Assimilation of Satellite Altimetry in Ocean Models

In this chapter we will look at some of the problems, both conceptual and practical, of assimilating one of the most widely available ocean data sets, that from satellite altimeters. The first sections will deal with conceptual issues. We consider how the ocean and atmospheric assimilation problems differ in some respects. We will look at the 4DVar (Four Dimensional Variational Assimilation) and 3D Sequential assimilation techniques to consider their merits from a physical perspective. Results are then shown from twin experiments of a 3D sequential assimilation approach which tries to account for the ocean physics when assimilating altimeter data. In the final sections we will show preliminary results from a study designed to assimilate TOPEX altimeter data into a global ocean model. Many new problems arise when real satellite data are used, some of which have been solved, and some not. We will summarise by describing the present state of the art and speculate on the likely developments over the next few years.1