A Guide to the World’s Operational Earth Observation Satellites

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Our Planet Under Watch

From an altitude of hundreds of kilometers, a fleet of silent sentinels keeps a constant watch over our world. These Earth observation satellites are humanity’s eyes in the sky, a global infrastructure that has fundamentally changed how we understand, manage, and live on our planet. They chart the retreat of glaciers, track the fury of hurricanes, guide farmers’ planting decisions, and provide the unblinking evidence of a changing climate. This orbital network is not a single entity but a complex, multi-layered ecosystem of different systems, orbits, and sensor types, each designed to answer specific questions about the Earth.

At the heart of this system are two primary orbital strategies. Many weather and communications satellites occupy a geostationary orbit, positioned 35,786 kilometers above the equator. At this specific altitude, a satellite’s orbital period matches Earth’s rotation, allowing it to remain fixed over the same spot on the surface. This provides a constant, wide-area “stare,” essential for tracking the rapid development of weather systems. In contrast, most high-resolution imaging satellites fly in a sun-synchronous polar orbit. Circling the Earth from pole to pole at a much lower altitude, these satellites are designed so that they pass over any given point on the planet at the same local solar time. This consistent lighting is invaluable for comparing images taken on different days, weeks, or years, making it possible to reliably detect changes on the ground, from urban expansion to deforestation.

The instruments these satellites carry are just as varied as their orbits. The most intuitive are passive optical sensors, which work much like a powerful digital camera. They capture sunlight reflected from Earth’s surface across various spectral bands, from the visible light our eyes can see to near-infrared and thermal infrared, revealing information about vegetation health, surface temperature, and land cover. Because they rely on the sun, they cannot see through clouds or capture images at night. To overcome this limitation, engineers developed active sensors, most notably Synthetic Aperture Radar (SAR). Instead of passively collecting light, a SAR satellite sends out its own microwave pulses and records the echoes that bounce back. This self-illumination allows it to “see” through clouds, darkness, smoke, and haze, providing an all-weather, day-and-night monitoring capability that is essential for applications like maritime surveillance, flood mapping, and measuring subtle ground deformation.

Together, these different orbits and sensor technologies form a complementary global system. Geostationary satellites provide the persistent watch needed for immediate, dynamic events, while polar-orbiting satellites provide the detailed, systematic scan required for long-term mapping and change detection. No single satellite can do everything. It is the integration of these diverse capabilities, from both government-funded programs and a nascent commercial sector, that gives us this unprecedented, comprehensive view of our home.

Governmental Earth Observation Programs: The Public Good

The foundation of global Earth observation is built upon large-scale, government-led programs. These missions, operated by national and international space agencies, provide the stable, long-term, and globally consistent data that serves as the scientific bedrock for understanding our planet. Typically offered to the public on a free and open basis, this data fuels academic research, informs environmental policy, and supports public safety and disaster response efforts around the world.

United States: NASA, NOAA, and USGS

The United States has long been a pioneer in Earth observation, with its programs managed through a coordinated effort between the National Aeronautics and Space Administration (NASA), the National Oceanic and Atmospheric Administration (NOAA), and the U.S. Geological Survey (USGS). NASA typically leads the design and launch of new scientific missions, NOAA operates the nation’s weather satellites, and the USGS manages the vast data archive of land-imaging programs like Landsat.

The Earth Observing System (EOS) Flagships: Terra, Aqua, and Aura

In the late 20th century, NASA embarked on one of its most ambitious scientific endeavors: the Earth Observing System (EOS). The program was conceived not just to launch individual satellites, but to study Earth as a single, integrated system of land, oceans, atmosphere, ice, and life. The program’s flagships—three large, multi-instrument satellites named Terra, Aqua, and Aura—were designed to take simultaneous, synergistic measurements, providing a holistic view of the planet’s health. Though now well beyond their original design lives, these aging sentinels continue to provide an invaluable climate data record. Their longevity presents a unique challenge. As they run low on the fuel needed to maintain their precise orbits, their observation conditions are changing, complicating the very long-term analysis for which they were designed. This transition underscores a central issue in climate science: the difficulty of maintaining the continuity of calibrated, long-term data records across generations of satellite hardware.

Terra (EOS AM-1)

Launched on December 18, 1999, Terra is the venerable flagship of the EOS program. Its name, Latin for “Earth,” reflects its comprehensive mission to study the planet’s lands, oceans, and atmosphere. Placed in a sun-synchronous orbit that crosses the equator in the morning (hence its “AM” designation), Terra was engineered to provide a baseline for understanding global climate dynamics. The satellite carries a suite of five distinct instruments that work in concert:

• ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer): A cooperative instrument with Japan, ASTER captures high-resolution (15 to 90 meters) stereo images of land, water, ice, and clouds in 14 different spectral bands. It is particularly useful for geology, monitoring volcanoes, and creating detailed digital elevation models. Its shortwave-infrared (SWIR) detector ceased functioning in 2008, but the visible, near-infrared, and thermal sensors remain operational.
• CERES (Clouds and the Earth’s Radiant Energy System): This instrument measures Earth’s total radiation budget—the balance between incoming solar energy and outgoing reflected and thermal energy. By quantifying this balance, CERES helps scientists understand the role of clouds in heating or cooling the planet.
• MISR (Multi-angle Imaging SpectroRadiometer): MISR is a unique instrument that consists of nine cameras fixed at different angles. As Terra flies overhead, each camera captures an image of the same scene from a different perspective. This multi-angle view allows scientists to distinguish between different types of clouds, aerosols (airborne particles), and land surfaces.
• MODIS (Moderate Resolution Imaging Spectroradiometer): One of the most versatile instruments ever flown, MODIS scans a wide 2,330-kilometer swath of the Earth every one to two days in 36 spectral bands. It provides a vast range of data products, including global maps of vegetation health, sea surface temperature, cloud cover, and active fires. An identical MODIS instrument also flies on the Aqua satellite.
• MOPITT (Measurements of Pollution in The Troposphere): Provided by the Canadian Space Agency, MOPITT is the first instrument to make long-term global measurements of carbon monoxide concentrations in the lower atmosphere, offering a important window into global air pollution patterns.

After more than two decades of service, Terra’s fuel for orbit-maintenance maneuvers was depleted. Since February 2020, the satellite has been in a “free drift” orbit, meaning its altitude is slowly decaying and its equatorial crossing time is becoming earlier. It was intentionally lowered in 2022 to ensure it will re-enter the atmosphere safely. Despite the orbital changes, its instruments continue to collect valuable scientific data, extending one of the longest continuous climate data records ever assembled. The mission is expected to be decommissioned around 2025 or 2026.

Aqua (EOS PM-1)

Following Terra into orbit, Aqua was launched on May 4, 2002. As its name suggests, Aqua’s primary focus is the global water cycle. Placed in an afternoon (“PM”) orbit, its observations complement Terra’s morning measurements, allowing scientists to study daily variations in Earth’s systems. For most of its operational life, Aqua flew as part of the “A-Train,” a constellation of several satellites following each other in close formation to gather near-simultaneous data. Like Terra, Aqua has now depleted its station-keeping fuel and has exited the A-Train, beginning its own slow orbital drift.

Aqua carries six instruments, some of which are counterparts to those on Terra:

• AIRS (Atmospheric Infrared Sounder): A high-resolution spectrometer that measures temperature and water vapor throughout the atmosphere’s vertical profile. AIRS data has significantly improved weather forecasting accuracy.
• AMSU-A (Advanced Microwave Sounding Unit-A): Working with AIRS, this microwave sounder provides atmospheric temperature data even in cloudy conditions.
• HSB (Humidity Sounder for Brazil): Provided by Brazil, this instrument measured atmospheric humidity but failed in early 2003, just a few months after launch.
• MODIS (Moderate Resolution Imaging Spectroradiometer): The second MODIS instrument provides continuity with Terra’s observations and captures afternoon views of global processes.
• CERES (Clouds and the Earth’s Radiant Energy System): Aqua carries two CERES instruments to continue the critical work of measuring Earth’s radiation budget.
• AMSR-E (Advanced Microwave Scanning Radiometer-EOS): A Japanese instrument that measured a wide range of water-related parameters, including precipitation, sea surface temperature, sea ice, and soil moisture. The instrument’s antenna stopped spinning in 2011, ending its primary mission, though it was operated at a reduced rate for several years for cross-calibration purposes.

Aqua’s mission has provided unprecedented insight into the movement of water through the Earth system, from evaporation from the oceans to the formation of clouds and the distribution of rainfall. The mission is expected to continue collecting data through the mid-2020s.

Aura (EOS CH-1)

The third and final great observatory of the EOS program, Aura, was launched on July 15, 2004. Its name, from the Latin for “breeze,” points to its mission: to study the chemistry of Earth’s atmosphere. Aura’s instruments are designed to answer key questions about the health of the ozone layer, the sources and transport of air pollution, and the connections between atmospheric chemistry and climate change.

Aura carries four specialized instruments:

• HIRDLS (High Resolution Dynamics Limb Sounder): A UK-US collaboration designed to measure infrared radiation from ozone, water vapor, and other trace gases by looking at the “limb” or edge of the atmosphere. A piece of plastic film blocked the instrument’s optical path shortly after launch, severely limiting its capabilities, and the instrument ceased functioning entirely in 2008.
• MLS (Microwave Limb Sounder): This instrument also scans the atmospheric limb but at microwave frequencies. It measures a wide range of chemical species, including many of the chlorine compounds responsible for ozone destruction, providing a detailed picture of the chemical processes occurring in the stratosphere.
• OMI (Ozone Monitoring Instrument): A Dutch-Finnish contribution, OMI is a spectrometer that maps global ozone levels and other pollutants like nitrogen dioxide and sulfur dioxide with unprecedented resolution. Its data provides daily global maps of air quality.
• TES (Tropospheric Emission Spectrometer): TES measures the thermal infrared energy emitted by the Earth’s surface and atmosphere, allowing it to create three-dimensional profiles of ozone, carbon monoxide, and other gases from the ground up.

Aura has been instrumental in monitoring the recovery of the Antarctic ozone hole and tracking the global movement of air pollution. Like its sister satellites, it is now operating well beyond its design life and is expected to continue its mission into the late 2020s.

The Landsat Program: An Unbroken Record of Our Changing Lands

No satellite program has provided a longer, more consistent record of Earth’s land surface than Landsat. A joint effort between the USGS and NASA since 1972, the program has created an unparalleled, multi-decadal archive of imagery that has become a cornerstone of Earth science. The program’s true significance lies less in the capability of any single satellite and more in the power of this continuous, carefully calibrated archive. It has become the “gold standard” against which other sensors are often measured.

A pivotal moment in the program’s history occurred in 2008 when the U.S. government made the entire Landsat archive available to all users at no charge. This policy transformed satellite data from a niche, expensive resource for governments and large corporations into a global public utility. The free and open access to this vast historical record spurred an explosion of innovation in science, software development, and commercial applications, creating the very ecosystem of data analysis that thrives today. Three Landsat satellites remain operational, working together to continue this invaluable record.

Landsat 7

Launched on April 15, 1999, Landsat 7 is the oldest operational satellite in the program. It carries the Enhanced Thematic Mapper Plus (ETM+) instrument, which captures images in eight spectral bands with a resolution of 30 meters for multispectral bands and 15 meters for its panchromatic (black-and-white) band. In May 2003, the satellite experienced a failure of its Scan Line Corrector (SLC), a mechanical component that compensates for the satellite’s forward motion. Without the SLC, the instrument now scans in a zig-zag pattern, resulting in wedge-shaped gaps of missing data on the sides of each image. Despite this “SLC-off” issue, the data in the center of each scene remains of high quality, and scientists have developed methods to fill the gaps. Landsat 7 continues to acquire images, contributing to the global archive and helping to increase the frequency of observations alongside its more modern successors.

Landsat 8

Launched on February 11, 2013, Landsat 8 represented a significant technological leap for the program. It carries two advanced instruments:

• OLI (Operational Land Imager): This instrument collects data in nine spectral bands, including a new deep blue band for coastal water studies and a new cirrus band for detecting high-altitude clouds. It uses a more advanced “push-broom” sensor design, which provides a better signal-to-noise ratio and improved radiometric performance compared to the “whisk-broom” scanners on previous Landsat missions.
• TIRS (Thermal Infrared Sensor): TIRS measures surface temperature in two thermal infrared bands. This provides more accurate temperature data than the single thermal band on previous Landsats.

With its improved sensors and data quality, Landsat 8 quickly became the workhorse of the program, capturing over 700 scenes of the Earth every day.

Landsat 9

To ensure the continuity of the Landsat record, Landsat 9 was launched on September 27, 2021. It is largely a copy of Landsat 8, carrying the improved OLI-2 and TIRS-2 instruments. By flying in an orbit eight days out of phase with Landsat 8, the two satellites work in tandem to image the entire landmass of the Earth every eight days. This increased revisit frequency is a major benefit for monitoring dynamic processes like crop growth, wildfire recovery, and the effects of drought. Together, Landsat 8 and 9 ensure that the invaluable record of our changing planet will continue for years to come.

The GOES Program: America’s Weather Watchers

NOAA’s Geostationary Operational Environmental Satellites (GOES) are the backbone of weather monitoring and forecasting for the Western Hemisphere. Positioned in a high geostationary orbit, they remain fixed over their designated locations, providing continuous coverage from the west coast of Africa to New Zealand. This constant vigil is essential for tracking rapidly developing weather phenomena. The current generation of satellites, the GOES-R series, represents a quantum leap in capability, moving from the slow-scan, static images of the past to high-definition, rapid-refresh “movies” of the atmosphere. This has fundamentally changed severe weather forecasting, improving the lead time for tornado warnings and enhancing the track and intensity forecasts for hurricanes. NOAA maintains a two-satellite operational constellation, GOES-East and GOES-West, with an additional satellite in orbit as a ready spare.

GOES-19 (GOES-East)

Launched on June 25, 2024, GOES-19 is the newest satellite in the U.S. weather fleet. After a period of on-orbit testing, it took over as the operational GOES-East satellite on April 7, 2025. From its position at 75.2 degrees west longitude, it monitors North and South America, the Caribbean, and the entire Atlantic Ocean basin. Its primary duties include tracking hurricanes, monitoring severe thunderstorms across the continental U.S., and identifying environmental hazards like wildfires and volcanic ash plumes.

GOES-18 (GOES-West)

Launched on March 1, 2022, GOES-18 became the operational GOES-West satellite on January 4, 2023. Positioned at 137.0 degrees west longitude, it watches over the western United States, Alaska, Hawaii, and the vast expanse of the Pacific Ocean. It is a critical tool for detecting “atmospheric rivers” that bring heavy rain and snow to the West Coast and for monitoring the development of storms in the eastern Pacific.

GOES-16 (On-Orbit Standby)

Launched on November 19, 2016, GOES-16 was the first of the revolutionary GOES-R series. It served as the operational GOES-East satellite for over seven years before being replaced by the newer GOES-19. It now resides in a central location at 104.7 degrees west longitude, serving as a fully functional on-orbit spare, ready to be moved into either the East or West position should one of the primary satellites experience a problem.

The GOES-R series satellites (which includes GOES-16, -17, -18, and -19) all carry a sophisticated suite of instruments. The Advanced Baseline Imager (ABI) is the primary instrument, an advanced camera that can view the Earth in 16 different spectral bands and can scan the continental U.S. every five minutes and a full hemisphere every 10 to 15 minutes. The Geostationary Lightning Mapper (GLM) is the first instrument of its kind, continuously mapping total lightning (both in-cloud and cloud-to-ground) across the Americas, which is a strong indicator of storm intensification. The satellites also carry instruments to monitor space weather, including a Solar Ultraviolet Imager (SUVI) and sensors that measure energetic particles and the magnetic field environment around the satellite, providing early warnings of solar storms that can disrupt communications and power grids.

Europe: The Copernicus Programme

The European Union’s Copernicus programme is arguably the most comprehensive and systematic Earth observation initiative in the world. Managed by the European Commission in partnership with the European Space Agency (ESA) and the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), it is more than just a collection of satellites; it is an end-to-end information system. The program’s space component is a dedicated fleet of satellites known as the Sentinels. Each Sentinel mission is designed as a constellation of “workhorse” satellites providing continuous, reliable streams of data. This data feeds into six thematic Copernicus services: Atmosphere, Marine, Land, Climate Change, Security, and Emergency. Like Landsat, all Sentinel data is available on a full, free, and open basis, making it a global resource.

Sentinel-1: The All-Weather Radar Constellation

The Sentinel-1 mission provides the all-weather, day-and-night imaging capability for Copernicus. It consists of two operational satellites, Sentinel-1A (launched April 3, 2014) and Sentinel-1C (launched December 5, 2024), which fly in the same orbit but 180 degrees apart. A third satellite, Sentinel-1B, suffered a power anomaly in late 2021 and its mission was officially ended in August 2022.

Each Sentinel-1 satellite carries an advanced C-band Synthetic Aperture Radar (SAR) instrument. The radar’s ability to penetrate clouds, rain, and darkness makes it invaluable for a wide range of applications that are impossible for optical satellites. Key uses include:

• Maritime Surveillance: Detecting oil spills, monitoring ship traffic for security, and tracking illegal fishing.
• Ice Monitoring: Mapping the extent and movement of sea ice in the polar regions, which is vital for shipping and climate science.
• Land Deformation: Using a technique called interferometry, Sentinel-1 can detect millimeter-scale changes in the ground surface, allowing it to monitor subsidence, volcanic activity, and the effects of earthquakes.
• Emergency Response: Providing rapid mapping of flooded areas during natural disasters, even when the region is covered by storm clouds.

The two-satellite constellation provides a six-day repeat pass over most of the globe, ensuring frequent and reliable monitoring.

Sentinel-2: The High-Resolution Land Observer

The Sentinel-2 mission is the primary land-monitoring workhorse of Copernicus. It consists of a pair of identical satellites, Sentinel-2A (launched June 23, 2015) and Sentinel-2B (launched March 7, 2017). Together, they provide high-resolution multispectral imagery of Earth’s land surfaces and coastal waters.

The mission’s Multi-Spectral Instrument (MSI) is a significant advancement in optical imaging. It captures data in 13 spectral bands with a spatial resolution of 10 meters in the visible and near-infrared bands. This is comparable to the resolution of commercial satellites just a decade ago, but Sentinel-2 provides this data systematically and for free. A key feature is the inclusion of several “red-edge” bands, which are particularly sensitive to the state of vegetation health. This makes Sentinel-2 data extremely valuable for precision agriculture, forestry management, and monitoring environmental health. The twin-satellite constellation provides a revisit time of just five days at the equator, and even more frequently at mid-latitudes, allowing for detailed tracking of land cover changes.

Sentinel-3: The Global Ocean and Land Monitor

While Sentinel-2 provides a detailed, high-resolution view of the land, the Sentinel-3 mission takes a broader, global perspective. It is designed to provide systematic measurements of Earth’s oceans, land, ice, and atmosphere. Like its siblings, it is a two-satellite constellation, with Sentinel-3A (launched February 16, 2016) and Sentinel-3B (launched April 25, 2018).

Each Sentinel-3 satellite carries a suite of powerful instruments:

• OLCI (Ocean and Land Colour Instrument): This instrument measures ocean color, which provides information on marine biology and water quality, and also observes land color for vegetation monitoring. It has 21 spectral bands and a spatial resolution of 300 meters.
• SLSTR (Sea and Land Surface Temperature Radiometer): SLSTR measures the temperature of the sea and land surface with high accuracy. It has a unique dual-view scanning technique that looks at the surface from two different angles to better correct for atmospheric effects.
• SRAL (SAR Radar Altimeter): This radar altimeter measures the precise height of the sea surface, which is used to map ocean currents and monitor sea-level rise. It also measures the height of ice sheets and inland water bodies.

With its suite of sensors, Sentinel-3 provides a daily global “health check” of the planet, delivering data essential for ocean forecasting, climate monitoring, and large-scale environmental management.

Sentinel-5P: The Atmospheric Watchdog

Sentinel-5 Precursor, or Sentinel-5P, is a dedicated mission to monitor the composition of our atmosphere. Launched on October 13, 2017, it was designed to bridge the data gap between atmospheric sensors and the future Sentinel-5 instrument.

The satellite carries a single, highly advanced instrument called TROPOMI (TROPOspheric Monitoring Instrument). TROPOMI is a spectrometer that measures sunlight backscattered from the Earth’s atmosphere. By analyzing the spectrum of this light, it can detect the chemical fingerprints of various trace gases. It maps a multitude of pollutants and greenhouse gases—including nitrogen dioxide, ozone, formaldehyde, sulfur dioxide, methane, and carbon monoxide—with a resolution as high as 3.5 x 5.5 kilometers. With its wide 2,600-kilometer swath, TROPOMI maps the entire planet every single day. This daily global coverage provides unprecedented detail on the sources and transport of air pollution, making Sentinel-5P a cornerstone of air quality forecasting and climate research.

Japan: JAXA’s Advanced Observers

The Japan Aerospace Exploration Agency (JAXA) operates a fleet of highly advanced and scientifically targeted Earth observation satellites. While programs like Landsat and Copernicus focus on broad, systematic monitoring, JAXA’s missions often feature unique, high-precision sensor technologies designed to measure specific physical parameters. This approach positions Japan as a key provider of specialized datasets that complement the more general-purpose monitoring of other global programs, particularly in areas like radar imaging and greenhouse gas measurement.

ALOS-2 “DAICHI-2”

The Advanced Land Observing Satellite-2 (ALOS-2), known in Japan as DAICHI-2, was launched on May 24, 2014. It is an advanced radar satellite carrying the PALSAR-2 (Phased Array type L-band Synthetic Aperture Radar-2) instrument. Unlike the C-band radar on Sentinel-1, PALSAR-2 uses a longer-wavelength L-band radar. This gives it a unique ability to penetrate through vegetation canopies to see the ground surface beneath, making it exceptionally useful for monitoring deforestation and forest biomass. Its high-resolution modes, with a spotlight capability down to 1 x 3 meters, are also highly effective for disaster monitoring and mapping subtle land deformation caused by volcanic or seismic activity. ALOS-2 has a 14-day revisit cycle and continues the legacy of its predecessor, ALOS, providing a critical source of L-band radar data to the international scientific community.

GCOM “SHIZUKU” and “SHIKISAI”

The Global Change Observation Mission (GCOM) is JAXA’s flagship program for long-term monitoring of Earth’s climate and water cycle. It consists of two complementary satellites.

• GCOM-W “SHIZUKU”: Launched on May 18, 2012, GCOM-W (for Water) is dedicated to observing the global water cycle. Its single instrument, the Advanced Microwave Scanning Radiometer 2 (AMSR2), is a large, rotating passive microwave sensor. It measures the faint natural microwave emissions from the Earth’s surface and atmosphere to derive a wealth of information, including sea surface temperature, wind speed over the ocean, the concentration of sea ice, precipitation, soil moisture, and snow depth. With its large 2-meter antenna, AMSR2 provides this data with high accuracy, and it scans over 99% of the Earth every two days.
• GCOM-C “SHIKISAI”: Launched on December 23, 2017, GCOM-C (for Climate) focuses on the carbon cycle and radiation budget. Its Second-generation Global Imager (SGLI) is an advanced optical sensor that observes in 19 bands from the near-ultraviolet to the thermal infrared. With a spatial resolution of 250 meters in many bands, it provides detailed information on clouds, airborne aerosol particles, ocean color (an indicator of phytoplankton), and the health of terrestrial vegetation. Its data is used to improve the accuracy of climate change prediction models.

GOSAT Series: “IBUKI” and “IBUKI-2”

Japan has taken a leading role in the space-based monitoring of greenhouse gases with its GOSAT (Greenhouse gases Observing SATellite) series. These missions are a joint project between JAXA, the Ministry of the Environment, and the National Institute for Environmental Studies.

• GOSAT “IBUKI”: Launched on January 23, 2009, GOSAT was the world’s first satellite dedicated to measuring the concentrations of carbon dioxide and methane, the two primary anthropogenic greenhouse gases, from space. Its main instrument, TANSO-FTS, is a spectrometer that precisely measures how these gases absorb infrared light in the atmosphere, allowing scientists to calculate their column-average concentrations.
• GOSAT-2 “IBUKI-2”: To continue and improve upon this record, GOSAT-2 was launched on October 29, 2018. It carries the enhanced TANSO-FTS-2 and TANSO-CAI-2 instruments. GOSAT-2 has improved accuracy and an intelligent pointing system that can automatically target cloud-free areas to maximize the amount of high-quality data collected. Together, the GOSAT satellites provide a vital independent dataset for verifying national emissions inventories and tracking progress toward climate goals.

India: ISRO’s Self-Reliant Constellations

The Indian Space Research Organisation (ISRO) has developed a formidable and largely self-reliant Earth observation capability driven by national strategic and developmental needs. Its satellite constellations are designed to provide India with autonomy in resource management, urban planning, disaster monitoring, and national security. This state-led success has also nurtured a growing private space sector, signaling a shift toward a hybrid public-private model that is poised to accelerate India’s role as a major space power.

Cartosat Series

The Cartosat series is a family of high-resolution satellites designed primarily for cartographic applications. These satellites provide detailed imagery used for mapping, infrastructure planning, rural and urban development, and strategic and defense purposes. The satellites are placed in a sun-synchronous orbit and can be steered to look at specific areas of interest, allowing for more frequent revisits. Several Cartosat satellites are currently operational, including:

• Cartosat-2 Series: This includes a number of satellites launched since 2007, such as Cartosat-2D, 2E, and 2F. They carry a panchromatic (black-and-white) camera with a spatial resolution of less than 1 meter, providing highly detailed imagery.
• Cartosat-3: Launched on November 27, 2019, Cartosat-3 represents a major leap in capability. It provides a panchromatic resolution of 25 centimeters, placing it among the highest-resolution civilian satellites in the world. It also carries a multispectral instrument with a resolution of 1 meter.

Oceansat Series

As its name implies, the Oceansat series is dedicated to oceanography. These satellites provide data on the physical and biological state of the oceans, which is used for weather forecasting, monitoring fisheries, and tracking climate patterns.

• Oceansat-2: Launched on September 23, 2009, Oceansat-2 carries an Ocean Colour Monitor (OCM) to measure phytoplankton concentrations and a Ku-band pencil-beam scatterometer (SCAT) to measure wind speed and direction over the ocean surface. The scatterometer stopped functioning after about four and a half years, leading to the launch of a dedicated continuity mission, SCATSAT-1, in 2016.
• Oceansat-3 (EOS-06): Launched on November 26, 2022, this is the most recent satellite in the series. It provides enhanced continuity for the OCM and also carries a Sea Surface Temperature Monitor and an advanced scatterometer, making it a comprehensive ocean-monitoring platform.

RISAT Series

The RISAT (Radar Imaging Satellite) series gives India an all-weather, day-and-night observation capability. These satellites use Synthetic Aperture Radar (SAR), which is essential for monitoring during India’s monsoon season when cloud cover is persistent.

• RISAT-2BR1: Launched on December 11, 2019, this is an X-band SAR satellite with a resolution of approximately 1 meter. Its primary applications are in agriculture, forestry, and disaster management.
• RISAT-1A (EOS-04): Launched on February 14, 2022, this is a C-band SAR satellite, a follow-on to the original RISAT-1 which ceased operations in 2016. C-band radar is highly versatile and is used for a wide range of applications, including monitoring land use, soil moisture, and flooding.

NISAR (NASA-ISRO SAR)

A landmark of international collaboration, the NISAR mission is a joint project between NASA and ISRO. Launched on July 30, 2025, it is the first satellite mission to use two different radar frequencies (L-band and S-band) simultaneously. NASA provided the L-band SAR, while ISRO provided the S-band SAR and the spacecraft bus. This dual-frequency capability will allow NISAR to measure changes in Earth’s surface—such as ice sheet collapse, earthquake deformation, and ecosystem changes—with unprecedented detail and accuracy. It will scan nearly all of Earth’s land and ice surfaces every 12 days, creating a massive and freely available dataset that will be a treasure trove for scientists studying Earth system processes.

China: The Prolific Gaofen System

China’s Earth observation program, managed by the China National Space Administration (CNSA), is characterized by its immense scale, rapid launch cadence, and comprehensive scope. The centerpiece of this effort is the Gaofen series, part of the China High-resolution Earth Observation System (CHEOS). This state-driven program is a strategic effort to achieve complete autonomy and leadership in Earth observation, developing a system that covers nearly every type of sensor technology. While the data serves civilian purposes like environmental protection and resource surveying, the increasing lack of public detail on later Gaofen satellites suggests a deep integration with national security objectives, reflecting the global reality of Earth observation as a critical dual-use technology.

The Gaofen family is a large and diverse constellation with dozens of satellites launched since 2013. Key operational satellites include:

• Gaofen-1 Series: The first satellite, Gaofen-1, was launched in 2013. It carries both a 2-meter resolution panchromatic camera and a 16-meter resolution wide-field imager, combining high-resolution spot imaging with broad coverage. Several follow-on satellites (GF-1-02, 03, 04) were launched in 2018 to increase revisit frequency.
• Gaofen-2: Launched in 2014, this satellite provides very-high-resolution optical imagery with a panchromatic resolution of better than 1 meter. It is primarily used for land and resource surveying and urban planning.
• Gaofen-3 Series: This is China’s C-band SAR satellite series. The first Gaofen-3 was launched in 2016, providing 1-meter resolution radar imagery. Two follow-on satellites, GF-3-02 and GF-3-03, were launched in 2021 and 2022, forming a constellation for improved monitoring.
• Gaofen-4: A unique satellite in the series, Gaofen-4 was launched in 2015 into a geostationary orbit. It provides visible and infrared imagery with a resolution of 50 meters, allowing it to stare continuously at the Asia-Pacific region for disaster prevention and monitoring.
• Gaofen-5 Series: This series is dedicated to atmospheric monitoring. Gaofen-5, launched in 2018, carries six advanced instruments, including hyperspectral and polarimetric cameras, to measure aerosols, greenhouse gases, and other trace gases. A follow-on, Gaofen-5-02, was launched in 2021.
• Gaofen-6: Launched in 2018, this satellite is similar to Gaofen-1 but with an emphasis on agricultural applications. It has a wide-field camera with red-edge bands for monitoring crop health.
• Gaofen-7: Launched in 2019, this is a high-resolution stereo mapping satellite. It carries two optical cameras to create 3D maps of the terrain with sub-meter resolution, essential for cartography and infrastructure projects.
• Gaofen-8 through Gaofen-14: A large number of additional Gaofen satellites with optical and radar sensors have been launched, though fewer technical details have been made publicly available about these later missions. They are believed to provide China with a robust and highly capable constellation for both civilian and government use.

The Commercial Earth Observation Sector: A New Space Race

While government programs provide the foundational data for global science, the commercial sector has ignited a revolution in Earth observation, driven by innovation, competition, and a focus on customer needs. Private companies now offer imagery with resolution and revisit rates that were once the exclusive domain of intelligence agencies. This market has largely split into two complementary segments. One focuses on providing the highest possible resolution on-demand, where a powerful satellite is “tasked” to look at a specific point of interest. The other focuses on high-frequency, broad-area monitoring, using large constellations of smaller satellites to scan the globe continuously.

Maxar Technologies: The High-Resolution Leader

Maxar Technologies is a long-standing leader in the commercial very-high-resolution market. Its constellation provides some of the most detailed and accurate satellite imagery available to commercial and government customers worldwide. Its operational fleet includes legacy satellites like GeoEye-1 (launched 2008) and the WorldView series (WorldView-1, WorldView-2, WorldView-3). WorldView-3, launched in 2014, set a new standard with a best resolution of 31 centimeters.

The future of Maxar’s constellation is WorldView Legion. This next-generation system consists of six identical, high-performance satellites. The first two were launched together on a SpaceX Falcon 9 rocket on May 2, 2024. The full constellation is designed to dramatically increase revisit rates. Once fully operational, the six Legion satellites will be able to revisit the most populated areas of the globe (between the mid-latitudes) up to 15 times per day. This allows for persistent monitoring of critical sites. Each satellite will provide 30-centimeter native resolution imagery, which can be further processed to 15-centimeter HD, maintaining Maxar’s position at the pinnacle of the high-resolution market.

Planet Labs: Imaging the World Every Day

Planet Labs (often just “Planet”) disrupted the Earth observation industry with a radically different approach based on “agile aerospace.” Instead of building a few large, exquisite satellites, Planet has deployed the world’s largest fleet of small, relatively inexpensive imaging satellites. This strategy allows them to achieve a monitoring capability that is unmatched in frequency and scale. Planet operates three main constellations:

• PlanetScope: This is the flagship constellation, consisting of more than 150 active “Dove” satellites, which are small 3U CubeSats about the size of a shoebox. Working together, this massive flock images nearly the entire landmass of the Earth every single day at a medium resolution of 3 to 5 meters. This daily scan is invaluable for monitoring large-scale changes in agriculture, forestry, and environmental conditions.
• SkySat: Planet also operates a constellation of 21 higher-resolution SkySat satellites. These are larger spacecraft that provide 50-centimeter resolution imagery. Unlike the continuously scanning Doves, the SkySats are taskable, meaning customers can request new imagery of specific locations. With 21 satellites, the constellation can revisit any point on Earth multiple times per day, and it is also capable of capturing high-definition video from orbit.
• Pelican: Pelican is Planet’s next-generation high-resolution constellation, designed to eventually replace the SkySats. The first tech demonstrator, Pelican-1, was launched in late 2023. The full constellation is planned to consist of 32 satellites that will offer 30-centimeter resolution, reduced data delivery times, and even higher revisit rates, positioning Planet to compete directly in the high-resolution tasking market.

Airbus Defence and Space: European VHR Imaging

Airbus is a major European player in the commercial Earth observation market, operating a multi-tiered constellation that serves a wide range of needs.

• SPOT: The SPOT (Satellite Pour l’Observation de la Terre) program is a long-running series that began in the 1980s. The currently operational satellites, SPOT 6 and SPOT 7, were launched in 2012 and 2014. They fly in the same orbit and provide 1.5-meter resolution imagery over a wide 60-kilometer swath, making them ideal for national-level mapping and agricultural monitoring.
• Pléiades: The Pléiades constellation consists of two identical satellites, Pléiades-1A (launched 2011) and Pléiades-1B (launched 2012). They provide very-high-resolution 50-centimeter imagery and are highly agile, allowing them to quickly acquire imagery of any point on the globe.
• Pléiades Neo: This is Airbus’s newest and most capable constellation, designed to compete at the highest end of the market. The first two satellites, Pléiades Neo 3 and Pléiades Neo 4, were launched in 2021. They provide 30-centimeter resolution imagery, on par with the best offerings from Maxar. The constellation was planned to have four satellites, but the final two, Pléiades Neo 5 and 6, were lost in a launch failure in December 2022. Despite this setback, the two operational satellites provide Airbus with a top-tier, high-resolution imaging capability.

Summary

The ecosystem of operational Earth observation satellites is a testament to human ingenuity—a vast, interconnected network providing a continuous stream of information about our home planet. This global infrastructure is built on the complementary strengths of public and private enterprise. Governmental programs, like the United States’ Landsat and Europe’s Copernicus, serve as the scientific backbone, providing the stable, long-term, and globally consistent data necessary to understand climate change, manage natural resources, and respond to large-scale disasters. Their commitment to free and open data has democratized access to space, fueling innovation and research worldwide.

In parallel, the commercial sector has introduced a new era of agility, offering unprecedented resolution and revisit rates. Companies like Maxar, Planet, and Airbus are pushing the boundaries of technology to serve on-demand needs for business intelligence, tactical monitoring, and rapid event response. This has created a dynamic market where different business models—from exquisite, high-resolution tasking to persistent, global monitoring—cater to a growing diversity of applications.

The overarching trend is toward a hybrid future where these sectors are increasingly intertwined. Public agencies are leveraging commercial data to supplement their own missions, while commercial companies build their services upon the foundational data and calibration standards established by government programs. This synergy is creating a more resilient and capable global observation system. As this network of satellites continues to expand and improve, it promises a future where our planet is monitored with a level of detail, frequency, and scope that was once unimaginable, empowering us to be better stewards of our only home.