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 - Funding Information: Financial support. Part of this work was supported by Ministerio de Economía y Competitividad from Spain (project INMENSE no. CGL2016-80688-P). The Altzomoni site UNAM (DGAPA (grant nos. IN111418 and IN107417)) was supported by the CONACYT (grant no. 290589) and PASPA. The Paris site has received funding from Sorbonne Université, the French research center (CNRS) and the French space agency (CNES). Operations at the Rikubetsu and Tsukuba sites are supported in part by the GOSAT series project. The SPbU team was supported by Russian Foundation for Basic Research (project no. 18-05-00011). The Lauder and Arrival Heights FTIR measurements are core funded by NIWA through New Zealand’s Ministry of Business, Innovation and Employment Strategic Science Investment Fund. Antarctica New Zealand supported the FTIR measurements at Arrival Heights, which includes test spectra collection. The Jungfraujoch FTIR experiment has received funding from the FRS – FNRS, Fédération Wallonie-Bruxelles, both in Brussels, Belgium, and from the GAW-CH program of MeteoSwiss. Eureka measurements were made at the Polar Environment Atmospheric Research Laboratory (PEARL), primarily supported by the Natural Sciences and Engineering Research Council of Canada (NSERC), Environment and Climate Change Canada, and the Canadian Space Agency. Toronto measurements were made at the University of Toronto Atmospheric Observatory (TAO), primarily supported by NSERC and the Uni- versity of Toronto. The National Center for Atmospheric Research is sponsored by the National Science Foundation. The NCAR FTS observation programs at Thule, GR, Mauna Loa, HI, and Boulder, CO, are supported under contract by the National Aeronautics and Space Administration (NASA). The Bremen, Garmisch, Izaña, Karlsruhe and Ny-Ålesund FTIR stations have been supported by the German Bundesministerium für Wirtschaft und Energie (BMWi) via DLR (grant nos. 50EE1711A-B and D). This work has been supported by the Federal Ministry of Education and Research (BMBF) Germany in the project TroStra (grant no. 01LG1904A). Publisher Copyright: © Author(s) 2021. This work is distributed under the Creative Commons Attribution 4.0 License. Copyright: Copyright 2021 Elsevier B.V., All rights reserved.

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.

KW - HIGH-RESOLUTION

KW - PRECISION

KW - SPECTRA

UR - http://www.scopus.com/inward/record.url?scp=85100943870&partnerID=8YFLogxK

U2 - 10.5194/amt-14-1239-2021

DO - 10.5194/amt-14-1239-2021

M3 - Article

AN - SCOPUS:85100943870

VL - 14

SP - 1239

EP - 1252

JO - Atmospheric Measurement Techniques

JF - Atmospheric Measurement Techniques

SN - 1867-1381

IS - 2

ER -