Simultaneous ground-based observations of O<sub>3</sub>, HCl, N<sub>2</sub>O, and CH<sub>4</sub> over Toronto, Canada by three Fourier transform spectrometers with different resolutions

Abstract

Abstract. An intercomparison of three Fourier transform spectrometers (FTSs) with significantly different resolutions is presented. The highest-resolution instrument has a maximum optical path difference of 250 cm, and the two lowerresolution instruments have maximum optical path differences of 50 cm and 25 cm. The results indicate that the two lower-resolution instruments can retrieve total column amounts of O 3 , HCl, N 2 O and CH 4 using the SFIT2 retrieval code with percent differences from the high-resolution instrument generally better than 4%. Total column amounts of the stratospheric species (O 3 and HCl) have larger differences than those of the tropospheric species (N 2 O and CH 4 ). Instrument line shape (ILS) information is found to be of critical importance when retrieving total columns of stratospheric gases from the lower-resolution instruments. Including the ILS information in the retrievals significantly reduces the difference in total column amounts between the three instruments. The remaining errors for stratospheric species total column amounts can be attributed to the lower sensitivity of the lower-resolution FTSs to the stratosphere.

Four Fourier transform spectrometers and the Arctic polar vortex: instrument intercomparison and ACE-FTS validation at Eureka during the IPY springs of 2007 and 2008

“…These differences are comparable in magnitude with other side-byside instrument comparisons carried out at Eureka (Fu et al, 2008;Paton-Walsh et al, 2009;Batchelor et al, 2009) and around the globe (Goldman et al, 1999;Griffiths et al, 2005;Wunch et al, 2007).…”

“…The only difference from that work is that for PARIS-IR, retrievals have been performed on a 29-rather than the 38-layer grid used for the DA8 and 125HR, to allow for its lower spectral resolution. This has been previously shown to result in differences in the retrieved column of less than 0.6% (Wunch et al, 2007), but helps to reduce unphysical oscillations in the retrieved profile. A priori VMR profiles and covariances, described in Sung et al (2010), were consistent for all three instruments, while ad hoc SNR ratios, which are used for determining the measurement covariance, were selected for each gas for each instrument using the trade-off curve method described in Batchelor et al (2009) to customize for the noise level in the spectra of the individual instruments.…”

Intercomparison of ground-based ozone and NO<sub>2</sub> measurements during the MANTRA 2004 campaign

“…Comparisons of these data sets are underway (Kerzenmacher et al, 2005;Sung et al, 2007). PARIS-IR and the U of T FTS also took part in an intercomparison study at the Toronto Atmospheric Observatory in August 2005 which is described by Wunch et al (2007).…”

Simultaneous trace gas measurements using two Fourier transform spectrometers at Eureka, Canada during spring 2006, and comparisons with the ACE-FTS

“…For the apodization function, the DA8 FTS used a Hamming function and PARIS-IR used a boxcar function. In earlier comparisons, it was demonstrated that it is necessary to have a well-characterized instrument line shape (ILS) in order to retrieve accurate total columns of stratospheric gases from PARIS-IR spectra (Wunch et al, 2007). In this current work, we used the LINEFIT program (Hase et al, 1999, version 11) to retrieve ILS information for the two FTSs from N 2 O features between 2400 and 2800 cm −1 .…”