Remote sensing of terrestrial water storage, soil moisture and surface waters

Comprehensive monitoring of terrestrial water is critical for characterizing changes in water availability, hydrologic extremes, to determine human impacts on the water cycle, and more generally, for enhanced predictive understanding of regional and global water cycles and their interactions within the Earth system. In this paper, the current and near-future capabilities of remote sensing of terrestrial water are assessed, with a focus on liquid water. The potential for GRACE observations of time-variable gravity to monitor monthly and longer changes in total water storage for regions greater than 200,000 km(2) is discussed. Near-future AMSR observations of surface soil moisture at 60 km resolution with 2-day repeat are described, as is the future HYDROS mission. Current and future capabilities of altimetric observations of terrestrial surface waters are reviewed. An important perspective of this paper is that the current and near-future sensors described in this paper will offer unprecedented opportunities for monitoring terrestrial hydrology, and that their joint use will enable new, simultaneous views of both the lateral and vertical distribution of water on land that have not been previously possible.