I am looking for a dataset of bathymetry data of Italy. I shall use it in an application for collision avoidance of vessels coming into the port.
I need to know how deep the sea bottom is at each point, and that's why data should be as precise and graded as possible. So I am considering only data with greater resolution than 3 arc-seconds.
Can someone help me to find open source or not too expensive data within these constraints?