Sastrugi snow patterns, Antarctica, satellite images. The image at left, taken by the Multi- angle Imaging Spectroradiometer (MISR) on NASA's Terra satellite, shows wavy patterns thought to be on the surface of an Antarctic ice field. To verify that the patterns were on the surface and were not clouds, MISR's Angular Signature Cloud Mask (ASCM) surveyed the area. The results are at right, with areas of cloud in white, areas that are thought to be cloud in yellow, areas of surface in dark blue and areas thought to be surface in light blue. This confirmed that the patterns are mega-sastrugi, long ridges of snow formed when high winds redistribute the snow particles in an abnormal fashion. The ridges are up to 4 metres tall. Image taken on 16 December 2004.