the university of toronto’s balloon-borne fourier transform spectrometer
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The University of Toronto’s Balloon-Borne Fourier Transform Spectrometer
Debra Wunch, James R. Drummond, Clive Midwinter, Jeffrey R. Taylor, Kimberly StrongUniversity of TorontoDejian Fu, Kaley A. Walker, Peter BernathUniversity of WaterlooC. T. McElroy, Hans FastEnvironment Canada
COSPAR ConferenceBeijing, July 16-22, 2006
COSPAR paper number A1.1-0068-06
COSPAR; Beijing, July 16-22, 2006 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; 750-4400 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
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°
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
1500 2000 2500 3000 3500 4000 4500 5000 5500
0
0.2
0.4
0.6
0.8
1MCT Spectrum from the MANTRA 2004 Flight: 2004/09/01 19:53:31
Wavenumber (cm-1)In
tens
ity (
arbi
trar
y un
its)
3625 3630 3635
0.5
1
CO2
2937.2 2938.4
0.5
0.6
0.7
0.8
0.9
1
CH4
Wavenumber (cm-1)
2207.54 2207.66
0.8
0.85
0.9
0.95
1
N2O
2099.6 2100.4
0.6
0.7
0.8
0.9
1
Nor
mal
ized
Int
ensi
tyO3
COSPAR; Beijing, July 16-22, 2006 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
PARIS-IR
U of T FTS
TAO
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)
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.”
0 50 100 150 200 250 3002.4
2.6
2.8
3
3.2
3.4
3.6
3.8x 10
15
Optical Path Difference (cm)
Tot
al C
olum
n A
mou
nt (
mol
ecul
es/c
m2 )
HCl - SNR = 250
Truth
A Priori
PHS/EAP Retrieved
Standard Retrieval
COSPAR; Beijing, July 16-22, 2006 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
0 50 100 150 200 250 3006.3
6.4
6.5
6.6
6.7
6.8
6.9
7x 10
18
Optical Path Difference (cm)
Tot
al C
olum
n A
mou
nt (
mol
ecul
es/c
m2 )
N2O - SNR = 250
Truth
A Priori
PHS/EAP Retrieved
Standard Retrieval
21
O3 Total Column Comparisons
32 34 36 38 40 42 44 46 487.4
7.6
7.8
8
8.2
8.4
8.6
8.8
9
9.2x 10
18
SZA
Tot
al C
olum
n (m
olec
ules
/cm
2 )O3
TAO 3040MW
PARIS 3040MW
U of T MCT 3040MW
22
HCl Total Column Comparisons
30 35 40 45 50 55 60 652.6
2.7
2.8
2.9
3
3.1
3.2
3.3
3.4
3.5x 10
15
SZA
Tot
al C
olum
n (m
olec
ules
/cm
2 )HCl
TAO 2925MW
PARIS 2925MW
U of T MCT 2925MW
23
N2O Total Column Comparisons
30 35 40 45 50 55 60 656.2
6.3
6.4
6.5
6.6
6.7
6.8
6.9x 10
18
SZA
Tot
al C
olum
n (m
olec
ules
/cm
2 )N2O
TAO 2482MW
PARIS 2482MW
U of T MCT 2482MW
24
CH4 Total Column Comparisons
30 35 40 45 50 55 60 653.6
3.65
3.7
3.75
3.8
3.85
3.9
3.95
4
4.05
4.1x 10
19
SZA
Tot
al C
olum
n (m
olec
ules
/cm
2 )
CH4
TAO 2859MW
PARIS 2859MW
U of T MCT 2859MW
COSPAR; Beijing, July 16-22, 2006 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% 0.4% 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
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.
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