Determining ocean circulation and sea level from satellite altimetry: Progress and challenges

Abstract

Satellite altimetry has revolutionized oceanography since the early 1990s after the launch of the TOPEX/Poseidon and ERS-1 missions. The progress made in the past 20 years is reviewed in the paper with a focus on the most recent advances. Precision altimetry measurements from TOPEX/Poseidon and its follow-ons have provided continuous global view of the large-scale ocean circulation and its changes over a time span approaching two decades. New discoveries range from El Niño to global sea level rise, from ocean general circulation to model-based estimation of the state of the ocean for a variety of scientific and societal applications. The combined data from precision missions with other missions have led to a wealth of new information on the details of ocean circulation, including the pathways of eddies and their interaction with the mean flow and bottom topography. It is now even possible to perform high-order computation of the flow field for studying the vorticity balance of ocean currents and the energy cascade in spectral space. Calculations of the flux of tidal energy have confirmed that half of the required mixing in the ocean to maintain its thermohaline circulation is provided by tidal dissipation in the deep ocean. The surprising finding of internal tidal signatures in altimetry data has revitalized the study of the subject of great importance to the understanding of ocean mixing and energy cycle. A new challenge for altimetry is to resolve ocean motions at scales shorter than 100 km that play a key role in the vertical exchange processes of the ocean and the cycle of ocean kinetic energy. These are important missing links in improving the understanding of the ocean's roles in climate change. The technology of radar interferometry for making high-resolution wide-swath altimetry measurement is a way to meet the challenge. A new mission called Surface Water and Ocean Topography (SWOT) is introduced as a next-generation altimetry mission for both oceanographic and land hydrological applications. © 2010 Springer Science+Business Media B.V.