Description of the data products that will be produced from the named scientific missions.

The following listing represents a survey and a short description of 'Earth Observing Mis sions' in alphabetical order. The listing in Part A considers completed-, operational-as well as planned missions on an international scale (Earth observations from space know no na tional boundaries). A look into past activities is important for reasons of heritage, context and of perspective. The document is intended for all who want to keep track of missions and sensors in the fast -growing field of Earth observations. There cannot be any claim to com pleteness, although a considerable effort was made to collect and integrate all known mis sions and sensors into this book. Earth observation by remote sensing changes our view and perception of the world. We be gin to realize the global character of remote sensing, its multidimensional and complemen tary nature, its vast potential to many disciplines, its importance to mankind as a whole. Re mote sensing permits for the first time in history a total system view of the Earth. The view from space toward Earth has brought about sweeping revisions in the Earth sciences, in par ticular in such fields as meteorology, oceanology, hydrology, geology, geography, forestry, agriculture, geodynamics, solar-terrestrial interactions, and many others.

The Global Geodetic Observing System (GGOS) has been established by the Int- national Association of Geodesy (IAG) in order to integrate the three fundamental areas of geodesy, so as to monitor geodetic parameters and their temporal varia- ?9 tions, in a global reference frame with a target relative accuracy of 10 or b- ter. These areas, often called ‘pillars’, deal with the determination and evolution of (a) the Earth’s geometry (topography, bathymetry, ice surface, sea level), (b) the Earth’s rotation and orientation (polar motion, rotation rate, nutation, etc. ), and (c) the Earth’s gravity eld (gravity, geoid). Therefore, Earth Observation on a global scale is at the heart of GGOS’s activities, which contributes to Global Change - search through the monitoring, as well as the modeling, of dynamic Earth processes such as, for example, mass and angular momentum exchanges, mass transport and ocean circulation, and changes in sea, land and ice surfaces. To achieve such an - bitious goal, GGOS relies on an integrated network of current and future terrestrial, airborne and satellite systems and technologies. These include: various positioning, navigation, remote sensing and dedicated gravity and altimetry satellite missions; global ground networks of VLBI, SLR, DORIS, GNSS and absolute and relative gravity stations; and airborne gravity, mapping and remote sensing systems.

NASA's Earth Science Division (ESD) conducts a wide range of satellite and suborbital missions to observe Earth's land surface and interior, biosphere, atmosphere, cryosphere, and oceans as part of a program to improve understanding of Earth as an integrated system. Earth observations provide the foundation for critical scientific advances and environmental data products derived from these observations are used in resource management and for an extraordinary range of societal applications including weather forecasts, climate projections, sea level change, water management, disease early warning, agricultural production, and the response to natural disasters. As the complexity of societal infrastructure and its vulnerability to environmental disruption increases, the demands for deeper scientific insights and more actionable information continue to rise. To serve these demands, NASA's ESD is challenged with optimizing the partitioning of its finite resources among measurements intended for exploring new science frontiers, carefully characterizing long-term changes in the Earth system, and supporting ongoing societal applications. This challenge is most acute in the decisions the Division makes between supporting measurement continuity of data streams that are critical components of Earth science research programs and the development of new measurement capabilities. This report seeks to establish a more quantitative understanding of the need for measurement continuity and the consequences of measurement gaps. Continuity of NASA's Earth's Observations presents a framework to assist NASA's ESD in their determinations of when a measurement or dataset should be collected for durations longer than the typical lifetimes of single satellite missions.