Ocean and Ice Shelf Tides from CryoSat-2 Altimetry

Abstract

AbstractA new empirical model of ocean tides has been developed for the Weddell Sea, south of 66°S, between 90°W and 0°, using six years of radar altimeter data from the CryoSat-2 satellite mission. Because of its long ground-track repeat period (368 days) and its diverse measurement modes, low-rate mode (LRM) over the ocean and synthetic aperture radar interferometric mode (SARin) over ice surfaces and parts of the ocean, the CryoSat-2 data pose a number of challenges for tidal analysis. The space and time sampling properties of the exact repeat, near-repeat, and crossover ground tracks have been analyzed to discover which tides may be estimated using a combination of conventional harmonic analysis and local spatial regression. Using this information, the M2, S2, K2, N2, K1, O1, P1, and Q1 tides have been mapped for both the ocean and floating ice shelves in this domain. Validation against independent in situ data, along with comparison with existing tide models, finds that the CryoSat-2-derived tides are consistent with previous estimates and that they are more accurate than other models at the M2 and S2 frequencies. The high inclination of the CryoSat-2 orbit causes the orbit plane to precess relatively slowly, which leads to significantly less accurate estimates of the K2 tide. This purely empirical model ought to provide improved tidal corrections for studies of low-frequency variability and secular trends in ice shelf thickness, and it suggests that further increases in quantitative accuracy could be achieved by assimilation of CryoSat-2 data into dynamical tide models.