Satellite estimation of suspended particle types using a backscattering efficiency-based model in the marginal seas

The particle composition of suspended matter provides crucial information for a deeper understanding of marine biogeochemical processes and environmental changes. Particulate backscattering efficiency (Q(bbe)(lambda)) is critical to understand particle composition, and a Q(bbe)(lambda)based model for classifying particle types was proposed. In this study, we evaluated the applicability of the Q(bbe)(lambda)-based model to satellite observations in the shallow marginal Bohai and Yellow Seas. Spatiotemporal variations of the particle types and their potential driving factors were studied. The results showed that the Q(bbe)(lambda) products generated from Moderate Resolution Imaging Spectroradiometer (MODIS) on the satellite Aqua agreed well with the in situ measured values, with determination coefficient, root mean square error, bias, and mean absolute percentage error of 0.76, 0.007, 16.5%, and 31.0%, respectively. This result verifies the satellite applicability of the Qbbe(.)-based model. Based on long-term MODIS data, we observed evident spatiotemporal variations of the Q(bbe)(lambda), from which distinct particle types were identified. Coastal waters were often dominated by minerals, with high Q(bbe)(lambda) values, though their temporal changes were also observed. In contrast, waters in the offshore regions showed clear changes in particle types, which shifted from organic-dominated with low Q(bbe)(lambda) levels in summer to mineral-dominated with high Q(bbe)(lambda) values in winter. We also observed long-term increasing and decreasing trends in Q(bbe)(lambda) in some regions, indicating a relative increase in the proportions of mineral and organic particles in the past decades, respectively. These spatiotemporal variations of Q(bbe)(lambda) and particle types were probably attributed to sediment re-suspension related to water mixing driven by wind and tidal forcing, and to sediment load associated with river discharge. Overall, the findings of this study may provide valuable proxies for better studying marine biogeochemical processes, material exchanges, and sediment flux.