This project represents the first effort to use satellite data to create a long-term, multi-satellite San Francisco Bay-specific turbidity dataset. Having accurate turbidity data will ultimately improve estimates of long-term gross primary productivity, and allow quantification of long-term trends in phytoplankton production. While some measurements of long-term turbidity in San Francisco Bay (SFB) are available from SFEI moored and mapping monitoring, USGS Peterson cruises, USGS sondes, and other sources, there are significant spatial and temporal gaps in the data. The spatial gaps include marginal habitats such as the South Bay shoals and shallow regions of San Pablo Bay–regions’ whose wide expanses and variable turbidity are important in determining bay-wide phytoplankton production. Satellite remote sensing is a natural fit for addressing this need, and this work used Sentinel-3 data collected approximately every two days from 2016 to present and MERIS data from 2002-2012 to begin assembling a turbidity dataset. Combining data from the two satellites required extensive testing and refinement, which included converting pixel values to units of turbidity (Formazin Nephelometric Units, FNU), identifying the appropriate spectrometric bands and atmospheric corrections, removing shallow areas that were subject to reflectivity-related interference, correcting for cloud shadows, and validation using data from moored sensor stations and cruises. The result of these efforts is a single, continuous turbidity dataset from 2002 to present, the first such application to SFB. While the data may currently miss some of the high FNU values observed in-situ samples, generally, the surface FNU values calculated from the remote sensed values are representative of expected conditions. Based on a preliminary assessment of the dataset, turbidity appears to be stable but highly variable at the San Pablo Bay region, while the South Bay shows a comparative decline in year-to-year variability. The Lower South Bay also shows increasing turbidity from 2016 onward. This work also assessed the influence of wind and tide, finding that both wind and tidal velocity generally increase observed turbidity in the shallow South Bay shoals. High tide tends to moderate and reduce observed turbidity, likely by reducing wind-based entrainment and encouraging settling. Future work will try to disentangle what trends in the record were caused specifically by wind or tide changes, and whether additional forcings can be integrated into the model.
| Attachment | Size |
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| 2026_Longterm_Forcing_Progress_Report.pdf | 6.31 MB |