Google Earth Engine Tutorial: Create Historical Timelapse Images

Google Earth Engine Tutorial: Create Historical Timelapse Images

Introduction

Google Earth Engine (GEE) is a powerful cloud-based platform that allows researchers and developers to analyze and visualize large-scale geospatial datasets. One of its most impressive capabilities is creating historical timelapse images that show how landscapes have changed over time. This tutorial will guide you through the process of creating stunning timelapse animations using satellite imagery available in Google Earth Engine.

Prerequisites

• A Google Earth Engine account (sign up at earthengine.google.com)
• Basic knowledge of JavaScript (GEE’s scripting language)
• Familiarity with GEE Code Editor

Getting Started

First, navigate to the Google Earth Engine Code Editor at code.earthengine.google.com. This is where we’ll write our script to create timelapse images.

Step-by-Step Tutorial

1. Define Your Area of Interest

// Define a point of interest
var point = ee.Geometry.Point([-122.0841, 37.4219]); // Stanford University coordinates
var areaOfInterest = point.buffer(5000); // Buffer by 5km radius

// Alternative: Define a polygon
var polygon = ee.Geometry.Polygon(
  [[[-122.5, 37.8], [-122.5, 37.6], [-122.3, 37.6], [-122.3, 37.8]]]);

2. Select Satellite Imagery Dataset

For timelapse creation, we typically use Landsat imagery due to its long temporal coverage and consistent quality:

// Load Landsat 8 collection
var collection = ee.ImageCollection('LANDSAT/LC08/C02/T1_L2')
  .filterBounds(areaOfInterest)
  .filterDate('2013-01-01', '2023-12-31')
  .filter(ee.Filter.lt('CLOUD_COVER', 20));

3. Create Visualization Parameters

// Define visualization parameters for RGB composite
var visParams = {
  bands: ['SR_B4', 'SR_B3', 'SR_B2'], // NIR, Red, Green
  min: 0,
  max: 0.3,
  gamma: [1.3, 1.3, 1.3]
};

4. Generate Timelapse Function

// Function to create timelapse frames
var createTimelapse = function(collection, visParams, region, frames) {
  var videoArgs = {
    dimensions: 768,
    region: region,
    framesPerSecond: frames,
    crs: 'EPSG:3857',
    min: visParams.min,
    max: visParams.max,
    bands: visParams.bands
  };
  
  return collection.getVideoThumbURL(videoArgs);
};

// Generate timelapse URL
var timelapseURL = createTimelapse(collection, visParams, areaOfInterest, 10);
print('Timelapse URL:', timelapseURL);

5. Alternative: Create Yearly Composites

For cleaner images, you might want to create yearly composites:

// Function to create yearly median composite
var createYearlyComposite = function(year) {
  var startDate = ee.Date.fromYMD(year, 1, 1);
  var endDate = startDate.advance(1, 'year');
  
  return ee.ImageCollection('LANDSAT/LC08/C02/T1_L2')
    .filterBounds(areaOfInterest)
    .filterDate(startDate, endDate)
    .filter(ee.Filter.lt('CLOUD_COVER', 20))
    .median()
    .set('system:time_start', startDate.millis())
    .set('year', year);
};

// Create image collection for multiple years
var years = ee.List.sequence(2013, 2023);
var yearlyComposites = ee.ImageCollection(years.map(createYearlyComposite));

6. Display Results

// Add results to the map
Map.centerObject(areaOfInterest, 10);
Map.addLayer(yearlyComposites.first(), visParams, 'Yearly Composite');

Advanced Techniques

Cloud Masking

// Function to mask clouds in Landsat 8 imagery
var maskClouds = function(image) {
  var qa = image.select('QA_PIXEL');
  var cloudMask = qa.bitwiseAnd(parseInt('11111', 2)).eq(0);
  return image.updateMask(cloudMask);
};

// Apply cloud masking to collection
var cloudFreeCollection = collection.map(maskClouds);

NDVI Timelapse

Create vegetation change timelapse using NDVI:

// Function to calculate NDVI
var calculateNDVI = function(image) {
  return image.normalizedDifference(['SR_B5', 'SR_B4']).rename('NDVI');
};

// Apply to collection
var ndviCollection = collection.map(calculateNDVI);

// NDVI visualization parameters
var ndviVis = {min: -1, max: 1, palette: ['blue', 'white', 'green']};

Exporting Timelapse

To export your timelapse video:

1. Run your script to generate the video URL
2. Click the “Run” button in the Code Editor
3. Wait for the URL to appear in the Console
4. Click the URL to open the video in a new tab
5. Right-click and save the video to your computer

Performance Tips

• Keep your area of interest small for faster processing
• Limit the time range to reduce processing time
• Use cloud-free filters to ensure consistent image quality
• Test with lower resolution first before exporting high-quality videos

Conclusion

Creating historical timelapse images with Google Earth Engine opens up new possibilities for visualizing landscape changes over time. Whether you’re studying urban development, deforestation, agricultural changes, or natural disasters, timelapse animations provide a compelling way to communicate temporal changes in land cover and use.

Remember to experiment with different visualization parameters, time ranges, and processing techniques to achieve the best results for your specific application. The key to successful timelapse creation lies in balancing data quality, processing efficiency, and visual appeal.