The HITRAN2024 methane update

TL;DR

The paper updates the HITRAN methane database to 2024 by incorporating new spectroscopic data, replacing thousands of lines, adding new ones, and improving parameters for remote sensing applications.

Contribution

It provides a comprehensive update to the HITRAN methane database with new lines, improved parameters, and validation, especially in regions relevant for remote sensing.

Findings

Approximately 80,000 lines replaced and 44,000 new lines added.

Extended the spectral coverage from 12,000 to 14,000 cm$^{-1}$.

Improved pressure broadening parameters using Padé-approximant functions.

Abstract

Spectroscopic parameters of methane from many different studies were gathered to improve the HITRAN database towards its 2024 version. After a validation process using high-resolution FTS and CRDS spectra, about 80,000 lines of the four most abundant isotopologues were replaced from the dyad to the triacontad regions. These changes amount to 51,000 transition wavenumbers, 18,000 line intensities, 33,000 pressure-broadening half-widths, and 3300 assignments. 44,000 new lines were added with 16,000 old lines removed, extending the database from 12,000 cm$^{-1}$ up to 14,000 cm$^{-1}$, and covering some gaps. A greater focus was brought on the pentad, octad, and tetradecad regions, targeted by several remote sensing instruments. In these regions, comparisons of spectral fits from multiple line lists were performed, taking only the parameters that provide best fit for each line. In the $\nu _3$ band, in addition to replacing the previous values, speed-independent pressure broadening parameters of $^{12}$CH$_4$ were gathered and used to fit Pad\'e-approximant functions. These functions then replaced any outdated experimental data in $\nu _3$, missing data in the new lines, as well as the values that were determined to be outside their physical boundaries. The CH$_3$D broadening parameters were replaced in the same manner, for missing and low or high values, using a semi-empirical formula instead.