F49a Checkpoint

Import libraries¶

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import ee
import geemap

import ee import geemap

Create an interactive map¶

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Map = geemap.Map(center=[40, -100], zoom=4)

Map = geemap.Map(center=[40, -100], zoom=4)

Add Earth Engine Python script¶

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# Add Earth Engine dataset
image = ee.Image("USGS/SRTMGL1_003")

#  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#  Chapter:      F4.9 Exploring Lagged Effects in Time Series
#  Checkpoint:   F49a
#  Authors:      Andréa Puzzi Nicolau, Karen Dyson, David Saah, Nicholas Clinton
#  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

# Define function to mask clouds, scale, and add variables
# (NDVI, time and a constant) to Landsat 8 imagery.
def maskScaleAndAddVariable(image):
    # Bit 0 - Fill
    # Bit 1 - Dilated Cloud
    # Bit 2 - Cirrus
    # Bit 3 - Cloud
    # Bit 4 - Cloud Shadow
    qaMask = image.select('QA_PIXEL').bitwiseAnd(parseInt('11111',
        2)).eq(0)
    saturationMask = image.select('QA_RADSAT').eq(0)

    # Apply the scaling factors to the appropriate bands.
    opticalBands = image.select('SR_B.').multiply(0.0000275).add(-
        0.2)
    thermalBands = image.select('ST_B.*').multiply(0.00341802) \
        .add(149.0)

    # Replace the original bands with the scaled ones and apply the masks.
    img = image.addBands(opticalBands, None, True) \
        .addBands(thermalBands, None, True) \
        .updateMask(qaMask) \
        .updateMask(saturationMask)
    imgScaled = image.addBands(img, None, True)

    # Now we start to add variables of interest.
    # Compute time in fractional years since the epoch.
    date = ee.Date(image.get('system:time_start'))
    years = date.difference(ee.Date('1970-01-01'), 'year')
    timeRadians = ee.Image(years.multiply(2 * math.pi))
    # Return the image with the added bands.
    return imgScaled \
        .addBands(imgScaled.normalizedDifference(['SR_B5', 'SR_B4']) \
            .rename('NDVI')) \
        .addBands(timeRadians.rename('t')) \
        .float() \
        .addBands(ee.Image.constant(1))


# Import region of interest. Area over California.
roi = ee.Geometry.Polygon([
    [-119.44617458417066,35.92639730653253],
    [-119.07675930096754,35.92639730653253],
    [-119.07675930096754,36.201704711823844],
    [-119.44617458417066,36.201704711823844],
    [-119.44617458417066,35.92639730653253]
])

# Import the USGS Landsat 8 Level 2, Collection 2, Tier 1 collection,
# filter, mask clouds, scale, and add variables.
landsat8sr = ee.ImageCollection('LANDSAT/LC08/C02/T1_L2') \
    .filterBounds(roi) \
    .filterDate('2013-01-01', '2018-01-01') \
    .map(maskScaleAndAddVariable)

# Set map center.
Map.centerObject(roi, 10)

# List of the independent variable names.
independents = ee.List(['constant', 't'])

# Name of the dependent variable.
dependent = ee.String('NDVI')

# Compute a linear trend.  This will have two bands: 'residuals' and
# a 2x1 band called coefficients (columns are for dependent variables).
trend = landsat8sr.select(independents.add(dependent)) \
    .reduce(ee.Reducer.linearRegression(independents.length(), 1))

# Flatten the coefficients into a 2-band image
coefficients = trend.select('coefficients') \
    .arrayProject([0]) \
    .arrayFlatten([independents])

# Compute a detrended series.

def func_mrd(image):
    return image.select(dependent) \
        .subtract(image.select(independents).multiply(
                coefficients) \
            .reduce('sum')) \
        .rename(dependent) \
        .copyProperties(image, ['system:time_start'])

detrended = landsat8sr.map(func_mrd)









# Function that creates a lagged collection.
def lag(leftCollection, rightCollection, lagDays):
    filter = ee.Filter.And(
        ee.Filter.maxDifference({
            'difference': 1000 * 60 * 60 * 24 * lagDays,
            'leftField': 'system:time_start',
            'rightField': 'system:time_start'
        }),
        ee.Filter.greaterThan({
            'leftField': 'system:time_start',
            'rightField': 'system:time_start'
        }))

    return ee.Join.saveAll({
        'matchesKey': 'images',
        'measureKey': 'delta_t',
        'ordering': 'system:time_start',
        'ascending': False, # Sort reverse chronologically
    }).apply({
        'primary': leftCollection,
        'secondary': rightCollection,
        'condition': filter
    })


# Create a lagged collection of the detrended imagery.
lagged17 = lag(detrended, detrended, 17)

# Function to stack bands.
def merge(image):
    # Function to be passed to iterate.
    def merger(current, previous):
        return ee.Image(previous).addBands(current)
    
    return ee.ImageCollection.fromImages(image.get('images')) \
        .iterate(merger, image)


# Apply merge function to the lagged collection.
merged17 = ee.ImageCollection(lagged17.map(merge))

# Function to compute covariance.
def covariance(mergedCollection, band, lagBand):
        image) {
        return image.toArray()
    }).reduce(ee.Reducer.covariance(), 8)


# Concatenate the suffix to the NDVI band.
lagBand = dependent.cat('_1')

# Compute covariance.
covariance17 = ee.Image(covariance(merged17, dependent, lagBand)) \
    .clip(roi)

# The output of the covariance reducer is an array image,
# in which each pixel stores a 2x2 variance-covariance array.
# The off diagonal elements are covariance, which you can map
# directly using:
Map.addLayer(covariance17.arrayGet([0, 1]),
    {
        'min': 0,
        'max': 0.02
    },
    'covariance (lag = 17 days)')

# Define the correlation function.
def correlation(vcArrayImage):
    covariance = ee.Image(vcArrayImage).arrayGet([0, 1])
    sd0 = ee.Image(vcArrayImage).arrayGet([0, 0]).sqrt()
    sd1 = ee.Image(vcArrayImage).arrayGet([1, 1]).sqrt()
    return covariance.divide(sd0).divide(sd1).rename(
        'correlation')


# Apply the correlation function.
correlation17 = correlation(covariance17).clip(roi)
Map.addLayer(correlation17,
    {
        'min': -1,
        'max': 1
    },
    'correlation (lag = 17 days)')

#  -----------------------------------------------------------------------
#  CHECKPOINT
#  -----------------------------------------------------------------------

# Add Earth Engine dataset image = ee.Image("USGS/SRTMGL1_003") # ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ # Chapter: F4.9 Exploring Lagged Effects in Time Series # Checkpoint: F49a # Authors: Andréa Puzzi Nicolau, Karen Dyson, David Saah, Nicholas Clinton # ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ # Define function to mask clouds, scale, and add variables # (NDVI, time and a constant) to Landsat 8 imagery. def maskScaleAndAddVariable(image): # Bit 0 - Fill # Bit 1 - Dilated Cloud # Bit 2 - Cirrus # Bit 3 - Cloud # Bit 4 - Cloud Shadow qaMask = image.select('QA_PIXEL').bitwiseAnd(parseInt('11111', 2)).eq(0) saturationMask = image.select('QA_RADSAT').eq(0) # Apply the scaling factors to the appropriate bands. opticalBands = image.select('SR_B.').multiply(0.0000275).add(- 0.2) thermalBands = image.select('ST_B.*').multiply(0.00341802) \ .add(149.0) # Replace the original bands with the scaled ones and apply the masks. img = image.addBands(opticalBands, None, True) \ .addBands(thermalBands, None, True) \ .updateMask(qaMask) \ .updateMask(saturationMask) imgScaled = image.addBands(img, None, True) # Now we start to add variables of interest. # Compute time in fractional years since the epoch. date = ee.Date(image.get('system:time_start')) years = date.difference(ee.Date('1970-01-01'), 'year') timeRadians = ee.Image(years.multiply(2 * math.pi)) # Return the image with the added bands. return imgScaled \ .addBands(imgScaled.normalizedDifference(['SR_B5', 'SR_B4']) \ .rename('NDVI')) \ .addBands(timeRadians.rename('t')) \ .float() \ .addBands(ee.Image.constant(1)) # Import region of interest. Area over California. roi = ee.Geometry.Polygon([ [-119.44617458417066,35.92639730653253], [-119.07675930096754,35.92639730653253], [-119.07675930096754,36.201704711823844], [-119.44617458417066,36.201704711823844], [-119.44617458417066,35.92639730653253] ]) # Import the USGS Landsat 8 Level 2, Collection 2, Tier 1 collection, # filter, mask clouds, scale, and add variables. landsat8sr = ee.ImageCollection('LANDSAT/LC08/C02/T1_L2') \ .filterBounds(roi) \ .filterDate('2013-01-01', '2018-01-01') \ .map(maskScaleAndAddVariable) # Set map center. Map.centerObject(roi, 10) # List of the independent variable names. independents = ee.List(['constant', 't']) # Name of the dependent variable. dependent = ee.String('NDVI') # Compute a linear trend. This will have two bands: 'residuals' and # a 2x1 band called coefficients (columns are for dependent variables). trend = landsat8sr.select(independents.add(dependent)) \ .reduce(ee.Reducer.linearRegression(independents.length(), 1)) # Flatten the coefficients into a 2-band image coefficients = trend.select('coefficients') \ .arrayProject([0]) \ .arrayFlatten([independents]) # Compute a detrended series. def func_mrd(image): return image.select(dependent) \ .subtract(image.select(independents).multiply( coefficients) \ .reduce('sum')) \ .rename(dependent) \ .copyProperties(image, ['system:time_start']) detrended = landsat8sr.map(func_mrd) # Function that creates a lagged collection. def lag(leftCollection, rightCollection, lagDays): filter = ee.Filter.And( ee.Filter.maxDifference({ 'difference': 1000 * 60 * 60 * 24 * lagDays, 'leftField': 'system:time_start', 'rightField': 'system:time_start' }), ee.Filter.greaterThan({ 'leftField': 'system:time_start', 'rightField': 'system:time_start' })) return ee.Join.saveAll({ 'matchesKey': 'images', 'measureKey': 'delta_t', 'ordering': 'system:time_start', 'ascending': False, # Sort reverse chronologically }).apply({ 'primary': leftCollection, 'secondary': rightCollection, 'condition': filter }) # Create a lagged collection of the detrended imagery. lagged17 = lag(detrended, detrended, 17) # Function to stack bands. def merge(image): # Function to be passed to iterate. def merger(current, previous): return ee.Image(previous).addBands(current) return ee.ImageCollection.fromImages(image.get('images')) \ .iterate(merger, image) # Apply merge function to the lagged collection. merged17 = ee.ImageCollection(lagged17.map(merge)) # Function to compute covariance. def covariance(mergedCollection, band, lagBand): image) { return image.toArray() }).reduce(ee.Reducer.covariance(), 8) # Concatenate the suffix to the NDVI band. lagBand = dependent.cat('_1') # Compute covariance. covariance17 = ee.Image(covariance(merged17, dependent, lagBand)) \ .clip(roi) # The output of the covariance reducer is an array image, # in which each pixel stores a 2x2 variance-covariance array. # The off diagonal elements are covariance, which you can map # directly using: Map.addLayer(covariance17.arrayGet([0, 1]), { 'min': 0, 'max': 0.02 }, 'covariance (lag = 17 days)') # Define the correlation function. def correlation(vcArrayImage): covariance = ee.Image(vcArrayImage).arrayGet([0, 1]) sd0 = ee.Image(vcArrayImage).arrayGet([0, 0]).sqrt() sd1 = ee.Image(vcArrayImage).arrayGet([1, 1]).sqrt() return covariance.divide(sd0).divide(sd1).rename( 'correlation') # Apply the correlation function. correlation17 = correlation(covariance17).clip(roi) Map.addLayer(correlation17, { 'min': -1, 'max': 1 }, 'correlation (lag = 17 days)') # ----------------------------------------------------------------------- # CHECKPOINT # -----------------------------------------------------------------------

Display the interactive map¶

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Map

Map