P.Y. Le Traon, P. Klein, B. Chapron,
J. Isern (Ifremer), G. Dibarboure (CLS)
Capabilities of conventional altimetry
Interpretation of altimeter wavenumber spectra
SWOT potential contributions
Summary of Jason-1/ENVISAT (T/P-ERS-1/2)
(based on formal mapping error analysis and simulations with Los Alamos North
Atlantic model) (Le Traon an Dibarboure, 1999; Le Traon et al., 2001, 2002)
Jason-1/ENVISAT : Sea level can be mapped with an
accuracy of 5 to 10% of the signal variance*. Velocity
mapping error from 20 to 40% of the signal variance.
3 or 4 altimeters needed to reduce errors by a factor of 3
(needed for surface currents)
*corresponds to periods < 20 days and/or wavelengths < 200 km (see next
figures and discussion on the role of high frequency signal in Le Traon and
Jason+ENVISAT maps Sea level
(wavelengths >200 km)
larger than 200
Ducet et al., 2000
Altimeter wavenumber spectral slopes
in the mesoscale band very closely
follow a k-11/3 slope as predicted by
surface quasi-geostrophic theory
(SQG) (Le Traon et al;, 2008; Lapeyre
and Klein, 2006; Klein et al., 2007)
SQG could thus be a much better
k-11/3 dynamical framework than the QG
turbulence theory to describe the
ocean surface dynamics.
These results point out the important
dynamical role of small scale
structures. They also offer new
perspectives for the analysis and
interpretation of satellite data.
In particular, the joint use of SST, OC
and altimetry should allow a much
better description of the 3D ocean
Le Traon, Klein, Hua and Dibarboure, JPO, 2008 state (including vertical velocity) (Isern
et al. , 2006)
High resolution altimetry
• Should allow a characterization
of submesoscale signals. Scales Conventional
altimeter noise level
(wavelengths/2) between 10 (2.5 cm – 7 km)
and 100 km.
• Noise is a major issue (a goal of
1 cm / 1 km for an uncorrelated
noise is quite challenging !).
• Time sampling will remain an
issue for some applications.
SWOT noise level ? (1 cm / 1 km)
Ducet et al., 2000
Proposed Ifremer / CLS investigations for SWOT
Analysis of sampling capabilities of SWOT using very high resolution
basin scale models (1 -2 km) (SSH, velocity and vorticity). Analysis
of SWOT measurement errors (white/correlated noise, roll errors)
and their impact on mission objectives. Use tools developed and
tested for conventional multiple altimeter and WSOA studies (Le
Traon et al. 2001, Le Traon and Dibarboure, 2002).
Science investigations on mesoscale/submesoscale dynamics. Use
very high resolution model to characterize
mesoscale/submesoscale signals and the potential contribution of
Analyze the synergy of high resolution altimetry with SST, OC and
SAR data in the framework of SQG dynamics. Use of SSH, SST and
OC to reconstruct 3 D ocean circulation (incl. Vorticity and vertical
velocity) (Isern et al., 2006, 2008). Impact for ocean forecasting.