This paper aims to assess the potential of Ocean Land Colour Instrument (OLCI) for the retrieval of chlorophyll-a (chl-a) over southern coastal waters of Vietnam. For that purpose, four chlorophyll-a ocean color (OC) algorithms (OC4ME and three new OC version 7 OC4, OC5, OC6) were applied based on water-leaving reflectance obtained from two atmospheric correction processors (C2RCC and DSF). To overcome high cloud coverage in the area of interest, full spatial data reconstruction was implemented using Data Interpolating Empirical Orthogonal Functions (DINEOF). Numerical error metrics of in situ measurements (n = 49) collected in different ship-based campaigns has been assessed for Sentinel-3A (S-3A) and 3B (S-3B) as well as on the combined products built from these two later satellites. Results showed that products based on C2RRC significantly outperformed DSF. For chl-a algorithms, C2RCC-based OC5 gave the most accurate retrieval while applied to S-3A (R²: 0.58, RMSE: 1.018 mg m⁻³, MAPE: 49.4 %), S-3B (R²: 0.75, RMSE: 0.776 mg m⁻³, MAPE: 37.3 %), and synergy datasets (R²: 0.70, RMSE: 0.844 mg m⁻³, MAPE: 42.5 %). With>50 % of observations missing due to cloud cover, DINEOF provides a promising solution to reconstruct the full spatial information. The successfully demonstrated retrieval of chl-a in our study presents potential for daily monitoring when combining observations from S-3A/B to further improve our understanding of the spatio-temporal dynamics of coastal ecosystems.

本文旨在评估海洋陆地颜色仪器 (OLCI) 在越南南部沿海水域反演叶绿素-a (chl-a) 的潜力。为此，基于从两个大气校正处理器（C2RCC 和 DSF）获得的离水反射率应用了四种叶绿素-a 海洋颜色 (OC) 算法（OC4ME 和三种新的 OC 版本 7 OC4、OC5、OC6）。为了克服感兴趣区域的高云覆盖率，使用数据插值经验正交函数 (DINEOF) 实现了完整的空间数据重建。已对 Sentinel-3A (S-3A) 和 3B (S-3B) 以及后来由这两者构建的组合产品评估了在不同舰载活动中收集的原位测量值 (n = 49) 的数值误差指标卫星。结果表明，基于 C2RRC 的产品明显优于 DSF。对于 chl-a 算法，基于 C2RCC 的 OC5 在应用于 S-3A（R² : 0.58, RMSE: 1.018 mg m ^-3 , MAPE: 49.4 %), S-3B (R ² : 0.75, RMSE: 0.776 mg m ^-3 , MAPE: 37.3 %)和协同数据集(R ² : 0.70, RMSE：0.844 mg m ^-3，MAPE：42.5 %)。由于云层覆盖导致超过 50% 的观测数据丢失，DINEOF 提供了一种很有前途的解决方案来重建完整的空间信息。在我们的研究中成功展示了对 chl-a 的检索，当结合来自 S-3A/B 的观察结果以进一步提高我们对沿海生态系统时空动态的理解时，这为日常监测提供了潜力。