CoAuthors

Florent Lyard (LEGOS/CNRS, France); Yannice Faugere (CLS, France); Romain Baghi (CLS, France); Jean-Michel Lachiver (CNES, France); Nicolas Picot (CNES, France)

Improving the Dynamic Atmospheric Correction for delayed-time and real-time applications of altimetry

L. Carrère1, F. Lyard2, Y. Faugère1, R. Baghi1, J.M. Lachiver3, N. Picot3
1 CLS, Space Oceanography Division, Toulouse, France. lcarrere@cls.fr
2 LEGOS, OMP Toulouse, France
3 CNES, Toulouse, France


Given its current accuracy and maturity, altimetry is considered a fully operational observing system dedicated to various applications such as operational oceanography and climate studies. Altimeter measurements are corrected for several geophysical effects in order to isolate the oceanic variability, and the Dynamic Atmospheric Correction (DAC) is the second most important one after the tide correction. This correction allows for the removal of high frequency ocean variability induced by the atmospheric forcing and aliased by the altimetric measurements.

The high frequency part of the DAC is based on a barotropic ocean model simulation forced by atmospheric pressure and winds (MOG2D; Carrere and Lyard 2003); the low frequency part is an inverse barometer response, with a 20-days cutoff-period corresponding to the Nyquist period of T/P-Jason reference altimeters’ sampling.

The purpose of the study is to improve the performances of the DAC for the three delivery mode corresponding to Near Real Time (NRT-OGDR) products, Short Time Critical (STC-IGDR) and Non Time Critical (NTC-GDR) and these improvements will directly benefit to all altimetry products, including current missions as well as the past time series.

Extending the meteorological forecast window until 10 days in the future (D+10) allows improving significantly the quality of the STC DAC correction: the improvement has been estimated on level-2 altimeter products (along-track and crossovers) and reaches 5-10 cm² in some deep ocean regions and also in shallow waters, which correspond to the areas where the high frequency response of the ocean to atmospheric forcing is maximum. The implementation of this new product is planned in 2017.

A specific work on the width of the filtering window shows a non-negligible impact on the amplitude of the DAC particularly in regions of high variability. The new high-resolution mesh and bathymetry provided by FES2014 study have been tested to improve the global DAC performances and results will be presented. Moreover a review of the correction of the S1 and S2 frequencies in altimeter processing has been performed and some ways of improvements are proposed.