Abstract
This study addresses the impact of satellite altimetry data processing on sea levelstudies at regional scale, with emphasis on the influence of various geophysical correctionsand satellite orbit on the structure of the derived interannual signal and sea level trend. Thework focuses on the analysis of TOPEX data for a period of over twelve years, for threeregions in the North Atlantic: Tropical (0o≤φ≤25o), Sub-Tropical (25o≤φ≤50o) and Sub-Arctic (50o≤φ≤65o). For this analysis corrected sea level anomalies with respect to a meansea surface model have been derived from the GDR-Ms provided by AVISO by applyingvarious state-of-the-art models for the geophysical corrections. Results show that sea leveltrend determined from TOPEX altimetry is dependent on the adopted models for the majorgeophysical corrections. The main effects come from the sea state bias (SSB), and from theapplication or not of the inverse barometer (IB) correction. After an appropriate modellingof the TOPEX A/B bias, the two analysed SSB models induce small variations in sea leveltrend, from 0.0 to 0.2 mm/yr, with a small latitude dependence. The difference in sea leveltrend determined by a non IB-corrected series and an IB-corrected one has a strong regionaldependence with large differences in the shape of the interannual signals and in the derivedlinear trends. The use of two different drift models for the TOPEX Microwave Radiometer(TMR) has a small but non negligible effect on the North Atlantic sea level trend of about0.1 mm/yr. The interannual signals of sea level time series derived with the NASA and theCNES orbits respectively, show a small departure in the middle of the series, which has noimpact on the derived sea level trend. These results strike the need for a continuousimprovement in the modelling of the various effects that influence the altimetermeasurement.
Highlights
Sea level change has significant environmental, social and economical impacts
DataSet5 - all corrections according to Table 1, except for the inverse barometer which has been applied by adopting a model which makes use of a variable reference surface atmospheric pressure (VRP) interpolated from global average values obtained from the Centre National d’Études Spatiales (CNES/CLS), [36], according to equation (5)
The curve for DataSet1 - DataSet2 reveals the difference between the Chambers [27] and the Labroue [34] sea state bias models for TOPEX
Summary
Sea level change has significant environmental, social and economical impacts. The importance of the estimates of the present rate of sea level change, for example for assessment of climate models or for coastal protection design, requires high accuracy and a realistic assessment of the involved uncertainties. In spite of the enormous advances in ERS data improvement, in the accuracy of the radial orbit, it is recognised that the TOPEX/Poseidon mission revolutionised sea level research, providing sea surface height (SSH) measurements with an unprecedented accuracy, overall better than 5 cm for a single pass and better than 2 cm at the global scale, [1]. This study focuses on the impact of satellite altimeter data processing on sea level studies with emphasis on the influence of various geophysical corrections and the orbit field in the structure of the derived interannual signal and sea level trend, including regional dependencies. Due to the potential impact of the altimetry data processing on the resulting sea level change estimates, it would be expected that sea level change studies would include a detailed description of the data used, of the geophysical and instrumental corrections applied and of eventual bias and drift corrections. The influence of the orbit field on sea level variation is investigated
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