Rugged optical mirrors for Fourier-Transform Spectrometers operated in harsh environments

Abstract. The Total Carbon Column Observing Network (TCCON) and the Network for the Detection of Atmospheric Composition Change (NDACC) operate a number of Fourier-Transform Spectrometers (FTSs) that measure trace gases in the atmosphere by observing solar spectra. To guide the sunlight into the FTS, a solar tracker has to be placed outside. This device needs high-quality optical mirrors with good reflectivity in the near and mid infrared. More and more FTS stations are operated in remote locations with harsh environments. Optical mirrors are usually made for laboratory conditions and might not last very long there. At the MPI-BGC's TCCON site on Ascension Island, several mirrors from different optical manufacturers were destroyed within weeks. To continue operation, the MPI-BGC had to develop rugged mirrors that could sustain the harsh conditions for months or even years. While commercially available mirrors are typically made from a substrate coverered with a thin reflective coating, these rugged mirrors were made from stainless steel with no additional coating. Except for their lower reflectivity (which can easily be compensated for), their optical properties are comparable to existing mirrors. However, their rugged design makes them mostly immune to corrosion and scratching. Unlike most coated mirrors, they can also be cleaned easily.

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Rugged optical mirrors for Fourier transform spectrometers operated in harsh environments

Atmospheric Measurement Techniques ◽

10.5194/amt-9-2381-2016 ◽

2016 ◽

Vol 9 (5) ◽

pp. 2381-2391 ◽

Cited By ~ 6

Author(s):

Dietrich G. Feist ◽

Sabrina G. Arnold ◽

Frank Hase ◽

Dirk Ponge

Keyword(s):

Fourier Transform ◽

Total Carbon ◽

Atmospheric Composition ◽

Harsh Environments ◽

Max Planck ◽

Reflective Coating ◽

Ascension Island ◽

Solar Tracker ◽

Optical Mirrors ◽

Harsh Conditions

Abstract. The Total Carbon Column Observing Network (TCCON) and the Network for the Detection of Atmospheric Composition Change (NDACC) operate a number of Fourier transform spectrometers (FTSs) that measure trace gases in the atmosphere by observing solar spectra. To guide the sunlight into the FTS, a solar tracker has to be placed outside. This device needs high-quality optical mirrors with good reflectance in the near and mid-infrared.More and more FTS stations are operated in remote locations with harsh environments. Optical mirrors are usually made for laboratory conditions and might not last very long there. At the TCCON site on Ascension Island which is operated by the Max Planck Institute for Biogeochemistry (MPI-BGC), several mirrors from different optical manufacturers were destroyed within weeks.To continue operation, the MPI-BGC had to develop rugged mirrors that could sustain the harsh conditions for months or even years. While commercially available mirrors are typically made from a substrate covered with a thin reflective coating, these rugged mirrors were made from stainless steel with no additional coating. Except for their lower reflectance (which can easily be compensated for), their optical properties are comparable to existing mirrors. However, their rugged design makes them mostly immune to corrosion and scratching. Unlike most coated mirrors, they can also be cleaned easily.

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Retrieval of xCO2 from ground-based mid-infrared (NDACC) solar absorption spectra and comparison to TCCON

Atmospheric Measurement Techniques ◽

10.5194/amt-9-577-2016 ◽

2016 ◽

Vol 9 (2) ◽

pp. 577-585 ◽

Cited By ~ 6

Author(s):

Matthias Buschmann ◽

Nicholas M. Deutscher ◽

Vanessa Sherlock ◽

Mathias Palm ◽

Thorsten Warneke ◽

...

Keyword(s):

Absorption Spectra ◽

Seasonal Cycle ◽

Total Carbon ◽

Atmospheric Composition ◽

Composition Change ◽

Solar Absorption ◽

Mid Infrared ◽

Infrared Spectral ◽

Ftir Spectrometer ◽

Total Column

Abstract. High-resolution solar absorption spectra, taken within the Network for the Detection of Atmospheric Composition Change Infrared Working Group (NDACC-IRWG) in the mid-infrared spectral region, are used to infer partial or total column abundances of many gases. In this paper we present the retrieval of a column-averaged mole fraction of carbon dioxide from NDACC-IRWG spectra taken with a Fourier transform infrared (FTIR) spectrometer at the site in Ny-Ålesund, Spitsbergen. The retrieved time series is compared to colocated standard TCCON (Total Carbon Column Observing Network) measurements of column-averaged dry-air mole fractions of CO2 (denoted by xCO2). Comparing the NDACC and TCCON retrievals, we find that the sensitivity of the NDACC retrieval is lower in the troposphere (by a factor of 2) and higher in the stratosphere, compared to TCCON. Thus, the NDACC retrieval is less sensitive to tropospheric changes (e.g., the seasonal cycle) in the column average.

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Strategy for high-accuracy-and-precision retrieval of atmospheric methane from the mid-infrared FTIR network

Atmospheric Measurement Techniques ◽

10.5194/amt-4-1943-2011 ◽

2011 ◽

Vol 4 (9) ◽

pp. 1943-1964 ◽

Cited By ~ 37

Author(s):

R. Sussmann ◽

F. Forster ◽

M. Rettinger ◽

N. Jones

Keyword(s):

Diurnal Variation ◽

Goodness Of Fit ◽

Regional Scale ◽

High Accuracy ◽

Total Carbon ◽

Atmospheric Composition ◽

Mid Infrared ◽

Dry Air ◽

Accuracy And Precision ◽

Retrieval Strategies

Abstract. We present a strategy (MIR-GBM v1.0) for the retrieval of column-averaged dry-air mole fractions of methane (XCH4) with a precision <0.3% (1-σ diurnal variation, 7-min integration) and a seasonal bias <0.14% from mid-infrared ground-based solar FTIR measurements of the Network for the Detection of Atmospheric Composition Change (NDACC, comprising 22 FTIR stations). This makes NDACC methane data useful for satellite validation and for the inversion of regional-scale sources and sinks in addition to long-term trend analysis. Such retrievals complement the high accuracy and precision near-infrared observations of the younger Total Carbon Column Observing Network (TCCON) with time series dating back 15 years or so before TCCON operations began. MIR-GBM v1.0 is using HITRAN 2000 (including the 2001 update release) and 3 spectral micro windows (2613.70–2615.40 cm−1, 2835.50–2835.80 cm−1, 2921.00–2921.60 cm−1). A first-order Tikhonov constraint is applied to the state vector given in units of per cent of volume mixing ratio. It is tuned to achieve minimum diurnal variation without damping seasonality. Final quality selection of the retrievals uses a threshold for the goodness of fit (χ2 < 1) as well as for the ratio of root-mean-square spectral noise and information content (<0.15%). Column-averaged dry-air mole fractions are calculated using the retrieved methane profiles and four-times-daily pressure-temperature-humidity profiles from National Center for Environmental Prediction (NCEP) interpolated to the time of measurement. MIR-GBM v1.0 is the optimum of 24 tested retrieval strategies (8 different spectral micro-window selections, 3 spectroscopic line lists: HITRAN 2000, 2004, 2008). Dominant errors of the non-optimum retrieval strategies are systematic HDO/H2O-CH4 interference errors leading to a seasonal bias up to ≈5%. Therefore interference errors have been quantified at 3 test sites covering clear-sky integrated water vapor levels representative for all NDACC sites (Wollongong maximum = 44.9 mm, Garmisch mean = 14.9 mm, Zugspitze minimum = 0.2 mm). The same quality ranking of the 24 strategies was found for all 3 test sites with one optimum, i.e. MIR-GBM v1.0. Seasonality of XCH4 above the Zugspitze (47° N) shows a minus-sine shape with a minimum in March/April, a maximum in September, and an amplitude of 16.2 ± 2.9 ppb (0.94 ± 0.17%). This agrees well with the WFM-DOAS v2.0 scientific XCH4 retrieval product. A conclusion from this paper is that improved spectroscopic parameters for CH4, HDO, and H2O in the 2613–2922 cm−1 spectral domain are urgently needed. If such become available with sufficient accuracy, at least two more spectral micro windows could be utilized leading to another improvement in precision. The absolute inter-calibration of NDACC MIR-GBM v1.0 XCH4 to TCCON data is subject of ongoing work.

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Accurate mobile remote sensing of XCO2 and XCH4 latitudinal transects from aboard a research vessel

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-8-7413-2015 ◽

2015 ◽

Vol 8 (7) ◽

pp. 7413-7453 ◽

Cited By ~ 2

Author(s):

F. Klappenbach ◽

M. Bertleff ◽

J. Kostinek ◽

F. Hase ◽

T. Blumenstock ◽

...

Keyword(s):

Absorption Spectrometry ◽

Total Carbon ◽

Atmospheric Composition ◽

Research Vessel ◽

Weather Forecasts ◽

Technical Developments ◽

Project Monitoring ◽

Solar Tracker ◽

Network Instrument ◽

Gosat Satellite

Abstract. A portable Fourier Transform Spectrometer (FTS), model EM27/SUN, is deployed onboard the research vessel Polarstern to measure the column-average dry air mole fractions of carbon dioxide (XCO2) and methane (XCH4) by means of direct sunlight absorption spectrometry. We report on technical developments as well as data calibration and reduction measures required to achieve the targeted accuracy of fractions of a percent in retrieved XCO2 and XCH4 while operating the instrument under field conditions onboard the moving platform during a six week cruise through the Atlantic from Cape Town (South Africa, 34° S, 18° E) to Bremerhaven (Germany, 54° N, 19° E). We demonstrate that our solar tracker typically achieves a tracking precision of better than 0.05° toward the center of the sun throughout the ship cruise which facilitates accurate XCO2 and XCH4 retrievals even under harsh ambient wind conditions. We define several quality filters that screen spectra e.g. when the field-of-view is partially obstructed by ship structures or when the lines-of-sight cross the ship exhaust plume. The measurements in clean oceanic air, can be used to characterize a spurious airmass dependency. After the campaign, deployment of the spectrometer side-by-side the TCCON (Total Carbon Column Observing Network) instrument at Karlsruhe, Germany, allows for determining a calibration factor that makes the entire campaign record traceable to World Meteorological Organization (WMO) standards. Comparisons to observations of the GOSAT satellite and concentration fields modeled by the European Centre for Medium-Range Weather Forecasts (ECMWF) within the project Monitoring of Atmospheric Composition and Climate – Interim Implementation (MACC-II) demonstrate that the observational setup is well suited to provide validation opportunities above the ocean and along interhemispheric transects.

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Intercomparison of arctic XH2O observations from three ground-based Fourier transform infrared networks and application for satellite validation

Atmospheric Measurement Techniques ◽

10.5194/amt-14-1993-2021 ◽

2021 ◽

Vol 14 (3) ◽

pp. 1993-2011

Author(s):

Qiansi Tu ◽

Frank Hase ◽

Thomas Blumenstock ◽

Matthias Schneider ◽

Andreas Schneider ◽

...

Keyword(s):

Fourier Transform ◽

A Priori ◽

Fourier Transform Infrared ◽

Total Carbon ◽

Atmospheric Composition ◽

Satellite Validation ◽

Ftir Spectrometer ◽

Priori Information ◽

Good Agreement

Abstract. In this paper, we compare column-averaged dry-air mole fractions of water vapor (XH2O) retrievals from the COllaborative Carbon Column Observing Network (COCCON) with retrievals from two co-located high-resolution Fourier transform infrared (FTIR) spectrometers as references at two boreal sites, Kiruna, Sweden, and Sodankylä, Finland, from 6 March 2017 to 20 September 2019. In the framework of the Network for the Detection of Atmospheric Composition Change (NDACC), an FTIR spectrometer is operated at Kiruna. The H2O product derived from these observations has been generated with the MUlti-platform remote Sensing of Isotopologues for investigating the Cycle of Atmospheric water (MUSICA) processor. In Sodankylä, a Total Carbon Column Observing Network (TCCON) spectrometer is operated, and the official XH2O data as provided by TCCON are used for this study. The datasets are in good overall agreement, with COCCON data showing a wet bias of (49.20±58.61) ppm ((3.33±3.37) %, R2=0.9992) compared with MUSICA NDACC and (56.32±45.63) ppm ((3.44±1.77) %, R2=0.9997) compared with TCCON. Furthermore, the a priori H2O volume mixing ratio (VMR) profiles (MAP) used as a priori information in the TCCON retrievals (also adopted for COCCON retrievals) are evaluated with respect to radiosonde (Vaisala RS41) profiles at Sodankylä. The MAP and radiosonde profiles show similar shapes and a good linear correlation of integrated XH2O, indicating that MAP is a reasonable approximation of the true atmospheric state and an appropriate choice for the scaling retrieval methods as applied by COCCON and TCCON. COCCON shows a reduced dry bias (−14.96 %) in comparison with TCCON (−19.08 %) with respect to radiosonde XH2O. Finally, we investigate the quality of satellite data at high latitudes. For this purpose, the COCCON XH2O is compared with retrievals from the Infrared Atmospheric Sounding Interferometer (IASI) generated with the MUSICA processor (MUSICA IASI) and with retrievals from the TROPOspheric Monitoring Instrument (TROPOMI). Both paired datasets generally show good agreement and similar correlations at the two sites. COCCON measures 4.64 % less XH2O at Kiruna and 3.36 % less at Sodankylä with respect to MUSICA IASI, whereas COCCON measures 9.71 % more XH2O at Kiruna and 7.75 % more at Sodankylä compared with TROPOMI. Our study supports the assumption that COCCON also delivers a well-characterized XH2O data product. This emphasizes that this approach might complement the TCCON network with respect to satellite validation efforts. This is the first published study where COCCON XH2O has been compared with MUSICA NDACC and TCCON retrievals and has been used for MUSICA IASI and TROPOMI validation.

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Strategy for high-accuracy-and-precision retrieval of atmospheric methane from the mid-infrared FTIR network

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-4-2965-2011 ◽

2011 ◽

Vol 4 (3) ◽

pp. 2965-3015 ◽

Cited By ~ 3

Author(s):

R. Sussmann ◽

F. Forster ◽

M. Rettinger ◽

N. Jones

Keyword(s):

Diurnal Variation ◽

Near Infrared ◽

Regional Scale ◽

High Accuracy ◽

Total Carbon ◽

Atmospheric Composition ◽

Mid Infrared ◽

Dry Air ◽

Accuracy And Precision ◽

Retrieval Strategies

Abstract. We present a strategy (MIR-GBM v1.0) for the retrieval of column-averaged dry-air mole fractions of methane (XCH4) with a precision <0.3 % (1-σ diurnal variation, 7-min integration) and a seasonal bias <0.14 % from mid-infrared ground-based solar FTIR measurements of the Network for the Detection of Atmospheric Composition Change (NDACC, comprising 22 FTIR stations). This makes NDACC methane data useful for satellite validation and for the inversion of regional-scale sources and sinks in addition to long-term trend analysis. Such retrievals complement the high accuracy and precision near-infrared observations of the younger Total Carbon Column Observing Network (TCCON) with time series dating back 15 yr or so before TCCON operations began. MIR-GBM v1.0 is using HITRAN 2000 (including the 2001 update release) and 3 spectral micro windows (2613.70–2615.40 cm−1, 2835.50–2835.80 cm−1, 2921.00–2921.60 cm−1). A first-order Tikhonov constraint is applied to the state vector given in units of per cent of volume mixing ratio. It is tuned to achieve minimum diurnal variation without damping seasonality. Final quality selection of the retrievals uses a threshold for the ratio of root-mean-square spectral residuals and information content (<0.15 %). Column-averaged dry-air mole fractions are calculated using the retrieved methane profiles and four-times-daily pressure-temperature-humidity profiles from National Center for Environmental Prediction (NCEP) interpolated to the time of measurement. MIR-GBM v1.0 is the optimum of 24 tested retrieval strategies (8 different spectral micro-window selections, 3 spectroscopic line lists: HITRAN 2000, 2004, 2008). Dominant errors of the non-optimum retrieval strategies are HDO/H2O-CH4 interference errors (seasonal bias up to ≈4 %). Therefore interference errors have been quantified at 3 test sites covering clear-sky integrated water vapor levels representative for all NDACC sites (Wollongong maximum = 44.9 mm, Garmisch mean = 14.9 mm, Zugspitze minimum = 0.2 mm). The same quality ranking of the 24 strategies was found for all 3 test sites with one optimum, i.e., MIR-GBM v1.0. Seasonality of XCH4 above the Zugspitze (47° N) shows a minus-sine shape with a minimum in March/April, a maximum in September, and an amplitude of 16.3 ± 2.9 ppb (1.0 ± 0.2 %). This agrees very well with newest-version scientific retrievals from SCIAMACHY (WFM-DOAS v2.0). A conclusion from this paper is that improved spectroscopic parameters for CH4, HDO, and H2O in the 2613–2922 cm−1 spectral domain are urgently needed. If such become available with sufficient accuracy, at least two more spectral micro windows could be utilized leading to another improvement in precision. The absolute inter-calibration of NDACC MIR-GBM v1.0 XCH4 to TCCON data is subject of ongoing work.

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A new fully automated FTIR system for total column measurements of greenhouse gases

Atmospheric Measurement Techniques ◽

10.5194/amt-3-1363-2010 ◽

2010 ◽

Vol 3 (5) ◽

pp. 1363-1375 ◽

Cited By ~ 33

Author(s):

M. C. Geibel ◽

C. Gerbig ◽

D. G. Feist

Keyword(s):

Greenhouse Gases ◽

Total Carbon ◽

Web Based ◽

Final Destination ◽

Ascension Island ◽

Multiple Processes ◽

First Results ◽

Solar Tracker ◽

The Tropics ◽

Total Column

Abstract. This article introduces a new fully automated FTIR system that is part of the Total Carbon Column Observing Network (TCCON). It will provide continuous ground-based measurements of column-averaged volume mixing ratio for CO2, CH4 and several other greenhouse gases in the tropics. Housed in a 20-foot shipping container it was developed as a transportable system that could be deployed almost anywhere in the world. We describe the automation concept which relies on three autonomous subsystems and their interaction. Crucial components like a sturdy and reliable solar tracker dome are described in detail. The automation software employs a new approach relying on multiple processes, database logging and web-based remote control. First results of total column measurements at Jena, Germany show that the instrument works well and can provide parts of the diurnal as well as seasonal cycle for CO2. Instrument line shape measurements with an HCl cell suggest that the instrument stays well-aligned over several months. After a short test campaign for side by side intercomaprison with an existing TCCON instrument in Australia, the system will be transported to its final destination Ascension Island.

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Shipborne measurements of XCO2, XCH4, and XCO above the Pacific Ocean and comparison to CAMS atmospheric analyses and S5P/TROPOMI

Earth System Science Data ◽

10.5194/essd-13-199-2021 ◽

2021 ◽

Vol 13 (1) ◽

pp. 199-211

Author(s):

Marvin Knapp ◽

Ralph Kleinschek ◽

Frank Hase ◽

Anna Agustí-Panareda ◽

Antje Inness ◽

...

Keyword(s):

Pacific Ocean ◽

Excellent Agreement ◽

Total Carbon ◽

Atmospheric Composition ◽

Solar Absorption ◽

The Pacific ◽

Before And After ◽

Infrared Spectral ◽

Solar Tracker ◽

The Pacific Ocean

Abstract. Measurements of atmospheric column-averaged dry-air mole fractions of carbon dioxide (XCO2), methane (XCH4), and carbon monoxide (XCO) have been collected across the Pacific Ocean during the Measuring Ocean REferences 2 (MORE-2) campaign in June 2019. We deployed a shipborne variant of the EM27/SUN Fourier transform spectrometer (FTS) on board the German R/V Sonne which, during MORE-2, crossed the Pacific Ocean from Vancouver, Canada, to Singapore. Equipped with a specially manufactured fast solar tracker, the FTS operated in direct-sun viewing geometry during the ship cruise reliably delivering solar absorption spectra in the shortwave infrared spectral range (4000 to 11000 cm−1). After filtering and bias correcting the dataset, we report on XCO2, XCH4, and XCO measurements for 22 d along a trajectory that largely aligns with 30∘ N of latitude between 140∘ W and 120∘ E of longitude. The dataset has been scaled to the Total Carbon Column Observing Network (TCCON) station in Karlsruhe, Germany, before and after the MORE-2 campaign through side-by-side measurements. The 1σ repeatability of hourly means of XCO2, XCH4, and XCO is found to be 0.24 ppm, 1.1 ppb, and 0.75 ppb, respectively. The Copernicus Atmosphere Monitoring Service (CAMS) models gridded concentration fields of the atmospheric composition using assimilated satellite observations, which show excellent agreement of 0.52±0.31 ppm for XCO2, 0.9±4.1 ppb for XCH4, and 3.2±3.4 ppb for XCO (mean difference ± SD, standard deviation, of differences for entire record) with our observations. Likewise, we find excellent agreement to within 2.2±6.6 ppb with the XCO observations of the TROPOspheric MOnitoring Instrument (TROPOMI) on the Sentinel-5 Precursor satellite (S5P). The shipborne measurements are accessible at https://doi.org/10.1594/PANGAEA.917240 (Knapp et al., 2020).

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TCCON and NDACC XCO measurements: difference, discussion and application

10.5194/amt-2019-266 ◽

2019 ◽

Author(s):

Minqiang Zhou ◽

Bavo Langerock ◽

Corinne Vigouroux ◽

Mahesh Kumar Sha ◽

Christian Hermans ◽

...

Keyword(s):

Fourier Transform ◽

A Priori ◽

Mean Value ◽

Scaling Factor ◽

Total Carbon ◽

Atmospheric Composition ◽

Composition Change ◽

Dry Air ◽

The Common ◽

Using Data

Abstract. Column-averaged dry-air mole fraction of CO (XCO) measurements are obtained from two ground-based Fourier transform infrared (FTIR) spectrometers networks: the Total Carbon Column Observing Network (TCCON) and the Network for the Detection of Atmospheric Composition Change (NDACC). In this study, the differences between the TCCON and NDACC XCO measurements are investigated and discussed based on six NDACC/TCCON sites using data over the period 2007–2017. The NDACC XCO measurements are about 5.5 % larger than the TCCON data at Ny-Ålesund, Bremen, and Izaña (Northern Hemisphere), and about 0.3 % larger than the TCCON data at St Denis, Wollongong and Lauder (Southern Hemisphere). The hemispheric dependence of the bias is mainly attributed to their smoothing errors. The systematic smoothing error of the TCCON XCO data varies in the range between 0.2 % (Bremen) and 7.9 % (Lauder), and the random smoothing error in the range between 2.0 % and 3.6 %. The systematic smoothing error of NDACC data is between 0.1 % and 0.8 %, and the random smoothing error of NDACC data is about 0.3 %. For TCCON data, the smoothing error can be significant in that it is much higher than the reported uncertainty for TCCON XCO. To reduce the influence from the a priori profiles and different vertical sensitivities, the scaled NDACC a priori profiles are used as the common a priori profiles for comparing TCCON and NDACC retrievals. As a result, the biases between TCCON and NDACC XCO measurements become more consistent (5.6–8.5 %) with a mean value of 6.8 % at these sites. To understand the remaining bias, regular AirCore measurements at Orleans and Sodankylä are compared to co-located TCCON measurements. It is found that TCCON XCO measurements are 6.0 ± 1.9 % and 6.9 ± 2.5 % smaller than the AirCore measurements at Orleans and Sodankylä respectively, indicating that the scaling factor of TCCON XCO data should be around 1.0000 instead of 1.0672. Further investigations should be carried out in the TCCON community to determine the correct scaling factor to be applied to the TCCON XCO data. This paper also demonstrates that the smoothing error must be taken into account when comparing FTIR XCO data, and especially TCCON XCO data, with model or satellite data.

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A fully automated FTIR system for remote sensing of greenhouse gases in the tropics

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-3-3067-2010 ◽

2010 ◽

Vol 3 (4) ◽

pp. 3067-3103 ◽

Cited By ~ 2

Author(s):

M. C. Geibel ◽

C. Gerbig ◽

D. G. Feist

Keyword(s):

Greenhouse Gases ◽

Total Carbon ◽

Final Destination ◽

Shipping Container ◽

Ascension Island ◽

First Results ◽

Solar Tracker ◽

Short Test ◽

The Tropics ◽

Total Column

Abstract. This article introduces a new fully automated FTIR system that is part of the Total Carbon Column Observing Network. It will provide continuous ground-based measurements of column-averaged volume mixing ratio for CO2, CH4 and several other greenhouse gases in the tropics. Housed in a 20-foot shipping container it was developed as a transportable system that could be deployed almost anywhere in the world. We describe the automation concept which relies on three autonomous subsystems and their interaction. Crucial components like a sturdy and reliable solar tracker dome are described in detail. First results of total column measurements at Jena, Germany show that the instrument works well and can provide diurnal as well as seasonal cycle for CO2. Instrument line shape measurements with an HCl cell suggest that the instrument stays well-aligned over several months. After a short test campaign for side by side intercomaprison with an existing TCCON instrument in Australia, the system will be transported to its final destination Ascension Island.

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Rugged optical mirrors for Fourier-Transform Spectrometers operated in harsh environments