Impact of the geophysical corrections on studies of sea level variation
M. Joana Fernandes(1) , Susana Barbosa(1) , and Clara Lázaro(1)
Faculty of Science, University of Porto,
Rua do Campo Alegre, 687,
Since the launch of ERS-1 in 1991 and Topex/Poseidon (T/P) in 1992, the progress achieved in sensor performance, satellite ephemeris accuracy and modelling of the major geophysical corrections rendered satellite altimeter data an invaluable tool for sea level studies. However, since sea level is a relatively weak signal, sea level variation determined from satellite altimetry is influenced by many factors. Amongst the most important are sensor characteristics and long term stability, the altimeter data processing, the mathematical techniques used to model sea level variation and the length of the altimeter time series.
This study addresses the impact of altimeter data processing on sea level studies, both at global and regional scales, with emphasis on the effects of the major geophysical corrections in the structure of the derived interannual signal and sea level trend.
The work focuses on the analysis of T/P data for a period of over twelve years. For this analysis corrected sea level anomalies with respect to a mean sea surface model have been computed from the MGDRs provided by AVISO using state-of-art models for the geophysical corrections. The effects of various models for the geophysical corrections on the interannual signal and sea level trend, with particular emphasis on the sea state bias (SSB), inverse barometer (IB) and radiometer wet tropospheric correction are analysed. The impact of each correction on the estimation of both global and regional sea level variation is discussed.
The advances in the modelling of the major corrections are reviewed and prospects of future improvements are discussed in view of their influence on sea level change. In spite of the advances in the modelling of these corrections, results show that the effect of applying different models can have an impact on the derived sea level trends of more than 1 mm/year.
The results strike the need for a continuous improvement of the various effects that influence the altimeter measurement and the importance of having follow-on altimeter missions which warrant the continuity of the present altimeter sea level records.