Landsat

Landsat is the longest-running Earth observation satellite program in history, jointly managed by NASA and the U.S. Geological Survey (USGS). Since the launch of Landsat 1 on July 23, 1972 — originally named the Earth Resources Technology Satellite — the program has provided an unbroken record of multispectral imagery spanning over five decades. Nine missions have been launched (Landsat 1 through 9), eight of which achieved orbit successfully (Landsat 6 failed to reach orbit in 1993). Today, Landsat 8 and Landsat 9 operate in tandem, together imaging the entire Earth every 8 days.

Each Landsat satellite orbits Earth in a sun-synchronous, near-polar orbit at approximately 705 km altitude. A single satellite revisits the same ground location every 16 days, capturing scenes across a 185 km swath. Early missions (Landsat 1–3) carried the Multispectral Scanner System (MSS) with four spectral bands at 80 m resolution. Landsat 4 and 5 introduced the Thematic Mapper (TM), offering seven bands at 30 m resolution. The current generation — Landsat 8 (launched 2013) and Landsat 9 (launched 2021) — use the Operational Land Imager (OLI/OLI-2) and Thermal Infrared Sensor (TIRS/TIRS-2), delivering 11 spectral bands: 30 m multispectral, 15 m panchromatic, and 100 m thermal infrared.

Landsat's 30 m spatial resolution is too coarse for applications requiring sub-meter detail such as building footprint extraction. The 16-day revisit cycle per satellite can be limiting for rapidly changing phenomena, and persistent cloud cover in tropical regions often reduces usable scenes significantly. Thermal bands are collected at 100 m resolution and resampled to 30 m, limiting surface temperature precision. The program has no SAR capability, so it cannot image through clouds or at night. Historical data from earlier missions has lower spectral and radiometric resolution, which can complicate multi-decadal time series analysis without careful cross-sensor calibration.

The Landsat program originated from a proposal in the 1960s to monitor Earth's resources from space. Landsat 1 launched on July 23, 1972, carrying the experimental Multispectral Scanner System (MSS). A major leap came with Landsat 4 in 1982, which introduced the Thematic Mapper (TM) sensor with 30 m resolution and seven spectral bands. Landsat 5, launched in 1984, became the longest-operating satellite in the program, transmitting data until 2013. Landsat 7 (1999) introduced the ETM+ sensor with a 15 m panchromatic band, though its Scan Line Corrector failed in 2003. Landsat 8, launched in 2013, brought the OLI and TIRS sensors with improved 12-bit radiometric resolution. Landsat 9, launched on September 27, 2021, is the newest satellite in the constellation. Planning is underway for the Landsat Next mission.