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The University of Toronto’s Balloon-Borne Fourier Transform Spectrometer

The University of Toronto’s Balloon-Borne Fourier Transform Spectrometer. Debra Wunch, James R. Drummond, Clive Midwinter, Jeffrey R. Taylor, Kimberly Strong University of Toronto Dejian Fu, Kaley A. Walker, Peter Bernath University of Waterloo C. T. McElroy, Hans Fast Environment Canada

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The University of Toronto’s Balloon-Borne Fourier Transform Spectrometer

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  1. The University of Toronto’s Balloon-Borne Fourier Transform Spectrometer Debra Wunch, James R. Drummond, Clive Midwinter, Jeffrey R. Taylor, Kimberly Strong University of Toronto Dejian Fu, Kaley A. Walker, Peter Bernath University of Waterloo C. T. McElroy, Hans Fast Environment Canada COSPAR Conference Beijing, July 16-22, 2006 COSPAR paper number A1.1-0068-06

  2. Outline • Motivation • MANTRA high-altitude balloon campaign • FTS instruments on MANTRA • Instrument: The University of Toronto’s FTS • History • Preparation for MANTRA • Flight data • Intercomparison • Instruments • Results • Conclusions and Future Work COSPAR; Beijing, July 16-22, 2006

  3. Motivation: MANTRA • Middle Atmosphere Nitrogen TRend Assessment • Investigate the changing chemical balance of the mid-latitude stratosphere, with a focus on the role of nitrogen chemistry on the depletion of ozone. • Scientific Objectives • Measurement of profiles of relevant chemical species • O3, NO, NO2, HNO3, HCl, ClONO2, N2O5, CFC-11, CFC-12, OH, H2O, N2O, CH4, J-values for O(1D) and NO2, aerosol, wind, pressure, temperature and humidity • Intercomparison between instruments • FTS, grating spectrometers, radiometers and sondes • Solar occultation, emission, in situ • Validation of satellite data • SCISAT: ACE-FTS, MAESTRO • Odin: OSIRIS, SMR • ENVISAT: SCIAMACHY, MIPAS, GOMOS COSPAR; Beijing, July 16-22, 2006

  4. Motivation: MANTRA • High-altitude balloon platform • Float height around 40 km • 18-24 hour flight duration • He-filled balloon • Payload size around 2 m by 2 m by 2 m • Main gondola pointing system • Four campaigns: 1998, 2000, 2002, 2004 in Vanscoy, Saskatchewan (52°N, 107°W) • Supported by extensive ground-based campaign • Launch balloons during late summer stratospheric zonal wind turnaround • Photochemical control regime • Low winds allow for longer float times • Launch window is August 26 – September 5 at 52°N COSPAR; Beijing, July 16-22, 2006

  5. Fourier Transform Spectrometers on MANTRA • Absorption FTS instruments measure solar absorption by atmospheric trace gases in the infrared • High spectral resolution, high signal-to-noise ratio • High vertical resolution (occultation mode – solar absorption through sunrise/sunset) • Broad-band: measure most atmospheric trace gas species of interest simultaneously • University of Denver FTS on 1998, 2002, 2004 • 30 years of flight heritage • 0.02 cm-1 resolution; 700-1300 cm-1 spectral range • PARIS-IR FTS on 2004 • Portable Atmospheric Research Interferometric Spectrometer for the Infrared, University of Waterloo • 0.02 cm-1 resolution; 750-4000 cm-1 spectral range • Ground- and balloon-based version of ACE FTS • U of T FTS on 2002, 2004 COSPAR; Beijing, July 16-22, 2006

  6. The Role of the U of T FTS on MANTRA • Develop a Canadian capacity for balloon-borne FTS measurements • Compare a well-understood instrument (U. Denver FTS) with new Canadian instruments (U of T FTS, PARIS-IR) • Measure trace gases that contribute to the ozone budget • Measure HCl, O3, N2O, CH4, etc. • Ground-based and balloon-based intercomparisons • Satellite validation COSPAR; Beijing, July 16-22, 2006

  7. The U of T FTS: History • Bomem DA2 instrument built in the 1980s • Purchased by the Meteorological Service of Canada (MSC) • Built as a ground-based instrument • Upgraded to a DA5 instrument with DA8 electronics (including the dynamic alignment) in the mid-1990s • Obtained by the University of Toronto from the MSC in 2001 • 0.02 cm-1 resolution; 1200-5000 cm-1 spectral range • InSb and MCT detectors that measure simultaneously, CaF2 beamsplitter • Flown on MANTRA 2002 and 2004 • MANTRA 2002 flight was an engineering flight • Test of temperatures and voltages COSPAR; Beijing, July 16-22, 2006

  8. The U of T FTS: History • Original Software • Software contained user prompts in the form of “pop-up” boxes • Inaccessible housekeeping information • Control software embedded in hardware (BIOS) • Original Hardware and Electronics • Dependable dynamic alignment (compensation for motion in moving mirror) • Large electronics box with circa 1990’s electronics boards and power supplies • Power consumption: 140 W • Mass: 90 kg COSPAR; Beijing, July 16-22, 2006

  9. Tasks in Preparation for MANTRA 2004 • Convert the U of T FTS from a ground-based FTS into an instrument that can take ground-based and balloon-based data • Update the software and electronics • Remove pop-up boxes • Use modern technology without compromising performance • Address issue of accurate pointing for solar occultation measurements COSPAR; Beijing, July 16-22, 2006

  10. Re-engineered control of the dynamic alignment system Almost entirely new electronics 3 boards kept (DA), 7 discarded Replaced two control computers with one low-power motherboard Wrote control software in LabVIEW Controls DA Includes automated scheduler No human intervention required Full uplink and downlink capabilities Housekeeping Temperatures, voltages, interferograms New power supply system Vicor power supplies New data acquisition system USB 16-bit ADC for interferograms USB 12-bit ADC for housekeeping Preparation for MANTRA 2004 COSPAR; Beijing, July 16-22, 2006

  11. Preparation for MANTRA 2004: Results • Mass reduction • Electronics box no longer necessary • All necessary electronics fit into spectrometer box • Mass reduced from ~90kg to ~55kg • Power reduction • Power reduced from ~140W to ~65W due to new electronic components • Improves temperature performance – less power means less heat • Now about half the mass/power of the other two FTS instruments COSPAR; Beijing, July 16-22, 2006

  12. Preparation for MANTRA 2004: Pointing • Obtained a dedicated sunseeker that tracks the sun within ±10 degrees in zenith and azimuth • Had flown before on other balloon campaigns • No longer dependent on main gondola pointing system • Only dependent on being pointed in general direction of sun • Would still get no data if payload rotated uncontrollably • True for any solar-mode instrument on payload COSPAR; Beijing, July 16-22, 2006

  13. MANTRA 2004 Flight • Flight on September 1st at 8:34 am • Successful launch, followed by loss of commanding to the payload • Pointing system overheated before sunset • Payload began rotating • Two spectra recorded on each detector at solar zenith angle of ~89° COSPAR; Beijing, July 16-22, 2006

  14. U of T FTS Flight Data • Instrument performed well under difficult conditions • Can resolve CO, CO2, O3, CH4, N2O, HCl • can retrieve slant columns • Signal-to-noise ratio reduced • lower SNR attributed to rotation of payload – tracker at ends of its field of view • Resolution reduced • reduced resolution attributed to rotation of payload, temperature, poor alignment before flight? • No vertical profile retrievals possible • No other flight opportunities

  15. Ground-based FTS Intercomparison in Toronto • Intercomparison campaign between three FTS instruments with different resolutions • Two balloon and ground-based instruments, one solely ground-based instrument • Toronto Atmospheric Observatory (TAO) • Complementary Network for the Detection of Atmospheric Composition Change (NDACC – formerly NDSC) Station • 250 cm MOPD • PARIS-IR • 25 cm MOPD • Ground- and balloon-based version of ACE FTS • U of T FTS • 50 cm MOPD COSPAR; Beijing, July 16-22, 2006

  16. Intercomparison Goals • To fully test the two balloon instruments • Develop analysis packages • Debug software/hardware • Determine the important parameters to consider in the intercomparison • Investigate whether instruments of differing spectral resolutions can retrieve the same column amounts of trace gases • Coincident measurements • Consistent a priori profiles, spectroscopic parameters, atmospheric ZPT profiles • Same retrieval package (SFIT2 v. 3.82) • Reduces comparison errors to instrument resolution or alignment COSPAR; Beijing, July 16-22, 2006

  17. Experimental Setup TAO U of T FTS PARIS-IR COSPAR; Beijing, July 16-22, 2006

  18. Instrument Line Shape (ILS) • Important to know ILS well • Any vertical information in the spectral line is retrieved from line shape • Ensure instrument broadening is not interpreted as higher atmospheric concentrations • ILS sensitive to temperature, instrument alignment • ILS should be taken into account, spectrum by spectrum • Can measure ILS prior to solar measurements with gas cell: appropriate for ground-based measurements, but for balloon-based retrievals, need a more robust method • SFIT2 provides switch to retrieve ILS parameters (PHS/EAP Retrieved) COSPAR; Beijing, July 16-22, 2006

  19. Stratospheric species: narrow absorption lines U of T FTS and PARIS-IR resolution broader than absorption line width Retrievals very sensitive to ILS for U of T FTS and PARIS-IR For U of T FTS: 20% improvement for ozone columns when retrieving ILS; 15% improvement for HCl columns when retrieving ILS Ensemble of simulated spectra with imperfect ILS, retrieved with SFIT2 ILS switch on (“PHS/EAP”) and off (“Standard”) Much better results obtained when ILS switch is “on.” Instrument Line Shape (ILS): Stratospheric Species

  20. Instrument Line Shape (ILS): Tropospheric Species • Tropospheric species: broad absorption lines • U of T FTS and PARIS-IR resolution on order of absorption line width • Retrievals much less sensitive to ILS • No drop-off of columns like in stratospheric case COSPAR; Beijing, July 16-22, 2006

  21. O3 Total Column Comparisons

  22. HCl Total Column Comparisons

  23. N2O Total Column Comparisons

  24. CH4 Total Column Comparisons

  25. Intercomparison Summary • The lower-resolution PARIS-IR and U of T FTS instruments, when retrieving ILS information from the spectrum can produce good agreement with the high-resolution TAO-FTS • Bold is statistically significant difference within 95% based on the student’s t-test. COSPAR; Beijing, July 16-22, 2006

  26. Conclusions and Future Work • U of T FTS • Lower power consumption • Lower mass • Robust software • Continuing work • Building “delta”-tracker with larger field of view • Uses camera to image sun • Intercomparisons • ILS vitally important for stratospheric species, less important for tropospheric species • Low-resolution instruments compare well with TAO for all species <3.5%. COSPAR; Beijing, July 16-22, 2006

  27. Acknowledgements • The authors wish to thank Pierre Fogal, John Olson, and the MANTRA 2002 and 2004 science teams. • Funding is provided by the Canadian Space Agency, Environment Canada, the Canadian Foundation for Climate and Atmospheric Sciences and the Natural Science and Engineering Research Council of Canada. COSPAR; Beijing, July 16-22, 2006

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