Throughout history the management of sediment in river basins and waterways has been an important issue. While ancient Egyptians were managing sediment in flood plains to provide the crops with nutrients, today the changing nature of sediment issues can be caused by various natural and anthropogenic stressors such as wind, rivers, volcanic eruptions, agriculture, aquaculture, forestry, sewage, dredging, draining, mining and dams. Earth observation has proven to be most valuable in assessing sedimentation dynamics through monitoring of various parameters such as total suspended matter, dissolved organic matter and turbidity. From the perspective of remote sensing, water bodies are categorized in two classes: “case 1”and “case 2” waters. Case 1 is pristine azure coloured open ocean water where the optical properties are determined by the concentration of phytoplankton and its associated chlorophyll, which in case 1, is usually low. Since chlorophyll estimation from spectral reflectance is now relatively well-established, case 1 optical properties are relatively easily to analyze and thus relatively easy to model. In contrast, Case 2 waters might be the muddy-brown to coffee-black riverine waters or the green waters loaded with chlorophyll, mixed with a little mud from the sea bottom as found in a coastal upwelling zone. Case 2 waters may have several other factors mixed together to create their optical characteristics. In addition to phytoplankton, these factors may include (inorganic) suspended sediments (like sand, clay or mud particles) and coloured dissolved organic matter (CDOM). The colour of water is determined by the electromagnetic interaction of light with water components via absorption or scattering processes within the water column or at the sea surface or bottom. The optical properties of matter such as dissolved organic and inorganic substances and algae may all affect the water colour. Consequently it is possible to measure the colour (spectral reflectance) with the use of, for example, a satellite-based spectrometer. |