SIRAL, a new generation of space altimeters and CryoSat’s
mission primary experiment
“Observation satellites are the only tools capable of providing virtually
global coverage of the Earth. The instruments carried by these
satellites are of course the core of these missions.”
Reynald Seznec, President and CEO of Thales Alenia Space
CryoSat, the ESA’s ice mission
From an altitude of just over 700 km and reaching latitudes of 92°, the ESA’s 720-kilogram
CryoSat satellite will monitor precise changes in the thickness of the polar ice sheets and
floating sea ice. The observations made over the five lifetime of the mission will provide
conclusive evidence of rates at which ice cover may be diminishing. The satellite, developed
by EADS Astrium as prime contractor, is scheduled for launch on February 25, 2010 from
Baikonour in Kazakhstan.
SIRAL, the mission primary experiment
Thales Alenia Space has manufactured SIRAL radar altimeters to be used on the ice sheet
monitoring satellite CryoSat. As main instrument of the CryoSat mission, SIRAL will measure
changes in the thickness of continental and at-sea ice fields, with unprecedented accuracy.
This programme has a crucial role in the evolution knowledge of our global climate. On
CryoSat-2 mission, the satellite features two identical Siral radar altimeters. The second will
be used only in the event of a failure of the primary instrument.
SIRAL heralds a new generation of space altimetry systems
because of its high resolution, enabling it to analyze the
ground in swaths 250 meters wide, and use interferometry to
measure gradients.
Following the success of oceanic altimetry missions, it will
pave the way to greater understanding of fluctuations in the
level and thickness of the polar icecaps and the great ice
sheets. This type of data is critical in the development of
models used to analyze and predict global warming trends.
Derived from the well-known Poseidon ocean altimeter on the Jason satellite, SIRAL
synthetic aperture radar (SAR) is a very compact assembly, weighing just 90 kilograms. It
combines three measurement modes to determine the topography of land and sea ice
masses, as well as ice floes and significant elevation transitions, especially between land
and ice fields:
• Low resolution, for conventional altimetry measurement limited to the
relatively flat terrain of the continental ice in the Antarctic;
• Synthetic aperture radar (SAR), to carry out high-resolution
measurements of floating sea ice (ice sheets), enabling the indirect
measurement of the sheets’ thickness;
• Interferometric radar mode, to study more contrasted terrains, like the
very active areas located at the junction of the ice sheet and the
Antarctic continent, or Greenland.
Thales Alenia Space, more than 20 years of success in space altimetry
Thales Alenia Space has worked on radar altimetry for over 20 years, and our instruments
are widely recognized as among the best in the field.
From 1980’s with the first Topex/Poseidon mission to current CryoSat satellite, Thales Alenia
Space has provided Earth Observation missions with state-of-the-art altimeters.
Jason-2 mission, a quadripartite program between CNES, NASA, NOAA and Eumetsat, has
been launched in June 2008 with onboard Poseidon-3 altimeter. This mission is dedicated to
overlap the Jason-1/Poseidon-2 mission launched in December 2001 with the aim of
measuring the global sea surface height to determine ocean circulation in support of weather
forecasting, climate monitoring and operational oceanography.
The extraordinary harvest of results these missions made one thing very clear: space
altimetry is an essential tool to investigate our oceans and better understand our planet’s
climate.
Thales Alenia Space also provided the RA-2 second-generation radar altimeter onboard the
advanced polar-orbiting Earth observation Envisat mission launched in February 2002 to
provide measurements of the atmosphere, ocean, land, and ice. The company will also
provide the Sentinel-3 SRAL altimeter, part of the GMES program, devoted to cover the
topography of ocean surfaces near coastal zones and ice masses as well as the AltiKa highfrequency altimeter that will fly onboard the SARAL oceanography satellite.
Focus on Jean-Louis Etienne, Pole Explorer and SIRAL godfather
Jean-Louis Etienne, polar explorer and physician, is the patron of the SIRAL radar altimeter
used on CryoSat satellite.
According to Jean-Louis Etienne, “Based on the observations made during my previous polar
expeditions, there is now an urgent need to take a closer look at the poles, where the effects
of global warming are beginning to be felt. The data collected by SIRAL will have a deep
impact on our climate change scenarios. SIRAL will provide scientific ground to the debate
on global warming and consequences on earth’s climate and future.”
He stated: “I am extremely proud to be associated with this instrument, which will play a
major role in studying these changes.”
Biography
Originally a medical doctor, Jean-Louis Etienne has participated in a number of expeditions over the
last 30 years, to the Himalayas, Greenland and Patagonia, as well as the north and south Polar
Regions. In 1986, he was the first person to reach the North Pole in a solo effort, pulling his own
“dogsled” for 63 days.
During the spring of 2002, Jean-Louis Etienne embarked on the Polar Observer for a three-month
“Mission Banquise” at the North Pole, to carry out research on climate warming phenomena.