Introduction to Google Earth Engine

Introduction:

Google Earth Engine is a cloud-based platform for planetary-scale environmental data analysis. It combines a multi-petabyte catalog of satellite imagery and geospatial datasets with computational capabilities to analyze and extract insights. In this blog, we will explore how to use Google Earth Engine, access its data, what types of analysis are possible, and how to produce composite images and measure deforestation.

Part I: Getting Started with Google Earth Engine

1.1: Setting Up

To begin, you will need to sign up for a Google Earth Engine account. Once approved, you can access the Code Editor at https://code.earthengine.google.com/.

1.2: Navigating the Interface

The Google Earth Engine Code Editor is divided into several panels:

Part II: Accessing Data

2.1: Image and ImageCollection

In Google Earth Engine, raster data are represented as Image objects. A collection of images is an ImageCollection. You can access satellite imagery and other raster datasets from the Earth Engine Data Catalog.

2.2: Example - Accessing Landsat Imagery

var image = ee.Image('LANDSAT/LC08/C01/T1_TOA/LC08_044034_20140318');
Map.addLayer(image, {bands: ['B4', 'B3', 'B2'], max: 0.3}, 'true color image');

Part III: Types of Analysis

3.1: Basic Operations

You can perform arithmetic operations on images, compute spectral indices, and extract statistics.

3.2: Example - NDVI Calculation

var ndvi = image.normalizedDifference(['B5', 'B4']);
Map.addLayer(ndvi, {min: 0, max: 1, palette: ['white', 'green']}, 'NDVI');

Part IV: Creating Composite Images

Creating a composite image involves combining several images into one. In the context of Google Earth Engine, you can create a composite image from an ImageCollection.

4.1: Example - Median Composite

var collection = ee.ImageCollection('LANDSAT/LC08/C01/T1_TOA')
    .filterDate('2019-01-01', '2019-12-31');

var composite = collection.median();

Map.addLayer(composite, {bands: ['B4', 'B3', 'B2'], max: 0.3}, 'composite image');

Part V: Measuring Deforestation with Google Earth Engine

Google Earth Engine can be used to monitor and measure deforestation. You can compute the difference between two images or track changes over time.

5.1: Example - Difference in NDVI

var image1 = ee.Image('LANDSAT/LC08/C01/T1_TOA/LC08_044034_20140101');
var image2 = ee.Image('LANDSAT/LC08/C01/T1_TOA/LC08_044034_20141231');

var ndvi1 = image1.normalizedDifference(['B5', 'B4']);
var ndvi2 = image2.normalizedDifference(['B5', 'B4']);

var difference = ndvi2.subtract(ndvi1);
Map.addLayer(difference, {min: -1, max: 1, palette: ['blue', 'white', 'green

']}, 'NDVI difference');

Conclusion:

Google Earth Engine is a powerful platform for large-scale geospatial data analysis. It provides an accessible interface for both accessing vast amounts of data and applying complex analyses to generate meaningful insights. As we’ve seen in the blog, it can be used to monitor and measure environmental phenomena such as deforestation. While we’ve only scratched the surface, I encourage you to explore the platform further, as the range of applications is vast.