Instrument for In Situ Measurement of the Volume Scattering Function and Attenuation Coefficient

An instrument named as Volume Scattering and Attenuation Meter (VSAM) is presented. The VSAM can simultaneously measure the attenuation coefficient and the volume scattering function (VSF) from 10° to 170° with an interval of 10° at 659 nm. Using ultrapure water and NCRM-traceable polystyrene microsphere beads, the VSAM was calibrated, and the conversion factor χ bθ for estimating the backscattering coefficient from the backward VSF was obtained based on Mie theory in the laboratory. For χ bθ , the average relative deviation was no more than 7.77% in the range of 100°-160° between the modeled result based on VSAM and the theoretical result by Boss. Subsequently, the VSAM and ECO-VSF3 were deployed in situ in Zhanjiang Bay. The backscattering coefficient and VSF at the same angles measured by the two instruments were quite consistent. Some remarkable changes in the shape and magnitude of the VSF profile at different stations were found, with land-based pollutants composing an important suspicious source of these changes.