Application of satellite data for investigation of water quality in coastal areas

The population growth in China together with the rapid industrialization and urbanization have increased the utilization of natural resources, leading to more waste being released to the environment. Thus, the environmental conditions have degraded in many regions to a point where environmentally related problems have become the main limiting factors for economical development and social progress. Most pollutants released to the environment will transfer to various water bodies and eventually be transported into the coastal areas and the ocean. Thus, the water quality may be used as a comprehensive, general index of the environmental conditions in a region. Water quality in coastal areas is of primary concern in China, not only for the Environmental Protection Agency and the State Ocean Administration, but also for the societal organizations and the public. Efficient and reliable methods to derive parameters characterizing the water quality in coastal areas are of great value for everyone concerned with the environmental situation in coastal and adjacent land areas.

This thesis focuses on the development of practical methods to apply remotely sensed data in water quality monitoring of coastal areas. First, the basic concepts in remote sensing methodologies are introduced and the systematic components of remote sensing techniques are described. Second, the basic knowledge on marine optics and ocean color remote sensing is reviewed and the properties of the main ocean color sensors are explained. Third, the two key techniques of ocean color remote sensing application, i.e., the atmospheric correction of ocean color remote sensing data and the development of inverse algorithms, are discussed. Finally, the application of ocean color remote sensing technique to monitor water quality in coastal areas is illustrated for several different water quality parameters based on the performed research work. In this thesis, the Pearl River estuary and the Daya Bay, both located in the Guangdong province, southern China, were taken as study areas.

The main achievements of this work include:
1. The improvement of atmospheric correction of SeaWiFS data for turbid coastal waters;
2. The retrieval of chlorophyll-a concentration in the Pearl River estuary;
3. The retrieval of gelbstoff absorption coefficient in the Pearl River estuary;
4. The remotely sensed assessment of water quality levels in the Pearl River estuary;
5. The long-term monitoring of thermal pollution in Daya Bay, and;
6. The use of remote sensing data to validate a numerical model of flow, salinity, and material transport in the Pearl River estuary.