66 research outputs found
Comments on On the determination of absolute velocities in the ocean by M. E. Fiadeiro and G. Veronis
Fiadeiro and Yeronis (1982, FY hereafter) proposed a procedure that they claimed would lead to the best reference level for computing the absolute velocities in the ocean by the inverse method as described in Wunsch (1978). According to FY, the reference level obtained by the procedure is best because the correction required of the absolute velocities at this level to satisfy a set of imposed constraints is minimum among all the possible levels. However, one likes to ask whether the velocity field resulting from this choice of reference level is necessarily the best in the sense of being closest to the true velocity field. This question was not addressed in FY, but its answer could clarify, to some extent, the perspective of their procedure in the long-pursued, controversial search for the absolute velocities in the ocean..
Paper Session I-C - The Ocean and Climate: Results from the TOPEX/ POSEIDON Mission
On August 10,1992, the United State and France launched their joint TQPEX/POSEIDON (abbreviated as T/P hereafter) satellite for making altimetric observations of the sea surface [3]. This is the first satellite altimetry system specifically designed for studying the circulation of the global oceans. The spacecraft is operating in an orbit which repeats its underlying ground-track every 10 days. Results to date show that the mission is producing observations of the global sea surface elevation with an unprecedented accuracy of 5 cm everywhere, and much better in some places. This precise knowledge of the shape of the sea surface is directly related to the dynamical processes governing ocean currents throughout the entire water column and provides oceanographers with the first true global observation system. Designed for a lifetime of 3-5 years, the satellite is providing the ability to describe and understand the dynamics of ocean circulation and its time variability with sampling adequate to understand its climatic consequences
The Ocean and Climate: Observations from Space
Since 1992, a satellite has been relaying data on the oceans' topography and circulation, and providing insight into such complexities of climate as global warming and last winter's heavy rains
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Observing large-scale temporal variablity of ocean currents by satellite altimetry : with application to the Antarctic circumpolar current
A new method is developed for studying large-scale temporal variability of ocean currents from
satellite altimetric sea level measurements at intersections (crossovers) of ascending and descending orbit
ground tracks. Using this method, sea level time series can be constructed from crossover sea level
differences in small sample areas where altimetric crossovers are clustered. The method is applied to
Seasat altimeter data to study the temporal evolution of the Antarctic Circumpolar Current (ACC) over
the 3-month Seasat mission (July-October 1978). The results reveal a generally eastward acceleration of
the ACC around the Southern Ocean with meridional disturbances which appear to be associated with
bottom topographic features. This is the first direct observational evidence for large-scale coherence in
the temporal variability of the ACC. It demonstrates the great potential of satellite altimetry for synoptic
observation of temporal variability of the world ocean circulation
Satellite altimetry and ocean dynamics
This paper provides a summary of recent results derived from satellite altimetry. It is focused on altimetry and ocean dynamics with synergistic use of other remote sensing techniques, in-situ data and integration aspects through data assimilation. Topics include mean ocean circulation and geoid issues, tropical dynamics and large-scale sea level and ocean circulation variability, high-frequency and intraseasonal variability, Rossby waves and mesoscale variability.This paper provides a summary of recent results derived from satellite altimetry. It is focused on altimetry and ocean dynamics with synergistic use of other remote sensing techniques, in-situ data and integration aspects through data assimilation. Topics include mean ocean circulation and geoid issues, tropical dynamics and large-scale sea level and ocean circulation variability, high-frequency and intraseasonal variability, Rossby waves and mesoscale variability. To cite this article: L.L. Fu, P.-Y. Le Traon, C. R. Geoscience 338 (2006)
Altimetric system: Earth observing system. Volume 2h: Panel report
A rationale and recommendations for planning, implementing, and operating an altimetric system aboard the Earth observing system (Eos) spacecraft is provided. In keeping with the recommendations of the Eos Science and Mission Requirements Working Group, a complete altimetric system is defined that is capable of perpetuating the data set to be derived from TOPEX/Poseidon, enabling key scientific questions to be addressed. Since the scientific utility and technical maturity of spaceborne radar altimeters is well documented, the discussion is limited to highlighting those Eos-specific considerations that materially impact upon radar altimetric measurements
An observing system simulation experiment for the calibration and validation of the surface water ocean topography sea surface height measurement using in situ platforms
Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 35 (2018): 281-297, doi:10.1175/JTECH-D-17-0076.1.The wavenumber spectrum of sea surface height (SSH) is an important indicator of the dynamics of the ocean interior. While the SSH wavenumber spectrum has been well studied at mesoscale wavelengths and longer, using both in situ oceanographic measurements and satellite altimetry, it remains largely unknown for wavelengths less than ~70 km. The Surface Water Ocean Topography (SWOT) satellite mission aims to resolve the SSH wavenumber spectrum at 15–150-km wavelengths, which is specified as one of the mission requirements. The mission calibration and validation (CalVal) requires the ground truth of a synoptic SSH field to resolve the targeted wavelengths, but no existing observational network is able to fulfill the task. A high-resolution global ocean simulation is used to conduct an observing system simulation experiment (OSSE) to identify the suitable oceanographic in situ measurements for SWOT SSH CalVal. After fixing 20 measuring locations (the minimum number for resolving 15–150-km wavelengths) along the SWOT swath, four instrument platforms were tested: pressure-sensor-equipped inverted echo sounders (PIES), underway conductivity–temperature–depth (UCTD) sensors, instrumented moorings, and underwater gliders. In the context of the OSSE, PIES was found to be an unsuitable tool for the target region and for SSH scales 15–70 km; the slowness of a single UCTD leads to significant aliasing by high-frequency motions at short wavelengths below ~30 km; an array of station-keeping gliders may meet the requirement; and an array of moorings is the most effective system among the four tested instruments for meeting the mission’s requirement. The results shown here warrant a prelaunch field campaign to further test the performance of station-keeping gliders.The authors would like to acknowledge the funding sources: the SWOT mission (JW, LF, DM); NASA Projects NNX13AE32G, NNX16AH76G, and NNX17AH54G (TF); and NNX16AH66G and NNX17AH33G (BQ). AF and MF were funded by the Keck Institute for Space Studies (which is generously supported by the W. M. Keck Foundation) through the project Science-driven Autonomous and Heterogeneous Robotic Networks: A Vision for Future Ocean Observations (http://kiss.caltech.edu/?techdev/seafloor/seafloor.html).2018-08-0
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Eddy dynamics from satellite altimetry
Most of the kinetic energy of ocean circulation is contained in ubiquitous
mesoscale eddies. Their prominent signatures in sea surface height have rendered satellite
altimetry highly effective in observing global ocean eddies. Our knowledge of ocean eddy
dynamics has grown by leaps and bounds since the advent of satellite altimetry in the
early 1980s. A satellite’s fast sampling allows a broad view of the global distribution of
eddy variability and its spatial structures. Since the early 1990s, the combination of data
available from two simultaneous flying altimeters has resulted in a time-series record of
global maps of ocean eddies. Despite the moderate resolution, these maps provide an
opportunity to study the temporal and spatial variability of the surface signatures of eddies
at a level of detail previously unavailable. A global census of eddies has been constructed
to assess their population, polarity, intensity, and nonlinearity. The velocity and pattern of
eddy propagation, as well as eddy transports of heat and salt, have been mapped globally.
For the first time, the cascade of eddy energy through various scales has been computed
from observations, providing evidence for the theory of ocean turbulence. Notwithstanding
the tremendous progress made using existing observations, their limited resolution has
prevented study of variability at wavelengths shorter than 100 km, where important
eddy processes take place, ranging from energy dissipation to mixing and transport of
water properties that are critical to understanding the ocean’s roles in Earth’s climate. The
technology of radar interferometry promises to allow wide-swath measurement of sea
surface height at a resolution that will resolve eddy structures down to 10 km. This approach
holds the potential to meet the challenge of extending the observations to submesoscales
and to set a standard for future altimetric measurement of the ocean
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