Measuring ambient ocean bubble fields using a multibeam sonar

For two weeks in July 2002 off the coast of San Diego, a 240 kHz SeaBat 8101 Multibeam Echosounder System was used to measure the backscatter from ambient bubble fields in the near surface layer. The sonar system was mounted approximately 12.5 meters below the surface on the hydraulic orientation unit of the research platform FLIP and was oriented so that its fan of 101 1.5 degree beams were looking at the surface at an angle of 45 degrees from the vertical. Data collection was part of a joint experiment involving the Applied Research Laboratory (ARL)/The Pennsylvania State University (PSU) and the Marine Physical Laboratory (MPL)/Scripps Institute of Oceanography (SIO). Although sea conditions were benign for most of the test period, wind wave activity near the end provided a number of opportunities to observe near surface bubble entrainment. The sonar system proved to be an effective tool for the observation of the lifetime, spatial structure and dimensions of the ambient bubble fields. [Work supported by ONR under Award No. N00014‐02‐1‐0156.]