Intercomparison of Four Level-4 Satellite Sea Surface Temperature Products in the Complex Coastal Seas of the Shandong Peninsula

Sea surface temperature (SST) is a key variable regulating ocean–atmosphere interactions, yet the performance of global Level-4 (L4) SST products in complex coastal environments remains insufficiently evaluated. This study assesses four global L4 SST products (C3SSST, OSTIA, MGDSST, and OISST) in the coastal waters surrounding the Shandong Peninsula using both the iQuam dataset and regional moored buoy (MB) observations. Statistical metrics (COR, RMSE, MAE, BIAS) were employed to quantify accuracy. All four SST products show strong agreement with in situ observations, with correlation coefficients exceeding 0.97. Validation against iQuam showed that OISST achieved the lowest RMSE (~1.008 °C), while coastal buoy observations showed that C3SSST achieved the lowest RMSE at Zhifudao (RMSE ≈ 0.833 °C). Pronounced warm biases at Shidao station during summer suggest that L4 SST products may underestimate coastal upwelling along the Shandong Peninsula. The leave-one-out (LOO) ensemble analysis further revealed consistent differences among the four L4 SST products, with C3SSST and OSTIA showing relatively higher consistency, while OISST exhibited larger deviations from the other products. These results indicate that L4 SST performance depends on both product characteristics, including observational data sources, and local environmental conditions. These findings provide useful guidance for SST dataset selection in the Shandong Peninsula.