Landsat is the longest-running Earth-observation programme in history: a continuous series of NASA/USGS satellites imaging the world’s land since 1972. Its open archive — free to anyone since 2008 — is the reference record of how the planet’s surface has changed across five decades, underpinning deforestation accounting, urban-growth studies, water monitoring and climate research worldwide.
What the satellites deliver
The current pair, Landsat 8 and Landsat 9, carry the OLI imager and TIRS thermal sensor: eleven bands spanning visible, near-infrared, shortwave infrared and thermal wavelengths at 30 m multispectral resolution (15 m panchromatic, 100 m thermal), each satellite revisiting every location on a 16-day cycle — 8 days combined.
30 m pixels will not map single buildings, but they resolve fields, forests, reservoirs and urban districts — precisely the scale at which regional land change unfolds, with radiometric quality engineered for measurement rather than mere pictures.
The archive is the treasure
Landsat’s irreplaceable asset is temporal depth: for most of the world, it is the only consistent imagery of the 1970s–1990s. Retrospective baselines — forest cover before a concession, a floodplain before encroachment, a city before its boom — are recoverable only because the archive exists and is calibrated end to end.
The USGS curates the collection to analysis-ready standards, with surface-reflectance processing and quality masks, making decades of scenes directly stackable into time series.
Where Landsat fits today
In a world of daily smallsats and 30 cm tasking, Landsat remains the calibration anchor and the long-baseline instrument. Programmes pair it with Sentinel-2 (harmonised products exist precisely for this) to densify observations while preserving continuity backwards in time.
For any study whose question begins “how has this changed since…”, the Landsat archive is usually where the answer starts.