European Remote-Sensing Satellite
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European Remote-Sensing satellite (ERS) was the European Space Agency's first Earth-observing satellite. It was launched on July 17, 1991 into a Sun synchronous polar orbit at a height of 782–785 km.
ERS-1 carried an array of earth-observation instruments that gathered information about the Earth (land, water, ice and atmosphere) using a variety of measurement principles. These included:
- A nadir-pointing radar altimeter operating in the Ku band
- A 4 channel infrared radiometer for measuring temperatures at the sea-surface and the top of clouds
- A microwave sounder
- A synthetic aperture radar
- A wind scatterometer.
To accurately determine its orbit, the satellite included the PRARE (Precision Range and Range-Rate Equipment) and a Laser Retroreflector. The PRARE was non-operational since launch. The Retroreflector was used for calibrating the Radar Altimeter to within 10 cm.
ERS-1 had various mission phases using 3-day, 35-day and a 336-day repeat cycle. The 336-day mission (Geodetic Mission) allowed for accurate mapping of the Earth's bathymetry and geoid over the seas.
ERS-1 failed on March 10, 2000, far exceeding its expected lifespan.
Its successor, ERS-2, was launched on April 21, 1995. It is largely identical to ERS-1, with the addition of the GOME (Global Ozone Monitoring Experiment) and absorption spectrometer. When ERS-2 was launched, ERS-1 shared the same orbital plane. This allowed a tandem mission, with ERS-2 passing the same point on the ground 1 day later than ERS-1. ERS-2 have a repeat cycle of 35 days.
ERS-2 has been operating without gyroscopes since February 2001, resulting in some degradation of the data provided by the instruments. The tape drive aboard failed on June 22, 2003, leaving the instruments operating only within visibility of a ground station. Since the tape drive failure additional ground stations have been brought online to increase the data gathering abilities of the satellite. The Wind Scatterometer and GOME were the only instruments of their kind until the launch of MetOp-A.
The successor to ERS-2 is Envisat.
