Launched on the Nimbus 7 satellite in 1978, the Stratospheric Aerosol Measurement 2 instrument mapped vertical profiles of small particles (aerosols) in the atmosphere over the Earth's polar regions. This included investigating the spatial and temporal character of aerosols due to seasonal and other meteorological variations, their chemistry and microphysics, and the influence of transient phenomena such as volcanic eruptions.
SAM 2 operated for fifteen years, providing key data at a critical juncture in the development of scientific models of the ozone hole and of Earth's climate, including impacts of human activity. This object is an engineering model used in development and testing, as well as for assessment of the in-flight unit during its operational life.
SAM 2 led to a subsequent series of instruments to study aerosols over the poles, the most recent of which is the Stratospheric Aerosol and Gas Experiment III, placed on the International Space Station in March 2016.