A new processing system now operational in ESA ground stations will help weather
forecasters to benefit once more from unique all-weather data from the ERS-2

Although the highly successful ERS global mission is formally over, the
spacecraft has been continuing to provide coverage over the north Atlantic.

Weather experts are keen to continue to receive data from its wind-measuring
instrument, the C-band scatterometer. This instrument is unique in the sense
that it is not affected by rain and can provide data day or night in all
conditions. So experts can get data just when they need it most — in bad weather!

The European Centre for Medium-Range Weather Forecasts (ECMWF) is especially
interested in using this data for measuring winds and waves over the north Atlantic.

"The ERS-2 scatterometer is particularly useful in the early detection of
Atlantic hurricanes and extreme winter storms," says Philippe Bougeault, head of
the Research Department at ECMWF. "It offers a unique opportunity to provide
marine users, such as operators of ships and oil platforms, with timely and
accurate information on marine weather and waves." "ERS scatterometer winds are
not affected by rain, and have proven to give valuable information near intense
cyclones and in baroclinic regions", explains ECMWF’s ocean-wave expert Hans

The scatterometer data has not been available to the user community since 2001
when the spacecraft’s gyros failed. An innovative rescue in January of that year
enabled ERS-2 to keep flying without the vital stabilising gyroscopes,
prolonging the lifetime of many of the instruments. However, although the
scatterometer continued to take measurements, this key wind data could no longer
be processed by forecasters.

Experts at ESA’s research centre in Italy immediately began looking for ways to
retrieve the precious information. Preliminary studies were encouraging,
specialists in industry got the go-ahead to develop a software tool to
compensate for the degraded satellite attitude and generate the scatterometer
measurements from the raw data.

The Belgian Royal Military academy (RMA) designed the new ESACA processor, while
Spacebel in Belgium produced the engineering code and Spacetec, Norway, had the
task of integrating the new system on the ground, at the three ground stations
in Kiruna (Sweden), Maspalomas (Canary Islands) and Gatineau (Canada), as well
as the reference station at ESA/ESRIN in Frascati (I). An installation at an
additional station in West Freugh (Scotland) will follow shortly, to optimise
coverage of the north Atlantic.

The new tool does more than it was asked for. While the original scatterometer
was intended to provide wind measurements over sea, a number of new and
previously unforeseen applications have emerged — covering not only wind, but
also land, sea ice, soil moisture and vegetation measurements.

The software algorithm will also be used to reprocess the mountain of archived
ERS-1 and -2 scatterometer data. The continuity of these observations offered by
ERS since 1991 is invaluable to researchers involved in long-term studies on
climate cycles. They already have their eye on the future — Europe’s MetOp.

The new processor is operational this week, good news for forecasters as the
cyclone season approaches.

Notes for editors

The first European remote-sensing satellite ERS-1 was launched by Ariane-4 in
July 1991. Its near-twin ERS-2 was launched on 21 April 1995. The suite of
instruments onboard these two highly successful satellites, have collected a
wealth of valuable data on the Earth’s land surfaces, oceans, and polar caps.
Both satellites continued to provide data well beyond their original lifetime.
ERS-1 completed its operation in 2000. Although its global mission is formally
over, ERS-2 continues to provide data over the north Atlantic region.

MetOp will be Europe’s first polar-orbiting satellite dedicated to operational
meteorology. It represents the European contribution to a new cooperative
venture with the United States providing data that will be used to monitor our
climate and improve weather forecasting.

A new generation of European instruments that offer improved remote sensing
capabilities to both meteorologists and climatologists will be carried with a
set of ‘heritage’ instruments provided by the United States. The new European
instruments will augment the accuracy of:

  • temperature and humidity measurements
  • wind speed and wind direction measurements, especially over the ocean
  • profiles of ozone in the atmosphere

MetOp is a series of three satellites to be launched sequentially over 14 years,
starting in 2005, and forms the space segment of EUMETSAT’s Polar System (EPS).

Related articles

* ERS-2 goes gyro-less

* ERS 1 and 2

* A decade of ERS Earth-watching

In depth

* More on ERS scatterometer

* More on cyclone tracking

* ECMWF home page

* MetOp website


[Image 1:
An example of the potential impact of recent ERS-2 user wind product (UWI) data
is illustrated in this image. It shows the analysis of 4 May 2003, 12 UTC
north-west of Scotland for mean-sea-level pressure (blue contours) and
streamlines (beige) of the 10 m surface winds. With the new tool ESACA ERS-2
scatterometer winds (white barbs), observed around 11:24 UTC, are displayed as
well. The detailed structure of the warm front is well presented by both the
analysis and the scatterometer winds.

However, the scatterometer winds suggest a small shift southwards of this front,
and besides, a shift towards the east of the low-pressure centre.

Credits: ECMWF

[Image 2:
This second image shows the difference between the 12H forecast starting from
the analysis of 4 May 2003 12 UTC (dashed black), and the verifying analysis of
5 May 2003 00 UTC (solid blue). The positional error of the low-pressure front
supports the dislocation observed 12 hours earlier by the scatterometer.

This confirms for forecasters the value of the ESACA processor. ERS-2
scatterometer wind data will now be re-introduced in ECMWF assimilation system.

Credits: ECMWF

[Image 3:
ASCAT’s three pairs of antennas dominate the MetOp payload module.