Satellite Meteorology

Satellite meteorology, the study of atmospheric phenomena using satellite data, is an indispensable tool for forecasting weather and studying climate on a global scale.

Types of Satellites and Instruments

Satellite meteorology is the study of atmospheric phenomena, notably weather and weather conditions, using information gathered by instruments aboard artificial satellites. These satellites, including the International Space Station, are equipped with instruments that monitor cloud cover, snow, ice, temperatures, and other parameters to give scientists a continuous and up-to-date view of meteorological conditions and activity over a large area. Satellite data is an important tool for forecasting weather, tracking storms, observing climate change over time, monitoring ozone levels in the stratosphere, and studying numerous other aspects of global weather and climate.

The satellites from which meteorological measurements are made can be categorized by their orbits. Some weather satellites have a geosynchronous, or geostationary, orbit, meaning that they travel around the globe at an altitude and speed that keep them above the same point over the equator. A near-polar, Sun-synchronous orbit, by contrast, is a north-south orbit that passes close to the poles such that a satellite on that orbital path passes over any given location on Earth at the same local time. Geosynchronous satellites have better temporal resolution: They provide updated information for an area every thirty minutes, while near-polar, Sun-synchronous satellites may take anywhere from a few hours to several days to transmit updates. However, near-polar satellites have a higher spatial resolution; that is, they are better at providing images in which closely spaced features can be identified. Geosynchronous satellites provide images with comparatively poor spatial resolution because they must orbit at a greater altitude (at least 35,000 kilometers above the surface). Examples of geosynchronous meteorological satellites include the US Geostationary Operational Environmental Satellite (GOES) series, the European Space Agency’s METEOSAT series, Russia’s Geostationary Operational Meteorological Satellite (GOMS) series, and Japan’s Geostationary Meteorological Satellite (GMS), or Himawan, series. Near-polar, Sun-synchronous meteorological satellites include the National Oceanic and Atmospheric Administration (NOAA) series of satellites and Russia’s Meteor series.

The various orbiting platforms carry different sets of instruments. The weather satellites launched in the 1960s and early 1970s included television camera systems as part of their instrument packages. Later, satellites relied instead on instruments such as specialized radiometers (instruments that measure the amounts of electromagnetic radiation within a specific wavelength range) and radar systems. Radiometers measure such parameters as surface, cloud, and atmospheric temperatures; atmospheric water vapor and cloud distribution; and scattered solar radiation. Radar-system measurements include satellite altitude and ocean-surface roughness. Television cameras and radiometers are passive sensors that record radiation reflected or emitted from clouds, landforms, or other objects below. Radar systems are active sensors that send out signals and record them as they are reflected back. The data collected by a satellite’s sensors are transmitted via radio to ground stations. If a near-polar orbiter is not within transmitting distance of a ground station, its onboard data-collection system will store the information until the satellite passes within range.

Weather Satellites

The Advanced Television Infrared Observation Satellite, or TIROS, and Next-Generation (ATN) near-polar orbiting satellites (NOAA-8 through 14) have carried various sophisticated instruments. Two of these satellites, NOAA-12 and NOAA-14, remained in operation into the late 1990s. All the ATN series satellites have included an advanced, very-high-resolution radiometer (AVHRR), which detects specified wavelength intervals within the visible, near-infrared, and infrared wavelength ranges to generate information on sea-surface and cloud-top temperatures and ice and snow conditions; a TIROS operational vertical sounder (TOVS), which measures emissions within the visible, infrared, and microwave spectral bands to provide vertical profiles of the atmosphere’s temperature, water vapor, and total ozone content from the ground surface to an altitude of 32 kilometers; and a solar proton monitor, which detects fluctuations in the Sun’s energy output, particularly those related to sunspot (solar storm) activity. Except NOAA-8 and NOAA-12, all these satellites have included the Earth radiation budget experiment (ERBE), which uses long-wave and short-wave radiometers to provide data pertaining to Earth’s albedo. All but NOAA-8, NOAA-10, and NOAA-12 have carried the solar backscatter ultraviolet (SBUV) radiometer, which measures the vertical structure of ozone in the atmosphere by monitoring the ultraviolet radiation that the atmosphere scatters back into space. Of the ATN series of satellites, NOAA-12 is the only one that has not also carried the Search and Rescue Satellite Aided Tracking (SARSAT) system, which detects distress signals from downed aircraft and emergency beacons from ocean vessels, then relays the signals to special ground stations.

Instrumentation aboard GOES satellites may include a sounder, which uses visible and infrared data to create vertical profiles of atmospheric temperature, moisture, carbon dioxide, and ozone; a five-band multispectral radiometer, which scans visible and infrared wavelengths to obtain sea-surface temperature readings, detect airborne dust and volcanic ash, and provide day and night images of cloud conditions, fog, fires, and volcanoes; and a search-and-rescue support system similar to the ones flown on the NOAA near-polar orbiters. The GOES satellites are also equipped with a space environment monitor (SEM), which uses a solar X-ray sensor, a magnetometer, an energetic particle sensor, and a high-energy proton alpha detector to monitor solar activity and the intensity of Earth’s magnetic field. There are generally two GOES satellites in active use at any given time: the GOES-EAST satellite and the GOES-WEST satellite. The GOES-EAST satellite is positioned above the equator at an approximate longitude of 75 degrees west, while the GOES-WEST satellite orbits above the equator at approximately 135 degrees west longitude. These locations are ideal for monitoring the climatic conditions across North America. From them, GOES-EAST can provide images of storms approaching the eastern seaboard across the Atlantic Ocean during hurricane season (June through November), and GOES-WEST can monitor the weather systems that move in from across the Pacific Ocean, which affect the western seaboard during most of the year. However, when instrument malfunctions impair a satellite’s ability to provide data, the National Weather Service can use small rocket engines aboard the satellites to reposition a more functional platform to provide the desired coverage until a replacement satellite can be launched. After the imaging system on GOES-6 failed in 1989, for example, GOES-7 was relocated several times to compensate.

In 2024, two GOES satellites were operational. GOES-16, launched in December 2017, occupies the EAST position. It is positioned at 75.2° W longitude and provides coverage for North and South America and the Atlantic Ocean to the west coast of Africa. GOES-18 (GOES-West) is located at 137.0° W longitude. It watches over the western contiguous United States, Alaska, Hawaii, Mexico, Central America, and the Pacific Ocean to New Zealand. In 2023, it replaced GOES-17. NOAA-21 is a polar-orbiting satellite that uses advanced instruments to provide data on long-term climate monitoring and numerical weather prediction models. Further, the ability to deliver and process data from these weather satellites has vastly improved. 

Radar and Satellite Data

While operational weather satellites have generally carried radiometers, radar instruments have been part of the instrument package aboard experimental satellites and space shuttle flights. One of the best-known orbiters using active sensors is Seasat, a short-lived experimental craft launched in 1978 to monitor the oceans. During its three months of operation, this Earth-resources satellite provided a wealth of data for meteorological study. Its radar altimeter determined the height of the sea surface, from which data scientists derived measurements of winds, waves, and ocean currents. Its radar scatterometer yielded information on wave direction and size that, in turn, provided insights into wind speed and direction. The most sophisticated of Seasat’s active sensors was its synthetic aperture radar (SAR) system. This radar imaging system created a “synthetic aperture” of view by using the platform's motion to simulate a very long antenna. Images of the ocean’s surface were obtained from SAR data.

Satellite data have become indispensable to meteorologists. From orbit, information is readily available for any location on the planet, regardless of its remoteness, inaccessibility, climatic inhospitality, or political affiliation. Satellites yield regular, repeated, and up-to-date coverage of areas at minimal cost. They make it possible to view large weather systems in their entirety and facilitate meteorological observations on a regional or global basis. Satellites also provide a single data source for multiple locations, alleviating the problem of individual variance of calibration and accuracy associated with separate ground-based observations for each location. However, it is essential to note that ground-based stations can make more accurate and detailed observations of a small area, and such details may be lost in a view from space. Important though it is to modern meteorology, the use of satellite data augments, rather than replaces, other methods of study.

Satellite meteorology provides a rapid and relatively inexpensive means of obtaining current and abundant information on temperature, pressure, moisture, and other atmospheric, terrestrial, and oceanic conditions that affect weather and climate. These data, collected in digital form, are processed and integrated with other information. Scientists gain insights into significant atmospheric phenomena and their short-term and long-term implications, through these ongoing observations from orbit.

Weather forecasting is the best-known application of satellite meteorology. Anyone who has watched a televised weather report is familiar with geostationary satellite images, usually presented in quick succession to show the recent movement of major weather systems. Meteorologists use computers to process the vast amounts of data provided by satellites and other information sources, including ground-based stations, aircraft, ships, and buoys. Data processing yields such forecasting aids as atmospheric temperature and water-vapor profiles, enhanced and false-color images, and satellite-image “movies.” Computer models of atmospheric behavior also assist meteorologists in short-range and long-range forecasting.

Satellite images of cloud cover alone yield a wealth of information for the forecaster. By comparing imagery from visible and infrared spectral regions, meteorologists can identify cloud types, structure, and degree of organization, then make assumptions and deductions concerning associated weather conditions. For example, the tall cumulus clouds that produce thunderstorms appear bright in the visible range, as they are deep and thus readily reflect sunlight. These clouds appear in infrared images as areas of coldness, indicating the altitude to which the clouds have climbed. Clouds that appear bright in visible-range imagery but that register as warm (low-altitude) in infrared scans may be fog or low-lying clouds. Wispy, high-altitude cirrus clouds, which are not precipitation-bearing, appear cold in infrared images but may not appear in visible-range scans.

Weather satellites have proved particularly useful in the science of hurricane and typhoon prediction. These large, violent, rotating tropical storms originate as relatively small low-pressure cells over oceans, where coverage by conventional weather-monitoring methods is sparse. Before the advent of satellites, ships and aircraft were the sole source of information on weather at sea, and hurricanes and typhoons often escaped detection until they were dangerously close to populated coastal areas. Using images and data obtained from orbiting satellites, meteorologists can track and study these storms continuously from their inception through their development and final dissipation. With accurate storm tracking and ample warning, inhabitants at risk can evacuate areas threatened by wind and high water, thereby minimizing loss of life.

Climate Studies

Meteorological satellites also provide scientists with a view of how human activity affects climate on a local, regional, and even global basis. Terrestrial surface-temperature measurements clearly show urban “heat islands,” where cities consistently radiate more heat energy than the surrounding countryside. In images obtained from orbit, thunderstorms can be seen developing along the boundaries of areas of dense air pollution: The haze layer inhibits heating of the ground surface, leading to unstable atmospheric conditions that produce rainfall. Satellite imagery has revealed that in sub-Saharan Africa, where the overgrazing of livestock owned by nomads has contributed substantially to the spread of desert areas, the resulting increase in albedo has led to a reduction in rainfall and subsequent reinforcement of drought conditions. Studies of deforestation in tropical areas have incorporated satellite data to determine whether replacing forests with agricultural land affects rainfall by reducing evaporation or altering albedo. Satellite data have also played a significant role in the ongoing debates regarding how human activity has affected global temperature trends and the ozone layer.

Satellite meteorology helps monitor the climatological effects of natural occurrences as well. The 1991 eruption of Mount Pinatubo in the Philippines marked the first time scientists could quantify the impact of a major volcanic eruption on global climate. Satellites equipped with ERBE instruments tracked the dissemination of the ash and sulfuric acid particles resulting from the violent eruption. The larger ash particles more readily drift down into the lower portion of the atmosphere, where they are typically removed in precipitation. However, the smaller sulfuric acid particles can remain suspended in the stratosphere for several years, eventually reaching lower altitudes where they combine with water to produce acidic precipitation. The ERBE instruments measured the amount of sunlight reflected by clouds, land surfaces, and particles suspended in the atmosphere. They detected the contribution of suspended particles, clouds, and trace gases such as carbon dioxide to the heat the atmosphere retained. The eruption was found to have brought about a uniform cooling of Earth, temporarily slowing the ongoing global warming trend observed since the 1980s.

Another natural phenomenon, El Niño, has also been the subject of satellite-based study. This periodic anomalous warming of the Pacific waters off the coast of South America is part of a large-scale oceanic and atmospheric fluctuation known as the Southern Oscillation, in which atmospheric pressure conditions alternately decline and rise over the eastern Pacific Ocean and Australia and the Indian Ocean. These widespread pressure changes influence rainfall patterns around the world. Satellite measurement of sea-surface temperatures facilitates the early detection of El Niño conditions, and satellite observations on a global basis help scientists to discern the climatic patterns that make up this complex phenomenon.

Meteorological satellites have also been used to gather data about “solar weather.” Using orbiting sensors that detect energetic particles from the Sun and more direct imaging methods, scientists can monitor and predict sunspots and other solar activity. Predicting the increases in solar emissions associated with sunspots allows scientists to anticipate the resulting ionospheric conditions on Earth, including magnetic storms and radio transmission disruption.

Principal Terms

active sensor: a sensor, such as a radar instrument, that illuminates a target with artificial radiation, which is reflected back to the sensor

albedo: the percentage of incoming radiation that is diffusely reflected by a planetary surface

El Niño: a periodic anomalous warming of the Pacific waters off the coast of South America; part of a large-scale oceanic and atmospheric fluctuation that has global repercussions

geosynchronous (geostationary): describing a satellite that orbits about Earth’s equator at an altitude and speed such that it remains above the same point on the surface of the planet

near-polar orbit: an orbit of Earth that lies in a plane that passes close to both the North and South Poles

passive sensors: sensors that detect reflected or emitted electromagnetic radiation that has been issued from another source

radiometer: an instrument that quantitatively measures reflected or emitted electromagnetic radiation within a particular wavelength interval

spatial resolution: the extent to which a sensor can differentiate between closely spaced features

Sun-synchronous orbit: for an Earth satellite, a near-polar orbit at an altitude such that the satellite always passes over any given point on Earth at the same local time

synthetic aperture radar (SAR): a space-borne radar imaging system that uses the motion of the spacecraft in orbit to simulate a very long antenna

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