SEA LEVEL ANOMALY AND DYNAMIC OCEAN TOPOGRAPHY ANALYTICAL COVARIANCE FUNCTIONS IN THE MEDITERRANEAN SEA FROM ENVISAT DATA

摘要

Monitoring and understanding of sea level change at various spatial and temporal scales have been the focus of many studies during the past decades. The advent of satellite altimetry and the realization of the GRACE/GOCE missions offer new opportunities for the estimation of sea level trends with heterogeneous data combination methods. In related studies, even though the data combination and processing strategies have been carried out carefully with proper control, error propagation through analytical data variance-covariance matrices has been given little attention. The latter is of importance since it can provide reliable estimates of the output signal error. This is especially evident in e.g., least-squares collocation (LSC), where analytical covariance function models for the disturbing potential, its second order derivatives and geoid heights are used. Analytical covariance models are not available for altimetric sea level anomalies making their incorporation in LSC-based combination schemes problematic. This work presents some new ideas and results on the determination of analytical covariance functions for the sea level anomalies in the Mediterranean Sea. The focus is based on singlemission altimetry data from ENVISAT for the entire duration of the mission (2002-2011). The estimation of the analytical covariance functions is performed using 2nd and 3rd order Gauss-Markov models, exponential ones, as well as a kernel similar to that of the disturbing potential. The analysis is carried out in order to come to some conclusions on the SLA spectral characteristics based on empirically derived properties.