Satellite Altimetry and Key Observations: What We've Learned, and What's Possible with New Technologies
The advent of high accuracy satellite altimetry in the 1990's brought the first global view of ocean dynamics, which together with a global network of supporting observations brought a revolution in understanding of how the ocean works [1]. At present a constellation of flying satellite missions routinely provides sea level anomaly, sea winds, sea surface temperature (SST), ocean colour, etc. with mesoscale resolution (50km to 100km, 20 to 150 days) on a near global scale. Concurrently, in situ monitoring is carried out by surface drifters, Argo floats, moorings, sea gliders as well as ship-borne CTD (Conductivity-Temperature-Depth) and XBT (Expendable Bathythermograph) (to measure profiles of temperature and salinity), and ADCP (Acoustic Doppler Current Profiler) (to measure current velocity profiles). This global observational system allowed observational oceanography to develop into an essentially quantitative science. This became possible because 1) the accuracy and volume of observations exceeded critical values, 2) numerous studies demonstrated good agreement between independent datasets, and critically 3) the data resolution crossed the threshold of revealing much of the mesoscale in two-dimensions, when previously it was only revealed in one-dimension along satellite ground tracks [2] with wide gaps in between. Fortuitously computing power kept pace allowing basin scale numerical ocean models to cross the threshold of revealing the mesoscale around the turn of the century [3]. The mesoscale is characterized by the most energetic motions and strong nonlinear interactions, issuing in a more complex range of phenomena. Below in Sect. 1 we present some highlights of this development. In Sect. 2, we describe future prospects, and Sect. 3 provides a reminder of the importance of maintaining continuity of high-quality observations. We conclude in Sect. 4 with discussion of integrating optimizing the observing system. The benefits to society from development of quantitative dynamical oceanography, as with most scientific disciplines, while indirect, are no less real. Ocean dynamics forms an important foundation for climate dynamics and biological oceanography, developments of which have direct impacts on agriculture and fishing. A critical development in the last decade has been global ocean forecasting, which was non-existent before the Global Ocean Data Assimilation Experiment (GODAE). Assimilation of satellite altimeter data, SST data, and in situ Argo data are all critical elements, without which GODAE could not be possible. This white paper comes at a critical juncture in ocean observing. While the utility of the observing network is firmly grounded in the success of the past, and technological advances promise the possibility of substantial gains, we still lack the commitment for sustained funding of even the existing observing network. We wish to express herein our sincere concern for the future of ocean observing, and in particular the satellite altimeter and supporting observations (especially scatterometer and drifter data).
Scott Robert B., Bourassa Mark, Chelton Dudley, Cipollini Paolo, Ferrari Raffaele, Fu Lee-Lueng, Galperin Boris, Gille Sarah, Huang Huei-Ping, Klein Patrice, Maximenko Nikolai, Morrow Rosemary, Qiu Bo, Rodriguez Ernesto, Stammer Detlef, Tailleux Remi, Wunsch Carl (2010). Satellite Altimetry and Key Observations: What We've Learned, and What's Possible with New Technologies. Proceedings of OceanObs'09: Sustained Ocean Observations and Information for Society. https://archimer.ifremer.fr/doc/00067/17791/