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; 750-4000 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

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)

Col

umn

Am

ount

(m

olec

ules

/cm

2 )

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)

Col

umn

Am

ount

(m

olec

ules

/cm

2 )

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

Col

umn

O3

TAO 3040

PARIS 3040

U of T MCT 3040

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

Col

umn

HCl

TAO 2925

PARIS 2925

U of T MCT 2925

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

Col

umn

N2O

TAO 2482

PARIS 2482

U of T MCT 2482

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

Col

umn

CH4

TAO 2859

PARIS 2859

U of T MCT 2859

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.