ERS (European Remote Sensing Satellite), European Space Agency

The ERS-1, 2 satellites are intended for global measurements of sea wind and waves, ocean and ice monitoring, coastal studies and land sensing using active and passive microwave remote sensing systems. ERS-1 was launched in July 1991 and ERS-2 in April 1995. ERS-1 uses a synthetic aperture radar (SAR) instrument to acquire images of ocean, ice and land regardless of cloud and sunlight conditions. Other microwave instruments measure sea state, sea surface winds, ocean circulation, sea and ice levels, as well as the sea's surface temperature. The near polar sun-synchronous orbit of the satellite enables a global mission providing world-wide geographical and repetitive coverage, primarily oriented towards ocean and ice monitoring, but with an all-weather high resolution microwave imaging capability over land and coastal zones.

ERS-2 is practically identical to ERS-1, with the addition of the GOME sensor for global ozone monitoring. The orbits of ERS-1 and 2 are such that ERS-2 follows the same ground track as ERS-1, except for a 1-day delay. This provides an opportunity to obtain tandem interferometric data of an area using the synthetic aperture radar on the two satellites. The tandem data has better coherence property than the data obtained from 35-day repeat passes of a single satellite. The tandem mission was operational from April to June, 1996 after the launch of ERS-2. ERS-1 has outlived its planned operational life and was deactivated after the tandem mission. Currently, only ERS-2 remains in active operation.

ERS-1,2 Orbit

Type Sun-Synchronous
Altitude 782 km
Inclination 98.5 deg
Period 100 min
Repeat Cycle 35 days


  • AMI (Active Microwave Instrument): The AMI operating at a frequency of 5.3 GHz (C-band, VV-polarised) combines the functions of a Synthetic Aperture Radar (SAR) and a Wind Scatterometer (WNS). Through its set of four antennae (three for the Scatterometer and one for the SAR - see the figure above), the Earth's surface is illuminated and the backscattered energy is received to produce data on wind fields and wave spectra (WNS mode), and to produce high resolution images (SAR mode) of the Earth's surface.
  • RA-1 (Radar Altimeter): The Radar Altimeter measures variations in the satellite's height above sea-level.
  • ATSR (Along Track Scanning Radiometer): This passive instrument monitors the thermal emission of the seas and oceans, from which the global sea surface temperature is derived.
  • GOME, on ERS-2 (Global Ozone Monitoring Experiment): The GOME is a passive spectrometer for monitoring the ozone content of the atmosphere.

ERS SAR Instrument Characteristics

Frequency 5.3 GHz (C band)
Polarisation Linear VV
Bandwidth 15.55 MHz
Peak power 4.8 kW
Antennae size 10 m x 1 m
Incidence angle 23o nominal
Swath width 100 km
Resolution 30 m (azimuth), 26.3 m (range)

Link to: ESA Earthnet (
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Please send comments/enquiries/suggestions about this tutorial to Dr. S. C. Liew at Copyright CRISP, 2001