European Remote Sensing satellite, ERS-1, launched in 1991, was ESA's first Earth Observation satellite (polar orbiting); it carried a comprehensive payload including an imaging Synthetic Aperture Radar (SAR), a radar altimeter and other powerful instruments to measure ocean surface temperature and winds at sea. ERS-2, which overlapped with ERS-1, was launched in 1995 with an additional sensor for atmospheric ozone research. ERS 1 was taken out of action in 2000 after nine years of service.