ESA satellites focusing on the Arctic   ESA’s Envisat ASAR data mosaic showing sea-ice coverage as of mid-August 2008. The red line indicates the all-time minimum Arctic sea-ice coverage in September 2007. The Arctic is one of the most inaccessible regions on Earth, so obtaining measurements of sea ice was difficult before the advent of satellites.   Envisat ASAR mosaic from mid-August 2008 showing an almost ice-free Northwest Passage. The direct route through the Northwest Passage is highlighted in the picture by an orange line. The orange dotted line shows the indirect route, called the Amundsen Northwest Passage, which has been passable for almost a month.     Sentinel-1, the first Earth observation satellite to be built for Europe’s Global Monitoring for Environment and Security programme. Release date: 3 December 2009