Abstract. The practical usefulness of a desktop optical spectrum analyzer (OSA) for measuring atmospheric CO₂ and CH₄ column densities at surface sites was examined in two separate measurement campaigns. The first comparison involved operating the OSA in parallel with a high resolution Fourier transform spectroscopy (FTS) situated at the University of Wollongong in Australia. Scale factors for the OSA were assigned for the column average volume mixing ratios of xCO₂ and xCH₄ by comparing with the well-studied FTS. The second method is a calibration against aircraft CO₂ profiles in situ over Tsukuba in Japan obtained during a GOSAT validation campaign carried out from 28 January to 7 February 2011. The xCO₂ values in the campaign, deduced by use of a derived OSA scale factor, were in excellent agreement with the integrated aircraft profiles.