North central Siberia is pictured in this Envisat image from 5 March 2012. In the lower-left corner we can see the Yenisei river, which flows north into the Kara Sea (not pictured). The Yenisei is considered to be the boundary between eastern and western Siberia. The majority of the area pictured lies above the Arctic Circle. This is also an area of continuous permafrost, where the soil is at or below freezing throughout the year. Although permafrost cannot be directly measured from space, factors such as surface temperature, land cover and snow parameters, soil moisture and terrain changes can be captured by satellites.