When ERS-1 was lofted into orbit by an Ariane-4 launcher on 17 July 1991, it
carried the hopes of Europe’s scientific community. For nerve-wracking minutes,
those hopes looked as though they might be dashed when contact was lost with
the craft as it rose into space. Hundreds of scientists and engineers breathed
a collective sigh of relief when an Australian tracking station re-established
communication.
Since then, ERS-1 and ERS-2 have provided a stream of data which has changed
our view of the world on which we live: more than 3500 scientists have
published over 30,000 scientific papers based on ERS data. The ERS programme
has provided striking new insights into the shape of our planet, the
chemistry of our atmosphere, the behaviour of our oceans, and the effects of
mankind’s activity on our environment.
The ERS programme went beyond its designers’ imaginings on 20 April 1995,
when ERS-1 was joined in orbit by its sister, ERS-2. “The most outstanding
success of the ERS programme is the interferometry application and the later
adaptation of the tandem mission for the two satellites,” comments Prof
Preben Gudmandsen, former Chairman of the European Association of Remote
Sensing Laboratories. “This was something the fathers’ of the satellite did
not think of — the few that dared to contemplate it ruled it out, worried
about the stability of the system and the techniques that would need to be
applied to retrieve the data.”
“The tandem mission became possible because ERS-1 lasted three times as long
as its design lifetime,” explains ESA’s Reinhold Zobl, the ERS-1 Project
Manager. “It was never expected, but the community of scientists and
engineers working on the ERS mission soon developed an entirely new
interferometry technique to take advantage of this new opportunity.”
The tandem mission did not yield the only unexpected results. “Using ERS
interferometry data covering periods following large earthquakes, we have
learned that, after an earthquake, physical processes take place in the
rocks adjacent to the fault, producing a regional stress readjustment over
several years. These post-seismic processes produce small and slow surface
shifts that have been observed for the first time using ERS, and these
quantitative observations are essential to understand the physics of the
Earth’s crust,” explains Gilles Peltzer, of CalTech’s Jet Propulsion
Laboratory.
Peltzer is clear about the new capabilities that ERS offered the seismology
community: “ERS provided the first complete images of the surface
deformation associated with geophysical processes. These images are
spectacular and will remain the first ever produced,” adds Peltzer.
Other scientists in different disciplines are equally impressed. “The ERS
mission’s most significant achievements to date are its detailed mapping of
the marine geoid and seafloor topography, and the use of SAR interferometry
to map deformations in the Earth’s crust,” says Dr Anny Cazenave, of
France’s CNES Laboratoire d’Etudes en GÈophysique et OcÈanographie Spatiale.
“The ERS programme has shown us that satellite altimetry is a new and
very valuable tool to monitor surface continental waters with important
applications to continental hydrology, regional climate variability and
water resources policy,” adds Dr Cazenave.
According to Dr Per Knudsen and Dr Ole Andersen, of Denmark’s KMS, “The ERS
mission gave us altimetry data which enabled us to study the marine gravity
field in very high detail; altimeter data which enabled us to study the
marine gravity field and ocean dynamics in polar regions; and we were able
to map the height of the entire ice sheet in Greenland — including the
altitude of the centre, which had never been measured before.”
“In atmospheric science, the ERS programme’s most significant achievements
have been the global measurement from space of minor trace gases responsible
for ozone depletion, measurements of air pollution (trace gases in the
troposphere) from space, and exploiting the possible synergy of different
sensors on the same platform, which is an important lesson for Envisat,”
explains Ankie Pieters from KNMI, the Royal Dutch Meteorological Institite.
“ERS showed us that it is possible to use global space measurements
to support global change studies, leading to political decisions on
international agreements and treaties, and changes in the behaviour of
society — companies adopting green labelling, for example,” Pieters adds.
ERS has not only made a major contribution to research. Data from ERS
instruments is being used operationally in a number of applications.
“ERS-SAR provided a unique data source, which enabled national organisations
to prototype and validate the operational infrastructure for oil spill
detection and sea ice mapping services. ERS SAR data was also important
for establishing agreements with end users to demonstrate the capabilities,
and these information services would not have the performance levels seen
today without the benefit of ERS SAR,” explains Jan-Petter Pedersen from
Tromsoe Satellite Station.
“Another very important contribution of ERS was to make SAR data available
to the science community on an unprecedented scale. ERS helped to build
scientific acceptance of the use of SAR for Earth System monitoring.”
comments Professor Werner Alpers from the University of Hamburg.
Another major success of the ERS mission has been the operational use of data
from the scatterometer, which measures the ‘roughness’ of the ocean surface,
from which wind speed and direction can be calculated, and oil leaks detected.
“In our wave forecasting service we use ERS SAR imagery to measure the
spacing between wave packets. We can then forecast local properties at our
customers’ operations sites. Without the ERS SAR imagery, such measurements
would be prohibitively costly,” explains Hafedh Hajji of France’s MeteoMer.
Adrian Huntley, of Infoterra in the UK adds, “The ERS SAR archive offers
a unique capability to distinguish genuine seepage slicks due to their
persistence between acquisitions. This is a major factor in our service to
the offshore oil and gas industry”.
Experience with the ERS programme has shaped its successor, Envisat. But ERS
also leaves a legacy of data still to be explored. “We’ve seen a pattern in
the evolution of the science from the ERS mission,” comments Professor Alpers.
“Initial research has focussed on what you can do with the data, followed by
validation of the use of data for deriving earth science measurements, and
then analysis of earth system processes using the data.
The continuing contribution of the ERS mission will be the use of the archive
as a 10 year snapshot of earth system parameters, such as land cover, ice
cover, global sea surface temperature measurements for ocean warming and
air-sea exchange, ocean variability records, and finally global wind fields
and wind stress,” Ankie Pieters adds. “Combining Envisat and ERS atmospheric
measurements will give us a ten year data set of atmospheric constituents,
which is the minimum timeframe necessary for long-term trend measurements.”
“We’re still getting new science from ERS data,” comments Gudmandsen, “for
example, we’re beginning to be able to monitor subsidence and land movements
of only a few millimetres using new techniques.”
“The ERS mission has shown conclusively how valuable remote sensing data
can be,” concludes Alpers, “we can directly observe climate change and its
effects, monitor changes in global forest cover through clouds, measure the
variation of sea levels globally, track pollution in the atmosphere and the
sea, observe global ocean currents, measure the true shape of the Earth and
watch it changing — without ERS some of these things would have been
impossible, and others would have needed hundreds of thousands of measurement
stations.”
Related articles
* Satellite view aids SaÙne flood mapping
http://www.esa.int/export/esaSA/ESAOAUUM5JC_earth_0.html
* ESA ERS data shows West Antarctica is thinning
http://www.esa.int/export/esaSA/GGGF59NPEIC_earth_0.html
* Satellite sniffs out chemical traces of atmospheric pollution
http://www.esa.int/export/esaSA/GGGSIXTZ0GC_earth_0.html
* Satellites help to clean up the sea
http://www.esa.int/export/esaSA/GGGP2L0UGEC_earth_0.html
Related Links
* ERS 1 and 2
http://www.esa.int/export/esaSA/GGGWBR8RVDC_earth_0.html
* ERS homepage
http://earth.esa.int/l2/2/ersnewhome
* ERS Instruments
* Earth Observation Homepage
* ESA’s Earth Watching website
IMAGE CAPTIONS:
[Image 1:
http://www.esa.int/export/esaCP/ESAI6C0VMOC_index_1.html]
Happy Birthday ERS.
[Image 2:
http://www.esa.int/export/esaCP/ESAI6C0VMOC_index_1.html#subhead1]
Like its predecessor ERS-1 (launched in July 1991 by Ariane 4 and successfully
put into orbit at an altitude of some 780 km), the ERS-2 satellite launched
on 21.04.95 by Ariane 4, monitors the Earth day and night under all weather
conditions thanks to its powerful sharp-eyed, cloud-piercing radars. ERS-2
also carries an instrument to help monitor the ozone layer around the Earth.
[Image 3:
http://www.esa.int/export/esaCP/ESAI6C0VMOC_index_1.html#subhead2]
The image shows the area of Turkey affected by the earthquake which occured
on 17 August 1999. The image has been generated from an ERS-SAR tandem pair
acquired on the 12th and 13th of August 1999, i.e. 4-5 days before the
earthquake.
[Image 4:
http://www.esa.int/export/esaCP/ESAI6C0VMOC_index_1.html#subhead3]
Surface winds around Antarctica (strongest in yellow-tinted areas) as seen
by the radar scatterometer on ERS-1.
[Image 5:
http://www.esa.int/export/esaCP/ESAI6C0VMOC_index_1.html#subhead4]
On the 2nd October 1994 the Panamanian oil tanker Cercal struck a rock while
entering the harbour of Leixoes (the Oporto harbour), releasing about 1,000
tonnes of crude oil into the sea. The ESA ERS-1 satellite acquired this SAR
image two days after the accident. Because of the damping effect of the oil,
the reduced roughness of the sea surface appears clearly as a black mark on
the SAR image. The spill can be seen floating along the coast and out into
the sea. The coastal city of Oporto, lying near the centre of the oil spill,
appears as a cluster of white dots. The rainy and foggy weather that
prevailed in that region of Portugal on the date of the accident made it
very difficult to evaluate the spill from an aircraft. However, thanks to
the all-weather capabilities of the ERS-1 SAR instrument it was possible to
acquire this very useful scene through the cloud cover. (Image processed by
ESA’s Earth Watching Team)
[Image 6:
http://www.esa.int/export/esaCP/ESAI6C0VMOC_index_1.html#subhead5]
Envisat in the clean room at ESA’s test facilities at ESTEC, Noordwijk,
spring 2001.
[Image 7:
http://www.esa.int/export/esaCP/ESAI6C0VMOC_index_1.html#subhead6]
Deforestation areas appear in light-coloured linear features of relatively high
temperatures, in this thermal image from ERS-2. Photo: Leicester University.
