The University of Toronto

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The University of Torontos 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

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Outline

• Motivation
• MANTRA high-altitude balloon campaign
• FTS instruments on MANTRA
• Instrument The University of Torontos FTS
• History
• Preparation for MANTRA
• Flight data
• Intercomparison
• Instruments
• Results
• Conclusions and Future Work

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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

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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 (52N, 107W)
• 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 52N

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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

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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

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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

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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 1990s
  electronics boards and power supplies
• Power consumption 140 W
• Mass 90 kg

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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

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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

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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

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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

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MANTRA 2004 Flight

• Flight on September 1st at 834 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

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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

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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

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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

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Experimental Setup
TAO
U of T FTS
PARIS-IR
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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)

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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.

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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

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O3 Total Column Comparisons
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HCl Total Column Comparisons
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N2O Total Column Comparisons
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CH4 Total Column Comparisons
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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 0.4 0.5
U of T FTS to PARIS-IR 2.5 1.5 0.8 1.7

• 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 students t-test.

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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 lt3.5.

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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.