The Advanced Plume Sensor System (APEX) is a multi-sensor package designed to probe the structure of the dense bubble plumes beneath ocean whitecaps on several simultaneous spatial scales and provide information about bubble plume scale and roughness, the bubble size distribution and turbulence within the plume.

Plumes are created by breaking waves beneath whitecaps and, amongst other things, generate ambient noise, scatter sound at the ocean surface and enhance air-sea gas exchange. The study of bubble plumes is important for predicting oceanic noise, modeling underwater communications and sonar performance, and understanding global climate change.