High‐Accuracy Near‐Infrared Carbon Dioxide Intensity Measurements to Support Remote Sensing

Abstract

Two cavity ring‐down spectrometers were employed to accurately measure line intensities in a series of near‐infrared carbon dioxide bands including (30012) ← (00001), (30013) ← (00001), and (30014) ← (00001) near 1.6 μm. Relative combined standard uncertainties for these band intensities were less than 0.1% and showed significant, percent‐level deviations with respect to many existing spectroscopic databases (although close agreement was observed with the HITRAN 2016 database in the (30013) ← (00001) and (30014) ← (00001) bands). Further, the resulting line intensities were utilized in Total Carbon Column Observing Network retrievals and led to significantly reduced biases in the (30012) ← (00001) and (30013) ← (00001) bands. These results indicate that refinements of spectroscopic databases are required to meet the accuracy targets of both ground‐ and satellite‐based remote sensing missions.

Absolute 13C/12C isotope amount ratio for Vienna PeeDee Belemnite from infrared absorption spectroscopy

“…To evaluate uncertainty in the predicted 13 C 16 O 2 transition intensities, we also calculated transition intensities for 12 C 16 O 2 and compared with highly accurate experiments 33,[47][48][49] . For ground-state rotational quantum numbers of J″ = 12 and J″ = 18 we find that, for five near-infrared vibrational bands of 12 C 16 O 2 , the standard deviation of a uniform distribution chosen to represent the experimental measurements relative to the predictions of our updated ab initio DMS is equal to 3.8 × 10 −3 .…”

The update of the line positions and intensities in the line list of carbon dioxide for the HITRAN2020 spectroscopic database

“…In particular, the accurate values of the line intensities with uncertainties as low as 0.3%-0.5% [49] are necessary for forward models used in retrievals of CO2 concentrations from some remote sensing missions. A number of very accurate measurements have become available after the release of HITRAN2016 in the NIR region: the most recent CRDS measurements from NIST [19,20] and FTS measurements from DLR reported in Birk et al [22] (with the corresponding measurements and line parameter database provided on Zenodo [21]).…”

“…For wavenumbers below 8000 cm -1 , we discuss line intensity updates to the HITRAN2016 line list for bands provided by the Carbon Dioxide Spectroscopic Databank (CDSD) based on global fits of semi-empirical models to measurements and those obtained by the ab initio calculations of University College London (UCL). In Section 4, we discuss new measurements with sub-percent relative uncertainty [19][20][21][22] that were used to improve some CO2 bands in the 1.4 to 2.1-µm region. In Section 5, we present new CO2 bands above 8000 cm -1 that have been included in the HITRAN2020 edition from the latest high-temperature line list of the ExoMol [18] database (with appropriate cut-off) for the main CO2 isotopologue and the CRDS spectra [14] for the 16 O 12 C 18 O isotopologue.…”

Synthesis of ab initio and effective Hamiltonian line lists for ozone

“…Variational line lists, such as the ones described in the previous section, have been shown to give excellent predicted transition intensities, in some cases with the accuracy better than the experimental one [31,32,33]; however they have two major drawbacks. The accuracy of the line positions are at best an order of magnitude worse than the experimental value.…”