A UV/visible wavelength diode array spectrometer was installed at Arrival Heights to allow off axis sunlight and moonlight measurements of ozone (O3), nitrogen dioxide (NO2), chlorine dioxide (OClO) and bromine oxide (BrO). The spectrometer works in the near ultraviolet and visible wavelengths and enables different viewing directions, including off axis measurements and moonlight measurements with ... the aid of a tracker. Raw data is times and recorded spectro of scattered light for several viewing directions. The derived data are column amounts of NO2, OClO, BrO and O3, which can be split into tropospheric and stratospheric parts. The spectrometer has an associated camera system to record sky conditions in field of view. Direct measurements of the instrumental line shape (ILS) with a nitrous oxide calibration cell before and after alignment adjustments are carried out three times a year and on a monthly basis to allow a much better characterisation of the ILS than simply assuming the theoretical ILS. This project is a collaboration with the University of Heidleberg. The technique is sometimes refered to as MAX-DOAS Multple-Axis Dual Optical Absorption Spectrometry. The spectrometer and control system was built in Heidelberg with the sun tracker built to a Lauder design. The instrument was originally configured with a photodiode array (DA) detector, but was reconfigured with a CCD detector and different software in 2007.