Measurement of Inland Surface Water from Multi-mission Satellite Radar Altimetry: Sustained Global Monitoring for Climate Change

Multi-mission satellite radar altimetry makes a unique contribution to the monitoring of global inland surface water; existing datasets already allow derivation of decadal time-series over hundreds of targets worldwide. These data are utilised both for climate change research, to inform water resource management, and, in synergy with GRACE data, to examine time-varying gravity signatures from land surfaces and (potentially) measure sub-surface hydrological flow. As the number of gauged catchments continues to fall, the importance of a global remote sensing measurement capability becomes ever more critical. The key to unlocking this potential is to retrack the complex waveforms returned from inland water targets, to identify and discard echo components returned from targets not directly beneath the satellite, and to discriminate successfully between wet land and inundated surface. This paper presents a global assessment of current capabilities, showcases decadal time-series from past and current altimeters, and demonstrates the Near Real Time measurement capability now running for the ENVISAT RA-2 and soon for Jason-2 as an ESA pilot system, allowing users access to these data within 3 days of measurement. The enhancement of this unique capability anticipated from the series of proposed future missions (such as CryoSat-2 and Sentinel-3) is discussed, and the key contribution to global climate change monitoring is demonstrated.