Introduction to Google Earth Engine (GEE)
**Google Earth Engine (GEE)** is a free, cloud-based platform that gives you access to petabytes of satellite imagery and geospatial datasets, along with the computing power to analyze them — all through your web browser, without downloading massive files. ---
📋 Prerequisites
- Registered Google Earth Engine account.
- Access to GEE Code Editor (code.earthengine.google.com).
Step-by-Step Instructions
Why Use Earth Engine?
- **No downloads needed** — data and processing both happen in the cloud - **Massive free archive** — Landsat, Sentinel, MODIS, climate data, and more, all pre-organized - **Powerful processing** — analyze years of data across entire countries in seconds - **JavaScript and Python APIs** — flexible for beginners and advanced coders ---
Sign Up for Earth Engine
1. Go to **earthengine.google.com** 2. Click **Sign Up** and register with a Google account (approval may take a short time for new accounts) 3. Once approved, open the **Code Editor** at code.earthengine.google.com ---
Explore the Code Editor Interface
- **Script Panel (left):** Write your JavaScript code - **Map Panel (bottom):** Displays your results interactively - **Console (right):** Shows printed output and errors - **Docs & Assets tabs:** Browse the data catalog and your saved files ---
Write Your First Script
Click **Run** — your satellite image appears on the map panel. ---
// Load a Sentinel-2 image
var image = ee.ImageCollection('COPERNICUS/S2_SR')
.filterDate('2024-01-01', '2024-03-01')
.filterBounds(ee.Geometry.Point([77.5946, 12.9716])) // example: Bangalore
.median();
// Display it on the map
Map.centerObject(image, 10);
Map.addLayer(image, {bands: ['B4','B3','B2'], min: 0, max: 3000}, 'True Color');Calculate NDVI in Earth Engine
This single script does what would normally require downloading and processing large files locally. ---
var ndvi = image.normalizedDifference(['B8', 'B4']).rename('NDVI');
Map.addLayer(ndvi, {min: -1, max: 1, palette: ['red','yellow','green']}, 'NDVI');Export Results
To save your output for use in QGIS or elsewhere: Go to the **Tasks** tab and click **Run** to start the export — the file will appear in your Google Drive. ---
Export.image.toDrive({
image: ndvi,
description: 'NDVI_Export',
scale: 10,
region: image.geometry(),
folder: 'GEE_Exports'
});Explore the Data Catalog
1. Click the **Docs** tab in the Code Editor 2. Search for datasets by name (e.g., "Landsat", "Sentinel", "SRTM", "population") 3. Each entry gives you the exact code snippet to load that dataset ---
🧠 Quick Recap & Practice Questions
## Quick Recap
- GEE = free cloud-based platform for satellite data + processing
- Sign up, then use the Code Editor to write JavaScript analysis scripts
- Common tasks: load imagery, calculate indices (like NDVI), export results
- The Data Catalog lets you discover and load hundreds of free datasets
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## Practice Questions
1. What is the main advantage of Earth Engine over downloading data manually?
2. What does `filterDate()` do in a GEE script?
3. Where would you find the code snippet to load a specific dataset?
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*Next Tutorial: SAR (Synthetic Aperture Radar) Basics & Applications*