Optical method for measuring size-distribution and lifetime of bubbles

A high resolution imaging method for measuring the size distribution of bubbles entrained by water jets between 10-1000 um in diameter is presented. The bubble clouds are similar to those produced by breaking water waves. The goal of these measurements is the validation of models for bubble mediated gas transfer. A Depth from Focus technique is used to determine the 3D position and the size of the bubbles at the same time. This yields the size-distribution and its dependence on depth. Additionally the velocity of the bubbles is estimated using repeatedly exposed images. To evaluate the lifetime of bubbles a high-speed camera is used to count the bubbles crossing the surface. The measuring principle, image analysis and first results are presented.