Quality assessment

Quality Assurance (QA) is a crucial aspect of working with Earth Observation data. This guide explains how to find and interpret quality assessment information in the Resource Catalogue, including both documentation quality and product validation metrics.

Not all collections have QA information available. To find collections that do:

1. Go to the Catalogue homepage
2. Look for the "Quality Assessment" dropdown in the top-right filters
3. Select "Available QA" to see collections with QA data

To view QA information for a collection:

1. Open the collection
2. Click the information (i) button in the top-right
3. Navigate to the QA tabs

The "Document QA" tab provides an assessment of the documentation quality for the collection. This assessment:

• Is provided by the National Physics Laboratory (NPL)
• Uses a standard developed by European Space Agency (ESA)
• Rates documentation quality from "Ideal" to "Basic" or "Not Accessible"

Documentation Quality Levels

The documentation quality level categories are defined below for reference.

Ideal. Comprehensive, well-structured documentation

Excellent. Very good documentation with minor limitations

Basic. Minimal but sufficient documentation

Not Accessible. Documentation exists but is not accessible

Not Assessed. Documentation has not been evaluated

Accessing Documentation

At the bottom of the Document QA page, you'll find:

• Hyperlinks to all referenced documents
• Direct access to specific documentation (e.g., geometric processing)
• Links to related technical specifications

The "Product Validation" tab provides metrics about the actual data quality. Currently, this focuses on:

Radiometric Uncertainty

• Assessment of radiometric accuracy
• Based on surveys and ground truth comparisons
• Shows accuracy criteria for each band (e.g., ±5%)

Validation Metrics

For each band and time period:

• Accuracy criteria
• Compliance status (Pass/Fail)
• Overall collection assessment

Understanding the Results

Pass. Collection meets all quality metrics

Fail. Collection does not meet quality metrics

Partial Pass. Some metrics pass while others fail

When using QA information, it is useful to consider the following factors when interpreting the results of the assessment. You should:

1. Check both documentation and product validation
2. Consider the time period of validation
3. Note any partial passes or specific band limitations
4. Review the underlying documentation for detailed information

The QA system is evolving. Currently, the scope of the QA assessment on the Hub focuses on quantifying radiometric uncertainty. Additional QA metrics will be added in the future, and new validation methods may be introduced.

1. Always check QA information before using data
2. Consider both documentation and product validation
3. Review the specific time periods covered by validation
4. Consult the linked documentation for detailed information
5. Be aware of any partial passes or limitations