Improving the quality of satellite altimetry data over continental shelves

Satellite altimetry has proven to be a useful tool to study oceanic processes in the deep ocean. Over continental shelves, however, the aliasing of unresolved high-frequency signals of tidal and wind-induced origin is the source of long-wavelength errors that corrupt altimetry measurements and limit their use in shallow waters. In 2005, SSALTO/DUACS performed a complete reanalysis of altimeter data to accommodate the latest tidal model (GOT2000) and a correction for the aliased high-frequency signals using a hydrodynamic model MOG2D-G. This paper examines the quality and the performance of the newly released altimetry data over the northwest European shelf. This region is known for complex tides and for frequent storm surges. The newly corrected maps of sea level anomalies were compared with a previous altimetry product. Residual tidal aliasing was analyzed, and the impact of MOG2D-G and GOT2000 models was assessed. Altimeter records were compared with tide gauge measurements. This research showed a significant reduction in the contamination of data by high-frequency aliasing achieved through the use of the aforementioned models. However, aliased shallow-water tidal constituents pose a serious problem, and it is obvious that future tidal corrections should feature local tides. Nonaliased, physical sea level variability was also studied focusing on interannual, seasonal, and intra-annual (periods from 20 days to 1 year) modes. The magnitudes and the contributions of each mode to the total variance were estimated. It was demonstrated that the newly corrected data can successfully be used to study the variability of sea level over continental shelves.