Two orbits, two purposes
Weather satellites operate in two fundamentally different orbits, each optimized for different observation needs. Geostationary satellites orbit at 35,786 km altitude, where their orbital period matches Earth's rotation — they appear stationary above a fixed point on the equator. Polar-orbiting satellites circle the Earth at 700–850 km altitude, passing over both poles and seeing different strips of the Earth on each orbit.
Geostationary satellites provide continuous, high-frequency imagery of the same hemisphere — ideal for tracking storm development, convective weather, and rapidly evolving events. Polar orbiters provide higher spatial resolution and global coverage over time — ideal for measuring atmospheric temperature and moisture profiles, sea surface temperature, and land surface properties.
GOES: America's weather eyes
The Geostationary Operational Environmental Satellite (GOES) system, operated by NOAA, consists of two operational satellites: GOES-East (positioned at 75.2°W) and GOES-West (positioned at 137.2°W). Together, they provide continuous coverage of the Western Hemisphere from the central Pacific to the west coast of Africa.
The current generation, GOES-R series (GOES-16 and GOES-18), carries the Advanced Baseline Imager (ABI) — a 16-channel radiometer that produces full-disk images every 10 minutes, continental US images every 5 minutes, and mesoscale images every 30–60 seconds. This temporal frequency is revolutionary for tracking thunderstorm development, tornado-producing supercells, wildfire detection, and volcanic ash plumes.
- ABI: 16 spectral bands from visible through longwave infrared
- Resolution: 0.5 km (visible), 1 km (near-IR), 2 km (infrared)
- Full disk: every 10 minutes — an image of the entire Western Hemisphere
- GLM: Geostationary Lightning Mapper detects total lightning (cloud-to-cloud and cloud-to-ground) continuously
Himawari: Japan's advanced geostationary imager
Japan's Himawari-8 and Himawari-9 satellites, operated by the Japan Meteorological Agency, cover the Asia-Pacific region from geostationary orbit at 140.7°E. The Advanced Himawari Imager (AHI) has similar capabilities to GOES ABI, with 16 spectral bands and full-disk imaging every 10 minutes.
Himawari is particularly important for monitoring tropical cyclones in the western Pacific — the most active tropical cyclone basin on Earth. It also provides critical observations of volcanic activity from Japan's numerous active volcanoes, dust transport from Asian deserts, and bushfire monitoring across Australia.
Meteosat: covering Europe, Africa, and the Indian Ocean
The European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) operates the Meteosat series from geostationary positions covering Europe, Africa, the Middle East, and the Indian Ocean. The current operational satellite, Meteosat-12, carries the Flexible Combined Imager (FCI) with 16 channels and 10-minute full-disk imaging.
EUMETSAT also operates the Indian Ocean Data Coverage (IODC) mission, with an older Meteosat satellite repositioned to provide additional coverage over the Indian Ocean basin. This ensures continuous geostationary observation of a region prone to tropical cyclones, monsoon flooding, and dust transport from the Sahara and Arabian Peninsula.
Polar orbiters: the detail providers
While geostationary satellites excel at temporal coverage, polar-orbiting satellites provide the highest spatial resolution and the most detailed atmospheric measurements. The US NOAA-20 and NOAA-21 satellites, ESA's Sentinel-3 and MetOp series, and NASA's Terra and Aqua carry instruments that measure temperature and humidity at dozens of vertical levels, sea surface temperature to 0.1°C accuracy, and land surface properties at 250–1000 meter resolution.
These measurements are critical inputs to numerical weather prediction models. The atmospheric profiles from polar orbiters constrain the initial conditions that models use to generate forecasts. Without this data, forecast accuracy — particularly beyond 2–3 days — would degrade significantly.
What satellite imagery channels show
Visible channels (roughly 0.5–0.7 micrometers) show clouds and surface features as they appear to the human eye — bright where clouds are thick, dark where the surface is exposed. They only work during daytime.
Infrared channels (roughly 6–14 micrometers) measure thermal emission, which is related to temperature. Cold cloud tops appear bright in standard IR imagery, indicating high-altitude, deep convective clouds. Warm surfaces and low clouds appear darker. IR imagery works day and night, making it essential for nighttime weather monitoring.
Water vapor channels (around 6.2 and 7.3 micrometers) detect moisture in the mid and upper troposphere. These channels reveal atmospheric flow patterns, jet stream positions, and the movement of moisture plumes even in cloud-free areas. They are invaluable for synoptic-scale weather analysis and for identifying regions favorable for future storm development.
How PlanetSentry uses satellite imagery
PlanetSentry integrates satellite imagery layers that can be overlaid on the 3D globe, providing visual context for the events displayed. Weather satellite imagery helps users see the atmospheric environment surrounding wildfires, tropical cyclones, and other events — cloud cover, moisture patterns, and thermal anomalies become visible alongside the discrete event markers.
The combination of discrete event data (earthquakes, fires, storms from EONET and other feeds) with continuous satellite imagery creates a richer monitoring experience. Events do not happen in isolation — they occur within an atmospheric and environmental context that satellite imagery reveals.