TY - JOUR
T1 - Characterization and potential for reducing optical resonances in Fourier transform infrared spectrometers of the Network for the Detection of Atmospheric Composition Change (NDACC)
AU - Blumenstock, Thomas
AU - Hase, Frank
AU - Keens, Axel
AU - Czurlok, Denis
AU - Colebatch, Orfeo
AU - Garcia, Omaira
AU - Griffith, David W.T.
AU - Grutter, Michel
AU - Hannigan, James W.
AU - Heikkinen, Pauli
AU - Jeseck, Pascal
AU - Jones, Nicholas
AU - Kivi, Rigel
AU - Lutsch, Erik
AU - Makarova, Maria
AU - Imhasin, Hamud K.
AU - Mellqvist, Johan
AU - Morino, Isamu
AU - Nagahama, Tomoo
AU - Notholt, Justus
AU - Ortega, Ivan
AU - Palm, Mathias
AU - Raffalski, Uwe
AU - Rettinger, Markus
AU - Robinson, John
AU - Schneider, Matthias
AU - Servais, Christian
AU - Smale, Dan
AU - Stremme, Wolfgang
AU - Strong, Kimberly
AU - Sussmann, Ralf
AU - Té, Yao
AU - Velazco, Voltaire A.
N1 - Publisher Copyright:
© Author(s) 2021. This work is distributed under the Creative Commons Attribution 4.0 License.
PY - 2021/2/17
Y1 - 2021/2/17
N2 - 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.
AB - 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.
UR - https://www.scopus.com/pages/publications/85100943870
U2 - 10.5194/amt-14-1239-2021
DO - 10.5194/amt-14-1239-2021
M3 - Article
AN - SCOPUS:85100943870
SN - 1867-1381
VL - 14
SP - 1239
EP - 1252
JO - Atmospheric Measurement Techniques
JF - Atmospheric Measurement Techniques
IS - 2
ER -