Assessing Dual-Satellite Altimetric Missions for Observing the Midlatitude Oceans

Abstract

This article looks at the problem of optimizing spatiotemporal sampling of the ocean circulation using single- or twin-satellite missions. A review of the basic orbital constraints is first presented and this, together 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 simulating the dynamic features of the ocean fields that are to be measured; it also enables the process of integrating data into models to be simulated. Several scenarios for two altimetric satellites flying simultaneously are evaluated with respect to their ability to monitor oceanic circulation as simulated with a numerical model. The twin-experiment 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 multilayered. The ocean model domain is at basin scale, centered on the midlatitudes. Model resolution (20 km) is fine enough to exhibit the intense mesoscale nonlinear variability typical of the midlatitudes. The assimilation technique used is sequential nudging of sea surface height applied to along-track data. Dual scenarios are built consisting of all possible combinations of satellites having 3-, 10- (Topex-Poseidon), 17- (Geosat) and 30-day orbital repeat periods. In the specific context of our modeling and assimilation approach, improved scenarios with respect to Topex-Poseidon, and a fortiori Geosat, appear to be those that favor improving temporal rather than spatial resolution. This unexpected result would, for example, suggest that a Topex-Poseidon- or Geosat-type satellite is satisfactory with regard to the spatial sampling of oceanic mesoscales. But any further gain would be acquired mostly by increasing temporal sampling, for example, by flying another Topex-Poseidon- or Geosat-type satellite offset in time by a typical half-period. Investigations of ground-track inclination effects are also presented.