A new global strategy for earth observationParis - Global initiatives to monitor climate change and the health of the planet took a major step forward with the establishment of a unique alliance between space agencies and scientific communities, which met at UNESCO Headquarters from May 30-31.
The meeting set new parameters to improve satellite observation of the environment, through the Integrated Global Observing System (IGOS), which is the only forum to link space and land-based scientific organizations. Created in 1998, IGOS is an umbrellaorganization for hundreds of research organizations, with a main decision-making body consisting of 14 partners, including diverse UN agencies and scientific organizations, like UNESCO and the World Meterological Organization as well as the Committee on Earth Observation Satellites (CEOS), which represents 23 space agencies.
"The space race has entered a new phase," said Walter Erdelen, co-chairman of IGOS and UNESCO Assistant Director-General for Science. "No longer is it a mere playing field for superpower rivalry, dominated by military concerns and national pride. Today, the race to space is fuelled by a far more critical goal than that of Cold War politics--the quest to understand the planet's life-support systems."
Since the end of the Cold War, space agencies have increasingly focused on environmental security by launching an expanding constellation of satellites equipped with optical, infrared and radar sensors to monitor the Earth. These satellites are often the only way to obtain suitabledata to understand and predict both man-made and natural changes to the atmosphere, land and oceans.
Countries of diverse financial means - from the United States, Japan and France to India, China, Brazil and Argentina - have invested in Earth observation satellites. Yet over the past several years, many space agencies have experienced steep budgetary constraints. While the cuts appear to have stabilized, agencies are trying to optimize scarce resources with tailor-made missions for the end-users, land-based scientists. IGOS enables them to consult directly with these communities to plan new missions.
"There are several global initiatives to observe the climate or the oceans, for example. But no single agency or organization can afford to implement one of these systems alone," said Dr. Tillman Mohr of CEOS. IGOS has begun by identifying several critical issues, notably: the ocean currents and climate change, the state of the world's water resources, the global carbon cycle, atmospheric chemistry and geo-hazards such as volcanic eruptions and landslides. Scientists specializing in these areas work in committees to develop strategies in the form of reports, which begin by identifying the type and duration of satellite data which might fill the gapsin current knowledge.
For example, there are fairly regular and accurate measurements of air-pollution levels for wealthy capitals. Satellites might provide a global monitoring system, necessary for understanding atmospheric chemistry.
Yet satellites alone cannot answer most of the critical questions facing scientists today. Satellites alone cannot measure the amount of carbon dioxide absorbed by forests or the rate of coastal erosion. IGOS is also developing strategies to integrate land and space based data. Satellite images of coastal erosion can transform the studies of a marine biologist. At the same time, space agencies need information from the field to interpret the signals sent by satellites.
"This marks a paradigm shift for both the space and land-based scientific communities," says Colin Summerhayes, who works closely with IGOS through UNESCO's Intergovernmental Oceanographic Commission. "Both are shifting to long-term research and blurring the boundaries between fundamental and applied science through remote sensing."
Oceanography offers a classic example and was the subject of the first IGOS report released in January 2001. Although it is too soon to evaluate the report's impact, there is one concrete result: the U.S. and European agreement to jointly launch Jason-2 in 2005. This satellite will follow in the footsteps of the Jason-1 and Topex/Poseidon, Franco-American satellites that revolutionized our understanding of oceanography.
Circling the Earth every 112 minutes, Topex/Poseidon was the first satellite (launched in 1992) capable of measuring the height and temperature of sea waves as well as related wind speed. This kind of data is the only way scientists can observe the major ocean currents that regulate our climate by shifting heat around the world. For the first time, scientists could watch major events unfold, like El Nino in which unusual wind conditions bring warm waters to the equatorial Pacific and disrupt normal weather patterns around the world.
The Topex/Poseidon was so successful that the U.S. and France launched a follow-up mission, Jason-1, in 2001. The satellite has just begun to send the most precise measurements of sea surface ever recorded, with an accuracy of a centimetre. Jason-1 should be operating for about ten years.
But a decade of data is just a drop in the bucket in scientific terms. "We now know that events like El Nino and the North Atlantic Oscillation (an atmospheric see-saw driving winter storms west to east across the ocean) don'tsimply occur on a year-to-year basis but follow decadal cycles," said Summerhayes. "With longer-term data, weather forecasters might provide practical information for agricultural planning, especially in arid regions."
IGOS is preparing a similar report on the world's water resources. We take for granted the satellite images shown by weather forecasters on television. A string of meteorological satellites followed the first U.S. mission launched in 1960. However, there are still gaping holes in scientists' understanding of the basic water cycle. Precipitation is notoriously difficult to evaluate: it has been estimated that only one to four percent of the globe's area is covered at any time by rainfall. And the intensity of that rainfall can vary widely in a matter of minutes or even seconds.
Yet scientists will soon have unprecedented quantity and quality of water-related data thanks to a new generation of satellites: Terra and Aqua (USA), Envisat (Europe) and Adeos-II (Japan). The challenge lies in harmonizing the different kinds of equipment and models used to interpret the data.
IGOS is weaving a global network to collect, compare and synthesize the data of the various satellites with land-based observations. The aim is to finalize the system within the next two years to prepare for what promises to be a technological milestone. In 2007, the U.S. and Japan will launch a constellation of nine Global Precipitation Measurement (GPM) satellites, which will be able to measure the rainfall at any spot on the globe every three hours.
IGOS is developing a similar strategy to study the impact of rising carbon dioxide (COČ), emissions. This is the most dangerous greenhouse gas because it can stay in the air for tens and even thousands of years, trapping heat in the atmosphere. To predict how atmospheric COČ levels and climate may change in the future, we must understand where and how it moves between the land, oceans and atmosphere in what is known as the global carbon cycle.
For example, the oceans absorb an estimated 30 to 50 percent of the COČ produced by burning fossil fuels, thanks mostly to microscopic plants, known as phytoplankton which live within the first 50 metres of the sea surface. Most of the carbon that the plants absorb through photosynthesis is released from the ocean within about a year. Yet some of it sinks deep in the ocean as the plants die. It can take centuries and even millennia before most of this dissolved carbon dioxide is released back into the atmosphere.
By studying satellite images of ocean colour, scientists can gauge phytoplankton levels globally. But to verify these estimates, they need more specific information provided by samples taken aboard ships and from special buoys. This verification is essential to develop models on how the carbon absorbed and released by the ocean interacts with the atmosphere and land.
"Today there are several models but the results they give can vary by as much as 50 percent," said Philippe Ciais of the French Atomic Energy Commission, leader of the IGOS strategy for the carbon cycle, which will be finalized within the next year. "These models will probably improve. But if we don't improve our current observations, we won't have a reference point to measure the extent to which the carbon cycle has changed between now and the next decade."