Mapping the Agulhas Current from space: An assessment of ASAR surface current velocities

Type Publication
Date 2010-10
Language English
Copyright 2010. American Geophysical Union. All Rights Reserved.
Author(s) Rouault M. J.1, 2, Mouche Alexis3, Collard Fabrice3, Johannessen J. A.4, 5, Chapron Bertrand6
Affiliation(s) 1 : CSIR, ZA-7700 Cape Town, South Africa.
2 : Univ Cape Town, Dept Oceanog, ZA-7925 Cape Town, South Africa.
3 : CLS, Direct Radar Applicat, F-29280 Plouzane, France.
4 : Nansen Environm & Remote Sensing Ctr, N-5006 Bergen, Norway.
5 : Univ Bergen, Inst Geophys, Bergen, Norway.
6 : IFREMER, F-29280 Plouzane, France.
Source Journal Of Geophysical Research-oceans (0148-0227) (Amer Geophysical Union), 2010-10 , Vol. 115 , P. -
DOI 10.1029/2009JC006050
WOS© Times Cited 25
Abstract Over 2 years of surface current information collected in the Agulhas Current region and derived from the Doppler centroid anomalies of Envisat's advanced synthetic aperture radar (ASAR) are examined. The sources of errors and potential use of ASAR surface current velocities for oceanographic research are assessed. ASAR surface current velocities are compared to surface drifter data and merged altimetry observations. Maps of sea surface temperature are used to establish the ASAR's capacity to capture the synoptic circulation. Discrepancies between observed and predicted ASAR velocities result predominantly from inadequate wind corrections combined with radar incidence angles below 30 degrees. Occasionally observed wind-induced outliers cause a bias in the estimated ASAR velocities but do not affect the ability of the ASAR to systematically image regions of strong surface current flow and shear. Time-averaged maps of ASAR-derived surface current velocity seem able to accurately capture the position as well as the intensity of the Agulhas Current. The ability of the ASAR to pick up the smaller features of the circulation along the shelf break also shows that variability along the Agulhas Bank is of the same order of magnitude as that observed in the Agulhas retroflection. ASAR surface current velocities offer a very good complement to altimetry in regions where the mean dynamic topography is poorly resolved. The quasi-synoptic nature of ASAR acquisitions combined with the relatively high resolution of ASAR surface current velocities also make it attractive for studies of submesoscale processes and western boundary current dynamics.
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