ductivity (Chapter 9), ocean currents and mesoscale features (Chapter 8), and global maps of winds (Chapter 8). Prior to the satellite era, even if it was possible to compose a global picture from individual surface observations (e.g., through the World Weather Watch, established in 1963), the coverage and density of the network and lack of vertical resolution left much to be desired. Other geophysical and biological phenomena were sampled much less frequently, often as a partial “snapshot” of an otherwise dynamic set of interacting Earth processes.
Discovery of the variability in the velocity of ice sheet flow is another example of how the dynamics of the system went undetected until reliable and repeated satellite observations became available (Chapter 7). This discovery revolutionized the study of ice sheet flow and yielded an important realization: sea-level change due to freshwater input from the continental ice sheets was not a function of the balance between ice sheet melting and precipitation at higher elevation, but a function of the flow dynamics. The increasing velocity of continental ice flow into the ocean in response to climate change and the collapse of the Larsen B Ice Shelf emphasized the sensitivity of ice sheet dynamics to a changing climate.
Satellite sensors provide a panoptic viewpoint, yet historically they suffered from poor resolution and calibration problems. On the other hand, ground-based instruments, although more precise and better calibrated, are limited to their particular locales, and problems arise since they must be coordinated and intercalibrated with other ground stations. As satellite sensors and data processing have become more sophisticated, equaling or surpassing those for ground-based measurements, scientists have obtained not only images but also quantitative global measurements of unprecedented precision. Intercalibration proved particularly challenging in putting together global maps of marine primary productivity from shipboard measurements (Chapter 9). Estimating marine primary productivity requires sample manipulation and measurements of 14C uptake rates at each location, which are sensitive to variations in sampling techniques and methods. Although global marine primary productivity estimates had been attempted before the satellites era, they were flawed because of intercalibration issues. More importantly, because it takes years to obtain global coverage of ground-based marine primary productivity measurements, satellites allowed for the first time observation of global marine primary productivity on a monthly and annual basis and detection of decadal-scale trends.
Satellite observations also provide access to otherwise virtually inaccessible regions, such as polar regions, the upper atmosphere, and the open oceans. Quantitative assessment and monitoring of the sea ice extent in the Arctic has only been possible since routine satellite observations became available. Without satellite images, it is unlikely that trends in decreasing Arctic summer sea ice would have been detected as readily, demonstrating univocally the drastic decline in summer ice over the past decades (Chapter 7). Satellite observations have become available and matured as scientific data at a time when they are critically important in helping society manage planetary-scale resources and environmental challenges. Although many scientific challenges remain, it is undeniable that satellite observations have allowed scientists to improve the ability to monitor and predict changes in the Earth system and manage life on Earth (NRC 2007a).
It is widely known that satellite data, particularly from the southern hemisphere, have contributed to improvements in weather prediction, resulting in protection of human lives and infrastructure (Chapter 3). Since the availability of satellite images, no tropical cyclone has gone undetected, and the advance warning allows crucial time to prepare. In fact, the advent of satellites has been heralded as unquestionably “the greatest single advancement in observing tools for tropical meteorology” (Sheets 1990). Furthermore, because satellite data give access to the largely undersampled ocean, hurricane track forecasts have improved dramatically, helping save lives and property every year (Considine et al. 2004). Other aspects of human welfare have and will also benefit from satellite observations. For example, it is also unlikely that a famine early warning system would be available to assist in planning aid distribution without the ability to observe vegetation cover and the availability of water resources from space (Chapter 10). Given the projected climate change and associated sea-level rise, having global satellite coverage available in the future will serve crucial societal needs unmet by any other observing system.
Conclusion 1: The daily synoptic global view of Earth, uniquely available from satellite observations, has revolutionized Earth studies and ushered in a new era of multidisciplinary Earth sciences, with an emphasis on dynamics at all accessible spatial and temporal scales, even in remote areas. This new capability plays a critically important role in helping society manage planetary-scale resources and environmental challenges.
The global view of Earth from satellites has imparted the understanding that everything is connected—land, ocean, and atmosphere. Interdisciplinary teams of researchers have explored these connections to better understand the Earth as a system beyond the sum of its elements. The concept of studying the Earth as an integrated system at a national level was led by the National Aeronautics and Space Administration (NASA), inspired by NASA’s “Ride report” (NASA 1987), and intended as the U.S. component to the International Geosphere-Biosphere Program. Consequently, NASA launched its mission to planet Earth to study the Earth’s geosphere and biosphere as an integrated system instead of discrete but interrelated components (CRS 1990).