Investigating differences in DOAS retrieval codes using MAD-CAT campaign data

Peters, Enno; Pinardi, Gaia; Seyler, André; Richter, Andreas; Wittrock, F.; Bösch, Tim; Roozendaël, Michel Van; Hendrick, F.; Δρόσογλου, Θεανώ; Bais, A. F.; Kanaya, Yugo; Zhao, Xiaoyi; Strong, Kimberly; Lampel, Johannes; Volkamer, Rainer; Koenig, Theodore K.; Ortega, Ivan; Puentedura, Olga; Navarro-Comas, Mónica; Gómez, Laura; Yela, Margarita; Piters, Ankie; Remmers, Julia; Wang, Yang; Wagner, Thomas; Wang, Shanshan; Saiz‐Lopez, Alfonso; García-Nieto, David; Cuevas, Carlos A.; Benavent, Nuria; Querel, Richard; Johnston, P. V.; Postylyakov, O. V.; Borovski, Alexander; Елохов, А. С.; Bruchkouski, Ilya; Liu, Haoran; Liu, Cheng; Hong, Qianqian; Rivera, Claudia; Grütter, Michel; Stremme, Wolfgang; Khokhar, Muhammad Fahim; Khayyam, Junaid; Burrows, J. P.

doi:10.5194/amt-10-955-2017

Cited by 21 publications

(19 citation statements)

References 40 publications

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“…M07 is the current instrument contributing to the continuous time series of stratospheric NO 2 from Lauder that started in 1980 and is part of the Network for Detection of Atmospheric Composition Change (NDACC) (Hofmann et al, 1995;Roscoe et al, 1999). The NDACC-certified M07 instrument has been described previously (McKenzie and Johnston, 1982;McKenzie et al, 1992;Hofmann et al, 1995) as has the STRATO retrieval software that was built inhouse (Peters et al, 2017). Briefly, M07 is a Czerny-Turner monochromator (320 mm focal length, ≈ 0.8 nm resolution, F/5 entrance field of view, 1 mm wide slit) with a bi-alkali photocathode photomultiplier detector.…”

Section: Niwa Spectrometermentioning

confidence: 99%

Intercomparison of Pandora stratospheric NO<sub>2</sub> slant column product with the NDACC-certified M07 spectrometer in Lauder, New Zealand

et al. 2017

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Abstract. In September 2014, a Pandora multi-spectral photometer operated by the SAGE-III project was sent to Lauder, New Zealand, to operate side-by-side with the National Institute of Water and Atmospheric Research's (NIWA) Network for Detection of Atmospheric Composition Change (NDACC) certified zenith slant column NO 2 instrument to allow intercomparison between the two instruments and for evaluation of the Pandora unit as a potential SAGE-III validation tool for stratospheric NO 2 . This intercomparison spanned a full year, from September 2014 to September 2015. Both datasets were produced using their respective native algorithms using a common reference spectrum (i.e., 12:00 NZDT (UTC + 13) on 26 February 2015). Throughout the entire deployment period both instruments operated in a zenith-only observation configuration. Though conversion from slant column density (SCD) to vertical-column density is routine (by application of an air mass factor), we limit the current analysis to SCD only. This omission is beneficial in that it provides an intercomparison based on similar modes of operation for the two instruments and the retrieval algorithms as opposed to introducing an air mass factor dependence in the intercomparison as well. It was observed that the current hardware configurations and retrieval algorithms are in good agreement (R > 0.95). The detailed results of this investigation are presented herein.

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Section: Niwa Spectrometermentioning

confidence: 99%

Intercomparison of Pandora stratospheric NO<sub>2</sub> slant column product with the NDACC-certified M07 spectrometer in Lauder, New Zealand

et al. 2017

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“…The different phenomenon of the intensity offset effect on HONO delta SCD between the two groups of institutes might be caused by differences in the implementation of intensity offset correction in the DOAS fit software codes. Peters et al (2017) have already demonstrated that different linear fit approach of the intensity offset correction implemented in the DOAS fit can considerably impact the retrieved dSCDs. However nonlinear fits used in QDOAS, WINDOAS and MDOAS were not included in their study.…”

Section: Synthetic Spectra and Inter-comparisonsmentioning

confidence: 99%

“…A description of the MAD-CAT measurement campaign can be found at http://joseba.mpch-mainz.mpg.de/ mad_cat.htm. Data from this campaign have been so far used in, for example, Ortega et al (2015), Lampel et al (2015Lampel et al ( , 2017a and Peters et al (2017).…”

Section: The Mad-cat Inter-comparison Campaignmentioning

confidence: 99%

MAX-DOAS measurements of HONO slant column densities during the MAD-CAT campaign: inter-comparison, sensitivity studies on spectral analysis settings, and error budget

et al. 2017

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Abstract. In order to promote the development of the passive DOAS technique the Multi Axis DOAS -Comparison campaign for Aerosols and Trace gases (MAD-CAT) was held at the Max Planck Institute for Chemistry in Mainz, Germany, from June to October 2013. Here, we systematically compare the differential slant column densities (dSCDs) of nitrous acid (HONO) derived from measurements of seven different instruments. We also compare the tropospheric difference of SCDs (delta SCD) of HONO, namely the difference of the SCDs for the non-zenith observations and the zenith observation of the same elevation sequence. Different research groups analysed the spectra from their own instruments using their individual fit software. All the fit errors of HONO dSCDs from the instruments with cooled large-size detectors are mostly in the range of 0.1 to 0.3 × 10 15 molecules cm −2 for an integration time of 1 min. The fit error for the mini MAX-DOAS is around 0.7 × 10 15 molecules cm −2 . Although the HONO delta SCDs are normally smaller than 6 × 10 15 molecules cm −2 , consistent time series of HONO delta SCDs are retrieved from the measurements of different instruments. Both fits with a sequential Fraunhofer reference spectrum (FRS) and a daily noon FRS lead to similar consistency. Apart from the mini-MAX-DOAS, the systematic absolute differences of HONO delta SCDs between the instruments are smaller than 0.63 × 10 15 molecules cm −2 . The correlation coefficients are higher than 0.7 and the slopes of linear regressions deviate from unity by less than 16 % for the elevation angle of 1 • . The correlations decrease with an increase in elevation angle. All the participants also analysed synthetic spectra using the same baseline DOAS settings toPublished by Copernicus Publications on behalf of the European Geosciences Union. Y. Wang et al.: MAX-DOAS measurements of HONO slant column densitiesevaluate the systematic errors of HONO results from their respective fit programs. In general the errors are smaller than 0.3 × 10 15 molecules cm −2 , which is about half of the systematic difference between the real measurements.The differences of HONO delta SCDs retrieved in the selected three spectral ranges 335-361, 335-373 and 335-390 nm are considerable (up to 0.57 × 10 15 molecules cm −2 ) for both real measurements and synthetic spectra. We performed sensitivity studies to quantify the dominant systematic error sources and to find a recommended DOAS setting in the three spectral ranges. The results show that water vapour absorption, temperature and wavelength dependence of O 4 absorption, temperature dependence of Ring spectrum, and polynomial and intensity offset correction all together dominate the systematic errors. We recommend a fit range of 335-373 nm for HONO retrievals. In such fit range the overall systematic uncertainty is about 0.87 × 10 15 molecules cm −2 , much smaller than those in the other two ranges. The typical random uncertainty is estimated to be about 0.16 × 10 15 molecules cm −2 , which is only 25 % of the total syst...

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“…Data from this campaign have been already published, e.g. in Ortega et al (2015), Lampel et al (2015), Peters et al (2017) and Wang et al (2017). …”

Section: Measurement Sitementioning

confidence: 99%

“…This option was originally introduced into the different analysis software to account for real shifts caused by instrumental instabilities (compare e.g. Peters et al, 2017). In fact, the observed shifts derived from the spectral analysis were usually attributed to such instrumental stabilities only.…”

Section: Introductionmentioning

confidence: 99%

The tilt effect in DOAS observations

et al. 2017

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Abstract. Experience of differential atmospheric absorption spectroscopy (DOAS) shows that a spectral shift between measurement spectra and reference spectra is frequently required in order to achieve optimal fit results, while the straightforward calculation of the optical density proves inferior. The shift is often attributed to temporal instabilities of the instrument but implicitly solved the problem of the tilt effect discussed/explained in this paper.Spectral positions of Fraunhofer and molecular absorption lines are systematically shifted for different measurement geometries due to an overall slope -or tilt -of the intensity spectrum. The phenomenon has become known as the tilt effect for limb satellite observations, where it is corrected for in a first-order approximation, whereas the remaining community is less aware of its cause and consequences.It is caused by the measurement process, because atmospheric absorption and convolution in the spectrometer do not commute. Highly resolved spectral structures in the spectrum will first be modified by absorption and scattering processes in the atmosphere before they are recorded with a spectrometer, which convolves them with a specific instrument function. In the DOAS spectral evaluation process, however, the polynomial (or other function used for this purpose) accounting for broadband absorption is applied after the convolution is performed.In this paper, we derive that changing the order of the two modifications of the spectra leads to different results. Assuming typical geometries for the observations of scattered sunlight and a spectral resolution of 0.6 nm, this effect can be interpreted as a spectral shift of up to 1.5 pm, which is confirmed in the actual analysis of the ground-based measurements of scattered sunlight as well as in numerical radiative transfer simulations. If no spectral shift is allowed by the fitting routine, residual structures of up to 2.5 × 10 −3 peak-topeak are observed. Thus, this effect needs to be considered for DOAS applications aiming at an rms of the residual of 10 −3 and below.

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Investigating differences in DOAS retrieval codes using MAD-CAT campaign data

Cited by 21 publications

References 40 publications

Intercomparison of Pandora stratospheric NO<sub>2</sub> slant column product with the NDACC-certified M07 spectrometer in Lauder, New Zealand

Intercomparison of Pandora stratospheric NO<sub>2</sub> slant column product with the NDACC-certified M07 spectrometer in Lauder, New Zealand

MAX-DOAS measurements of HONO slant column densities during the MAD-CAT campaign: inter-comparison, sensitivity studies on spectral analysis settings, and error budget

The tilt effect in DOAS observations

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Investigating differences in DOAS retrieval codes using MAD-CAT campaign data

Cited by 21 publications

References 40 publications

Intercomparison of Pandora stratospheric NO&lt;sub&gt;2&lt;/sub&gt; slant column product with the NDACC-certified M07 spectrometer in Lauder, New Zealand

Intercomparison of Pandora stratospheric NO&lt;sub&gt;2&lt;/sub&gt; slant column product with the NDACC-certified M07 spectrometer in Lauder, New Zealand

MAX-DOAS measurements of HONO slant column densities during the MAD-CAT campaign: inter-comparison, sensitivity studies on spectral analysis settings, and error budget

The tilt effect in DOAS observations

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Intercomparison of Pandora stratospheric NO<sub>2</sub> slant column product with the NDACC-certified M07 spectrometer in Lauder, New Zealand

Intercomparison of Pandora stratospheric NO<sub>2</sub> slant column product with the NDACC-certified M07 spectrometer in Lauder, New Zealand