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 NASA detects solar flare pulses at Sun and Earth
17.11.2017 | NASA/Goddard Space Flight Center

nachricht Pluto's hydrocarbon haze keeps dwarf planet colder than expected
16.11.2017 | University of California - Santa Cruz

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: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

Im Focus: Wrinkles give heat a jolt in pillared graphene

Rice University researchers test 3-D carbon nanostructures' thermal transport abilities

Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

NASA detects solar flare pulses at Sun and Earth

17.11.2017 | Physics and Astronomy

NIST scientists discover how to switch liver cancer cell growth from 2-D to 3-D structures

17.11.2017 | Health and Medicine

The importance of biodiversity in forests could increase due to climate change

17.11.2017 | Studies and Analyses

VideoLinks
B2B-VideoLinks
More VideoLinks >>>