Uncertainties in altimetry-based velocity estimates

[1] Three methods to estimate ocean geostrophic surface currents from satellite altimetry measurements are evaluated for several single- and multiple-satellite configurations, with specific emphasis on resulting uncertainties. Altimetric sea surface height measurements are simulated by sampling along satellite ground tracks the surface pressure output from the 1/10° North Atlantic run of the Los Alamos Parallel Ocean Program model and by subsequently adding realistic instrument and orbit errors. The effects of both sampling and data errors on the velocity estimates are discussed. The satellite orbit configurations considered represent current missions or candidates for future coordinated tandem missions. Data error budgets are based on those of existing missions and on estimates for new altimetric technology currently under development. In midlatitude regions characterized by strong variability, such as the Gulf Stream region, velocities estimated at crossovers of interleaved tracks, and along a virtual ground track between two parallel tracks with a 0.75° zonal offset, are found to be comparable in accuracy and more accurate than velocities estimated from optimally interpolated sea surface height maps. Error variances as low as 15-25% of the local signal variance can be obtained from all three methods near the Gulf Stream core. Larger relative errors are found almost everywhere else with the exact details of the error in the two velocity components depending on data error, orbit configuration, latitude, estimation method, and smoothing. Several scientific applications of the configurations and methods are discussed, including the estimation of Reynolds stresses, momentum fluxes, velocity spectra, and covariance functions. Accuracy and applicability suggest that the newly proposed parallel track configuration is a viable option for future tandem missions.