A week-long ESA campaign co-ordinated across land, sea and air is
gathering data on key variables of thin but crucial liquid layers of the
Earth’s skin: the saltiness of the ocean surface and the moisture levels
of topsoil. The EuroSTARRS campaign is focused on these twin factors
because they play a major role in determining climate.

The final results from this week’s campaign will help scientists to
prepare for an ESA Earth Explorer spacecraft to provide global
measurements for both these variables. Called the Soil Moisture and
Ocean Salinity Mission (SMOS), it is due for launch in 2006. SMOS
is scientifically led by Dr Yann Kerr from CESBIO (Centre d’Etudes
Spatiales de la Biosphere), France and Dr Jordi Font from ICM (Institute
de Ciencies del Mar), Spain.

For EuroSTARRS, a Dornier 228 aircraft, operated by DLR, Germany, is
carrying an instrument specially built to detect sample levels of sea
salinity and soil moisture, at the same time backed up by ground-based
researchers taking readings as well as instruments based on board ocean
buoys, vessels and an oil platform.

Mounted under the aircraft’s fuselage, the instrument is known as the
STARRS (Salinity Temperature and Roughness Remote Scanner) radiometer.
Lent to ESA by its owner, the US Naval Research Laboratory, STARRS is
the closest match to the planned SMOS instrument currently available.
It measures passive microwave radiation emitted by land and water at
a wavelength that allows scientists to determine their respective
moisture and salinity levels.

"The EuroSTARRS campaign involves a total of six test sites across
different terrains, from forest to ocean to the Pyrenees mountains,"
explained Michael Berger, ESA’s SMOS project scientist. "It enables
us to learn how the passive microwave signal is affected by different
vegetation coverage and to what level it could be corrected for by
observing the emitted signal under different viewing angles. We can
then use this information to feed back into the SMOS ground segment
design". And as the aircraft flies STARRS above various European
locales, from forests outside Toulouse and Bordeaux, to vineyards
around Valencia and out over the Bay of Biscay, EuroSTARRS organisers
have ensured there are also researchers on the ground taking concurrent
readings. Off the coast of Barcelona, an existing ESA experiment called
the Wind and Salinity Experiment (WISE) was co-ordinated with the
STARRs overflights.

A set of instruments aboard the Casablanca Tower oil rig, linked to
nearby buoys, measured wind speed, temperature and sea salinity at the
same time as the aircraft flew overhead. And next week a Danish-built
radiometer is being flown over the North Sea by Denmark’s Air Force
as part of another linked experiment called L-band Ocean Salinity
Airborne Campaign (LOSAC).

"EuroSTARRS is one of the most complex campaigns ESA has done, and
one of the fastest-paced," Berger explained. "We have to make sure
organisations across Europe combine together at the right places and
times, as well as working together with the Navy Research Laboratory."
The size of ESA’s effort reflects the importance of the two variables,
which need to be better understood to make future climate modeling
more accurate. Soil moisture levels determine the health of vegetation
across the world and, through phenomena such as evaporation and
run-off, play a key role with how incoming solar energy interacts with
the terrestrial surface.

Sea salinity is ultimately responsible for ocean currents, major engines
of global climate. In currents such as the Gulf Stream, warm surface
water gradually becomes cooler and saltier due to evaporation, then
sinks down to the deeper ocean where it travels back to the equator,
warming up and becoming less salty as it rises again.

"For Europe, the warm waters of the Gulf Stream means countries like
The Netherlands are spared very, very cold winters, something like
Siberia," Berger said. "But climate change could mean an influx of
freshwater from melting polar regions and the Gulf Stream could
disappear. Improved climate models would give us an early warning."

Related links

* WISE 2000


[Image 1:
Soil moisture measurements made concurrently with the overflights. The
image shows a device called the Theta probe.

[Image 2:
Inside the DLR aircraft, showing the rack equipment and Rainer Ziegler.

[Image 3:
The STARRS radiometer mounted on the DLR aircraft in data acquisition
position. The instrument is tilted to one side of the aircraft by about
12 deg to simulate the SMOS observation geometry as much as possible.

[Image 4:
Installation of the LAURA, UPC L-band radiometer on the Casablanca oil
drilling platform.