On July 23, 1972, the first Landsat spacecraft was launched. At the time it was known as the Earth Resources Technology Satellite and it was the first satellite launched to study the earth’s landmasses. In 1975, the name was changed to Landsat. Since then, this program has been continuously monitoring changes in the earth and its archive represents the longest and continuous space-based record of changes on the Earth’s surface. The Landsat program is managed jointly by NASA and the U.S. Department of the Interior through the U.S. Geological Survey (USGS).
The USGS and NASA explain:
Previous satellites relied on film cameras (ejecting the exposed film to be caught by planes) or transmitted the signal from television cameras. The scanning sensor and its successor sensors on subsequent Landsat satellites revolutionized how we study our home planet.
Throughout the decades, Landsat satellites have given us a detailed view of the changes to Earth’s land surface. By collecting data in multiple wavelength regions, including thermal infrared wavelengths, the Landsat fleet has allowed us to study natural disasters, urban change, water quality and water usage, agriculture development, glaciers and ice sheets, and forest health.
To date, there have been eight Landsat satellites launched of which only Landsat 6 failed to reach orbit. Landsat 5 (March 1, 1984 – June 5, 2013) was the longest running earth-observing satellite mission in history with a record 29 years, 3 months and 4 days in orbit. The latest Landsat satellite is Landsat 8 which was launched February 11, 2013 and, along with Landsat 7 (launched April 15, 1999), are the two currently active satellites in the program.
All archived Landsata data from 1972 to the present is available for free from the USGS’s EarthExplorer mapping interface.
A montage of Landsat’s contributions is shown in the video below: