There are several satellite sensors specifically designed for monitoring of coastal and oceanic waters. The estimation of a certain water quality parameter using remote sensing, depends on the sensor’s characteristic sensitivity to certain wavelengths or spectral bands. In complex coastal regions, because the concentration of water constituents is spatially variable, conventional methods for studying water quality by point sampling are expensive, time consuming and spatially incomplete. Remote sensing is therefore important in providing a synoptic view for detailed retrieval over large regions.
Hong Kong has a complex marine environment due to terrestrial discharges from the Pearl River Delta in the west, urban pollutants in the center and the clearer waters of the South China Sea in the east. Monitoring this complex near-shore environment requires retrieval of water quality parameters such as Chl-a and SS concentrations at high spatial and temporal resolutions. In this research project synergy of high spatial resolution data from sentinel 2 A,B and Landsat OLI will be used to map Chl-a, SS and turbidity in the Pearl River Estuary and adjacent coastal area of Hong Kong. Other meteorological data such as rainfall and wind direction and wind velocity will be used to study the varying pattern of these water quality constituents.
Chlorophyll-a (Chl-a) is a pigment found in all plants and algae. In coastal productive waters, Chl-a is an important water quality parameter (measured in micro gram per liter, µg/l) which provides food to aquatic life. It also indicates pollution from high nutrient inputs from land drainage. Of these, phosphorus and nitrogen are the main factors which enhance the growth of algae and ultimately reduces oxygen availability for marine organisms. In extreme cases eutrophication leads to the formation of algal blooms. Therefore, measuring Chl-a as an indicator of algal biomass can help in assessment of water quality and serve as a health indicator of the marine system.
Suspended Solids (SS) are defined as the particles larger than 2 microns, found in water column and mostly comprise inorganic materials. Measured in milligrams per liter of water (mg/l), suspended solid concentrations and total suspended solid readings are based on filtered and dried water samples. The main difference between total suspended solid and suspended solid concentrations is in the amount of water sample analyzed. After filtering a water sample with a 2 µm filter, the particles are dried and weighed to determine suspended solids. When an entire sample is filtered, dried and weighed, the American Society for Testing of Materials (ASTM) considers the measurement to be the suspended solid concentration. If a water sample is further sub-sampled, the subsequent mass measurement will be the total suspended solids measurement.
Submitted Chapter: Hafeez S., Wong M. S., Abbas S., Kowk C. Y. T., Nichol J. E., Lee K. H., Tang D. (Submitted), Detection and monitoring of marine pollution using remote sensing technologies, Monitoring of Marine Pollution | IntechOpen
Submitted Paper: Hafeez S., Wong M. S., Ho H. C., Nazeer M., Nichol J. E., Tang D., Lee K. H., Pun L. (Submitted), Evaluation of machine learning algorithms for retrieval of water quality indicators in case-II subtropical areas: a case study of Hong Kong, Science of Total environment.
Coastal Water Quality Monitoring in Hong Kong
Hong Kong, an affluent city with a service-based economy is situated at the mouth of the Pearl River, whose delta region, spanning Hong Kong, Macau and Guangdong Province of China, has undergone lightning-paced industrial and urban development over the last 20 years. Accompanying this, the Pearl River Delta (PRD) region itself has suffered many adverse environmental changes including sea level rise, increased storminess and changes in salinity, sea surface temperature, nutrient, phytoplankton and sediment content, and sediment transport profiles. Also, Extensive algal blooms or red tide events occur around Hong Kong in late summer or early autumn. These algal blooms are mostly dominated by diatoms and dinoflagellates, which cause massive mortalities of aquaculture fish and numerous ecological and health impacts. Coasts of Hong Kong during this period. Hong Kong's coastal environment is complex, exhibiting different types of water in eastern, western and central areas, which makes accurate remote sensing retrieval of water quality parameters challenging. This research project will develop advance statistical methods using high resolution satellite data and in-situ water quality data to classify coastal ecosystems and map water quality parameters such as Chl-a, Suspended solids, Secchi Disk depth and turbidity with high frequency of observations.