Characterization and potential for reducing optical resonances in Fourier transform infrared spectrometers of the Network for the Detection of Atmospheric Composition Change (NDACC)

Although optical components in Fourier transform infrared (FTIR) spectrometers are preferably wedged, in practice, infrared spectra typically suffer from the effects of optical resonances (“channeling”) affecting the retrieval of weakly absorbing gases. This study investigates the level of channeling of each FTIR spectrometer within the Network for the Detection of Atmospheric Composition Change (NDACC). Dedicated spectra were recorded by more than 20 NDACC FTIR spectrometers using a laboratory mid-infrared source and two detectors. In the indium antimonide (InSb) detector domain (1900–5000 cm−1), we found that the amplitude of the most pronounced channeling frequency amounts to 0.1 ‰ to 2.0 ‰ of the spectral background level, with a mean of (0.68±0.48) ‰ and a median of 0.60 ‰. In the mercury cadmium telluride (HgCdTe) detector domain (700–1300 cm−1), we find even stronger effects, with the largest amplitude ranging from 0.3 ‰ to 21 ‰ with a mean of (2.45±4.50) ‰ and a median of 1.2 ‰. For both detectors, the leading channeling frequencies are 0.9 and 0.11 or 0.23 cm−1 in most spectrometers. The observed spectral frequencies of 0.11 and 0.23 cm−1 correspond to the optical thickness of the beam splitter substrate. The 0.9 cm−1 channeling is caused by the air gap in between the beam splitter and compensator plate. Since the air gap is a significant source of channeling and the corresponding amplitude differs strongly between spectrometers, we propose new beam splitters with the wedge of the air gap increased to at least 0.8∘. We tested the insertion of spacers in a beam splitter's air gap to demonstrate that increasing the wedge of the air gap decreases the 0.9 cm−1 channeling amplitude significantly. A wedge of the air gap of 0.8∘ reduces the channeling amplitude by about 50 %, while a wedge of about 2∘ removes the 0.9 cm−1 channeling completely. This study shows the potential for reducing channeling in the FTIR spectrometers operated by the NDACC, thereby increasing the quality of recorded spectra across the network.

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Author Blumenstock, Thomas
Hase, Frank
Keens, Axel
Czurlok, Denis
Colebatch, Orfeo
Garcia, Omaira
Griffith, David W. T.
Grutter, Michel
Hannigan, James W.
Heikkinen, Pauli
Jeseck, Pascal
Jones, Nicholas
Kivi, Rigel
Lutsch, Erik
Makarova, Maria
Imhasin, Hamud K.
Mellqvist, Johan
Morino, Isamu
Nagahama, Tomoo
Notholt, Justus
Ortega, Ivan
Palm, Mathias
Raffalski, Uwe
Rettinger, Markus
Robinson, John
Schneider, Matthias
Servais, Christian
Smale, Dan
Stremme, Wolfgang
Strong, Kimberly
Sussmann, Ralf
Té, Yao
Velazco, Voltaire A.
Publisher UCAR/NCAR - Library
Publication Date 2021-02-17T00:00:00
Digital Object Identifier (DOI) Not Assigned
Alternate Identifier N/A
Resource Version N/A
Topic Category geoscientificInformation
Progress N/A
Metadata Date 2023-08-18T18:08:30.095761
Metadata Record Identifier edu.ucar.opensky::articles:24075
Metadata Language eng; USA
Suggested Citation Blumenstock, Thomas, Hase, Frank, Keens, Axel, Czurlok, Denis, Colebatch, Orfeo, Garcia, Omaira, Griffith, David W. T., Grutter, Michel, Hannigan, James W., Heikkinen, Pauli, Jeseck, Pascal, Jones, Nicholas, Kivi, Rigel, Lutsch, Erik, Makarova, Maria, Imhasin, Hamud K., Mellqvist, Johan, Morino, Isamu, Nagahama, Tomoo, Notholt, Justus, Ortega, Ivan, Palm, Mathias, Raffalski, Uwe, Rettinger, Markus, Robinson, John, Schneider, Matthias, Servais, Christian, Smale, Dan, Stremme, Wolfgang, Strong, Kimberly, Sussmann, Ralf, Té, Yao, Velazco, Voltaire A.. (2021). Characterization and potential for reducing optical resonances in Fourier transform infrared spectrometers of the Network for the Detection of Atmospheric Composition Change (NDACC). UCAR/NCAR - Library. Accessed 23 September 2023.

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