the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Digitization and calibration of historical solar absorption infrared spectra from the Jungfraujoch site
Abstract. This study describes the digitization and calibration of historically significant solar absorption spectra recorded at the Jungfraujoch International Scientific Station in the 1950s. Using a homemade Pfund-type grating spectrometer, these spectra were recorded on paper rolls to study the solar spectrum which was then used to compile a solar atlas between 2.8 and 23.7 microns (~421 to 3571 cm−1) that later contributed to the development of the HITRAN database. We now digitized these old spectra to make them available for atmospheric studies. Our approach involves image processing techniques, including colour masking for digitization and peak detection for accurate wavenumber calibration against a synthetic spectrum.
We also developed a validation method by re-digitizing degraded FTIR spectra to the same resolution as the old spectra to evaluate the digitization accuracy. Furthermore, we studied the influence of line thickness on the digitization error.
The number of spectra transformed into a machine-readable format is 108 (freely available for download), with an average digitization error of 1.55 % and a wavenumber shift standard diviation of 0.075 cm−1. These digitized and calibrated spectra now offer a valuable resource for atmospheric studies, providing essential historical data for atmospheric research. This work not only helps to preserve scientific heritage but also enhances the utility of historical data in contemporary research.
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RC1: 'Comment on amt-2024-93', Anonymous Referee #1, 03 Oct 2024
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Review of “Digitization and calibration of historical solar absorption infrared spectra from the Jungfraujoch site”. amt-2024-93 by
Jamal Makkor, Mathias Palm, Matthias Buschmann, Emmanuel Mahieu, Martyn P. Chipperfield, and Justus Notholt
This paper describes the technical details of digitizing analog recorded spectra on paper rolls about 75 years old and calibrating the spectra for trace gas abundance measurements. This is an important and interesting contribution and should be published.
The paper loses clarity in the discussion of the ‘calibration’. See below for more detail/questions. The section on calibration should have a major revision. The accounting of airmass and wavenumber dependent spectral resolution need to be detailed and properly accounted for. The fitting process needs more detail. The use of re-digitized printed spectra is interesting but re-affirms only a small source of possible quantitative error.
L4: “microns (~421 to 3571cm−1 ) that later contributed to the development of the HITRAN database.” rather: “microns (~421 to 3571cm−1 ) that *in particular* later contributed to the development of the HITRAN database”
L4: “We now digitized these old… rather: “We now digitized these analog recorded…
L17: technologies (Zander et al., 2008). Its strategic location at high altitude, coupled with minimal interference from pollution and… Are there other instruments a the JFJ / Sphinx that are no described in Zander 2008? Should there be other references?
L21: “from the late 1950 to 1980 a seven” rather: “from the late 1950’s to 1980 a seven…
L22: “near-UV near-IR” rather: “near-UV to near-IR…
L30: “covering a broad range of wavenumbers… rather: “covering a wide spectral range…
L35: “through visual comparison with high-resolution spectra. -> which high resolution spectra?
Fig 1b. Was the instrument using a multipass cell in particular? There are multi pass cell Pfund types but not all are multi cell. An accurate diagram here is important.
L104: “This gives us a relative mean digitization error of about: ε = (9.3∗100)/600 = 1.55%”. If there are 9.3 pixel uncertainty in a page not an inch. So a page (or ordinate scale) of (for instance) 5 inches has 3000 pixels so the nominal error is ~x5 less?
L121: “The choice of the apodization function for the interferograms is connected to the instrumental properties of a grating spectrometer, since for a diffraction limited resolution, where the image of the spectral line is no longer the same shape as the entrance slit but controlled by the diffraction pattern, the instrumental line function in the spectral domain corresponds to a sinc2 func-“
This description should be more detailed or better yet left out and simply use a reference. Development or explanation of a grating instrument function is not important here.
L 126: Since the spectral resolution variation of the grating wrt wavenumber is known why was this variation not used? Or discrete smaller sections of the spectrum fitted with slight increasing (or decreasing) resolutions.
L133: its not clear what specific calibration is being performed. There is baseline, spectral resolution, wavenumber scale, 100% transmission to be considered.
L147: Is this the SFIT fitting or some other fitting technique using the sfit generated spectrum? What parameters are being fitted? Perhaps a defined equation would be clearer.
L150: “saved as a text format… rather “saved in a text format file…
L173: Its not clear what this description is for? Do we not believe PVLIB?
For a record time of ~1.5h and more : what time was used for SZA / airmass calculation?
The term detection boundary and detection limit are used interchangeably perhaps better is the term ‘peak threshold’ would be clearer, less ambiguity, that we are talking about the ordinate region where peaks are determined.
Citation: https://doi.org/10.5194/amt-2024-93-RC1
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