# Authoritative sources

- Last verified: 2026-07-19
- Review cadence: every 6 months
- Refresh triggers: sensor collection reprocessing, validation protocol revision, or product retirement

## Canonical sources

- [USGS Landsat Collection 2](https://www.usgs.gov/landsat-missions/landsat-collection-2) — processing levels, calibration, quality, and collection lifecycle.
- [CEOS Land Product Validation](https://lpvs.gsfc.nasa.gov/) — validation framework and protocols for land products.
- [Copernicus Sentinel-2 mission documentation](https://documentation.dataspace.copernicus.eu/Data/SentinelMissions/Sentinel2.html) — product and sensor semantics.

Record the exact collection, processing level, acquisition time, mask, and validation protocol used. Never substitute a current landing page for a versioned product identifier in deliverables.