Tides on the Filchner-Ronne Ice Shelf from ERS Satellite Radar Altimetry

We present results of crossover analyses of ERS-1 and ERS-2 radar altimeter data collected on the Filchner-Ronne Ice Shelf (FRIS), Antarctica, between April 1992 and March 2000. For freely floating ice, much of the total variance of the crossover height difference is due to the ocean tide displacement over the time elapsed between the ascending and descending passes. Although the non-tidal component of total height variability combined with measurement noise is significant compared with the tide signal, the time series is sufficiently long that the method generates accurate (about 3 cm RMS error in amplitude per constituent) estimates for 2 of the 4 most energetic tidal constituents (M₂ and O₁). The nature of the ERS orbit means that the other two most energetic constituents cannot be resolved: S₂ is aliased to zero frequency and K₁ cannot be separated from P₁ or the annual cycle. The differences between ERS-derived tidal fields and those produced by our Circum-Antarctic Tidal Simulation (CATS) model suggest ways in which CATS may be improved. In particular, we focus on potential errors in grounding line location and water column thickness. We will also explore the assimilation of ERS data in the inverse version of our tides model (the Circum-Antarctic Data Assimilation model; CADA). From the amplitude and phase of the displacement for the largest constituent, M₂, we can detect the transition zone between fully floating and fully grounded ice, although the resolution is only on the order of a few kilometers. Much more precise data of this type will be available for the Antarctic ice shelves following the launch of the Geoscience Laser Altimeter System (GLAS) onboard ICESat in 2002. We demonstrate that GLAS will be capable of resolving 8 major tidal constituents at { ~}50 km resolution after a 3-5 year anticipated mission life. GLAS will significantly improve our maps of tides under the ice shelves and, when combined with InSAR, will be a powerful tool for monitoring the grounding zone locations of Antarctica.