Andrew Yee
March 15th 06, 03:24 PM
ESA News
http://www.esa.int
15 March 2006
Radar altimetry revolutionises the study of the ocean
Imagine a space tool so revolutionary it can determine the impact of
climate change, monitor the melting of glaciers, discover invisible waves,
predict the strength of hurricanes, conserve fish stocks and measure river
and lake levels worldwide, among other scientific applications. This
instrument is not the subject of a science-fiction novel. In fact, four of
them are already operating 800 kilometres above Earth.
Fifteen years ago this ground-breaking instrument, called a radar
altimeter, was launched into orbit, despite speculation of its usefulness
from the wider oceanographic community. Although it took over a decade for
its full impact to be realised, its accomplishments have been so great
that it is credited with having revolutionised the field of physical
oceanography.
In honour of altimetry, oceanographers, glaciologists, hydrologists and
geodesists from around the world have gathered in Venice Lido, Italy, at
the '15 Years of Progress in Radar Altimetry' symposium, organised by ESA
and the French Space Agency (CNES), to celebrate its success. Signifying
its vast array of achievements, many have come to honour it for different
reasons.
According to one of the pioneers of the altimeter, Massachusetts Institute
of Technology's (MIT) Carl Wunsch, its biggest contribution is conceptual
rather than scientific because it changed the way scientists viewed the
ocean.
"The greatest achievement of the altimeter is that it has showed us that
the ocean system changes rather dramatically everyday and has shifted the
view of it from this almost geological phenomenon creeping along very
slowly to something much more interesting in which fluid is moving in all
directions at all times," Wunsch said.
The radar altimeter offers valuable information on the state of the ocean
by providing measurements of the height of the ocean surface. This is done
by sending 1800 separate radar pulses down to Earth per second then
recording how long their echoes take to bounce back.
Knowing the height of the sea surface tells scientists a great deal about
what is happening at lower depths. Before the advent of radar altimetry,
oceanographers had no way of looking at the ocean as a whole, which is
essential because changes in one part of the ocean will eventually affect
the whole rest of the ocean.
Lee-Lueng Fu of NASA's Jet Propulsion Laboratory came to the symposium to
honour the altimeter's precision: "We are here to celebrate our success
because we have managed to measure the height of sea surface with such
extreme sensitivity that we are able to detect even two centimetres
difference over 100 kilometres."
Because of this extraordinary ability oceanographers are able to measure
changes in ocean currents and create a weather chart of ocean circulation
for the first time -- which Pierre-Yves Le Traon of the French Research
Institute for Exploitation of the Sea (IFREMER) states as the instrument's
most outstanding achievement.
Ocean forecasting behaves much the same as weather forecasting: if there
is high pressure (signified by higher sea levels), an anticyclonic ocean
circulation takes place, which usually translates into good weather
conditions, while low pressure (signified by lower sea levels) signifies
that a cyclonic ocean current is present.
This type of forecasting has enormous societal and economical
consequences. For example, it allows scientists to forecast El Nino events
and the flooding of low-lying areas (such as Venice), as well as predict
the trajectory of pollutants, which allows oil spills to be contained more
quickly by placing barriers in their pathways.
The ability to measure the sea surface height, which varies across the
ocean, with such accuracy allowed oceanographers to discover planetary
waves, which Paolo Cipollini, of the National Oceanography Centre in the
UK, names as the real success story of radar altimetry.
Planetary waves, also called Rossby waves, were theorised to have existed
in the ocean as far back as 1930, but it was impossible to know for sure
because they occur internally and are very small on the surface, about 10
centimetres high, making them impossible to detect from onboard an
oceanographic research vessel.
According to Cipollini, radar altimetry offered proof of these waves for
the first time. As oceanographers started mapping the sea surface height,
they began seeing the internal waves, which extend 500 or 1000 kilometres
underneath the ocean, moving by following the measurements on the surface.
These waves are thought to be very important because they may be
responsible for setting the main circulation patterns in the ocean.
Cipollini said: "It has been suggested that planetary waves are one
mechanism which brings nutrients from the deep sea up to the surface,
which would make them important for the carbon cycle.
"So it could be that these mysterious waves that up until 20 years ago we
weren't even able to see are also important for biologists and for people
studying how the ocean is reacting to global warming."
ESA has had radar altimeters in orbit since July 1991, when ERS-1 was
launched, which was followed by ERS-2 in 1995 and Envisat in 2002. The
joint French Space Agency (CNES) and NASA mission TOPEX-Poseidon launched
an altimeter in 1992, with follow-up mission Jason-1 flown in 2001.
Related news
* International Symposium on Radar Altimetry in Venice, 13 to 18 March
2006
http://www.esa.int/esaCP/SEMVT6NVGJE_index_0.html
* Envisat altimeter watches Pacific for cold tongue of La Nina
http://www.esa.int/esaCP/SEMBFVMVGJE_index_0.html
* Taking measure of the world: radar altimetry in spotlight at Venice
event
http://www.esa.int/esaEO/SEMPI66Y3EE_index_0.html
Related missions
* Envisat overview
http://www.esa.int/esaEO/SEMWYN2VQUD_index_0_m.html
* ERS overview
http://www.esa.int/esaEO/SEMGWH2VQUD_index_0_m.html
In depth
* Radar Altimetry Symposium
http://earth.esa.int/venice06/
Related links
* DORIS
http://www.ign.fr/fr/PI/activities/geodesie/DORIS/index-en.html
* Argo
http://www.argo.ucsd.edu/
* CNES
http://www.cnes.fr/html/_455_.php
[NOTE: Images supporting this release are available at
http://www.esa.int/esaCP/SEMB1RNVGJE_index_1.html ]
http://www.esa.int
15 March 2006
Radar altimetry revolutionises the study of the ocean
Imagine a space tool so revolutionary it can determine the impact of
climate change, monitor the melting of glaciers, discover invisible waves,
predict the strength of hurricanes, conserve fish stocks and measure river
and lake levels worldwide, among other scientific applications. This
instrument is not the subject of a science-fiction novel. In fact, four of
them are already operating 800 kilometres above Earth.
Fifteen years ago this ground-breaking instrument, called a radar
altimeter, was launched into orbit, despite speculation of its usefulness
from the wider oceanographic community. Although it took over a decade for
its full impact to be realised, its accomplishments have been so great
that it is credited with having revolutionised the field of physical
oceanography.
In honour of altimetry, oceanographers, glaciologists, hydrologists and
geodesists from around the world have gathered in Venice Lido, Italy, at
the '15 Years of Progress in Radar Altimetry' symposium, organised by ESA
and the French Space Agency (CNES), to celebrate its success. Signifying
its vast array of achievements, many have come to honour it for different
reasons.
According to one of the pioneers of the altimeter, Massachusetts Institute
of Technology's (MIT) Carl Wunsch, its biggest contribution is conceptual
rather than scientific because it changed the way scientists viewed the
ocean.
"The greatest achievement of the altimeter is that it has showed us that
the ocean system changes rather dramatically everyday and has shifted the
view of it from this almost geological phenomenon creeping along very
slowly to something much more interesting in which fluid is moving in all
directions at all times," Wunsch said.
The radar altimeter offers valuable information on the state of the ocean
by providing measurements of the height of the ocean surface. This is done
by sending 1800 separate radar pulses down to Earth per second then
recording how long their echoes take to bounce back.
Knowing the height of the sea surface tells scientists a great deal about
what is happening at lower depths. Before the advent of radar altimetry,
oceanographers had no way of looking at the ocean as a whole, which is
essential because changes in one part of the ocean will eventually affect
the whole rest of the ocean.
Lee-Lueng Fu of NASA's Jet Propulsion Laboratory came to the symposium to
honour the altimeter's precision: "We are here to celebrate our success
because we have managed to measure the height of sea surface with such
extreme sensitivity that we are able to detect even two centimetres
difference over 100 kilometres."
Because of this extraordinary ability oceanographers are able to measure
changes in ocean currents and create a weather chart of ocean circulation
for the first time -- which Pierre-Yves Le Traon of the French Research
Institute for Exploitation of the Sea (IFREMER) states as the instrument's
most outstanding achievement.
Ocean forecasting behaves much the same as weather forecasting: if there
is high pressure (signified by higher sea levels), an anticyclonic ocean
circulation takes place, which usually translates into good weather
conditions, while low pressure (signified by lower sea levels) signifies
that a cyclonic ocean current is present.
This type of forecasting has enormous societal and economical
consequences. For example, it allows scientists to forecast El Nino events
and the flooding of low-lying areas (such as Venice), as well as predict
the trajectory of pollutants, which allows oil spills to be contained more
quickly by placing barriers in their pathways.
The ability to measure the sea surface height, which varies across the
ocean, with such accuracy allowed oceanographers to discover planetary
waves, which Paolo Cipollini, of the National Oceanography Centre in the
UK, names as the real success story of radar altimetry.
Planetary waves, also called Rossby waves, were theorised to have existed
in the ocean as far back as 1930, but it was impossible to know for sure
because they occur internally and are very small on the surface, about 10
centimetres high, making them impossible to detect from onboard an
oceanographic research vessel.
According to Cipollini, radar altimetry offered proof of these waves for
the first time. As oceanographers started mapping the sea surface height,
they began seeing the internal waves, which extend 500 or 1000 kilometres
underneath the ocean, moving by following the measurements on the surface.
These waves are thought to be very important because they may be
responsible for setting the main circulation patterns in the ocean.
Cipollini said: "It has been suggested that planetary waves are one
mechanism which brings nutrients from the deep sea up to the surface,
which would make them important for the carbon cycle.
"So it could be that these mysterious waves that up until 20 years ago we
weren't even able to see are also important for biologists and for people
studying how the ocean is reacting to global warming."
ESA has had radar altimeters in orbit since July 1991, when ERS-1 was
launched, which was followed by ERS-2 in 1995 and Envisat in 2002. The
joint French Space Agency (CNES) and NASA mission TOPEX-Poseidon launched
an altimeter in 1992, with follow-up mission Jason-1 flown in 2001.
Related news
* International Symposium on Radar Altimetry in Venice, 13 to 18 March
2006
http://www.esa.int/esaCP/SEMVT6NVGJE_index_0.html
* Envisat altimeter watches Pacific for cold tongue of La Nina
http://www.esa.int/esaCP/SEMBFVMVGJE_index_0.html
* Taking measure of the world: radar altimetry in spotlight at Venice
event
http://www.esa.int/esaEO/SEMPI66Y3EE_index_0.html
Related missions
* Envisat overview
http://www.esa.int/esaEO/SEMWYN2VQUD_index_0_m.html
* ERS overview
http://www.esa.int/esaEO/SEMGWH2VQUD_index_0_m.html
In depth
* Radar Altimetry Symposium
http://earth.esa.int/venice06/
Related links
* DORIS
http://www.ign.fr/fr/PI/activities/geodesie/DORIS/index-en.html
* Argo
http://www.argo.ucsd.edu/
* CNES
http://www.cnes.fr/html/_455_.php
[NOTE: Images supporting this release are available at
http://www.esa.int/esaCP/SEMB1RNVGJE_index_1.html ]