While satellite radar altimetry has been revolutioning our understanding of the oceans, there has been an unprecedented increase in the use of tide gauges over the last twenty years, both in terms of the technology and the applications. The increased need for coastal observations of sea level in digital form and easily accessible using modern means of communication, goes beyond the traditional boundaries of hydrography, tide prediction and navigation.
Of course tide gauges are still widely used today for the purposes of navigation close to the coast, but the data they provide are increasingly used in numerous other applications which are employed to study the environment and the physical mechanisms which govern it, together with coastal development. The figure to the right illustrates the variety of signals contained in tide gauge recordings. By subtracting our knowledge of the tide (prediction by the model) from the observation, we obtain a "residual" (observation minus prediction) whose scientific and practical value may be considerable in areas other than navigation or hydrography.