The last sentence in the previous paragraph is key. MTPE and its components are not a science and/or technology mission per se, but rather comprise a mission that will make use of science and technology to give planners, policy-makers, and decision-makers the tools they need to understand our planet and to manage its resources appropriately. This brings a human dimension into the equation, i.e., not only what is the role of humans in accelerating global change, but how does global change affect humans?

MTPE includes ongoing and near-term satellite missions, new missions under development, planned future missions, management and analysis of satellite and in situ data, and a continuing basic research program focused on process studies, modeling, and data analysis. The space-based components of MTPE will provide a constellation of satellites to monitor the Earth from space. Sustained observations will allow researchers to monitor Earth's climate variables over time to determine trends; however, space-based monitoring alone is not sufficient. A comprehensive data and information system, a community of scientists performing research with the data acquired, and extensive ground and airborne campaigns are all important components. More than any other factor, the commitment to make Earth science data easily available to the research and end-user community is critical to mission success.

To address the need for quantitative analysis of the Earth and its various subsystems, MTPE's principal element, the Earth Observing System (EOS) will provide systematic, continuous observations from low Earth orbit for a minimum of 15 years after first launch. In so doing, EOS is creating an integrated scientific observing system to foster multidisciplinary study of the Earth's critical, life-enabling, interrelated processes involving the atmosphere, oceans, land surfaces, and polar regions, and the dynamic and energetic interactions among them. It will also develop a comprehensive data and information system (EOSDIS), including a data retrieval and processing system, to serve the needs of scientists contributing to an integrated, multidisciplinary study of planet Earth. It also supports the overall USGCRP by acquiring and assembling a global database of remote-sensing measurements from space, in keeping with the research priorities listed above.

Once scientists have determined the specifics of the kinds of measurements they must make to address the many questions we face, those requirements have to be translated into a means of obtaining those measurements. This process results in the design of a sensor, that is, an electronic or optical-electronic device that will make the necessary measurements. Such devices require a great deal of supporting hardware, including physical support structures, power assemblies, data storage, data transmission, calibration, and more. Constraints on many of these are levied owing to cost and time, but other matters arise, such as the amount of room, power, and data transmission resources available on planned spacecraft (see below). In addition, if there are to be other instruments flown in concert with a given instrument (as is often the case), fields-of-view and other considerations must be addressed.

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