A weather satellite is an artificial satellite equipped with sensors designed to observe Earth's atmosphere, clouds, land and oceans for meteorological and environmental purposes. Its observations are transmitted to ground stations where they are processed into information used for weather forecasting, storm monitoring, climate research and environmental analysis. Weather satellites are broadly divided into geostationary satellites and polar-orbiting or other low-altitude Earth-observation satellites.
Geostationary satellites remain over approximately the same longitude and continuously observe a large region, making them particularly valuable for tracking rapidly developing weather systems. Polar-orbiting satellites travel around Earth in lower orbits and progressively observe different parts of the planet, providing detailed measurements and broad global coverage. Modern meteorological satellite systems combine visible-light imagery, infrared measurements, microwave observations, atmospheric sounding and other instruments to create a multidimensional picture of Earth's atmosphere and surface.
Weather satellites perform remote sensing, meaning they measure physical properties from space without physically contacting the atmosphere or surface being studied. Optical instruments can detect reflected sunlight and therefore provide detailed information during daylight, while infrared instruments can measure thermal radiation and continue observing at night. Different infrared wavelengths reveal information about cloud-top temperature, atmospheric moisture and other properties.
Microwave instruments can often observe through some cloud layers and provide measurements associated with temperature, moisture, precipitation, sea ice and ocean conditions. Atmospheric sounders use multiple spectral channels to infer vertical profiles of temperature and humidity. The instruments do not simply produce ordinary photographs; many satellite products are quantitative measurements derived from electromagnetic radiation and sophisticated calibration and retrieval algorithms.
Geostationary weather satellites operate at approximately 35,786 kilometres above Earth's equator, where their orbital period matches Earth's sidereal rotation period. Because they orbit in the same direction and at the appropriate altitude, they appear nearly stationary relative to a fixed point on Earth's surface. This makes them particularly useful for frequent imaging of a specific continent, ocean basin or weather region.
Their major strength is temporal coverage: a sequence of images can show clouds developing, fronts moving, thunderstorms intensifying and tropical cyclones changing structure. Their major limitation is spatial coverage and viewing geometry. From such a great distance, individual features may be harder to resolve than from lower orbits, and areas near the edges of the visible disc can be viewed obliquely. Polar-orbiting satellites provide complementary high-resolution and global observations.
Polar-orbiting meteorological satellites typically operate in low Earth orbit and pass over or near the polar regions on successive orbits. Because Earth rotates underneath the orbital track, the satellite can build up extensive global coverage. Many meteorological polar satellites are placed in sun-synchronous orbits, allowing observations to occur at similar local solar times on successive passes, which improves consistency for some types of measurement.
Instruments on these satellites can provide detailed atmospheric profiles, sea-surface information, snow and ice observations, precipitation measurements and other environmental data. Some satellites use active instruments, such as radar or lidar, which transmit energy and measure its return, while many others use passive sensors that detect naturally emitted or reflected radiation. Combining measurements from different instruments allows meteorologists to estimate properties that cannot be obtained reliably from a single spectral band.
Weather satellites are essential inputs to numerical weather prediction. Numerical weather prediction models divide the atmosphere into a computational representation and use physical equations together with observations to estimate its current state and future evolution. Satellite observations are particularly valuable over oceans and remote areas where conventional weather stations, radiosondes, aircraft observations and surface networks are sparse. Before being used operationally, observations undergo calibration, quality control, processing and data assimilation.
Assimilation systems combine satellite measurements with other observations and a previous model estimate to construct an improved representation of atmospheric conditions. Satellite data can therefore affect forecasts even when a satellite image is not directly visible to the public. Modern forecasting depends on a complex observing system in which satellites provide a large and strategically important portion of the available measurements.
Weather satellites are also important for severe-weather warnings and disaster management. Meteorological agencies can use rapid sequences of geostationary imagery to identify convective development, monitor tropical cyclones and observe large-scale cloud systems. Infrared imagery can help estimate cloud-top temperatures, with very cold cloud tops often associated with strong vertical development, although such measurements require careful interpretation and do not directly measure surface rainfall or storm intensity.
Microwave observations from low-orbit satellites can provide information about precipitation structure and atmospheric water content. Satellite observations also support monitoring of volcanic ash, wildfire smoke, dust, flooding, sea ice and snow cover. These applications demonstrate that modern meteorological satellites are environmental monitoring platforms as well as traditional weather-observation systems.
A weather satellite does not itself produce a complete weather forecast. It provides observations that must be interpreted, calibrated and combined with physical models and other observations. A colourful satellite image is therefore not necessarily a direct representation of what a human observer would see. Different colours in processed imagery often represent temperature ranges, moisture characteristics, spectral differences or other derived quantities. Another common misconception is that every weather satellite can observe every weather phenomenon equally well.
Sensor wavelength, orbital altitude, viewing angle, spatial resolution, temporal resolution and atmospheric absorption all influence what can be measured. A geostationary satellite may provide imagery every few minutes over a region but with lower spatial detail than a low-orbit sensor, while a polar-orbiting instrument may provide high-quality global measurements but only observe a particular location during individual passes.
The historical development of weather satellites transformed meteorology by providing routine observations from above the atmosphere. Early meteorological satellites demonstrated that cloud imagery could reveal enormous weather structures that were difficult or impossible to observe comprehensively from the ground. Subsequent generations added increasingly sophisticated infrared, microwave and atmospheric-sounding instruments, higher-resolution imaging, faster data delivery and improved calibration. Current systems form part of international observing networks in which different countries and organisations operate complementary spacecraft and exchange meteorological data.
Their long-term measurements also contribute to climate science by documenting changes in clouds, atmospheric composition, sea ice, snow and other environmental variables. Weather satellites therefore serve both operational forecasting, where rapid information is crucial, and scientific observation, where consistent measurements over decades can help researchers understand Earth's changing climate system.
