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