The following work represents the first vertical deformation measurement of the ground in coastal waters obtained through the use of a BPR sensor (Bottom Pressure Recorder) installed in shallow water, with an accuracy comparable with that of the measures carried out by a GPS network placed on the mainland. The described measurement method allows the use of pressure sensors - based on quartz technology - as a possible and low cost integration, which allows the extension in the coastal waters of the geodetic monitoring networks located on the mainland. The area under investigation is the caldera of Campi Flegrei (Pozzuoli) in which even the bradyseism is continually monitored by the Vesuvius Observatory surveillance system in Naples. In the Gulf of Pozzuoli, which is the submerged part of...