FT spectroscopy in support of atmospheric spectroscopic databases: Recent advances at DLR

Abstract

High resolution Fourier Transform spectroscopy of atmospheric trace gas has been carried out at DLR since 1990. The primary focus is on supplying well characterized uncertainties. The core instrument is the commercial high-resolution Bruker IFS 125 HR Fourier-transform spectrometer operating from 10 to 40000 cm-1. The laboratory infrastructure has been continuously improved over the last 30 years, especially the absorption cells. A 22 cm absorption path 200-350 K cell features two windows pairs allowing quasi-simultaneous measurement from FIR to UV. A 200 m absorption path multireflection cell operates in the temperature range 200-350 K with high temperature homogeneity. Line fitting software was steadily improved, resulting in a multispectrum fitting tool with several line shape models including the Hartmann-Tran profile. The instrumental line shape of the Fourier-transform spectrometer is adopted from the LINEFIT software by Frank Hase, IMK, which is also used by the TCCON community. Recent results are a spectroscopic database of the O3 fundamentals and temperature dependent UV absorption cross sections for O3, together solving the 4% discrepancy between UV and MIR atmospheric O3 columns, a comprehensive H2O spectroscopic database in the range 1850-4300 cm-1, a new method to obtain H2O continua, H2O foreign- and self-continua in the 3 µm region, and a CO2 database in the range 6000-7000 cm-1 with absolute intensity uncertainties <0.15%. Most of these results have become part of the HITRAN20 database.