Residual Tidal Signal in the Great Barrier Reef Region from Conventional and Retracked Altimetry
Andersen, Ole Baltazar1; Nurul, Idris2; Deng, Xiaoli2; Cheng, Yongcun1; Cheng, Yongcun1
1DTU Space, DENMARK; 2University of Newcastle, NSW, AUSTRALIA
The Great Barrier Reef is generally complex to model handled only through its effect on bathymetry in most global ocean tide models (i.e., FES and OTIS models) and state of the art global ocean tide models exhibit a somewhat strange behaviour of maximum tidal amplitude on the outside of the Great Barrier Reef and somewhat smaller amplitudes along the tropical east coast of Australia some 30-50 km away. This is in contradiction to SLAs data from regional coastal station i.e. Townsville and Bundaberg which typically exhibit a significant larger tidal signal with amplitudes of 30-60 cm higher tidal amplitude than global ocean tide models (GOT4.7 or FES2004). We have investigated if this residual signal is still present with newer empirical tidal model (EOT2011, DTU2010) using altimetry from more and newer satellites, and also investigates ways of modelling this un-modelled tidal signal using satellite altimetry from the interleaved missions of TOPEX and Jason-1. On the ocean side of the Great Barrier Reef only very small compound and over tides are found from satellite altimetry (i.e., very small M4), but we have investigated if this constituents can explain some of the larger discrepancies with tide gauges very close to the coast in the region. Tidal signal generally has a large spatial extend so retracking is generally not particularly important for ocean tide retrieval. However, with the local conditions in both sea state and presumed complex ocean tide signal in the region, an evaluation of the importance of retracking satellite altimetry in the Great Barrier Reef Region for tidal purposed have been made. Here we have been using an optimised iterative coastal waveform retracking system based on fuzzy approach by Idris and Deng (2012)). Using the system, several waveform retracking algorithms have been applied to reprocess various shapes of waveforms. It includes the fitting function of the Brown model to the full-waveforms and sub-waveforms, and the empirical method of threshold retracking with 30%, 20% and 10% threshold levels.