OASIS (Ocean-Atmosphere Sensing Interferometer System) is built around a commercially available double-pendulum interferometer system for ground based atmospheric and ocean surface remote sensing. In order to cover both, the thermal and near infrared spectrum, it is fitted with two detector units. For permanent calibration it is equipped with two blackbody units of high emissivity and an integrating sphere. To look into the calibration cavities and to various observation directions a turnable 45 deg mirror in front of the entrance window is positioned by an automated procedure. It is operated by the Max Planck Institute of Meteorology.