Abstract

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, the principal component of the crossover height difference is due to the ocean tide displacement over the time elapsed between the ascending and descending passes. Although the noise on individual ERS estimates of height is quite large compared to the tide signal, the time-series is sufficiently long enough that the method generates amplitude and phases fields for 2 of the 4 most energetic constituents (M2 and O1) that are qualitatively consistent with our Circum-Antarctic Tidal Simulation model (CATS). The nature of the ERS orbit means that the other two major constituents cannot be resolved: S2 is aliased to zero frequency and K1 cannot be separated from S1 or the annual cycle. The differences between modeled and ERS-derived tidal fields suggest ways in which CATS may be improved. In particular, we focus on potential errors in cavity geometry (grounding line location and water column thickness). We will also explore the assimilation of ERS-derived tides in the inverse version of our tides model (Circum-Antarctic Data Assimilation model; CADA).

From the amplitude and phase of the displacement, it is possible to detect the transition zone between fully floating and fully grounded ice, although the resolution is only on the order of a few kilometres. With the launch of the Geoscience Laser Altimeter System (GLAS) onboard ICESat in 2002, much more precise data of this type will be available for the Antarctic ice shelves. We can look forward to improved tide models in these difficult-to model regions, and also to obtaining more information about the behavior of the ice in the transition zones. GLAS combined with InSAR will be a powerful method of monitoring the grounding zone locations of Antarctica.