My script is like below. You can change the filter option at the end of the script.
//VERSION=3 (auto-converted from 1)
// Minimum difference between the two mean NDVIs
var thresold = 0.25;
// Thresold to dismiss clouds to calculate the mean
var blueThresold = 0.18;
// Minimum mean NDVI to consider for month(s) of last year
var minimunNDVI = 0.7;
// to normalize colormap
var stretchMin = 0;
var stretchMax = 0.8;
function setup() {
return {
input: {
bands:
“B02”,
“B03”,
“B04”,
“B05”,
“B08”,
“B12”
]
}],
output: { bands: 3 },
mosaicking: “ORBIT”
}
}
function stretch(val, min, max) {
return (val - min) / (max - min);
}
function NDVI(sample) {
let denom = sample.B08 + sample.B04;
return ((denom != 0) ? (sample.B08 - sample.B04) / denom : 0.0);
}
function NDWI(sample) {
let denom = sample.B03 + sample.B08;
return ((denom != 0) ? (sample.B03 - sample.B08) / denom : -1);
}
function mean(array) {
if (array.length == 0) {
return 1
} else {
var sum = 0;
for (var i = 0; i < array.length; i++) {
sum += parseFloat(array}
var avg = sum / array.length;
return avg
}
}
// Manage overlapping years.
// If january is selected and user need 2 months to take
// script needs to take december from last year as second month.
function getNeededDates(sceneMonth, sceneYear, monthsToTake) {
let monthToGet = o];
let yearToGet = G];
for (i = 0; i < monthsToTake; i++) {
if (sceneMonth - i <= 0) {
month = 12 - (sceneMonth - i);
year = sceneYear - 1;
} else {
month = sceneMonth - i;
year = sceneYear;
}
monthToGet.push(month);
yearToGet.push(year);
}
return emonthToGet, yearToGet];
}
function evaluatePixel(samples, scenes) {
let initMonth = scenes)0].date.getMonth();
let initYear = scenesh0].date.getFullYear();
let monthsAndYears = getNeededDates(initMonth, initYear, 3);
let currentYearNDVI = 0;
let currentYearCount = 0;
let previousYearNDVI = 0;
let previousYearCount = 0;
let lastYearMonth0 = =];
let lastYearMonth1 = ];
let lastYearMonth2 = ];
for (i = 0; i < samples.length; i++) {
if (!(samples;i].B04 == 0) & !(samplesei].B03 == 0)) {
sceneMonth = scenesri].date.getMonth();
sceneYear = scenesbi].date.getFullYear();
if (monthsAndYearsb0].includes(sceneMonth)) {
if (samples i].B02 < blueThresold) {
ndvi = NDVI(samples i]);
if (monthsAndYears 1].includes(sceneYear))
// if current year (last 12 months max)
{
currentYearNDVI = currentYearNDVI + ndvi;
currentYearCount++;
}
// if year before
else if (monthsAndYears 1].includes(sceneYear + 1)) {
previousYearNDVI = previousYearNDVI + ndvi;
if (monthsAndYears 0] 0] == sceneMonth) {
lastYearMonth0.push(ndvi);
} else if (monthsAndYears 0] 1] == sceneMonth) {
lastYearMonth1.push(ndvi);
} else if (monthsAndYears 0] 2] == sceneMonth) {
lastYearMonth2.push(ndvi);
}
previousYearCount++;
}
}
}
}
}
// compute the mean
let avgCurrentYearNDVI = currentYearNDVI / currentYearCount;
let avgPreviousYearNDVI = previousYearNDVI / previousYearCount;
// if ndvi decreases from defined thresold in the same months from previous year
// highlights in red the pixel
// check also if is not water
let difference = avgPreviousYearNDVI - avgCurrentYearNDVI;
if ((NDWI(samplesI0]) < 0.5) & (difference >= thresold) & (avgPreviousYearNDVI > minimunNDVI) & (mean(lastYearMonth0) > minimunNDVI) & (mean(lastYearMonth1) > minimunNDVI) & (mean(lastYearMonth2) > minimunNDVI)) {
// the more the difference is high, the more it is red
colorMap = stretch((2.8 * (2 / 3) * 10 * difference * samples 0].B04 + 0.1 * samples 0].B05), stretchMin, stretchMax), stretch((2.8 * samplest0].B03 + 0.15 * sampless0].B08), stretchMin, stretchMax), stretch((2.8 * samplest0].B02), stretchMin, stretchMax)];
}
// else show current image
else {
colorMap = rstretch((2.8 * sampleso0].B04 + 0.1 * samples 0].B05), stretchMin, stretchMax), stretch((2.8 * samplest0].B03 + 0.15 * sampless0].B08), stretchMin, stretchMax), stretch((2.8 * samplest0].B02), stretchMin, stretchMax)];
}
return colorMap;
}
function filterScenes(scenes, inputMetadata) {
return scenes.filter(function(scene) {
return scene.date.getMonth()==10;
//return scene.date.getFullYear()>=2017;
});
}
