ERS-1/2 SAR land applications: overview and main results

On 17 July 1991 the European Space Agency launched ERS-1 into a Sun-synchronous, polar orbit at an altitude of about 780 km, followed by ERS-2 in 1995. ERS-1 is observes the ocean, sea ice, the cryosphere and the land surface. The satellite carries three active microwave instruments: a synthetic aperture radar (SAR), a wind scatterometer, and a radar altimeter (RA) and an infrared-visible Along Track Scanning Radiometer (ATSR). The RA instruments collect data continuously while the Active Microwave Instrument (AMI) containing the SAR and the wind scatterometer are configured in an alternating operation so that the SAR wave mode runs jointly with the wind while the SAR image mode only runs with the scatterometer turned off. The satellite has a standard orbit repeat cycle of 35 days. Two other repeat cycles of 3 days and 168 days have also been operated. Characteristics of the AMI are: 5.3 GHz C-band frequency at VV polarization; resolutions in various modes are given. The RA operates at 13.8 GHz and a Laser RetroReflector (LRR) is provided for precise orbit estimation. In addition to the payload of ERS-I it carries an instrument for Global Ozone Monitoring Experiment (GOME). On ERS-2 the ATSR (now called ATSR-2) is equipped with two additional visible channels, making it suitable for observing land surface characteristics. For twelve months in 1995-1996, during the Tandem mission, ERS-1 and ERS-2 were operated in the same 35 day repeat orbit, one day apart. ERS-2 is foreseen to operate for at least another couple of years to provide nearly 10 years of regular active microwave observations. Moreover, the intention is to allow for intercalibration and possible tandem operation of ERS-2 with ESA's new Earth and atmospheric ENVIronmental SATellite (ENVISAT) mission.