New Along-Track Mean Sea Surface Model for TOPEX and JASON Altimeter Data

To investigate sea level variability and other important ocean phenomena measured by satellite altimetry, an accurate mean sea surface (MSS) is required. A previous investigation has shown that the MSS can be represented as a plane over small regions 2 km wide by 7 km along the satellite ground-track, and the parameters can be estimated directly from the sea surface height measurements. However, this model also may not represent the MSS as well in all areas, for example in places where the MSS changes significantly within the boundaries of the plane. In order to improve the accuracy of the along-track MSS model in these regions, a new surface with more degrees of freedom has been tested. The new surface allows for different along-track and cross-track gradients in different quadrants of the region. Because of this shape, it is designated the pyramid MSS model. Parameters of the model are calculated using TOPEX data from January 1993 to December 2000. To quantify improvement when using the new pyramid MSS model compared to the plane model, the global and the local statistics of sea level anomalies are computed and compared, using observations from both the TOPEX and JASON altimeters. Comparisons are also made at several tide gauge sites. The results show significant improvement using the new pyramid MSS model.