Google Earth Engine Tutorial: Beginners Guide 4 View Image Metadata

Google Earth Engine Tutorial: Beginners Guide 4 – View Image Metadata

Understanding image metadata is crucial for effective remote sensing analysis in Google Earth Engine. Metadata provides essential information about satellite imagery including acquisition dates, cloud cover, sensor specifications, and processing details. This tutorial will guide you through accessing and interpreting image metadata.

What is Image Metadata?

Image metadata contains comprehensive information about satellite imagery stored in Google Earth Engine. This includes technical specifications, acquisition parameters, quality indicators, and processing history. Accessing metadata helps you make informed decisions about data selection and analysis.

Basic Metadata Access Methods

Method 1: Using getInfo() Function

// Load a Landsat 8 image
var image = ee.Image('LANDSAT/LC08/C02/T1_L2/LC08_044034_20140318');

// Get all metadata
print('All metadata:', image.getInfo());

// Get specific metadata properties
print('Image ID:', image.get('system:id'));
print('Acquisition Date:', image.get('DATE_ACQUIRED'));
print('Cloud Cover:', image.get('CLOUD_COVER'));

Method 2: Using get() and getProperty()

// Access specific properties
var cloudCover = image.get('CLOUD_COVER');
var acquisitionDate = image.get('DATE_ACQUIRED');
var spacecraft = image.get('SPACECRAFT_ID');

print('Cloud Cover:', cloudCover);
print('Acquisition Date:', acquisitionDate);
print('Spacecraft:', spacecraft);

Method 3: Using propertyNames()

// Get all available property names
var propertyNames = image.propertyNames();
print('All Property Names:', propertyNames);

// Sort property names alphabetically
var sortedNames = propertyNames.sort();
print('Sorted Property Names:', sortedNames);

Working with Image Collections Metadata

// Load a collection
var collection = ee.ImageCollection('LANDSAT/LC08/C02/T1_L2')
    .filterDate('2020-01-01', '2020-12-31')
    .filterBounds.geometry();

// Print collection information
print('Collection Size:', collection.size());
print('Collection Metadata:', collection.getInfo());

// Get metadata for first image
var firstImage = ee.Image(collection.first());
print('First Image Metadata:', firstImage.getInfo());

Advanced Metadata Extraction

Extracting Band Information

// Get band names and information
var bandNames = image.bandNames();
print('Band Names:', bandNames);

// Get specific band metadata
var bandInfo = image.select('SR_B4').getInfo();
print('Band 4 Information:', bandInfo);

System Properties vs Regular Properties

// System properties (start with 'system:')
print('System Time Start:', image.get('system:time_start'));
print('System Time End:', image.get('system:time_end'));

// Regular properties
print('Sensor ID:', image.get('SENSOR_ID'));
print('WRS Path:', image.get('WRS_PATH'));

Practical Examples

Filter Images by Metadata

// Filter collection by cloud cover
var lowCloudCollection = ee.ImageCollection('LANDSAT/LC08/C02/T1_L2')
    .filterDate('2020-01-01', '2020-12-31')
    .filterMetadata('CLOUD_COVER', 'less_than', 20);

print('Low Cloud Images:', lowCloudCollection.size());

Create Metadata Summary Table

// Function to extract metadata
var extractMetadata = function(image) {
    return ee.Feature(null, {
        'image_id': image.get('system:id'),
        'date': image.get('DATE_ACQUIRED'),
        'cloud_cover': image.get('CLOUD_COVER'),
        'spacecraft': image.get('SPACECRAFT_ID')
    });
};

// Apply to collection
var metadataTable = collection.map(extractMetadata);
print('Metadata Table:', metadataTable);

Best Practices for Metadata Usage

• Always check cloud cover percentage before analysis
• Verify acquisition dates for temporal studies
• Use system timestamps for time-series analysis
• Filter collections based on quality indicators
• Document metadata parameters in your analysis

Common Metadata Properties