The first European Remote-Sensing Satellite (ERS-1) was launched in July 1991 and it was the most advanced European satellite for the Earth observation. In particular, this ESA mission provided information of ocean and atmosphere in the microwave spectrum. However, several applications were found also for ice and land. ERS-1 is characterized by a Sun-synchronous near-circular polar orbit, with 98.52Â° inclination and altitude of 782 -785 km. During the first phases of the mission, ERS-1 had a high-frequency repeat cycle of 3 days, which changed to a 35-day repeating orbit during the mapping phase. ERS-1 mission ended in March 2000; however, since 1995 ERS-2 replaced the satellite on its same nominal track.