Currently, satellite ocean color imageries play an important role in monitoring of water properties in various oceanic, coastal, and inland ecosystems. Although there is a long-time and global archive of such valuable data, no study has comprehensively used these data to assess the changes in the Caspian Sea. Hence, this study assessed the variability of bio-optical properties of the upper-water column in the Southern Caspian Sea (SCS) using the archive of the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) and the Moderate Resolution Imaging Spectroradiometer (MODIS). The images acquired from SeaWiFS (January 1998 to December 2002) and MODIS Aqua (January 2003 to December 2015) satellites were used to investigate the spatial–temporal variability of bio-optical properties including Chlorophyll-a (Chl-a), attenuation coefficient, and remote sensing reflectance, and environmental parameters such as sea surface temperature (SST), wind stress and the El Nino-southern oscillation (ENSO) phenomena at different time lags in the study area. The trend analysis demonstrated an overall increase of 0.3358 mg m⁻³ in the Chl-a concentration during 1998–2015 (annual increase rate of 0.018 mg m⁻³ year⁻¹) and four algal blooms and in turn an abnormal increase in Chl-a concentration were occurred in August 2001, September 2005, 2009, and August 2010. The linear model revealed that Chl-a in the northern and middle part of the study area had been influenced by the attenuation coefficient after a one-month lag time. The analysis revealed a sharp decline in Chl-a concentration during 2011–2015 and showed a high correlation with the turbidity and attenuation coefficient in the southern region, while Kd_490nm and remote sensing reflectance did a low one. Generally, Chl-a concentration exhibited a positive correlation with the attenuation coefficient (r = 0.63) and with remote sensing reflectance at the 555 nm (r = 0.111). This study can be used as the basis for predictive modeling to evaluate the changes of water quality and bio-optical indices in the Southern Caspian Sea (SCS).

中文翻译：

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里海南部生物光学特性的时空变化：海洋颜色数据的历史分析

当前，卫星海洋彩色图像在监测各种海洋，沿海和内陆生态系统的水质方面起着重要作用。尽管此类有价值的数据已有长期的全球存档，但尚无研究全面使用这些数据来评估里海的变化。因此，本研究使用了海视宽视场传感器（SeaWiFS）和中分辨率成像分光光度计的档案资料，评估了南里海（SCS）上水柱生物光学特性的变异性（MODIS）。从SeaWiFS（1998年1月至2002年12月）和MODIS Aqua（2003年1月至2015年12月）获得的图像用于研究生物光学特性的时空变化，包括叶绿素a（Chl-a），衰减系数，遥感反射率以及环境参数，如研究区域在不同时滞上的海表温度（SST），风应力和厄尔尼诺-南极振荡（ENSO）现象。趋势分析表明，整体增加了0.3358 mg m1998-2015年期间Chl-a浓度为⁻³（每年增加0.018 mg m ^-3年^-1）和4次藻华，并在2001年8月，2005年9月，2009年和2010年8月发生了Chl-a浓度的异常增加。线性模型显示，研究区域北部和中部的Chl-a含量高。滞后一个月后，衰减系数会对其产生影响。分析显示，2011-2015年期间Chl-a浓度急剧下降，并且与南部地区的浊度和衰减系数高度相关，而Kd_490nm和遥感反射率则较低。通常，Chl-a浓度与衰减系数（r = 0.63）和555 nm处的遥感反射率（r = 0.111）呈正相关。