A new NASA mission, Surface Water and Ocean Topography (SWOT), will be capable of measuring key hydraulic variables associated with rivers, lakes, wetlands, and reservoirs over much of the Earth’s surface regardless of the amount of cloud cover. Thus, SWOT represents a viable method of routinely mapping and quantifying river hydraulics and developing time series of changes in these variables. This ability enables the effective integration of remote sensing data into monitoring of the world’s freshwater bodies, as either supplemental information to dense networks or as primary information where data are sparse. Although SWOT will only “see” any given river reach on an 11-day repeat cycle, the SWOT mission will provide large-scale mapping capabilities and detailed reach-scale information about rivers of interest, where changes in slope and river width may be key to tracking floods, monitoring droughts, and assessing flow direction in sensitive areas.
The USGS-led Science Definition Team (SDT) contributed expertise on Hydrological Mission Objectives and Additional Synergistic Objectives, which included 1) calibrating and validating SWOT and AirSWOT water surface elevations and derived products such as river slope, streamflow, and reservoir storage; 2) compiling and delivering USGS streamgage and other datasets to the SWOT science team for development and validation; 3) developing discharge algorithms and demonstrating the computation of streamflow using physically- and statistically-based models applied at the reach-scale; 4) applying SWOT and AirSWOT water surface elevations to problems involving reach-scale measurement of river hydraulic variables and discharge; and 5) providing summary documentation.