Abstract. Over 20 global ocean tide models have been developed since 1994, primarily as a consequence of analysis of the precise altimetric measurements from TOPEX/POSEIDON and as a result of parallel developments in numerical tidal modeling and data assimilation. This paper provides an accuracy assessment of 10 such tide models and discusses their benefits in many fields including geodesy, oceanography, and geophysics. A variety of tests indicate that all these tide models agree within 2-3 cm in the deep ocean, and they represent a significant improvement over the classical Schwiderski 1980 model by approximately 5 cm rms. As a result, two tide models were selected for the reprocessing of TOPEX/POSEIDON Geophysical Data Records in late 1995. Current ocean tide models allow an improved observation of deep ocean surface dynamic topography using satellite altimetry. Other significant contributions include theft applications in an improved orbit computation for TOPEX/POSEIDON and other geodetic satellites, to yield accurate predictions of Earth rotation excitations and improved estimates of ocean loading corrections for geodetic observatories, and to allow better separation of astronomical tides from phenomena with meteorological and geophysical origins. The largest differences between these tide models occur in shallow waters, indicating that the current models are still problematic in these areas. Future improvement of global tide models is anticipated with additional high-quality altimeter data and with advances in numerical techniques to assimilate data into high-resolution hydrodynamic models.

We describe the application of ocean levelling to worldwide height system unification. The study involves a comparison of ‘geodetic’ and ‘ocean’ approaches to determination of the mean dynamic topography (MDT) at the coast, from which confidence in the accuracy of stateof- the-art ocean and geoid models can be obtained. We conclude that models are consistent at the sub-decimetre level for the regions that we have studied (North Atlantic coastlines and islands, North American Pacific coast and Mediterranean). That level of consistency provides an estimate of the accuracy of using the ocean models to provide an MDT correction to the national datums of countries with coastlines, and thereby of achieving unification. It also provides a validation of geoid model accuracy for application to height system unification in general. We show how our methods can be applied worldwide, as long as the necessary data sets are available, and explain why such an extension of the present study is necessary if worldwide height system unification is to be realised.

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The last few years have witnessed the foundation and development of a new discipline, coastal altimetry, and the coalescence of an active community of researchers who are now enthusiastically developing the topic. In the present community white paper, we summarize the technical challenges that satellite altimetry faces in the coastal zone, and the research that is currently being carried out to overcome those challenges. We introduce the new coastal altimetry data that are becoming available, and describe how we can calibrate/validate those data. Then we show several of the possible applications of coastal altimetry and conclude by looking at the future of the discipline, and at how we can build capacity in coastal altimetry.

OVERVIEWSea level is one of the most useful oceanographic parameters. Sea level data are vital to scientists for studies of fluctuations in major ocean currents and global climate change, to engineers for the design of coastal installations, to a large community engaged in what is now called "operational oceanography" (e.g. the provision of flood warnings from storm surges and tsunamis), and in local applications such as provision of tide tables and real-time data for port operations. For nearly 25 years, the Global Sea Level Observing System (GLOSS) has provided oversight for the operation of tide gauge networks and has ensured that requirements for accuracy, frequency and latency of sea level data are met for a broad base of users. After a brief background of the program, we present a status report of GLOSS in 2009, and provide community recommendations for the future role of GLOSS in the coming decade.