Chapter 12: Cloud Masking¶
This chapter provides a workflow to iterate through an image collection and calculate the cumulative NDVI difference for imagery in Rocky Mountain National Park, Colorado, United States. The full GEE code can be found here.
Functions¶
/**
* Mask Landsat 8 image with cloud and shadow masks
* @param {ee.image} image - Landsat 8 image
* @return {ee.Image} - Masked Landsat 8 image
*
* Function adapted from:
* https://developers.google.com/earth-engine/datasets/catalog/LANDSAT_LC08_C01_T1_SR
*/
var mask_clouds_landsat8 = function(image) {
// Bits 3 and 5 are cloud shadow and cloud, respectively
var cloudShadowBitMask = (1 << 3); // 1000 in base 2
var cloudsBitMask = (1 << 5); // 100000 in base 2
// Get the pixel QA band
var qa = image.select('pixel_qa');
// Both flags should be set to zero, indicating clear conditions
var mask = qa
.bitwiseAnd(cloudShadowBitMask).eq(0)
.and(qa.bitwiseAnd(cloudsBitMask).eq(0));
// Mask image with clouds and shadows
return image.updateMask(mask);
};
/**
* Clip image to RMNP boundary
* @param {ee.image} image - Image
* @return {ee.Image} - Clipped image
*/
var clip_rmnp = function(image) {
return image.clip(rmnp_boundary);
};
Data Acquisition & Preprocessing¶
// Load RMNP boundary from GEE Assets
var rmnp_boundary = ee.FeatureCollection("users/calekochenour/Rocky_Mountain_National_Park__Boundary_Polygon");
// Get mean of unmasked images for summer 2013-2020
var rmnp_unmasked_mean = ee.ImageCollection('LANDSAT/LC08/C01/T1_SR')
.filter(ee.Filter.calendarRange(2013, 2020, 'year'))
.filter(ee.Filter.calendarRange(6, 9, 'month'))
.filterBounds(rmnp_boundary)
.map(clip_rmnp)
.mean();
// Get mean of masked images for summer 2013-2020
var rmnp_masked_mean = ee.ImageCollection('LANDSAT/LC08/C01/T1_SR')
.filter(ee.Filter.calendarRange(2013, 2020, 'year'))
.filter(ee.Filter.calendarRange(6, 9, 'month'))
.filterBounds(rmnp_boundary)
.map(clip_rmnp)
.map(mask_clouds_landsat8)
.mean();
Data Processing¶
// No data processing in this lab.
Data Postprocessing¶
// No data postprocessing in this lab.
Data Visualization¶
// Define Landsat 8 RGB visualization parameters
var l8_vis_params_rgb = {
'bands': ['B4', 'B3', 'B2'],
'min': 0,
'max': 3000
};
// Define Landsat 8 CIR visualization parameters
var l8_vis_params_cir = {
'bands': ['B5', 'B4', 'B3'],
'min': 0,
'max': 3000
};
// Center map to Rocky Mountain National Park, Colorado
Map.setCenter(-105.6836, 40.3428, 10);
// Add unmasked and masked composites
Map.addLayer(
rmnp_unmasked_mean,
l8_vis_params_rgb,
'Landsat 8 - RGB - RMNP Unmasked Mean Composite');
Map.addLayer(
rmnp_masked_mean,
l8_vis_params_rgb,
'Landsat 8 - RGB - RMNP Masked Mean Composite');
Map.addLayer(
rmnp_unmasked_mean,
l8_vis_params_cir,
'Landsat 8 - CIR - RMNP Unmasked Mean Composite');
Map.addLayer(
rmnp_masked_mean,
l8_vis_params_cir,
'Landsat 8 - CIR - RMNP Masked Mean Composite');
Data Export¶
// No data export in this lab.