Water detection in Sentinel Hub

water_combined.js

//VERSION=3
const colorRamp = [[0, 0x000000], [1, 0xFFFFFF]];  // Color ramp for water detection (black for water)

let viz = new ColorRampVisualizer(colorRamp);

function setup() {
  return {
    input: ["B02", "B03", "B04", "B08", "B11", "dataMask"],
    output: [
      { id: "default", bands: 4 },  // RGBA output for combined visualization
      { id: "index", bands: 1, sampleType: 'FLOAT32' },  // Binary index output
      { id: "eobrowserStats", bands: 2, sampleType: 'FLOAT32' },  // Stats for mNDWI and data mask
      { id: "dataMask", bands: 1 }  // Mask output
    ]
  };
}

function evaluatePixel(samples) {
  // Step 1: Create True-Color RGB Image (using B04, B03, B02)
  let trueColor = [samples.B04 * 2.5, samples.B03 * 2.5, samples.B02 * 2.5];  // Adjust brightness
  
  // Step 2: Calculate indices for water detection
  let mNDWI = (samples.B03 - samples.B11) / (samples.B03 + samples.B11);
  let NDVI = (samples.B08 - samples.B04) / (samples.B08 + samples.B04);
  let EVI = 2.5 * (samples.B08 - samples.B04) / (samples.B08 + 6 * samples.B04 - 7.5 * samples.B02 + 1);
  
  // Step 3: Apply water detection criteria from Xia et al.
  let isWater = (mNDWI > NDVI && EVI < 0.1) && (mNDWI > EVI && EVI < 0.1);
  
  // Step 4: Create Overlay for Water Detection: Black for water, transparent for non-water
  let overlay = isWater ? [0, 0, 1, 0.6] : [0, 0, 0, 0];  // Water is black, non-water is transparent

  // Step 5: Combine True Color Image and Water Detection Overlay
  let combined = [
    trueColor[0] * (1 - overlay[3]) + overlay[0], trueColor[1] * (1 - overlay[3]) + overlay[1],trueColor[2] * (1 - overlay[3]) + overlay[2],samples.dataMask 
  ];

  let indexVal = samples.dataMask === 1 ? (isWater ? 1 : 0) : NaN;

  return {
    default: combined,  // Visualization: True color + water detection overlay
    index: [indexVal],  // Binary index (1 for water, 0 for non-water)
    eobrowserStats: [mNDWI, samples.dataMask],  // Output mNDWI for analysis
    dataMask: [samples.dataMask]  // Data mask
  };
}

water_detector.js

//VERSION=3
const colorRamp = [[0, 0xFF69B4], [1, 0x000000]];

let viz = new ColorRampVisualizer(colorRamp);

function setup() {
  return {
    input: ["B02", "B03", "B04", "B08", "B11", "dataMask"],
    output: [
      { id: "default", bands: 4 },  // RGBA output for combined visualization
      { id: "index", bands: 1, sampleType: 'FLOAT32' },  // Binary index output
      { id: "eobrowserStats", bands: 2, sampleType: 'FLOAT32' },  // Stats for mNDWI and data mask
      { id: "dataMask", bands: 1 }  // Mask output
    ]
  };
}

function evaluatePixel(samples) {
  // Step 1: RGB
  let trueColor = [samples.B04 * 2.55, samples.B03 * 2.55, samples.B02 * 2.55];  

  // Step 2: water detection
  let mNDWI = (samples.B03 - samples.B11) / (samples.B03 + samples.B11);
  let NDVI = (samples.B08 - samples.B04) / (samples.B08 + samples.B04);
  let EVI = 2.5 * (samples.B08 - samples.B04) / (samples.B08 + 6 * samples.B04 - 7.5 * samples.B02 + 1);
  
  // Step 3: Apply water detection
  let isWater = (mNDWI > NDVI && EVI < 0.1) && (mNDWI > EVI && EVI < 0.1);
  
  // Step 4: Create Overlay
  let overlay = isWater ? [1, 0.11, 0.71, 0.8] : [0, 0, 0, 0];  // Water is pink, non-water is transparent

  // Step 5:
  let combined = [
    trueColor[0] * (1 - overlay[3]) + overlay[0],  // Red channel
    trueColor[1] * (1 - overlay[3]) + overlay[1],  // Green channel
    trueColor[2] * (1 - overlay[3]) + overlay[2],  // Blue channel
    samples.dataMask  // Alpha channel (transparency based on mask)
  ];

  // Step 6: Handle index and stats output
  let indexVal = samples.dataMask === 1 ? (isWater ? 1 : 0) : NaN;

  return {
    default: combined,
    index: [indexVal],
    eobrowserStats: [mNDWI, samples.dataMask], dataMask: [samples.dataMask] 
  };
}