Water Quality Products
Within the Terrascope Sentinel-2 workflow, a separate branch was developed to obtain micro- and macrophysical water properties that give indications on the water quality. In contrast to the Sentinel-2 Land data products, the in-house developed iCOR atmospheric correction, specifically dedicated to these applications, is used to derive these products. In addition, the scene classification used differs from Sentinel-2 Land. Table 1 summarizes the differences between Sentinel-2 Land and Water products.
| Terrascope S2 Land | Terrascope S2 Water | |
|---|---|---|
| Scene classification | Sen2Cor v2.5.5 | Idepix v2.8 |
| Atmospheric correction | Sen2COR v2.5.5 | iCOR v3.0 |
For RHOW, more information on methodology, limitations, and quality assurance can be found in the RHOW ATBD. For CHL, SPM, and TUR, this information is compiled in the Water Quality ATBD.
Water-leaving reflectance (RHOW)
The Sentinel-2 RHOW product is a geometrically and atmospherically corrected version of the original Copernicus Sentinel-2 Level-1C observations with additional information on pixel classification, Aerosol Optical Thickness (AOT), and angle information: Solar Zenith Angle (SZA), Viewing Zenith Angle (VZA), and Relative Azimuth Angle (RAA).
Figure 1 shows the data content.
Figure 1: Sentinel-2 RHOW data file overview.
Turbidity (TUR)
Turbidity indicates the relative opacity of the water column. It is an optical water property and a measure for the amount of light scattered by constituents in the water column. The higher the scattered light intensity, the higher the turbidity. Constituents that causes water to be turbid include clay, silt, very tiny inorganic and organic matter, algae, dissolved coloured organic compounds, plankton, and other microscopic organisms. Turbidity is expressed in Formazin Nephelometric Units (FNU, according to the ISO 7027 standard).
Suspended Particulate Material (SPM)
Suspended Particulate Matter concentration is the mass concentration of nano-scale to sand-size particles suspended in the water column. Some particles are present naturally in water, such as plankton, fine plant debris, and minerals (sand, silt or clay), while others originate from human activity (organic and inorganic matter). SPM and turbidity are linked: increased SPM concentrations will increase the water turbidity. SPM is expressed in mg L-1 or g m-3.
Chlorophyll-a concentration (CHL)
Chlorophyll-a is a green pigment found in plants. It absorbs sunlight and converts it into sugar during photosynthesis. Chlorophyll-a concentrations are an indicator of phytoplankton abundance and biomass in inland, coastal, and estuarine waters. CHL is expressed in μg L-1 or mg m-3.