Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

A voyage from space to sea with Envisat

11.02.2002


Envisat guarding the planet


Envisat, whose launch is scheduled end of February 2002, will tirelessly sweep the Earth`s surface and atmosphere, using a suite of ten different scientific instruments.

Over a 35-day cycle, the satellite`s orbit will cover the entire planet, and then start all over again. Two thirds of the time it will be over water. Because of the sheer size of the oceanic currents, the complexity of thermal exchanges, and ocean-atmosphere coupling, the ocean is a crucial factor in explaining the way our planet`s climate operates and how it is changing.

Beginning with the first brief American Seasat mission in 1978, satellite observation has created a revolution in our understanding of how the ocean behaves. Since the 1990s, a continuous stream of scientific data has been flowing from ESA`s ERS satellites and the joint French-US Topex/Poseidon altimetry satellite. This first generation is now being succeeded by Envisat`s instruments designed not only to advance science but also to lead to a range of operational applications services.



The data obtained with a radar altimeter, RA-2, will ensure continuity with the original RA system on the ERS satellites. It will also provide a valuable complement to Topex/Poseidon and its follow-on, the small satellite Jason, launched on 7 December 2001. The two systems provide altimetric observation of the ocean from different orbits. A low satellite repetition ensures that Envisat, like the ERS spacecraft before it, obtains excellent spatial resolution, needed to study complex phenomena like eddies and describe the distribution of water mass with precision. Topex/Poseidon and Jason, on the other hand, with a repetitivity of just ten days, will provide better temporal resolution.

CLS, a French company, is handling the operational exploitation of altimetry measurements from both Envisat and Jason. "We will integrate data from these two sources, to get the maximum benefit," explains Philippe Gaspar, Head of satellite oceanography at CLS. "The combinatorial algorithm has been in use since 1998, allowing CLS to offer state-of-the-art data products".

Hydrosphere, atmosphere, ionosphere: a close relationship

The products developed by CLS will be of interest, first and foremost, for scientists who use them as inputs for ocean modelling and forecasting. In conjunction with atmospheric models, this forms a starting point for predicting climate change. "It is now possible to forecast some major events such as El Niño, but smaller-scale phenomena such as the North Atlantic oscillation pose much more of a problem," Gaspar said.
To obtain the best performance from a forecasting model, initial conditions must be described as precisely as possible, and this is where satellite data is indispensable. "Before the advent of satellites, forecasting of this type would have been unthinkable," as Gaspar reminds us.

Radar altimetry measurements are correlated with high-precision orbitographical data from an instrument called "DORIS", and with those of a microwave radiometer, so that errors caused by atmospheric water can be corrected. The use of a dual-frequency altimeter further makes it possible to correct for the distorting effects of the ionosphere. In this way two significant sources of error are eliminated, in the order of 40 to 50 cm for water vapour and 20 to 30 cm for the ionosphere.

The continuity of altimetry data is vital, as Gaspar explains. "The usefulness of the scientific work would be seriously impaired if the service was interrupted. And once commercial applications are on the market, continuity will become absolutely indispensable."

Managing the traffic at sea

In addition to oceanography and climate studies, the radar altimeter has an important contribution to make to marine traffic management. Dispersion of the reflected radar signal gives information on the height of waves, with a precision of ±25 cm, while the advanced synthetic aperture radar (ASAR) determines wave direction. Taken together with information on major currents, this will make it possible to optimise routing of maritime traffic for speed and fuel economy, a substantial boon to international shipping. The ASAR also tracks drifting ice and monitors the pack ice and its limits.

Two other Envisat instruments are designed primarily to study the hydrosphere. MERIS (for Medium Resolution Imaging Spectrometer) is a fifteen-band optical system spanning the visible and near-infrared spectrum, and will be used for ocean colour measurements. The AATSR radiometer covers more of the IR spectrum. It will measure ocean surface temperatures, continuing the work of earlier ATSR systems on the ERS satellites. These two instruments together will have major applications in studies of plankton and fish movements.

As instrument data comes in, Envisat puts it provisionally into its onboard mass-memory devices. Transmission may be to one of the ground stations in Kiruna, Sweden, or Svalbard, Norway or via a high-speed link to the Artemis data relay satellite, which will be positioned in geostationary orbit and forward the data to ESA`s establishment ESRIN, located in Frascati, Italy, for near-real time processing.

The data gathered will be made available to the world scientific community at archiving centres distributed throughout Europe and linked with very high speed leased lines. A data server will be put on line for access via the Internet. Two consortiums have been set up with data processing/commercialisation experts: Sarcom, led by Spot Image, and Emma, by Eurimage, will handle the commercial exploitation of the application products developed from Envisat data.

By concentrating such an array of instruments on a single orbital platform, it becomes possible to integrate the information received in near-real time. This opens exciting opportunities for new products, building on recent progress in our understanding of the mechanisms, which determine the behaviour of the Earth`s oceans and atmosphere. Thanks to a continuous flow of data, these products could revolutionise the management of our Planet and our environment.

Jacques Louet | alphagalileo
Further information:
http://www.esa.int

More articles from Physics and Astronomy:

nachricht Applicability of dynamic facilitation theory to binary hard disk systems
08.12.2016 | Nagoya Institute of Technology

nachricht Will Earth still exist 5 billion years from now?
08.12.2016 | KU Leuven

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Significantly more productivity in USP lasers

In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.

Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

Closing the carbon loop

08.12.2016 | Life Sciences

Applicability of dynamic facilitation theory to binary hard disk systems

08.12.2016 | Physics and Astronomy

Scientists track chemical and structural evolution of catalytic nanoparticles in 3-D

08.12.2016 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>