Mesoscale resolution capability of altimetry: Present and future

Abstract

Wavenumber spectra of along‐track Sea Surface Height from the most recent satellite radar altimetry missions [Jason‐2, Cryosat‐2, and SARAL/Altika) are used to determine the size of ocean dynamical features observable with the present altimetry constellation. A global analysis of the along‐track 1‐D mesoscale resolution capability of the present‐day altimeter missions is proposed, based on a joint analysis of the spectral slopes in the mesoscale band and the error levels observed for horizontal wavelengths lower than 20km. The global sea level spectral slope distribution provided by Xu and Fu () with Jason‐1 data is revisited with more recent altimeter missions, and maps of altimeter error levels are provided and discussed for each mission. Seasonal variations of both spectral slopes and altimeter error levels are also analyzed for Jason‐2. SARAL/Altika, with its lower error levels, is shown to detect smaller structures everywhere. All missions show substantial geographical and temporal variations in their mesoscale resolution capabilities, with variations depending mostly on the error level change but also on slight regional changes in the spectral slopes. In western boundary currents where the signal to noise ratio is favorable, the along‐track mesoscale resolution is approximately 40 km for SARAL/AltiKa, 45 km for Cryosat‐2, and 50 km for Jason‐2. Finally, a prediction of the future 2‐D mesoscale sea level resolution capability of the Surface Water and Ocean Topography (SWOT) mission is given using a simulated error level.

Improving Mesoscale Altimetric Data From a Multitracer Convolutional Processing of Standard Satellite-Derived Products

“…It clearly stresses the better match between the true SSH fields and the reconstruction using model (2) compared to the optimally-interpolated field. As such, model (2) provides a more consistent view of the spectral properties of the upper ocean dynamics [3]. FIGURE 2: High-resolution SSH reconstruction, February, 10, 2010 : first row, from left to right, high-resolution SSH, lowresolution SSH, reconstructed SSH using model (2) with parameterization H 1,Iso + H 2,Iso , high-resolution SST detail ; second row, from left to right, gradient magnitudes of the high-resolution, low-resolution , and reconstructed SSH fields of the highresolution SSH (magenta), low-resolution SSH (black), reconstructed SSH (blue) and high-resolution SST (cyan).…”

The Benefits of the Ka-Band as Evidenced from the SARAL/AltiKa Altimetric Mission: Scientific Applications

“…By calculating wavenumber spectra from along-track SSH anomalies from the recent missions, we have been able to estimate the background noise levels of each mission, and the corresponding observable ocean scales, where the signal-to-noise is greater than 1. This statistical estimate of the altimetric noise and the observable scales has been performed over the global oceans using Jason-2 (Ku-band), SARAL/AltiKa (Ka-band) and CryoSat-2 in low-resolution mode (LRM) by [5], and from Jason-2, SARAL/AltiKa and Sentinel-3 in Synthetic Aperture Radar (SAR) mode by [6]. Regional analyses have also been performed over the western Mediterranean Sea by [7] using Jason-2, SARAL/AltiKa and CryoSat-2 SAR mode.…”

Remote sensing of ocean surface currents: a review of what is being observed and what is being assimilated

“…During the last few years there have been major improvements in radar altimetry technology that have not only reduced noise levels (Dufau et al, 2016) but also reduced the impact of inhomogeneities in measurements (Dibarboure et al, 2014). Nevertheless, current altimeters still present strong limitations in observing small-scale features O(10 km) not only due to noise but also due to temporal sampling (Chavanne and Klein, 2010).…”

“…Moreover, the level of noise strongly depends on the sea state, which makes it highly variable in space and time, implying that the effective resolution of altimetric measurements is also variable. In a recent study, Dufau et al (2016) have shown that the smallest scale that can be resolved by the new generation of altimeters is 40-50 km in areas of strong currents, but it can be as large as 90-100 km. This variability has motivated the development of adaptive approaches to better exploit the sampling capabilities of current altimeters (Isern-Fontanet et al, 2016a).…”