The ERS-1 satellite, launched on 17 July 1991, carried a Synthetic Aperture Radar (SAR). It 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.