--Sandra Smalley (s.e.smalley@larc.nasa.gov), SAGE Science Manager, Aerosol Research Branch, NASA Langley Research Center
On August 27, 1996, a Science Team meeting for the Stratospheric Aerosol and Gas Experiment (SAGE) III was conducted at the National Oceanic and Atmospheric Administration (NOAA) facilities in Boulder, Colorado. The objective of this science team meeting was primarily to discuss the Algorithm Theoretical Basis Document (ATBD) development status. Other topics included an explanation of the revised roles of the Principal Investigator and the Associate Principal Investigator, a review of the instrument development status, and the validation plan.
M. Patrick McCormick opened the Science Team meeting with an overview of his current status. McCormick recently retired from NASA Langley Research Center and is now a professor in the Physics Department at Hampton University, in Hampton, Virginia. Currently, McCormick is attempting to change the SAGE III Principal Investigator position to his current position at Hampton University. In this way, he will maintain leadership and advisory roles from a science standpoint. William P. Chu, NASA Langley Research Center (LaRC), will now become the Associate Principal Investigator. In this role, Chu will speak for resources associated with NASA's sponsorship of the Science Team and provide additional management of the team.
In addition, McCormick reviewed the status of items from the last meeting. The ATBDs are currently on schedule for a November 1996 delivery to the EOS Senior Project Scientist. In addition, the Data Validation Plan is also on schedule for delivery to EOS. These products will undergo several reviews prior to their release.
Lemuel E. Mauldin, SAGE III Project Manager, presented the status of instrument development. The SAGE III Critical Design Review was held on August 28 and 29, 1996, with no major issues open in the development of the instrument. With the successful completion of this review, the SAGE III project transitions from a design phase to a production phase. Mauldin reported that the SAGE III Project is on-schedule and under-budget.
Michael Cisewski, SAGE III Mission Operations Manager, gave an overview of the SAGE III Mission Operations with respect to the Meteor-3M Mission. Cisewski provided a schedule of near-term events with respect to mission operations planning.
Chauncey Uphoff, Orbit Mechanics Engineer, Fortune-8, Inc., gave an overview of the SPOT-5 Orbit Mechanics Analysis he has been performing with respect to the SAGE III/SPOT-5 Phase A study. This study is for both the SAGE III and SPOT-5 projects to study the feasibility of flying SAGE III on the SPOT-5 spacecraft. The 10:30 p.m. orbit limits the number of lunar encounters for SAGE III. It will have only 50-60% of the lunar encounters for the Meteor-3M mission. Most of the lunar encounters found on SPOT-5 will occur during the spring.
Chu gave an overview of the Joint Russian/U.S. Science Plan. This plan is a result of a joint agreement made under the Mission to Planet Earth Joint Working Group. The plan is to detail Russian participation in SAGE III science. Possible participation lies in the areas of scientific investigation, algorithm development, mission operations, and data validation.
Joseph Zawodny, LaRC, reported on his attendance at the EOS Payload Panel Meeting. This meeting concentrated on a framework in which an instrument can demonstrate its needs (for instance, to fly with other complementary instruments). With respect to the health of the SAGE Program, Zawodny reported that SAGE's international relationships and cooperations are helpful to program longevity. In addition, SAGE will definitely fly on the International Space Station, though the 2001 date may change. Ideas for helping the SAGE program include focusing on technology advances for SAGE III and on the new way of doing business. There is a new stress on infusing new technology. In addition, Zawodny reported that there was some discussion of breaking up the CHEM spacecraft into three platforms, and that the time line of EOS beyond CHEM-1 is being looked at. Things will change significantly. Overall, the meeting produced positive results for the future of SAGE III.
Zawodny and Gary Hansen, STC/LaRC, then reported on the status of the Test Occultation Instrument (TOI), which consists of the SAGE III spectrometer/telescope and associated electronics. This unit will be used for testing and instrument performance verification and to verify Ball test data. The TOI will assist in algorithm development. In addition, it will transition to a ground-based radiometer instrument for data validation.
Hansen has prepared LaRC for acceptance of the TOI hardware. The date of delivery is dependent on selection of the desired telescope primary mirror, as the mirror which is currently in the TOI is not the same design as that found in the flight model. However, it may be acceptable for the desired use. Capabilities and features of the TOI include transportability and rastering. Laboratory measurements that can be taken in order to characterize the instrument are (i) scattered light analysis, (ii) image mapping of the solar disk and lunar disk, and (iii) full spectral images of the moon in order to gain real data for the algorithms. McCormick requested that Zawodny put together a list of capabilities of the TOI.
Michael Rowland, Science Applications International Corporation, gave an overview of the SAGE III home page, which was recently opened to the public. The URL of the home page is http://arbs8.larc.nasa.gov/sage3/sage3.html.
Chu presented the status of the ATBDs, which have been revised with suggestions made by Science Team members. He reported that the electronic versions of these documents are available for download. There are outstanding issues regarding clouds and inhomogeneity. A significant point that should be considered is that these documents are usually completed three years prior to launch. However, for the Meteor-3M launch there will only be one-and-a-half years prior to launch. This fact will lead to comments and changes that can be made to the documents later. Chu requested a list of potential reviewers for these documents.
David Woods and Chip Trepte presented the validation status. Woods has investigated the use of resources for validation, and provided an overview of available resources. Trepte discussed budget issues relative to validation. Some potential solutions for aircraft-based validation include (i) attempting to have other experiments dovetail with SAGE validation for flight time and (ii) using NCAR aircraft with support from the university community. Important elements to validate include refractive index, chemistry changes, size distribution and algorithms/line of sight. A discussion was held with regard to the importance of validating measurements made in polar regions during active dynamical periods (the most expensive validation element). Options for validation of other species include: aerosols/water vapor--balloons from Fairbanks; NO3--TOI; and OClO--other instruments in operation simultaneously. Because SAGE II history already exists for most species, it may be possible to do one validation per fiscal year. The decision on this matter will be left open until all avenues are researched.
Eric P. Shettle, Naval Research Laboratory in Washington, DC, discussed his work on the spectroscopic assessments for gaseous constituent retrievals in the visible and ultraviolet spectral regions.
Benjamin M. Herman, University of Arizona, gave a presentation regarding temperature measurements using SAGE II data. Looking at the sun, one can make an estimate of the refractive bending angle of the rays. Using the index of refraction, which is dependent on density, one can get the density profile. From the density profile, one can derive the pressure profile and use the equation of state to obtain the temperature profile. The process should start at the highest level at which reasonable data can be obtained (50 km). A problem is that the pointing angle of the mirror is not known to the accuracy or precision needed. Averages must be taken of the downscan and upscan, which produce many uncertainties. Another problem is that the angular dimension of the sun is changing across the data set on the order of tenths of minutes. Mike Cisewski reported that SAGE III will have more accurate scan mirror control and spacecraft attitude information as well as an independent measure of temperature.
Zawodny gave a status of the reprocessing of SAGE II data with respect to lessons learned. The current release of software is 5.93. Version 5.94 has been in process for a year. It contains a fix for thermal shock, which affects sunrise NO2 data. This version can be made available immediately. Version 5.95 will improve the characteristics of 600-nm aerosol. A new set of coefficients was developed by Larry Thomason to increase the altitude range by 2-3 kilometers, with agreement to ozonesonde data during the peak of the Pinatubo period. There is no single set of linear coefficients which fits the theoretical data for the whole family of aerosol distributions. Therefore, a set of coefficients (non-linear versus linear) will be developed. The 5.96 version will address the degradation of NO2 absorption data. The current version shows a 30% decrease, which may be corrected by modeling the change in wavelength and bandpass of the 448-nm channel. Version 5.97 will improve the tropospheric ozone retrievals by correcting for some water vapor absorption at 600 nm via unification of the water vapor processing with the processing for retrieval of the other species. (It is currently processed separately ignoring the mutual interference between ozone and water vapor.) This release will probably be available by the beginning of 1997. Version 6 transmission will show a finer altitude grid, an adjustment to edge times, better size-of-disk estimates, and a spectral dependence of refraction . Efforts to look at SAGE I data with SAGE II methods (after version 6 release) will result in many lessons learned.
Zawodny also gave a summary of the SPARC meeting. SAGE went first with a report of lessons learned. Later, the balloon sounding method was discussed by the scientists to explain problems with ozonesonde profiles, which show large pump efficiency problems at high altitude. This can introduce large trends in data. SAGE II is the only global data set that can show trends in the lower stratosphere and upper troposphere with high (1 km) vertical resolution.
David A. Rogers, Ball Aerospace, SAGE III Project Manager, hosted a tour of the Ball facilities in Boulder, including progress made on SAGE III test equipment, software, and hardware.