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approach to studying the earth--to establish and maintain a global observation system in space. What would such a system look like? It would include a suite of experiments and sensors in polar orbit, in low inclination orbit and in geosynchronous orbit. It would also, most importantly, include a data managing and processing system that would integrate data from space, and data from in situ measurements, to enable scientists to monitor, to document, and over the years to understand and model the earth system.

The experiments would measure global cloud cover, vegetation cover, ice cover, rainfall and moisture. Other experiments would measure ocean chlorophyll, ocean levels, motion of the tectonic plates, and atmospheric concentrations of ozone, methane, and carbon dioxide. It is clear that a program like this could contribute to our understanding of global change, and in particular to our understanding of issues such as ozone depletion, the buildup of greenhouse gasses, and the extent of the effects of acid rain.

Several different space-based elements would be required to gather this information. To meet the objectives of a scientifically comprehensive global observing system, Mission to Planet Earth would include four sun-synchronous polar orbiting platforms; five geosynchronous satellites (the number required to cover the whole earth from geosynchronous orbit); experiments and satellites carried to orbit by the space shuttle and by expendable rockets and experiments attached to the space station. A crucial, and often overlooked element would be a data management system that would process and integrate the information, and make it available for analysis by scientists in a variety of disciplines worldwide.

Since this is a global study, making global observations, it no only invites international participation, it requires it. It is inherently international in scope, and must be an international effort. Other nations have supported the concept, and have endorsed Mission to Planet Earth as primary focus of International Space Year in 1922. I believe the United States should provide leadership for Mission to Planet Earth, will all members of the international community invited and encouraged to provide both space- and ground-based experiments. The NASA study suggested, for example, that two of the polar platforms and two of the geostationary platforms be provided by other nations or groups of nations.

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