EVI (Enhanced Vegetation Index)

//VERSION=3
// Enhanced Vegetation Index  (abbrv. EVI)
// General formula: 2.5 * (NIR - RED) / ((NIR + 6*RED - 7.5*BLUE) + 1)
// URL https://www.indexdatabase.de/db/si-single.php?sensor_id=96&rsindex_id=16
function setup() {
   return {
      input: ["B02", "B04", "B08", "dataMask"],
      output: { bands: 4 }
   };
}

const ramp = [
   [-0.5, 0x0c0c0c],
   [-0.2, 0xbfbfbf],
   [-0.1, 0xdbdbdb],
   [0, 0xeaeaea],
   [0.025, 0xfff9cc],
   [0.05, 0xede8b5],
   [0.075, 0xddd89b],
   [0.1, 0xccc682],
   [0.125, 0xbcb76b],
   [0.15, 0xafc160],
   [0.175, 0xa3cc59],
   [0.2, 0x91bf51],
   [0.25, 0x7fb247],
   [0.3, 0x70a33f],
   [0.35, 0x609635],
   [0.4, 0x4f892d],
   [0.45, 0x3f7c23],
   [0.5, 0x306d1c],
   [0.55, 0x216011],
   [0.6, 0x0f540a],
   [1, 0x004400],
];

const visualizer = new ColorRampVisualizer(ramp);

function evaluatePixel(samples) {
   let evi = 2.5 * (samples.B08 - samples.B04) / ((samples.B08 + 6.0 * samples.B04 - 7.5 * samples.B02) + 1.0);
   let imgVals = visualizer.process(evi);
   return imgVals.concat(samples.dataMask)
}

//VERSION=3
function setup() {
    return {
        input: ["B02", "B03", "B04", "B08", "dataMask"],
        output: [
            { id: "default", bands: 4 },
            { id: "index", bands: 1, sampleType: "FLOAT32" },
            { id: "eobrowserStats", bands: 2, sampleType: 'FLOAT32' },
            { id: "dataMask", bands: 1 }
        ]
    };
}

const ramp = [
    [-0.5, 0x0c0c0c],
    [-0.2, 0xbfbfbf],
    [-0.1, 0xdbdbdb],
    [0, 0xeaeaea],
    [0.025, 0xfff9cc],
    [0.05, 0xede8b5],
    [0.075, 0xddd89b],
    [0.1, 0xccc682],
    [0.125, 0xbcb76b],
    [0.15, 0xafc160],
    [0.175, 0xa3cc59],
    [0.2, 0x91bf51],
    [0.25, 0x7fb247],
    [0.3, 0x70a33f],
    [0.35, 0x609635],
    [0.4, 0x4f892d],
    [0.45, 0x3f7c23],
    [0.5, 0x306d1c],
    [0.55, 0x216011],
    [0.6, 0x0f540a],
    [1, 0x004400],
];

const visualizer = new ColorRampVisualizer(ramp);

function evaluatePixel(samples) {
    let val = 2.5 * (samples.B08 - samples.B04) / ((samples.B08 + 6.0 * samples.B04 - 7.5 * samples.B02) + 1.0);
    // The library for tiffs works well only if there is only one channel returned.
    // So we encode the "no data" as NaN here and ignore NaNs on frontend.
    const indexVal = samples.dataMask === 1 ? val : NaN;
    const imgVals = visualizer.process(val);

    return {
        default: imgVals.concat(samples.dataMask),
        index: [indexVal],
        eobrowserStats: [val, isCloud(samples) ? 1 : 0],
        dataMask: [samples.dataMask]
    };
}

function isCloud(samples) {
    const NGDR = index(samples.B03, samples.B04);
    const bRatio = (samples.B03 - 0.175) / (0.39 - 0.175);
    return bRatio > 1 || (bRatio > 0 && NGDR > 0);
}

//VERSION=3
function setup() {
    return {
        input: ["B02", "B04", "B08"],
        output: {
            bands: 1,
            sampleType: "FLOAT32"
        }
    };
}

function evaluatePixel(samples) {
    return [2.5 * (samples.B08 - samples.B04) / ((samples.B08 + 6.0 * samples.B04 - 7.5 * samples.B02) + 1.0)]
}

Evaluate and Visualize

General description of the script

For Sentinel-2, the index looks like this:

\[EVI = 2.5 \cdot (\frac{B8-B4}{B8+6 \cdot B4-7.5 \cdot B2 +1})\]

In areas of dense canopy cover, where leaf area index (LAI) is high, the blue wavelengths can be used to improve the accuracy of NDVI, as it corrects for soil background signals and atmospheric influences.

Values description: The range of values for EVI is -1 to 1, with healthy vegetation generally around 0.20 to 0.80.

Description of representative images

EVI, Italy. Acquired on 08.10.2017, processed by Sentinel Hub.

EVI