Use of a high-resolution model to analyze the mapping capabilities of multiple-altimeter missions

The contribution of merging multiple-satellite altimeter missions to the ma pping of sea level is analyzed from a North Atlantic high-resolution (1/10 degrees) numerical simulation. The model is known to represent the mesoscal e variability quite well and offers a unique opportunity for assessing the mapping capability of multiple-altimeter missions. Several existing or plan ned orbits [TOPEX/Poseidon (T/P), Jason-1, ERS-1/2-ENVISAT, GEOSAT-GFO] are analyzed, and Jason-1 and T/P orbits are assumed to be interleaved. The mo del sea level anomaly fields are first subsampled along T/P, ERS, GFO, and Jason-1 tracks and a random noise of 3-cm rms is added to the simulated alt imeter data. A suboptimal mapping method is then used to reconstruct the 2D sea level anomaly from alongtrack data and the reconstructed fields are co mpared with the reference model fields. Comparisons are performed in the No rth Atlantic and over a complete year. These results confirm the main concl usions of the Le Traon and Dibarboure study based on formal error analysis. There is, in particular, a large improvement in mapping capability when go ing from one to two satellites. Mapping errors (in percentage of the signal variance) are, however, larger than the ones derived from formal error ana lysis (by a factor between 1.5 and 2) and do not decrease as rapidly. This is mainly due to the high-frequency (periods, 20 days) and high- wavenumber signals of the Los Alamos model, which cannot be resolved with any of the analyzed multiple-satellite configurations.