CAPTURING 3D VELOCITY FIELDS OF EXPERIMENTAL LABORATORY PLUMES

Turbulent eddies, the mixing mechanism of explosive volcanic plumes, are driven by plume velocity. Due to the hazards associated with these eruptions, volcanologists rely on remote sensing techniques to study these physical processes. Using video, they can determine the optical flow velocity of the plume surface. Optical flow fields only show the apparent movement of the plume in two dimensions, which at best disregards movement in and out of the plane of the frame and at worst warps the entire flow field. We present a method of capturing 3D flow fields of explosive volcanic plumes using stereo imaging. Using two CASIO digital cameras, we recorded scaled plumes in an analogue laboratory environment. The videos are merged to produce 3D, time-dependent point clouds in order to determine the flow fields. We modified Flow3J, a package from the ImageJ toolbox, to calculate the 3D flow fields. From these flow fields we determined the expansion rate of individual eddies and relate it to the bulk vertical velocity of the eddy. This methodology can be applied to actual volcanic plumes.