The Terra (formerly known as EOS AM-1) satellite is the flagship of NASA’s Earth Science Enterprise. It will be the first EOS platform and will provide global data on the state of the atmosphere, land, and oceans, as well as their interactions with solar radiation and with one another.

One century ago, Swedish scientist Svante Arrhenius asked the important question "Is the mean temperature of the ground in any way influenced by the presence of the heat-absorbing gases in the atmosphere?" He went on to become the first person to investigate the effect that doubling atmospheric carbon dioxide would have on global climate.¹ The question was debated throughout the early part of the twentieth century and is still a main concern of Earth scientists today. Other equally important questions have arisen concerning the "health" of our planet that also require further scientific investigation and are discussed in this brochure.

Arrhenius' first climate model was based on Samuel Langley's infrared measurements of the temperature of the moon, from which Arrhenius derived the infrared transmissions of carbon dioxide and water vapor. Since then, climate models were developed to include other trace gases and many processes in Earth's atmosphere, lands, and oceans. But scientists now recognize that climate models using trace gas forcing alone cannot adequately explain temperature trends. To predict future climates we need to introduce into the models Earth parameters that are highly varying in space and time, such as clouds, aerosols, water vapor, land use, ocean productivity, and the interactions between these parameters. Today, the prime tools for measuring these parameters are highly precise satellite sensors. Consequently, the World Climate Research Program, the International Geosphere-Biosphere Program, and the U.S. Global Change Research Program formed the framework for NASA's Earth Science Enterprise. The design and construction of the Earth Observing System (EOS) and its associated scientific efforts are the Enterprise's main foci.

In 1998, NASA will launch the first EOS satellite—Terra—with five state-of-the-art instruments to observe and measure the state of the Earth system, and to monitor global environmental changes over time. Each instrument is uniquely designed to provide data with unprecedented precision, quality, and scope. These data will be processed into continuous long-term measures of the state of the land, ocean, and atmosphere. Terra's measurements, together with those of other satellite systems launched by NASA and other international space agencies, begin a new self-consistent data set that is expected to revolutionize climate change models. Follow-up missions are planned to extend this data set continously for at least the next 18 years.