ASSESSING DUAL-SATELLITE ALTIMETRIC MISSIONS FOR OBSERVING THE MIDLATITUDE OCEANS

This article looks at the problem of optimizing spatiotemporal samplin g of the ocean circulation using single or twin-satellite missions. A review of the basic orbital constraints is first presented and this, t ogether with some elementary sampling considerations, provides a solid foundation for choosing satellite orbital parameters. A modeling and assimilation approach enables even further progress to be made by simu lating the dynamic features of the ocean fields that are to be measure d; it also enables the process of integrating data into models to be s imulated. Several scenarios for two altimetric satellites flying simul taneously are evaluated with respect to their ability to monitor ocean ic circulation as simulated with a numerical model. The twin-experimen t approach is used: simulated data are assimilated into the numerical model, while a benchmark experiment provides the necessary dataset for validation and intercomparison. The model is quasigeostrophic and mul tilayered. The ocean model domain is at basin scale, centered on the m idlatitudes. Model resolution (20 km) is fine enough to exhibit the in tense mesoscale nonlinear variability typical of the midlatitudes. The assimilation technique used is sequential nudging of sea surface heig ht applied to along-track data. Dual scenarios are built consisting of all possible combinations of satellites having 3-, 10- (Topex-Poseido n), 17- (Geosat) and 30-day orbital repeat periods. In the specific co ntext of our modeling and assimilation approach, improved scenarios wi th respect to Topex Poseidon, and a fortiori Geosat, appear to be thos e that favor improving temporal rather than spatial resolution. This u nexpected result would, for example, suggest that a Topex-Poseidon- or Geosat-type satellite is satisfactory with regard to the spatial samp ling of oceanic mesoscales. But any further gain would be acquired mos tly by increasing temporal sampling, for example, by flying another To pex-Poseidon- or Geosat-type satellite offset in time by a typical hal f-period. Investigations of ground-track inclination effects are also presented.