Detection of diffuse seafloor venting using structured light imaging

Currently, we lack a systematic and remote method for locating and quantifying diffuse seafloor venting using underwater robotic vehicles. Diffuse flow is characterized by both low temperature and low flux rates, which cannot readily be distinguished using current remote visual, acoustic, or vehicle-mounted environmental sensors. The result is a poor understanding of the distribution, contribution, and context of diffuse flow sources. An underwater structured light imaging system, also used for high-resolution seafloor bathymetric mapping, has however shown promise in detecting diffuse flows while completing seafloor imaging surveys at a typical altitude of 3 m. The system creates sequential bathymetric profiles by imaging a laser line projected on the seafloor. In the presence of venting fluids, the laser line exhibits a detectable level of distortion due to variations in the refractive index along the optical path. By characterizing the degree of distortion, it is possible to create maps indicating areas of potential venting with sub-meter spatial resolution. Results from three distinct vent fields are presented and discussed. Analysis of these data sets indicates this system is capable of detecting both small point source vents and near bottom diffuse flow.