Sentinel-1 continues the C-band SAR Earth Observation heritage of ESA's ERS-1, ERS-2 and ENVISAT, and Canada's RADARSAT-1 and RADARSAT-2.
ERS-1 and ERS-2
Figure 1: ERS-2 Satellite
The European Remote Sensing (ERS) satellites have achieved several milestones in Earth Observation. Launched in July 1991, ERS-1 introduced reliable and stable radar from space with its Active Microwave Instrument (AMI). ERS-2, launched in April 1995, shared the same orbital plane with ERS-1 allowing for a tandem mission in 1995 and 1996, where interferometric data was collected one day apart. ERS-1 was in operation until March 2000 while ERS-2 far exceeded its expected lifespan, acquiring images until 2011.
Figure 2: ENVISAT Satellite
ENVISAT provided 10 years of SAR data mapping from March 2002 to May 2012, five years longer than its designed mission duration. With 10 instruments aboard and at 8 tons, ENVISAT is the largest civilian Earth Observation mission put into space. ENVISAT added new capabilities over ERS with its Advanced Synthetic Aperture Radar (ASAR) sensor including wide swaths, dual polarisation and simultaneous acquisitions from its MERIS sensor.
SENTINEL-1 provides enhancements over previous missions in the form of reliability, revisit time, geographical coverage and rapid data dissemination.