Global Surface Water Occurrence Change Intensity visualisation script 

//VERSION=3

//This script visualizes the occurrence change intensity layer according to the Global Surface Water data user guide.

//Set up input and output settings
function setup() {
  return {
    input: ["change"],
    output: {
      bands: 3,
      sampleType: "AUTO"
    }
  }
}

//Create color ramp
const ramps = [
  [0, 0xff0000],    //-100% loss of occurrence (Pure red)
  [100, 0x000000],  //No change (Black)
  [200, 0x00ff00]   //100% increase in occurrence (Pure lime green)
];

//Create visualizer
const visualizer = new ColorRampVisualizer(ramps);

//EvaluatePixel function
function evaluatePixel(sample) {
  if (sample.change == 253){  //Not water
    return [1, 1, 1]          //Return White
  }else if (sample.change == 254){  //Unable to calculate a value due to no homologous months
    return [0.533, 0.533, 0.533]    //Return Dark gray
  }else if (sample.change == 255){  //No data
    return [0.8, 0.8, 0.8]          //Return Light gray
  }else if (sample.change <= 200){  //loss and increase of occurrence
    return [visualizer.process(sample.change)[0], visualizer.process(sample.change)[1], visualizer.process(sample.change)[2]];  //Return color ramp values
  }
}

General description of the script

This script visualizes the Occurrence Change Intensity layer from the Global Surface Water dataset according to the official symbology (Table 1). The Occurrence Change Intensity layer visualises changes in water occurrence between two different epochs, the first ranging from March 1984 to December 1999, and the other covering the period from January 2000 to December of the selected review year.

Table 1: Occurrence Change Intensity Symbology

Value Symbol Colour Label
0 0xff0000 -100% loss of occurrence
100 0x000000 No change
200 0x00ff00 100% increase in occurrence
253 0xffffff Not water
254 0x888888 Unable to calculate a value due to no homologous months
255 0xcccccc No data


Description of representative images

Occurrence Change Intensity layer visualisation in EO Browser for a section of the Padma River, the main distributary of the Ganges, in Bangladesh.

Occurrence Change Intensity Ganges in Bangladesh

Resources