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PARIS-IR U of T FTS
TAO
Figure 1. The experimental setup for the mini-MANTRA FTS intercomparison campaign.
The University of Toronto’s Balloon-Borne Fourier Transform Spectrometer and
the Mini-MANTRA Ground-Based Campaign
Debra Wunch*, Jeffrey R. Taylor, James R. Drummond, Clive Midwinter, Kimberly StrongDepartment of Physics, University of Toronto
Dejian Fu, Kaley A. Walker, Peter BernathUniversity of Waterloo
A Fourier Transform Spectrometer (called the U of T FTS) was built to fly on the Middle Atmosphere Nitrogen TRend Assessment (MANTRA) high-altitude balloon platform in September, 2004. The spectrometer was derived from a Bomem DA5 Michelson-type interferometer built in the 1980s and purchased by the Meteorological Service of Canada. The software and nearly all the original electronics were replaced in preparation for flight. Since the MANTRA 2004 campaign, the U of T FTS has participated in a ground-based FTS intercomparison campaign in Toronto. The two other FTS instruments involved in the campaign are the Toronto Atmospheric Observatory (TAO) FTS and the University of Waterloo’s Portable Atmospheric Research Interferometric Spectrometer (PARIS-IR). Preliminary column amounts are shown, and the U of T FTS shows good agreement with the TAO FTS for O3 and HCl, and is somewhat high for N2O and CH4. PARIS-IR columns compare well with TAO for O3, N2O and CH4, and are slightly high for HCl.
The Instruments
The U of T FTS is a linear, Bomem DA5 FTS and was redesigned in 2003/2004 for balloon-borne solar occultation measurements of trace gas species, such as O3, N2O, CH4 and HCl. The instrument had an electronics overhaul from its original design, in order to improve its robustness and portability. This was accomplished using off-the-shelf components, which resulted in a significantly smaller instrument that was reduced in mass from around 90kg to 55kg, with a reduced power consumption from around 140W to 65W. The original software was replaced by LabVIEW control software, making the instrument easy to control and adaptable to either remote control or lab-based work. The dynamic alignment system, the signature component of a Bomem DA-series instrument, ensures that the system maintains its alignment as the moving mirror of the spectrometer scans. This system was the only electronic system that was left untouched during the refurbishment of the FTS. It is now controlled by the LabVIEW software.
The U of T FTS has flown on the MANTRA 2002 and MANTRA 2004 balloon payloads.
The Toronto Atmospheric Observatory (TAO) FTS is a linear, Bomem DA8 FTS, and is housed at a complementary NDSC site in a rooftop laboratory at the University of Toronto It is solely a ground-based FTS, and records solar absorption measurements during every clear-sky opportunity throughout the year. TAO has been in commission since 2001. This instrument will be used as the reference for the column comparisons.
The Portable Atmospheric Research Interferometric Spectrometer (PARIS-IR) was built by ABB Bomem in 2001 as a ground-based adaptation of the Atmospheric Chemistry Experiment (ACE) FTS, that is currently on orbit on-board the SCISAT-1 platform. The optical design for PARIS-IR is a double-pass, pendulum-style interferometer, which differs significantly from the design of Bomem’s DA-line of instruments. PARIS-IR is designed for both ground-based and balloon-borne operation and it has flown on the MANTRA 2004 payload.
A summary of the instrument characteristics is shown in Table 1.
Summary and Future Work
The University of Toronto’s Fourier transform spectrometer compared its data to that of the TAO FTS and the PARIS-IR instrument. The results were reasonable, however the U of T FTS retrieves high levels of N2O and CH4, whereas the PARIS-IR instrument retrieves high HCl column amounts. Detailed instrument line shape analyses and an investigation into other possible causes of these column amount discrepancies are ongoing.
Future work will include comparisons with coincident ACE-FTS overpasses and SCIAMACHY columns.
Funding for this work is provided by the Canadian Space Agency, the Meteorological Service of Canada and NSERC.
EnvironmentCanada
MeteorologicalService ofCanada
EnvironnementCanada
Service météorologiquedu Canada
PARIS-IR U of T FTS TAO
Maximum Optical Path Difference 25 cm
(0.02 cm-1)
50 cm
(0.02 cm-1)
250 cm
(0.004 cm-1)
Scan Time 20 s 50 s 5 min
Spectral Range 750–4400 cm-1 1200–5000 cm-1 650–4400 cm-1
Measurement Days (span) August 24-Sept. 2 May 26-Sept. 12 Year-round
Table 1. Description of the three FTS instruments involved in the mini-MANTRA intercomparison at the University of Toronto.
Goals for the mini-MANTRA Intercomparison Campaign
There are two main goals of the intercomparison. The first is to ensure preparedness of the balloon instruments for flight and the ensuing data analysis. Since PARIS-IR and the U of T FTS are relatively new, there is much to learn from the data that can suggest ways to improve the instrumentation.
The second goal of the intercomparison is to answer the scientifically interesting question: How different are the column amounts of trace gas species retrieved by three FTS instruments, looking at the same solar signal simultaneously, but with different designs and resolutions? The experimental setup is shown in Figure 1. All three instruments were measuring simultaneously using pick-off mirrors from the TAO instrument’s sun tracker. This isolates the problem to one of instrumentation.
Preliminary Results from the mini-MANTRA Intercomparison Campaign
The three instruments have completed their first attempts at retrieving O3, HCl, N2O and CH4. The O3 columns are also compared with the Brewer Spectrophotometer co-located with these instruments. The results are all within 5% of the TAO retrieved values, except for the U of T FTS’ results for CH4. The resulting column amounts are displayed in Figure 2.
Figure 2. First panel: Ozone columns for TAO, the U of T FTS, PARIS-IR and the Brewer Spectrophotometer; Second panel: HCl columns for TAO, the U of T FTS and PARIS-IR; Third panel: N2O columns for TAO, the U of T
FTS and PARIS-IR; Fourth panel: CH4 columns for TAO, the U of T FTS and PARIS-IR.
