Category: Processing and quality
Quality Mask (QA)
A quality mask is a layer that flags pixels with issues such as clouds, shadows, saturation, or low confidence.
Also known as: QA band, quality layer
Expanded definition
Quality masks describe whether a pixel is reliable and why it might not be. They often include flags for clouds, cirrus, cloud shadow, snow, saturated pixels, and algorithm confidence.
QA masks are not optional. If you ignore them, you can get false change signals and unstable statistics.
If a product includes both a cloud mask and a QA mask, the QA mask usually covers a broader set of problems than clouds alone.
Related terms
Cloud Mask
A cloud mask labels pixels likely affected by clouds so they can be excluded or handled differently.
Cloud Shadow
Cloud shadow is the darkening of the surface caused by clouds blocking sunlight, often mistaken for real change.
NoData
NoData is a special value that means a pixel has no valid measurement, for example due to clouds or missing coverage.