1. Introduction
The Sentinel-1 mission is the first of the Sentinel dedicated missions part of the European Copernicus programme (formerly Global Monitoring for Environment and Security - GMES), led by the European Union, and for which ESA is in charge of the space component. Sentinel-1 is based on a constellation of two SAR satellites that ensures continuity of C-band SAR observations. Sentinel-1A and Sentinel-1B have been launched from Kourou on a Soyuz rocket on 3rd April 2014 and 25 April 2016 respectively.