A small DOAS device for student training

Differential optical absorption spectroscopy (DOAS) has become a standard method for analysing the amount of various molecular species in the Earth's atmosphere. For student education we have developed a small device aiming to be used for practising this technique. It is based on three 50mm aperture sized telescopes, which are aligned on a SkywatcherAZ-EQ5 astronomical mount enabling a multi-axis movement. Each of the three telescopes feeds an individual spectrograph to cover the entire wavelength range between 300 and 980nm in three arms: Ultraviolett/blue (UVB) arm, ranging from 300-507nm (Stellarnet BLUE-Wave UV2-14 spectrometer, 0.2nm resolution, 14µm slit); Visual (VIS) arm covering 500-680nm (Stellarnet BLUE-Wave NIR4-14, 0.2nm resolution, 14µm slit); red/near-infrared (NIR) arm: 600-980nm (Stellarnet  BLUE-Wave NIR2-14, 0.4nm resolution, 14µm slit). All three spectrometers are equipped with a detector amplification lens upgrade. The main lens of the telescope feeding the UVB arm was replaced by one with a fused silica glass for a better UV transparency. In addition, we use wavelength-optimised 600µm fibres in each spectral arm.

The software to take the spectra is SpectraWiz v5.33. The data calibration is done with MIDAS, a software specifically developed for astronomical purposes. The final DOAS measurements are done with molecfit, a software originally developed to remove absorption features from astronomical spectra by fitting model-based synthetic transmission spectrum to absorption features in scientific data.

In this presentation we show a technical overview of this instrument, the concept of the experiment and some results.