Marine sensors needs to be tested in real and controlled environments in order to assure, both, proper functionality of the sensor and good enough measurements. Most of the times is not enough testing on the lab, field tests and an inter-comparison with similar sensors (if exists) can help instruments manufactures, platform operators and scientist to validate the instrument. This abstracts introduce OBSEA, a permanent underwater cabled seabed observatory located in front of the Catalan’s coast near Barcelona, at 20 m depth, and some of the current activities where the observatory is used as a test site for different experiments related with marine sensors metrology.