The ERS-1 satellite launched on 17 July 1991 and ERS-2 followed on 21 April 1995, providing continuity for ERS-1. Both satellites carried a Synthetic Aperture Radar (SAR).

The ERS SAR operated in parallel with another instrument – the Wind Scatterometer (WS). Together the SAR/WS configuration was called the Active Microwave Instrument (AMI). AMI had three modes of operation, which allowed the instruments to image land during day or night or through clouds.

The ERS-1 mission ended on 10 March 2000, far exceeding its expected lifespan.

The last ERS-2 SAR data was acquired on 4 July 2011 and the ERS-2 mission itself ended on 5 September 2011.