Measurements of Acoustic Volume backscattering from Harmful algae using Underwater Ultrasonic Sensor

Abstract

Harmful algae (or called red tide) seriously damages to coastal fisheries activities in Korea, especially aquaculture. Currently, high density red tide (blooming) is detected from optical counting of water sample or visual monitoring. Although the methods have the advantage of understanding species composition, it has a limit on detection of red tide at an early stage. In this study, we tried to detect red tide at an early stage using ultrasonic transducer. Acoustic volume backscattering strength (Sv) measurements were conducted on red tide (Cochlodinium polykrikoides) using an underwater ultrasonic sensors (3.5 and 5 MHz) in the field and laboratory. For comparing acoustic data, density of red tide was counted with microscope. With two ultrasonic transducers were attached to the side of a fishing boat, in situ acoustic measurements and water sampling were performed with GPS data in the survey areas, simultaneously. The field experiments were carried out in July and August 2008 near the coastal region in the South coast of Korea. From comparing acoustic data and directly counting data of red tide, the two methods have a relatively good agreements. These results have allowed us to apply the acoustic method to real-time early detection of harmful algal blooms.