Measurements of backscattering strengths of the red tide species (Akashiwo sanguinea and Alexandrium affine) using ultrasound

Abstract

The overgrowth of phytoplankton leads to negative effects such as harmful algal blooms (HABs, also called red tides) in marine environments and coastal aquaculture sites. From an economic perspective, the rapid detection of red tides is critical to reduce damage. However, traditional detection techniques require a substantial amount of time. One alternative method is an acoustic technique using ultrasonic sound. However, before performing a hydroacoustic approach, the acoustic properties of red tide species must be understood. In this study, as an essential data, acoustic properties were measured for two red tide species, Akashiwo sanguinea and Alexandrium affine, which appear in coastal oceanic waters during summer and autumn in Korea. The ultrasonic sound frequency was set to 3.5 MHz and the experiments were conducted under laboratory and field conditions.In the laboratory measurements, the signal received from each species was directly proportional to the density of the population. From these measurements, we derived a relationship between cell number and the acoustic signal received for each species. In the field experiments, when A. sanguinea blooms appeared at a density greater than 3,000 cells mL-1, the acoustic signals varied with cell density, and there was a good correlation between the signal and density. This confirms that acoustic measurements of HABs can be used for the monitoring and early detection tical to reduce damage. However, traditional detection techniques require a substantial amount of time. One alternative method is an acoustic technique using ultrasonic sound. However, before performing a hydroacoustic approach, the acoustic properties of red tide species must be understood. In this study, as an essential data, acoustic properties were measured for two red tide species, Akashiwo sanguinea and Alexandrium affine, which appear in coastal oceanic waters during summer and autumn in Korea. The ultrasonic sound frequency was set to 3.5 MHz and the experiments were conducted under laboratory and field conditions.In the laboratory measurements, the signal received from each species was directly proportional to the density of the population. From these measurements, we derived a relationship between cell number and the acoustic signal received for each species. In the field experiments, when A. sanguinea blooms appeared at a density greater than 3,000 cells mL-1, the acoustic signals varied with cell density, and there was a good correlation between the signal and density. This confirms that acoustic measurements of HABs can be used for the monitoring and early detection