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 A

2. Outline Motivation Instrument: The University of Toronto’s FTS
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; 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; 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; 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. Preparation for MANTRA 2004
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
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. Instrument Line Shape (ILS): Stratospheric Species
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.”

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
% Difference of Means O3
HCl
N2O
CH4
U of T FTS to TAO
3.3%
1.7%
0.4%
2.3%
PARIS-IR to TAO
0.8%
3.2%
0.5%
U of T FTS to PARIS-IR
2.5%
1.5%
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