y. The the retrieval of vertical profile information from the MAX-DOAS mea- surements requires the simulation of the coupled snowpack- atmosphere radiative transfer, which is subject of Sect.4. The analysis [...] telescope is mounted on the roof of the Neumayer trace gas observa- tory, at a height of approximately 7 m over the snow surface. The viewing plane of the telescope is directed to the north. UV and Vis spectra [...] Hereλk is the centre wavelength of thekth detector pixel. The wavelength window of the retrieval,[λ(K1),λ(K2)], is chosen in order to optimise the signal-to-noise ratio of the trace gases of interest,