• Water quality refers to the chemical, physical, and biological characteristics of water. It is a crucial aspect of the environment, public health, and various industries that rely on water for different purposes. Water quality is assessed using suitable mathematical/computational models to predict the behaviour of specific water quality parameters in a water body and determine if water is ideal for various uses, such as drinking, agriculture, industrial processes, and supporting aquatic ecosystems.

  • Notable water quality parameters include pH, Dissolved Oxygen (DO), Nutrients (nitrogen and phosphorus), Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Heavy metal, Coliform bacteria, Chlorophyll-a concentration (Chl-a), absorption coefficient of Colored Dissolved Organic Matter (aCDOM) and Total Suspended Solids (TSS).

  • Only optically active parameters such as Chl-a (in mg m-3), TSS (in g m-3), and aCDOM(440) (in m-1) are considered valid inputs to the present Water Quality Index model and estimated directly from satellite-derived Level-2 water reflectance images after applying suitable bio-optical/machine learning algorithms. These three parameters are then used for the calculation of the Trophic State Index (TSI), TSS Index (TI), and CDOM Index (CI). Later, TSI, TI and CI are supplied to the Fuzzy Inference System (FIS) model as inputs to generate the Water Quality Index (WQI) raster image.

  • The calculated TSI, TI, CI, and WQI rasters will have values between 0-100 (Unitless), and the significance of these indexes for analysing water quality can be easily interpreted from table below.

TSIWater type (based on TSI range)TIWater type (based on TI range)CIWater type (based on CI range)WQIWater quality (based on WQI)
0–30Ultra-Oligotrophic0–40Low turbid0–41Low CDOM80–100Good
30–40Oligotrophic40–54Moderate turbid41–47Moderate CDOM60–80Average
40–50Mesotrophic54–60High turbid47–77High CDOM40–60Poor
50–60Eutrophic60–100Very high turbid77–100Very high CDOM20–40Very Poor
60–100Hypertrophic––––0–20Extremely Poor

​
Input and Output

  • Input
ParametersDescriptions
Area of InterestArea for which you want to perform water quality analysis
  • Output

The model generates seven single-band raster files, visualized over the Area of Interest (AOI), highlighting all water areas with corresponding values and colors based on a predefined color scale. Non-aquatic areas will be transparent, revealing the base image.

Output and parametersDescriptionTypeDownloadable as
Chl-a (Chlorophyll-a)Measures the amount of chlorophyll-a pigment in water, indicating algal growth and biomass. High levels can signal excessive algae and potential water quality issues.Single band raster fileGeoTiff File format
aCDOM(440) (Absorption coefficient of CDOM)Measures the absorption coefficient of Colored Dissolved Organic Matter at 440nm, indicating organic pollution from sources like agricultural or urban runoff and wastewater discharge. High levels reduce water transparency and affect ecosystems.Single band raster fileGeoTiff File format
TSS (Total Suspended Solids)Indicates concentration of suspended particles. High TSS can result from soil erosion, sediment runoff, or pollution, impacting water clarity and aquatic life.Single band raster fileGeoTiff File format
TSI (Trophic State Index)A normalized version of Chl-a indicating the trophic status.Single band raster fileGeoTiff File format
CI (CDOM Index)A normalized version of the absorption coefficient of CDOM at 440nm(aCDOM(440)).Single band raster fileGeoTiff File format
TI (TSS Index)A normalized version of TSS.Single band raster fileGeoTiff File format
WQI (Water Quality Index)Assesses the chemical, physical, and biological characteristics of water using mathematical/computational models.Single band raster fileGeoTiff File format
TableTable shows quantification of area for different ranges of a particular parameter.TableCSV file
GraphsGraph is a better visualization for the table created.Bar GraphJPEG image

​
Expected Model Run Time

AOI Size Range (in Sq KM)Estimated Model Run Time
0–50012 minutes
500–200050 minutes
2000–250062 minutes
2500–300075 minutes
3000–350090 minutes
3500–4000105 minutes
4000–4500118 minutes
4500–5000131 minutes

​
Additional Details

Minimum size of Area of Interest required (in Sq KMs.): No such restrictions

Maximum size of Area of Interest supported (in Sq KMs.): 5000 Sq KMs

Geographies supported: All geographies

Sensors Supported: Sentinel-2. (It will support Pixxel FireFly in future)

WQI images may not show enough variability if TSI, TI, and CI values stay almost constant, which usually happens when the area of the inland water body is tiny (in order of few Sq KMs) and in open ocean waters.