SEA LEVEL MEASUREMENTS IN MEDITERRANEAN COAST

The great travels for the geographical studies made it necessary, in order to establish the height of the elevations, to refer all the heights to the same surface to which to attribute the zero level, to make the results comparable. The sea surface was immediately thought of as a reference level, but unfortunately it is neither the same nor constant throughout the Earth and, moreover, it varies over time. As early as the 17th century, measurement protocols were proposed to establish the sea level. However, only in the first half of the 19th century, with the advent of tide gauge with automatic recording, were obtained, for many seas, sufficiently numerous and reliable series of measurements to establish a shared methodology to define the tide level zero. From that moment on, procedures and instruments quickly improved to the current satellite instruments that measure altitudes with the uncertainty of about 2 centimeters. This work is limited to the first stages of this fascinating story referring, in particular, to the Mediterranean basin.