The First and Second European Remote-Sensing Satellites
(ERS-1 and ERS-2)
are developped by the European Space Agency as a family of
multi-disciplinary Earth Observation Satellites. They orbit the Earth in
about 100 minutes and in 35 days have covered nearly every corner of the
globe at least once.
are still in good health and provide a wealth of observations through their
excellent suite of instruments:
Synthetic Aperture Radar (SAR)
The SAR provides cloud-free radar images of mainly the Earth's surfaces,
monitoring and vegatation and growth, floadings, cultivation of land. When
two consecutive images are merged though the technique of interferometry
(INSAR), the instrument can even detect landslides and depressions over
an approximately 100x100 km area.
Wind Scaterrometer (SCAT)
This instrument (together with the SAR forming the Active Microwave
Instrument, AMI) maps the wind speed and wind direction over ocean
Radar Altimeter (RA)
The Radar Altimeter is a purely nadir looking instrument with a
footprint of a few kilometers. It sends radar signals to the earth and
ocean surface and collects the return pulse. The returned power as a
function of travel time is called the wave form. Processing of the
waveform provides information on: the wave height and wind speed (over
oceans), the surface backscatter, and the height of the satellite
above the surface. Together with a precisely
computed orbital altitude, the latter gives the height of the surface above a
well-defined geocentric reference frame. This provides the possibility
to monitor the global ocean circulation,
but also regional current systems, and
study the marine gravity field.
Along-Track Scanning Radiometer (ATSR)
A sweeping mirror detects and maps infrared radiation in various
wavelengths along the satellite track. When the sky is cloud-free,
these measurements can be converted to land and sea surface
Operating together with the ATSR, the Microwave Sounder provides
a measurement of the total water vapour content in the Earth's atmosphere
vertically below the satellite orbit. This measurement is essential for the
correction of the RA height measurement.
Global Ozon Monitoring Experiment (GOME)
The GOME is a new instrument on ERS-2 that was not available on ERS-1.
At is intended to map the ozon content in the upper atmosphere and provide
more conclusive statistics of the development of the Ozon Hole and the
effect of polution on this.
Precise Range and Range-Rate Equipment (PRARE)
PRARE is an active satellite tracking equipment. It sends signals to
transponders positioned on Earth (currently some 20 are deployed).
After reception of the return signal the relative range and range-rate
(velocity) of the satellite to up to 4 transponders can be determined
simultaneously. This provides a perfect means to determine the satellite
position (latitude, longitude, and altitude) all around the orbit.
The PRARE instrument on ERS-1 unfortunately failed soon after launch.
Laser Retro-Reflector (LRR)
The Laser Retro-Reflector is a purely passive ``instrument'' and can
be compared to reflectors on cars and bicycles. It reflects laser pulses
transmitted from Satellite Laser Ranging (SLR) systems on Earth back to the
systems. The total travel time of the laser pulse (once received back by
the laser system) is a direct measure for the distance between the
satellite and the station. For ERS-1 this was the only means to compute a
precise satellite orbit; for ERS-2 it is a helpful addition to be used in
the orbit determination and for calibrating the PRARE instrument.