This paper presents the oceanographic objectives and plans for calibration and validation, science investigations and applications for the Surface Water and Ocean Topography (SWOT) Mission. SWOT, an international mission planned for launch in 2021, will make high-resolution observations of the ocean surface topography as a next-generation altimetry mission utilizing the technique of radar interferometry.

Over the last two decades, satellite altimetry has provided one of the most important tools for global monitoring and understanding of ocean dynamics, ranging from large-scale to smaller mesoscale processes. This paper will present some recent results using altimetry to detect smaller ocean processes in the open ocean and in coastal regions. The space and time scales being analysed by standard gridded altimetric maps and from alongtrack data will be reviewed, and compared to the scales we are expecting in the ocean, derived from models or in-situ spectra. The future SWOT altimetric mission will provide sea surface height observations with a 1 km resolution globally [1], which will enable us to observe the smaller scales open ocean and coastal processes. A review of these processes will be presented.

The primary objective of the National Research Council (NRC) Decadal Survey recommended SWOT (Surface Water and Ocean Topography) Mission is to measure the water elevation of the global oceans, as well as terrestrial water bodies (such as rivers, lakes, reservoirs, and wetlands), to answer key scientific questions on the kinetic energy of ocean circulation, the spatial and temporal variability of the world's surface freshwater storage and discharge, and to provide societal benefits on predicting climate change, coastal zone management, flood prediction, and water resources management. In this paper, we present the overall concept of the SWOT mission, as well as the scientific rational, objectives and development status of the technology items currently under development.

In 1992, NASA and the French space agency launched the first high-precision satellite altimeter to measure changes in sea surface height. With it began a new era in oceanography. Data from satellite altimeters continues to be used to estimate global sea level rise, sea surface height, geostrophic velocity, significant wave height and atmospheric water vapor over the global oceans. In combination with other ocean observations such as color, winds, and gravity, as well as temperature, salinity and velocity from profiling floats, researchers continue to discover new insights into a wide variety of ocean processes and are increasingly able to discern more mesoscale structures. Precision satellite altimetry has matured to the stage where responsibility for the observations is being transitioned from research agencies to operational agencies. Maintaining these observations over the long term will have important implications for climate monitoring as well as scientific and operational use.

The elevation of the ocean surface has been measured for over two decades from spaceborne altimeters. However, existing altimeter measurements are not adequate to characterize the dynamic variations of most inland water bodies, nor of ocean eddies at scales of less than about 100 km, notwithstanding that such eddies play a key role in ocean circulation and climate change. For terrestrial hydrology, in situ and spaceborne measurements of water surface elevation form the basis for estimates of water storage change in lakes, reservoirs, and wetlands, and of river discharge. However, storage in most inland water bodies, e.g., millions of Arctic lakes, is not readily measured using existing technologies. A solution to the needs of both surface water hydrology and physical oceanography communities is the measurement of water elevations along rivers, lakes, streams, and wetlands and over the ocean surface using swath altimetry. The proposed surface water and ocean topography (SWOT) mission will make such measurements. The core technology for SWOT is the Ka-band radar interferometer (KaRIN), which would achieve spatial resolution on the order of tens of meters and centimetric vertical precision when averaged over targets of interest. Average revisit times will depend upon latitude, with two to four revisits at low to mid latitudes and up to ten revisits at high latitudes per$\sim$20-day orbit repeat period.