tangent-height determination technique. Line-by-line calculations of the absorption spectrum were performed, the onion peeling method was used for vertical profiling, and a non-linear least square method was used for spectrum fitting. In the future, the ILAS II instrument will add a mid-infrared spectrometer for aerosol/PSCs and a narrow band spectrometer for OClO and NO2. ILAS II is scheduled for a 1999 launch with a 5-year life expectancy.
Patrick Hamill, Professor of Physics at San Jose State University, presented a proposal for a cooperative SAGE III/Global Ozone Monitoring Experiment (GOME) mission to capitalize on the synergies between these instruments if operated on the same satellite in a near-equatorial orbit. Hamill has been working with Giorgio Fiocco at the Universita di Roma. Hamill gave an overview of the GOME capabilities, the scientific rationale, the synergisms between the instruments, and other considerations. He explained that GOME is a nadar-viewing instrument that measures light scattered from the atmosphere between 240 and 790 nm, using a differential optical absorption spectrometer to determine total column ozone, trace gases, and aerosols. It is a scaled-down version of the Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) instrument. Profiles are determined by using the temperature dependence of the Huggins band. The sun and moon are used for radiometric calibration. GOME is scheduled to fly on the ERS-2 satellite and operate in three different modes to measure the following species: 03, NO, NO2, BrO, H2O, O2-O4, and aerosols. Hamill cited interest in the equatorial region and SAGE/GOME synergisms as the scientific justification for a two-instrument/two-satellite mission. Coverage would be limited to the tropics but that coverage would be very detailed. The tropical region is of interest because of such phenomena as volcanoes, which are a source of stratospheric sulfate particles, and because it is a reservoir for tropical aerosols, has interesting dynamics and cloud cover, has biomass burning, and has cloud absorption anomalies.
Vin Saxena, North Carolina State University co-investigator, and John Anderson, also from North Carolina State University, presented proposed SAGE III investigations to: (1) retrieve aerosol microphysical characteristics down to 6 km from a shape-constraint-free algorithm for use as a correlative measurement during validation; (2) determine the aerosol optical depths and associated UV-B transmission at southern and northern latitudes during the validation/correlative phase in cooperation with John DeLuisi; and (3) delineate the presence and transport of lower tropospheric aerosols such as arctic haze. Anderson also provided an outline of the RMST (Randomized Minimization Search Technique) along with preliminary results of retrievals with synthetic test data.
Colette Brogniez presented the Laboratoire d'Optique Atmospherique activities concerning SAGE III measurements with a focus on water vapor inversion and aerosol characteristic retrieval. She presented the methodology used for the inversion process. Three cases were presented: one mono-modal and two bi-modal with two inversion methods (a least squares fit method and the King method).
Didier Rault, NASA LaRC, reviewed the Forward Simulation methodology presented during the January Science Team Meeting and provided a status of the simulation. Rault has studied the effects of inhomogeneity of atmospheric density and temperature. He conducted a detailed comparison of the Forward Simulation with SAGE II measurements and ran simulated SAGE III scans. A systematic error from 5-15% between the SAGE II inversion code and the Forward Simulator was attributed to the Earth oblateness, Rayleigh scatterings, atmospheric refraction, and edge times. Rault has prepared the simulator for SAGE III operating conditions, which requires additional channels, a higher spectral resolution, and SAGE III instrument characteristics.
Eleonor Tchayanova, Russian Central Aerological Observatory (CAO), presented the status of the Russian NO2 algorithm development in the spectral region 430-450 nm. The algorithm calculated optical depths for the chosen atmospheric model followed by retrieval of NO2, ozone, and aerosol extinction profiles. Inverted profiles were then compared with the forward calculations of NO2, O3, and aerosol extinction profiles.
Chu provided an overview of the limb scattering discussions. The current modeling status will depend on the data to be obtained from a GSFC limb scattering instrument to be flown on the Shuttle this November. GSFC, LaRC, and the University of Arizona have been collaborating on the limb scattering methodology. GSFC and the University of Arizona are currently in the process of modeling inhomogeneous clouds. Determination of the optimum limb scattering geometry which results in the best sensitivity for the various species requires identification of the spectral region and operating modes. The Department of Defense (DOD) instrument Midcourse Space Experiment (MSX) will be taking limb scattering data in August this year for the GSFC scientists to analyze. GSFC will provide LaRC with modeling information based on the MSX data to support reprogramming SAGE III for limb scattering measurements. A follow-on meeting is scheduled in September.
The next SAGE III Science Team meeting will be scheduled in conjunction with the flight instrument pre-ship test and review scheduled during the second quarter of FY 98.