Optical Measurement of Bubbles: System Design and Application

Abstract

Affordable high quality charge-coupled device (CCD) video cameras and image processing software are powerful tools for bubble measurements. Because of the wide variation between bubble populations, different bubble measurement systems (BMSs) are required depending upon the application. Two BMSs are described: a mini-BMS designed to observe the background bubble population from breaking waves, and a large-BMS designed to noninvasively determine the time-resolved bubble distribution inside dense bubble plumes and near the interface, as are details of the analysis techniques. Using the two systems in conjunction with each other allowed size distributions over the range 15?5000-?m radius to be obtained. The BMSs were designed for application to breaking-wave bubble plumes in the field or laboratory. Distributions measured by both BMSs in aerator-generated plumes agreed very well for the overlapping size range. Also presented are observations of bubble plumes produced by breaking waves in a large wind-wave flume, and calibration experiments showing the effect on measured bubble size due to blur induced by slow shutter speeds.