Improved Determination of Particle Backscattering Coefficient Using Four-Angle Volume Scattering Measurements

The backscattering coefficient of aquatic particles (bbp(λ)) is one of the most important inherent optical properties in remote sensing. Due to the practical difficulties associated with measurements of the volume scattering function (VSF) over the whole backward hemisphere (90°–180°), bbp(λ) is estimated using either a single-angle approach, which employs the VSF at a fixed angle multiplied by a conversion factor χp(θ;λ), or a multi-angle approach, which uses the VSF at multiple angles with polynomial fitting. The angular variation in the VSF in the backward angles introduces uncertainties into bbp(λ) estimation. In this study, 178 VSF datasets from the global ocean were investigated. χp exhibited wavelength, regional, and angular variations. Although χp exhibited the lowest variability, at 120° (χp(120°;λ)), the single-angle approach exhibited a 12.71% mean absolute percent difference (MAPD) and a root mean squared error (RMSE) of approximately 4.02×10−3m−1. χp(140°;λ) exhibited larger variations at different wavelengths and in coastal regions. The three-angle approach exhibits wavelength independence and lower uncertainties, but the uncertainty of the polynomial fitting results at angles greater than 150° is relatively large, and the MAPD is still up to 10.92%. A better four-angle approach (100°, 120°, 140°, and 160°) was proposed, which could accurately determine bbp(λ) with the lowest MAPD (3.12%) and RMSE (0.86×10−3m−1). Notably, expanding to five angles provided minimal additional improvements, with the reduction in the MAPD being less than 1% compared to that under the four-angle approach. This study provides valuable insights into developing advanced optical sensors with better angular configurations for measuring bbp(λ).