The longest-running satellite program for Earth observation, providing continuous multispectral imagery since 1972. Landsat data are fundamental to water resource monitoring, land use change detection, and environmental assessment.
Landsat is a series of Earth-observing satellites jointly managed by NASA and the USGS, beginning with Landsat 1 in 1972 and continuing with Landsat 9 launched in 2021. The program provides moderate-resolution (30 m visible/near-infrared, 100 m thermal) multispectral imagery with a 16-day revisit cycle per satellite (8 days when two satellites operate simultaneously). Landsat data are critical for water resource applications including surface water extent mapping, water quality assessment using turbidity and chlorophyll algorithms, wetland monitoring, irrigated area mapping, and snow cover analysis. The free and open data policy adopted in 2008 revolutionized Earth observation science, making the entire 50+ year archive available at no cost. Key spectral bands for hydrology include the shortwave infrared (SWIR) bands used in NDWI calculations and the thermal infrared bands used for evapotranspiration estimation. Landsat Collection 2 provides analysis-ready surface reflectance and surface temperature products with improved radiometric and geometric calibration. The Landsat archive is the backbone of long-term environmental change analysis, enabling researchers to track water body dynamics, deforestation, urbanization, and glacier retreat over five decades.