processes such as postglacial rebound. ESA’s Gravity Field and Steady-State Ocean Circulation Mission (GOCE) satellite will provide experience with satellite gravity gradiometry, and the proposed near-term NASA mission would test satellite-to-satellite interferometry. A careful analysis of these and perhaps other approaches will help NASA choose the most appropriate gravity measurement technology to replace GRACE in the long term.
Surface Properties Using Imaging Spectroscopy. We support implementation of the stated and implied SESWG recommendations, including continuation of the Airborne Visible/ Infrared Imaging Spectrometer (AVIRIS) and development of a hyperspectral (less than 10-nanometer bandwidth) visible-near-infrared spaceborne instrument. Rather than simply refining existing techniques, new sensor technologies will be required to enable identification of minerals, rocks, and soils and to monitor landscape change, volcanism, tectonics, and ice dynamics. In addition to airborne and spaceborne hyperspectral capabilities, continued operation of multispectral instruments would help meet a number of scientific objectives, although multispectral equivalent products could be derived from hyperspectral data if choices must be made.
Overall, we find that the observational strategies outlined in the SESWG report would take advantage of NASA’s skills in sensor development and yield important data for addressing major earth-science challenges. Equally important to the success of NASA’s solid-earth program will be the analysis of data from existing and planned instruments flown by NASA and space agencies in other countries, especially to meet the gravity and magnetics scientific objectives. Although adjustments might be necessary as new technology is developed, we believe that the observational strategies provide a sound basis for guiding NASA’s solid-earth science program in the coming decades.