—Wireless sensor networks enable large amount of surveillance applications especially for critical and even hostile environments, for example, the sea monitoring. In OceanSense, we make the pioneer attempt to explore the possibility of deploying networked sensors on the sea surface, monitoring the sea depth, temperature, as well as other valuable environmental parameters. Sea depth monitoring is a critical task to ensure the safe operation of harbors. Traditional schemes largely rely on labor-intensive work and expensive hardware. We present a new solution for measuring the sea depth with Restricted Floating Sensors. Data without location is meaningless, to address the problem of node localization on the critical sea environment, we propose Perpendicular Intersection (PI), a novel mobile-assisted localization scheme. Network diagnosis is of great importance for an operational sensor networks, in OceanSense project, we propose the concept of passive diagnosis as well as the PAD approa...