The 12th TES/AES Science Team meeting was held at AER Inc. in Cambridge, MA on December 12-15, 1995. Our hosts were Tony Clough and Pat Brown of AER. This was a very well-attended meeting with several representatives from each of the institutions involved in TES and AES.
The meeting began with an overview by Joe McNeal (NASA HQ) of the recent multiple reviews of TES and the CHEM-1 platform that were initiated as a consequence of the National Academy's Board on Sustainable Development (BSD) report of last summer. In particular, a community-wide workshop was convened at the Goddard Institute for Space Studies (GISS) in November to investigate not only TES but the whole issue of the interplay of remote sensing and the more traditional in situ studies of tropospheric chemistry, including the contributions of our colleagues in Japan and Europe. The workshop general chair was Daniel Jacob (Harvard), and working groups on Policy, Atmospheric Chemistry, and Aerosols were led by Dan Albritton (NOAA), Jennifer Logan (Harvard), and Pat McCormick (NASA LaRC), respectively. The workshop was strongly supportive of TES, but there is no doubt that it has caused us to re-evaluate our strategy for making global surveys of tropospheric ozone and its precursors and to focus more strongly on limb retrievals, especially for the active nitrogen species.
Tom Glavich (JPL) then brought us up-to-date on the TES instrument project. As the engineering team has grown, so has the level of detail in the design. The focus now is to produce a viable baseline design for the System Concept Review (what used to be called Conceptual Design and Cost Review) to be held mid-year 1996.
Jennifer Logan (Harvard) discussed the atmospheric chemistry portion of the GISS workshop, which concluded that while several pre-CHEM-1 instruments (from the US, ESA, and Japan) would provide some information useful to tropospheric chemistry, only TES has the potential for measuring O3, CO and the critical upper-tropospheric precursors NO, HNO3 and H2O near-simultaneously and in the same air-mass and that, therefore, it is essential that TES retain this capability (which demands both limb and nadir-viewing). The workshop further found that TES has been descoped continuously over the past few years to the point that further reductions would eliminate necessary capabilities, although the TES team continues to seek new technologies to reduce demands on resources (in space and on the ground). It was further agreed by all that a collaborative, rather than competitive, approach among the developers and deployers of remote sensing systems and the more-traditional in situ techniques is essential for the future health of the field.
Reinhard Beer (JPL) then presented a draft of the report of the Atmospheres Panel of the EOS Payload Panel (kindly provided by the chairman, Rich Zurek) that enthusiastically endorsed the conclusions of the GISS workshop and further proposed that such workshops become regular events.
Tony Clough and Pat Brown (AER) showed preliminary results of trial limb retrievals of ozone precursors, based on profiles provided by Daniel Jacob and Jennifer Logan. The provisional conclusions were that HNO3 and H2O could be done down to cloud tops with excellent precision (1-2%), NO is likely to be more difficult (20-30% precision) and NO2 may be impossible (in the troposphere). One added difficulty with NO is the high temperature (~1000K), and probable non-LTE (local thermodynamic equilibrium), thermospheric component, which must be corrected for. These studies will be continued for a wide variety of conditions, the climatology for which will be provided by the Harvard group.
Consequences of both the GISS workshop and the AER study were that: (i) we must spend a considerably greater fraction of a month generating global distributions than we had originally planned (because of concerns about persistent cloud cover in particular regions), and (ii) that the specific observational strategy must be more-heavily weighted towards limb views of the upper troposphere, especially for NO. The impact of these new requirements on component lifetime will be investigated by the engineering team and resolved in time for the next edition of the Science Requirements Document (planned to be issued in April 1996).
Some discussion ensued on the subject of publication policy ("free for all" on the ATMOS model vs. group publication on the High Energy Physics model vs PI directives). Joe McNeal promised to provide a copy of the policy adopted by the UARS project, and we will revisit this topic at a future meeting.
Following this, we had the first of 3 sessions discussing the Algorithm Theoretical Basis Document (ATBD -- the primary deliverable of the Science Team). We began by reviewing a draft outline that was generated at a special meeting held in Denver last summer. The outline was refined, and a new version will be issued in a subsequent newsletter when some additional input from Clive Rodgers (Oxford) and Tony Clough becomes available. The team nevertheless re-iterated its intention to develop a new "community," Level 2 retrieval algorithm that will draw on the best features of LBLRTM and SEASCRAPE (and, incidentally, be compared to them as part of the validation process).
Tony Clough showed the outcome of his analysis of the role of spectral resolution on remote sensing from space. This shows that we have made the correct choice (spectral resolution comparable to the width of weak features). Coarser resolution provides insufficient information (retrieval error increases dramatically), and is much more susceptible to systematic error because signal-to-noise ratio does not increase indefinitely, as simple-minded analyses suggest.
Clough followed with an analysis of the probability of seeing to the surface as a function of season, based on the old IRIS-D data. The results are very interesting and will be very helpful in the replanning of our global observation strategy.
Jack Margolis (JPL) discussed some of the "lessons learned" from AES calibration. It seems clear that we have underestimated the frequency with which we must perform TES radiometric calibrations, and this, too, must be factored into our updated observation strategy.
Peter Venters (Oxford) showed his current design for the TES in-flight calibration sub-system (little changed from last year) and then described his initial efforts at generating a full calibration budget. This suggests that the required 1% accuracy is feasible below about 1500 cm-1, marginal between 1500 and 2500 cm-1, and probably impossible (by a factor of 2-3) above 2500 cm-1. This conclusion is not unexpected and should not have a major impact on retrieval accuracy because the signal-to-noise ratio will decline at about the same rate, i.e., measurement error is still likely to dominate.
Following two more sessions on the ATBD, Steve Larson (JPL) explained the software development and change control process. There remains some concern among the Science Team that such controls either insulate the team from the process (which may be desirable) or, alternatively, take up much of the team's time in trying to follow, and validate, what is going on. Nevertheless, the team recognizes that some form of control must be exercised, but remains apprehensive.
Helen Worden (JPL) outlined the final version of the paper on the two western wildfires measured by AES in 1994. The paper has been submitted to JGR. The results show that significant useful information about biomass burning can be extracted from spectral remote sensing that is complementary to that acquired during controlled burns, although it does seem that there is no such thing as a "typical" wildfire.
David Rider and Helen Worden (JPL) then described progress on the analysis of data from the 1995 Southern Oxidants Study Nashville Intensive Campaign. The high humidity and air stagnation conditions that prevailed during the week that we made our observations (in addition to problems of determining the transmittance of the ZnSe aircraft window under flight conditions) are making analysis more difficult than we had anticipated. Nevertheless, our retrieved temperature and humidity profiles compare well to radiosonde data acquired at the same time, so we expect the remaining difficulties to be solved in the near future.
Curt Rinsland (LaRC) showed some test results from an improved solar irradiance model obtained from Harvard/Smithsonian Astrophysical Observatory. There are still concerns: (i) about validating this model against (essentially non-existent) observations, and (ii) modeling the major expected variations in solar CO during the solar cycle. The MAPS experiment has shown that over, for example, desert areas the solar reflection contribution even in the CO fundamental region is not negligible.
An invitation to hold a 1996 team meeting at Oxford was tentatively accepted. However, we will first hold a meeting at JPL shortly before the System Concept Review in order that the Science Team can become better acquainted with the Engineering Team.
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