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spatialthoughtsspatialthoughts
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add new script
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‎code/end_to_end_gee/Supplement/Image_Collections/Interval_Composites

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// Example script showing how to create composite images
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// at regular intervals
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// Let's create 15-day composites
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// Change the parameters below for custom intervals
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// i.e. For monthly composites, use interval=1 and unit='month'
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// Define the interval
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var interval = 15;
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// Define the unit of interval
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// 'year', 'month' 'week', 'day', 'hour', 'minute', or 'second'.
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var unit = 'day';
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// Define the period
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var startDate = ee.Date.fromYMD(2023, 1, 1);
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var endDate = ee.Date.fromYMD(2024, 1, 1);
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// Get the total units in the period
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var totalUnits = endDate.difference(startDate, unit);
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print('Total ' + unit, totalUnits);
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// Create a list of dates at start of each interval
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var intervals = ee.List.sequence(0, totalUnits, interval);
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var startDates = intervals.map(function(interval) {
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var intervalStart = startDate.advance(interval, unit);
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return intervalStart;
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});
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print('Start dates for each interval', startDates);
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// Now we create the composites
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// Define collection and apply filters
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var s2 = ee.ImageCollection("COPERNICUS/S2_SR_HARMONIZED")
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var basin = ee.FeatureCollection("WWF/HydroSHEDS/v1/Basins/hybas_7")
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var arkavathy = basin.filter(ee.Filter.eq('HYBAS_ID', 4071139640))
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var geometry = arkavathy.geometry()
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Map.centerObject(geometry, 11)
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// Function to remove cloud pixels from Sentinel-2 SR image
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function maskCloudAndShadowsSR(image) {
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var cloudProb = image.select('MSK_CLDPRB');
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var snowProb = image.select('MSK_SNWPRB');
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var cloud = cloudProb.lt(10);
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var scl = image.select('SCL');
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var shadow = scl.eq(3); // 3 = cloud shadow
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var cirrus = scl.eq(10); // 10 = cirrus
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// Cloud probability less than 10% or cloud shadow classification
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var mask = cloud.and(cirrus.neq(1)).and(shadow.neq(1));
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return image.updateMask(mask).divide(10000)
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.copyProperties(image, ['system:time_start']);
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}
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var filtered = s2
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.filter(ee.Filter.bounds(geometry))
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.map(maskCloudAndShadowsSR)
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// We map() a function that takes each date from the startDates
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// and applies a filter for images in that interval
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var compositeImages = startDates.map(function(startDate) {
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var intervalStartDate = ee.Date(startDate);
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var intervalEndDate = intervalStartDate.advance(interval, unit);
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// Remember that end dates are not included in EE Filters
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// So we get images upto the end date.
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var intervalFiltered = filtered.filter(
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ee.Filter.date(intervalStartDate, intervalEndDate));
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// Count the number of images
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// This will be used later to filter out
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// composites with no matching images
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var intervalImageCount = intervalFiltered.size();
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var composite = intervalFiltered.median();
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return composite.set({
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'system:time_start': intervalStartDate.millis(),
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'system:time_end': intervalEndDate.millis(),
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'start_date': intervalStartDate.format('YYYY-MM-dd'),
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'end_date': intervalEndDate.format('YYYY-MM-dd'),
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'image_count': intervalImageCount
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});
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});
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var compositeCol = ee.ImageCollection.fromImages(compositeImages);
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var compositeColFiltered = compositeCol.filter(
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ee.Filter.neq('image_count', 0));
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print('Composites at ' + interval + ' ' + unit + ' intervals',
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compositeColFiltered);

‎docs/code/end_to_end_gee/Supplement/Image_Collections/Interval_Composites

Lines changed: 89 additions & 0 deletions
Original file line numberDiff line numberDiff line change
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1+
// Example script showing how to create composite images
2+
// at regular intervals
3+
4+
// Let's create 15-day composites
5+
// Change the parameters below for custom intervals
6+
// i.e. For monthly composites, use interval=1 and unit='month'
7+
8+
// Define the interval
9+
var interval = 15;
10+
11+
// Define the unit of interval
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// 'year', 'month' 'week', 'day', 'hour', 'minute', or 'second'.
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var unit = 'day';
14+
15+
// Define the period
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var startDate = ee.Date.fromYMD(2023, 1, 1);
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var endDate = ee.Date.fromYMD(2024, 1, 1);
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// Get the total units in the period
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var totalUnits = endDate.difference(startDate, unit);
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print('Total ' + unit, totalUnits);
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// Create a list of dates at start of each interval
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var intervals = ee.List.sequence(0, totalUnits, interval);
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var startDates = intervals.map(function(interval) {
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var intervalStart = startDate.advance(interval, unit);
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return intervalStart;
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});
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print('Start dates for each interval', startDates);
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// Now we create the composites
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// Define collection and apply filters
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var s2 = ee.ImageCollection("COPERNICUS/S2_SR_HARMONIZED")
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var basin = ee.FeatureCollection("WWF/HydroSHEDS/v1/Basins/hybas_7")
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var arkavathy = basin.filter(ee.Filter.eq('HYBAS_ID', 4071139640))
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var geometry = arkavathy.geometry()
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Map.centerObject(geometry, 11)
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// Function to remove cloud pixels from Sentinel-2 SR image
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function maskCloudAndShadowsSR(image) {
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var cloudProb = image.select('MSK_CLDPRB');
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var snowProb = image.select('MSK_SNWPRB');
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var cloud = cloudProb.lt(10);
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var scl = image.select('SCL');
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var shadow = scl.eq(3); // 3 = cloud shadow
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var cirrus = scl.eq(10); // 10 = cirrus
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// Cloud probability less than 10% or cloud shadow classification
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var mask = cloud.and(cirrus.neq(1)).and(shadow.neq(1));
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return image.updateMask(mask).divide(10000)
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.copyProperties(image, ['system:time_start']);
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}
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var filtered = s2
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.filter(ee.Filter.bounds(geometry))
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.map(maskCloudAndShadowsSR)
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// We map() a function that takes each date from the startDates
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// and applies a filter for images in that interval
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var compositeImages = startDates.map(function(startDate) {
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var intervalStartDate = ee.Date(startDate);
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var intervalEndDate = intervalStartDate.advance(interval, unit);
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// Remember that end dates are not included in EE Filters
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// So we get images upto the end date.
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var intervalFiltered = filtered.filter(
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ee.Filter.date(intervalStartDate, intervalEndDate));
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// Count the number of images
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// This will be used later to filter out
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// composites with no matching images
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var intervalImageCount = intervalFiltered.size();
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var composite = intervalFiltered.median();
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return composite.set({
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'system:time_start': intervalStartDate.millis(),
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'system:time_end': intervalEndDate.millis(),
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'start_date': intervalStartDate.format('YYYY-MM-dd'),
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'end_date': intervalEndDate.format('YYYY-MM-dd'),
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'image_count': intervalImageCount
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});
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});
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var compositeCol = ee.ImageCollection.fromImages(compositeImages);
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var compositeColFiltered = compositeCol.filter(
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ee.Filter.neq('image_count', 0));
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print('Composites at ' + interval + ' ' + unit + ' intervals',
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compositeColFiltered);

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