Contribution of wide-swath altimetric cross-track measurements in the North Sea – Impact of the satellite roll errors
Matthieu Le Hénaff(1) , Pierre De Mey(1) , Pierre-Yves Le Traon(2) , and Florent Lyard(1)
18 av Edouard Belin,
(2) Ifremer, BP 70 Technopole Brest-Iroise, 29280 Plouzané, France
The classical nadir-observing altimetric satellites, such as Topex Poseidon or Jason, provide the scientific community with sea level data from single measurement points under the path of the satellite. Though sufficient to efficiently capture the wide scale ocean dynamics, they are not well designed for coastal ocean applications. The interferometric technology such as the one which had been proposed for the Wide Swath Ocean Altimeter (WSOA), by measuring the sea level also in the cross-track direction, may be a good way to reach the space and time observation requirements to capture the coastal ocean dynamics.
In this study, we develop a simple configuration of an observing system representing the WSOA contribution. It is composed of a 10 day orbit satellite measuring both the sea level and the oceanic slope at the nadir. The impact of this system is evaluated using a 2D barotropic model of the North Sea, and by assimilating the simulated observations by the EnKF technique (Mourre et al., 2004). The slope measurement happens to have a wider influence zone than a single sea level measurement, and to significantly improve the reduction of the current velocity error variances.
This system is also used to investigate the impact of the roll of the satellite. Indeed the interferometer is much more sensitive to the platform behavior, whose roll can lead to large measurement errors if not adequately processed. The EnKF is currently one of the best assimilation techniques for dealing with non linear errors, such as roll errors which exhibit correlation along the track of the satellite. As an overall result, these roll errors do not seem to significantly deteriorate the quality of a cross-track observation system based on a wide-swath instrument.