Electromagnetic radiation emitted by all objects based on their temperature, detectable by satellite sensors in the 8-14 micrometer wavelength range. Thermal infrared imagery is essential for mapping land and water surface temperatures.
Thermal infrared (TIR) radiation occupies the 3-14 micrometer portion of the electromagnetic spectrum, with the 8-14 micrometer atmospheric window being most useful for remote sensing of Earth's surface. Unlike visible and near-infrared wavelengths that measure reflected sunlight, TIR sensors detect emitted radiation governed by the Stefan-Boltzmann law, enabling measurement of land surface temperature (LST) and water surface temperature. In hydrology, TIR data are fundamental for energy balance-based evapotranspiration models (SEBAL, METRIC, ALEXI) that rely on LST to partition available energy between sensible and latent heat fluxes. TIR imagery can identify groundwater discharge zones in rivers and coastal areas, as groundwater typically maintains a more constant temperature than surface water. Thermal pollution from power plants and industrial facilities is routinely monitored using TIR satellite data. Landsat's TIRS instrument provides 100 m resolution thermal data, while MODIS and VIIRS provide daily global LST products at 1 km resolution. The diurnal temperature cycle captured by geostationary satellites (GOES) reveals soil moisture patterns, as wet soils have higher thermal inertia and smaller day-night temperature differences than dry soils.