Infrastructure

The EM27/SUN is a portable ground-based Fourier Transform InfraRed (FTIR) spectrometer developed by KIT in cooperation with Bruker Optics GmbH to measure direct solar radiation in the near-infrared spectral range (4000–12000 cm⁻¹) with a resolution of 0.5 cm⁻¹. It is designed to observe total column abundances of key atmospheric gases such as CO₂, CH₄, CO, and H₂O. The compact system consists of a spectrometer and an integrated solar tracker equipped with a camera and image-processing software, allowing highly accurate solar pointing better than 0.01°. With a total weight of about 27 kg, the instrument is easily transportable and well suited for field deployments. Each measurement is completed in approximately 58 seconds using double-sided interferograms. Gas columns are retrieved in units of molecules per cm². To reduce sensitivity to surface pressure and other systematic effects, column-averaged dry-air mole fractions (Xg) are calculated by normalizing the gas columns with the dry-air column derived from O₂ measurements. Since the atmospheric O₂ mixing ratio is constant, this approach yields robust and comparable greenhouse gas observations.

The SkySpec-2D system developed by Airyx GmbH (https://airyx.de/item/skyspec/) is a passive remote sensing instrument that leverages the Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) technique for the retrieval of the total and tropospheric vertical columns, vertical distribution, and surface concentrations of various trace gases, such as NO2, HCHO, SO2, O3, HONO, CHOCHO. The instrument can also deliver information on the aerosol optical depth and extinction profile indirectly from O4 slant column retrievals. The system comprises two spectrometers, one operating in the ultraviolet (UV) and one in the visible (VIS) spectral region, and performs spectrally resolved measurements in the wavelength range from 300 nm to 550 nm approximately. The telescope of the system is motorized in both viewing elevation and azimuthal axis, providing full hemisphere coverage and enabling both direct-sun and scattered sky radiance observations.