Uncomment the following line to install geemap if needed.

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# !pip install geemap

How to find out the greenest day of the year¶

Import libraries¶

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import ee
import geemap

Create an interactive map¶

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Map = geemap.Map()
Map

Define a region of interest (ROI)¶

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countries = ee.FeatureCollection('users/giswqs/public/countries')
Map.addLayer(countries, {}, 'coutries')

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roi = countries.filter(ee.Filter.eq('id', 'USA'))
Map.addLayer(roi, {}, 'roi')

Filter ImageCollection¶

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start_date = '2019-01-01'
end_date = '2019-12-31'

l8 = ee.ImageCollection('LANDSAT/LC08/C01/T1_TOA') \
    .filterBounds(roi) \
    .filterDate(start_date, end_date)

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# print(l8.size().getInfo())

Create a median composite¶

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median = l8.median()

visParams = {
  'bands': ['B4', 'B3', 'B2'],
  'min': 0,
  'max': 0.4,
}

Map.addLayer(median, visParams, 'Median')

Define functions to add time bands¶

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def addNDVI(image): 
    ndvi = image.normalizedDifference(['B5', 'B4']).rename('NDVI')
    return image.addBands(ndvi)

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def addDate(image):
    img_date = ee.Date(image.date())
    img_date = ee.Number.parse(img_date.format('YYYYMMdd'))
    return image.addBands(ee.Image(img_date).rename('date').toInt())

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def addMonth(image):
    img_date = ee.Date(image.date())
    img_doy = ee.Number.parse(img_date.format('M'))
    return image.addBands(ee.Image(img_doy).rename('month').toInt())

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def addDOY(image):
    img_date = ee.Date(image.date())
    img_doy = ee.Number.parse(img_date.format('D'))
    return image.addBands(ee.Image(img_doy).rename('doy').toInt())

Map over an ImageCollection¶

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withNDVI = l8.map(addNDVI).map(addDate).map(addMonth).map(addDOY)

Create a quality mosaic¶

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greenest = withNDVI.qualityMosaic('NDVI')

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greenest.bandNames().getInfo()

Display the max value band¶

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ndvi = greenest.select('NDVI')
palette = ['#d73027', '#f46d43', '#fdae61', '#fee08b', '#d9ef8b', '#a6d96a', '#66bd63', '#1a9850']
Map.addLayer(ndvi, {'palette': palette}, 'NDVI')

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Map.addLayer(greenest, visParams, 'Greenest pixel')
Map

Display time bands¶

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Map.addLayer(greenest.select('month'), {'palette': ['red', 'blue'], 'min': 1, 'max': 12}, 'Greenest month')

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Map.addLayer(greenest.select('doy'), {'palette': ['brown', 'green'], 'min': 1, 'max': 365}, 'Greenest doy')

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Last update: 2021-02-25