Landsat programme

From a proposal to a satellite

In 1966 Interior Secretary Stewart Udall announced the EROS programme, an Earth resources observation programme, and the USGS geologist William Pecora argued for a civil satellite to survey the land. The Earth Resources Technology Satellite, ERTS-1, was launched on 23 July 1972 from Vandenberg; it was renamed Landsat 1 in 1975 and decommissioned on 6 January 1978.

Landsat 1 carried a multispectral scanner that recorded four bands, two visible and two near-infrared, with a pixel of about 80 metres, over a swath of 185 kilometres. The same swath width and orbit design continue.

A continuous record

Landsat satellites have launched, with overlaps, ever since: Landsat 5 worked for nearly twenty-nine years, to 2013, and Landsat 8 launched in 2013, and Landsat 9 on 27 September 2021. Every satellite is calibrated against its predecessor, with overlapping observations, so that a field imaged in 1985 can be compared with one imaged in 2025. The archive covers more than fifty years at 30-metre resolution, which no other civil programme matches.

The record has documented the growth of cities, the retreat of glaciers, the clearing of forests and the drying of lakes.

Free and open

For decades, scenes were sold, at a price that rose to hundreds of dollars. On 21 April 2008 the USGS announced that Landsat data would be free and open to all. Downloads rose from some thousands of scenes a year to millions, and uses spread, from national forest monitoring to commercial agriculture. Landsat is run jointly by NASA, which builds and launches the satellites, and the USGS, which operates them and holds the archive.

Continuity as a policy

Landsat's history includes long periods in which the future of the programme was uncertain: satellites ran past their design lives, commercial operation was tried and abandoned, and Landsat 6 was lost at launch in 1993. The record remained continuous because individual satellites survived and because successive administrations supported the programme. The free and open data policy of 2008 was seen by many as a reward for that continuity. The archive's value rests on a consistent calibration across sensors, which the programme maintains with great care, and on the decision to keep every scene.

Instruments and technologies

• Multispectral scanner (Landsat 1) A scanning mirror and detectors recorded four bands of reflected light line by line as the satellite moved.
• Operational Land Imager (Landsat 8 and 9) A pushbroom sensor with nine bands from visible to shortwave infrared, with 30-metre pixels and 15-metre panchromatic.
• Thermal Infrared Sensor A sensor in two thermal bands measures land surface temperature.

The people

• William T. Pecora USGS geologist and director who championed the programme.
• Stewart Udall Interior Secretary who announced the EROS programme in 1966.

Timeline

• 1966 Interior Secretary Stewart Udall announces the EROS programme on 21 September.
• 1972 ERTS-1 launched on 23 July from Vandenberg.
• 1975 ERTS-1 renamed Landsat 1.
• 1978 Landsat 1 decommissioned on 6 January.
• 2008 USGS announces the free and open data policy on 21 April.
• 2021 Landsat 9 launched on 27 September.

Key lessons for observation today

• Continuity needs overlap Each new satellite flies alongside the old one for a time, so that sensors can be cross-calibrated. Overlap is how a record outlasts its instruments.
• Free and open data changes practice Opening the archive in 2008 increased use by orders of magnitude. The data policy is a design choice as important as the sensor.
• Keep the archive as long as the mission Fifty years of scenes are a resource only because they were kept. Archives need a steward and a format plan.

Sources

• NASA, Landsat 1
• USGS, Free and open Landsat data unleashed the power of remote sensing a decade ago
• NASA Science, William T. Pecora: pioneer of Earth science from space
• Congressional Research Service, Landsat 9 and the future of the Sustainable Land Imaging Program