基于静止轨道水色卫星数据的渤海总吸收系数遥感反演和逐时变化研究

Remote Sensing Retrieval and Hourly Variation Analysis of Total Absorption Coefficient in the Bohai Sea with Geostationary Ocean Color Imager

渤海是我国的半封闭内海,受陆源影响显著,水体光学性质复杂多变,静止轨道水色卫星(GOCI)的高时间分辨率数据为研究渤海水体总吸收系数的时空变化特征,特别是逐时变化提供了可能。针对GOCI波段设置,利用实测数据建立了基于遥感反射率波段比值的412、443、555 nm波段渤海总吸收系数遥感反演模型,经独立实测数据检验,模型反演值与实测值的相关系数大于0.8,平均相对误差(APD)小于13%,中值相对误差小于9%,优于已有典型算法(精度提高约10%);经独立现场-卫星时空匹配数据检验,基于该模型和GOCI卫星数据的总吸收系数遥感反演平均相对误差在35%以内。基于2015年5月4日1天8景的GOCI影像和所建立的模型,研究了渤海总吸收系数的逐时变化特征。结果表明,8:30—15:30期间总吸收系数变幅主要分布范围是0.2~0.3 m^(-1),最大变幅可达到0.8 m^(-1),变幅极大值主要分布在辽东湾、渤海湾和莱州湾近岸海域。结合潮汐数据的分析发现,辽东湾、渤海湾北部总吸收系数与潮高的逐时变化具有较好的一致性,总吸收系数极小值出现时刻滞后于低潮时刻0~1.5 h;莱州湾西部总吸收系数与潮高逐时变化呈明显负相关性;渤海湾南部、莱州湾东部总吸收系数与潮高变化未见显著相关性。

The optical properties of the semi-closed Bohai Sea are complex due to significant terrigenous influence.The high temporal resolution data from geostationary ocean color imager（GOCI） makes it possible to explore the temporal and spatial variability characteristics in the Bohai Sea, especially on the hourly temporal scale. A remote sensing algorithm is developed to retrieve the total absorption coefficients at 412, 443, 555 nm in the Bohai Sea based on the GOCI band ratio of remote sensing reflectance. The algorithm is validated with independent field data. The correlation coefficient between the retrieved and measured data is higher than 0.8, the average absolute percentage difference（APD） is less than 13%, and the median absolute percentage difference is less than 9%. The performance is better than that of previous typical algorithms（improvement over 10%）. Based on the independent field-satellite match-up data, the APD between the retrieved and measured data is less than 35%. On the basis of the GOCI image（May 4th,2015） and the new model, the spatial and hourly variation characteristics in the Bohai Sea are discussed.The results show that diurnal variability magnitude is mainly 0.2~0.3 m^（-1）, and the maximum can reach 0.8 m^（-1）. High diurnal variability values are found mainly in the Liaodong Bay, the Bohai Bay and the Laizhou Bay. The total absorption coefficient is analyzed together with tide data, and the variations are generally consistent with the corresponding tidal height variations in the Liaodong Bay and the north of the Bohai Bay, though the minimal total absorption coefficient appears about 0~1.5 h later than the lowest tide moment. The total absorption coefficient shows significant negative correlation with tide height in the west of the Laizhou Bay. The total absorption coefficient and tidal height have no obvious correlation in the south of the Bohai Bay and the east of the Laizhou Bay.