Beam Reach

Sound propagation and drive-by's

Tuesday, September 25, 2007

Shannon and Tim woke up early to go for a morning hike before breakfast and returned just in time for oatmeal. After chores and a never-ending deck wash, we used the mechanical pump out at Reid Harbor before heading out. Conditions were calm and skies were clear, so we set up an experiment to measure sound propagation. We deployed our high frequency hydrophone and array, and Marla deployed her array as well. Val and Tim boarded the dinghy with a speaker while Anne, Sam, Ashleigh, and Marla recorded the calls and clicks played. Shannon gave the distance between the dinghy and Gato Verdeusing the range finder and Alex and Todd held the hydrophones away from the boat’s hull as they were pushed by the current. After recording both calls and clicks at a range of distances (approximately 25 m to 300 m), a number of dinghy drive-bys were recorded with the high frequency hydrophone. Alex heated up the eggplant parmesan, while Shannon prepared egg salad for lunch. After lunch, Val recorded the speed of sound (1484.55 m/s), the students analyzed their data, and Shannon wrote this. Data analysis continued into the late afternoon, as Tim and Anne tried to troubleshoot the high frequency hydrophone. As the sun was beginning to hang low in the horizon, Val and Sam boarded the dinghy for more drive-bys. Anne set up the high frequency hydrophone with the boat hook as an outrigger, Tim recorded the data, and Shannon perfected her range-finding abilities. We said goodbye to a lone male elephant seal and headed for Prevost Harbor on Stuart Island for the night as Anne was preparing veggie and tofu stir-fry.