Envisat image of ice above Lake Vostok

Envisat wide-swath radar image of ice above the sub-glacial Lake Vostok, acquired 13 March 2003. The freshwater lake's full extent was first mapped using ERS-1 data in the early 90s, because the ice floating over the lake has a smoother surface than the ground-based ice surrounding it. More recently, ERS InSAR results have comfirmed its waters are influenced by tides.