The significance of monitoring, conserving, and, if necessary, improving the quality of water resources in the open ocean, coastal regions, estuaries, and inland water bodies cannot be neglected. As the interface between terrestrial environments and open oceans, coastal waters include many unique habitats and serve important human needs. Coastal habitats consist of estuaries, coastal wetlands, seagrass meadows, coral reefs, mangrove forests, kelp forests, and upwelling areas. Coastal waters support many fish species and provide habitat for many other organisms such as marine mammals, corals, sea turtles, and submerged aquatic vegetation.

Remote sensing of ocean color from spaceborne and airborne systems has become handier in the studies on water quality, especially in coastal and littoral waters, within the last decade. This is because remote sensing offers valuable information on water quality with a high spatial and temporal resolution for a vast area at a time. Through the analysis of changes in water quality and exposure of harmful algal blooms, it is possible to manage the assessment of environmental issues and potential health risks. Several remote sensing programs deliver historical data for studies of trends in water quality and the potential impacts of natural and anthropogenic activities on water quality.

Nevertheless, challenges persist in producing data products that are reliably accurate and can be regularly used for effective water quality monitoring. Although successful for open-ocean waters, atmospheric correction is still a challenge for coastal, estuarine, and inland waters because the widely variable and complex optical conditions encountered in these waters invalidate some basic assumptions in typical atmospheric correction models. Another challenge is the interference between emitted signals of different suspended or dissolved matter at the top layer of the water column.

In light of these and many other challenges, a special issue of Remote Sensing of Coastal Water Quality and Challenges has been dedicated to address the current status, challenges, and future research priorities for the remote sensing of coastal water quality.