Characterization and potential for reducing optical resonances in Fourier transform infrared spectrometers of the Network for the Detection of Atmospheric Composition Change (NDACC)
Artikel i vetenskaplig tidskrift, 2021

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.

Författare

T. Blumenstock

Karlsruher Institut für Technologie (KIT)

F. Hase

Karlsruher Institut für Technologie (KIT)

Axel Keens

Bruker Optics Inc.

Denis Czurlok

Bruker Optics Inc.

Orfeo Colebatch

University of Toronto

O. Garcia

Meteorological State Agency of Spain (AEMET)

David W.T. Griffith

University of Wollongong

M. Grutter

Universidad Nacional Autonoma de Mexico

J. W. Hannigan

National Center for Atmospheric Research

Pauli Heikkinen

Finnish Meteorological Institute

Pascal Jeseck

Université Pierre et Marie Curie (UPMC)

N. Jones

University of Wollongong

Rigel Kivi

Finnish Meteorological Institute

Erik Lutsch

University of Toronto

M. V. Makarova

Saint Petersburg State University - Spsu

Hamud K. Imhasin

Saint Petersburg State University - Spsu

Johan Mellqvist

Chalmers, Rymd-, geo- och miljövetenskap, Mikrovågs- och optisk fjärranalys

Isamu Morino

National Institute for Environmental Studies of Japan

Tomoo Nagahama

Nagoya University

J. Notholt

Universität Bremen

Ivan Ortega

National Center for Atmospheric Research

Mathias Palm

Universität Bremen

U. Raffalski

Institutet for rymdfysik

M. Rettinger

Karlsruher Institut für Technologie (KIT)

John Robinson

National Institute of Water and Atmospheric Research, New Zealand

Matthias Schneider

Karlsruher Institut für Technologie (KIT)

C. Servais

Universite de Liège

Dan Smale

National Institute of Water and Atmospheric Research, New Zealand

W. Stremme

Universidad Nacional Autonoma de Mexico

K. Strong

University of Toronto

R. Sussmann

Karlsruher Institut für Technologie (KIT)

Yao Té

Université Pierre et Marie Curie (UPMC)

V. Velazco

University of Wollongong

Atmospheric Measurement Techniques

1867-1381 (ISSN) 1867-8548 (eISSN)

Vol. 14 2 1239-1252

Ämneskategorier

Acceleratorfysik och instrumentering

Atom- och molekylfysik och optik

Signalbehandling

DOI

10.5194/amt-14-1239-2021

Mer information

Senast uppdaterat

2021-03-18