Messung von stratosphärischem Chlormonoxid und Wasserdampf in der Arktis : Erweiterung und Optimierung des passiven Mikrowellenradiometers RAM in Ny °Alesund Spitzbergen The Radiometer for Atmospheric Measurements is a passive microwave radiometer which measures the rotational emission lines of water vapor ozone and chlorine monoxide. As part of the αNetwork for the Detection of Stratospheric Change± the RAM is situated in Ny Ålesund at 79ʿ North at the Spitsbergen archipelago. This location is special because in arctic winter it mostly lies under the polar vortex which is essential for the measurement of chlorine activation and therefore the observation of ozone depletion.Since the designation of heterogenous chemistry as basic cause for the Antarctic ozone hole the observation of stratospheric chlorine monoxide is more important than ever. The RAM is the only instrument in the Arctic for long term monitoring of this crucial species. Within the scope of this work several improvements have been made on the instrumentś hard and software. We will show measurements of stratospheric chlorine monoxide from 2000 which have been analyzed with a newly implemented retrieval software. In this context we will show measured diurnal chlorine monoxide cycles as well as the comparison to other instruments and models.As tracer for global warming and participant in catalytic ozone depletion water vapor is an important species for atmospheric physics. In the last decades stratospheric water vapor has increased noticeably in lower stratosphere which not can be explained by current theories. In this work we will present the technical realization of the new installed instrument the water vapor retrieval software as well as some evaluated measurements.Tropospheric water vapor is also a disturbing factor to microwave measurements. In this work we have inspected several sites for their suitability as location of a newly planned 278 GHz chlorine monoxide radiometer. As result we discovered Summit in Greenland and Mérida in Venezuela as ideal places which eventually lead to the installation of two new instruments.