A technique used by Earth-observation satellites to acquire images from several angles simultaneously. NASA's Multi-Angle Imaging Spectroradiometer (MISR), launched on the Terra satellite in December 1999, acquires Earth images at nine angles using nine cameras pointing forwards, backwards, and downwards along its flight path. Its images of the Pine Island Glacier in Antarctica taken in March 2001 revealed differences in the surface texture and could distinguish between rough crevasses and smooth ice.