Geodetic remote sensing satellites

Geodetic remote sensing (RS) satellites are orbital spacecraft equipped with a wide range of sensory technology. These systems conduct detailed surveys of the earth's topography, taking into account changes in landmass positioning and elevation, magnetic fields, and seismic and volcanic activity. The use of RS satellite technology in geodetic studies helps scientists generate invaluable data on variations in the earth's geophysical systems, including postglacial rebound, plate tectonics, and ocean circulation. Using the data collected from such technologies, geodesists can create working models of the earth's geophysical characteristics.

Basic Principles and History

In the study of Earth's shape, topography, and physical features and forces (the field known as geodesy), it is often critical to obtain a comprehensive profile before study can begin. Geodesists have increasingly looked to satellite technology to assist them in analyzing a wide range of geodynamic processes and geological events (such as volcanism and earthquakes). The remote sensing (RS) technologies aboard these spacecraft utilize many different types of survey approaches. Among the RS technologies used are laser and radar altimeters, global positioning systems (GPSs), synthetic aperture radar, and satellite-to-satellite tracking systems.

The geodetic RS satellite is rapidly becoming an invaluable tool in the study of geophysics and geodynamics. For example, RS satellites can be used to study fault zones, the movement of Earth's tectonic plates as identified by the theory of plate tectonics, and postglacial rebound, the gradual uplift and deformation of Earth’s crust and mantle after the melting of massive ice sheets. RS satellites use infrared, thermographic, and three-dimensional imaging systems to give detailed surveys that are difficult, time-consuming, or limited in coverage to conduct from the ground. These systems can focus on even the tiniest changes in the earth's surface, changes that would otherwise go unnoticed by the naked eye.

Background and History

The size, shape, and profile of the earth have for millennia been points of interest and debate among scientists. The fourth-century BCE philosopher Aristotle provided observational arguments that the earth is spherical. The Greek astronomer and mathematician Eratosthenes is generally credited with the first known calculation of Earth’s circumference. He used geometric measurements based on the angle of the sun’s rays at different locations. Variations of this geometric approach were used for centuries as scholars sought to better understand not only Earth’s size but also its shape.

In the eighteenth century, the French Academy of Sciences in Paris looked to end the debate over Earth's shape by sending expeditions to Lapland, near the Sweden–Finland border, and to the region of modern-day Ecuador. Once on site, the teams measured the length of a degree of latitude to compare Earth’s curvature at different latitudes, confirming that Earth is an oblate spheroid, slightly flattened at the poles.

By the early nineteenth century, the United States and other countries began to establish scientific networks to map their respective coastlines and borders. The precision of these networks varied and was limited by available measurement technology. With satellite geodesy, especially systems like GPS and satellite laser ranging, measurements became far more precise and globally consistent.

In the 1960s, the US Army's Ballistic Research Laboratory used satellite positioning to triangulate an area spanning Maryland to Minnesota to Mississippi. Building on that test, researchers were able to connect each mapping network and generate a precise profile of the United States. Satellites are far more advanced now, and they can carry a wide array of technologies. These technologies can provide comprehensive, multidimensional profiles of the entire Earth and monitor changes and events that occur in specific locations.

Geodesy: Active and Passive Sensor Applications

Two general types of remote sensors are used in this arena. The first type of sensor is passive: It simply detects emissions from the target source. An example of this type of sensor is the radiometer, which detects naturally generated microwave energy radiating from within the earth. The second sensor type is active: It sends a signal to the target area and measures the energy based on the return signal. An example of an active remote sensor is radar, which sends a radio signal to the target area and captures the echo.

There is a wide range of applications for remote sensing technologies in the fields of geology, geophysics, and geodesy. One area involves the study of long-term changes to the earth's outer crust and surface (a process known as deformation). In some cases, researchers use satellite gravity missions to detect changes in Earth’s mass distribution, which can be related indirectly to large-scale surface deformation processes.

For example, in 2010, scientists utilized the remote sensors aboard the Gravity Recovery and Climate Experiment (GRACE) satellites to study the thickness of the lithosphere (the layer of rock plates continually moving beneath the earth's outer crust). GRACE compiled more than seven years of data, monitoring fluctuations in the earth's gravitational field as it passed over one geographic location (the region comprising Scandinavia and parts of northern Europe and Eastern Europe known as Fennoscandia). Using these data, researchers created one-and three-dimensional models of the lithosphere and determined the approximate viscosity of the layer of molten rock located between the core and the lithosphere, called the mantle.

RS satellites are also useful for tracking crustal movement. According to the theory of plate tectonics, the lithosphere is broken into tectonic plates. These plates are in constant motion, driven primarily by mantle convection, slab pull, and ridge push forces. For example, the lithosphere is pushed down (a process called subduction). When a glacier dissipates, the lithosphere slowly pushes back out. Scientists use evidence of postglacial rebound, the viscoelastic uplift of Earth’s crust and mantle after the melting of large ice sheets, to analyze the movement of the earth's crust and to understand the geological history of a given area.

In this arena, geodetic RS satellites have proved highly useful. Researchers have used GPS, coupled with altimeters (which use lasers and radar to calculate the elevation of a surface object) and space-based imaging systems, to calculate the speed at which the crust beneath the Antarctic ice sheet is moving.

In some cases, instead of causing the formation of mountains and ridges, crustal deformation causes rock to pull horizontally along the surface. Using GPS, scientists in the Baltic region calculated the rate of horizontal strain occurring along the crust in three separate areas. However, in each area, horizontal deformation occurred at different rates. This information led scientists to conclude that horizontal strain in this region is caused not by one but by several geodynamic processes.

Sometimes, the geodynamic changes occurring on the earth's surface are accompanied by the emission of energy, such as energy in seismic waves or the release of heat. While it is possible to detect some form of energy emissions from the ground, geodetic remote sensing satellites can detect surface thermal anomalies and land cover changes over large areas. For example, from the early 2000s onward, scientists used the infrared and other thermal imaging systems aboard the National Aeronautics and Space Administration's Moderate-Resolution Imaging Spectroradiometer to classify the different types of land cover on the earth's surface (types including snow, ice forest, and rock). This study helps geodesists analyze the different forms of energy emissions from beneath the outer crust and how they travel through various types of surface cover.

Radar

Like their ground- and air-based counterparts, satellite radar RS systems are active sensors, sending their targets radio waves that in turn bounce back in the form of an echo. Radar has undergone a significant evolution recently, particularly with regard to its ability to provide a clear and precise image of its target. This characteristic is particularly important for geodetic RS satellite applications, because satellites must be both effective from a great distance and able to operate in all types of weather and at any time of day.

One of the most useful radar RS systems in geodesy is the Synthetic Aperture Radar (SAR). This type of radar emits microwaves at the target, illuminating the target in any weather condition and at any time of day. SAR is also beneficial because its signal coherently returns to the system uncorrupted by the sun's rays. Furthermore, SAR can retain all the information it obtains during a flyover. With repeated flyovers, the satellite can therefore conduct a phase comparison. Such a comparison is useful in tracking even minute changes in the position of the earth's surface.

Thermal/Infrared Imaging

Geodesy is often concerned with the differences in radiation emitted from a target. For example, variations in heat along an ice pack indicate different levels of thickness in the ice pack or activity under the ice. In this regard, many satellites used for geodetic surveys will include thermal and infrared sensors alongside other technologies. Thermal imaging also helps scientists understand fluctuations in temperature in the oceans—fluctuations potentially stemming from seismic or volcanic activity or other types of geodynamic phenomena.

Since the 1970s, for example, scientists have used passive thermal and infrared sensors to map the ice pack in the Antarctic. Their studies have also enabled them to effectively map the various degrees of sea-surface temperatures. In addition, scientists use infrared and thermal imaging sensors to record and study temperature variations in the lithosphere, shedding light on changes in plate tectonics in a given area.

Global Positioning System

GPS has become one of the most integral components of geodesy. GPS helps scientists pinpoint changes in the earth's crust down to a few millimeters. This level of accuracy has proved highly useful in monitoring crustal movements and seismic activity. For example, Turkey, a country with a long history of severe earthquakes, maintains extensive GPS/GNSS monitoring networks in and around the Marmara region and the North Anatolian Fault. This intricate network has helped scientists study with greater effectiveness the activity along that fault zone, calculating any horizontal stress that occurs during a seismic event.

The use of the GPS network in geodetic study is not limited to land-oriented applications. Because of its accuracy, GPS is also used by scientists to study the ocean floor. Such studies are difficult because they often use other forms of sensors, mostly those used for determining ocean depth. However, GPS has been known to provide a greater degree of accuracy. Scientists have combined the use of GPS technologies with acoustic positioning systems to create an effective survey system for mapping the ocean floor and monitoring noteworthy changes.

Relevant Groups and Organizations

Because of the implications of using satellite-based RS systems to create detailed geodetic surveys, a number of groups and organizations are involved.

Government agencies frequently play an important role in organizing and funding geodetic surveys. The US Geological Survey (USGS) has collaborated with NASA on the Landsat program, which provides long-term Earth observation data widely used in mapping, environmental monitoring, and geospatial analysis. Landsat 5 and Landsat 7 contributed significantly to one of the world’s largest archives of satellite imagery. The Landsat 5 and Landsat 7 crafts have helped the USGS develop one of the most extensive remote sensor data archives in the world. Also, in 2011, the National Oceanic and Atmospheric Administration (NOAA) launched its update of the extensive surveys and maps in its vast archives. NOAA has modernized many of its coastal and geospatial datasets by integrating GPS, satellite imagery, lidar, and other remote sensing technologies to improve mapping accuracy and environmental monitoring.

With the ever-increasing availability of GPS technology, a large number of university geology, geography, and earth science departments are using geodetic RS satellite technologies. Based at such institutions, scientists are using the data collected by these satellite systems to study volcanic and seismic activity, climate change (such as rising water levels and shrinking ice packs), and plate tectonics.

Geodetic surveys using RS satellite technologies are not limited to academic or government arenas. Data recorded by satellite-borne RS systems are proving highly beneficial for energy companies in search of new oil, gas, and mineral deposits. These companies often use two-and three-dimensional imaging systems, GPS, and other RS systems aboard satellites like Landsat 7 and Spot-5 to locate new sites for exploratory drilling. These companies also use such technologies for risk assessment and management purposes, calling upon them to locate and mitigate oil spills.

Implications and Future Prospects

Geodesy has seen tremendous evolution, thanks largely to the introduction of GPS and other RS technologies on low- and high-altitude satellites. Whereas approaches to geodesy were until the twentieth century, somewhat limited, the advent of the satellite and its many uses has enabled cartographers and geodesists to fill in most of the gaps left by ground-based technologies and approaches.

RS satellite systems are far more precise and powerful than those developed even in the mid-to late twentieth century. According to the US Naval Observatory, thirty-two operating GPS satellites, along with hundreds of other orbiting spacecraft, are now in orbit. Many of the onboard sensors are capable of penetrating thick cloud cover and hundreds of feet of seawater from high orbit. Hurdles for scientists and engineers still need to be overcome. For example, some GPS satellites are negatively influenced by the ionosphere (part of the earth's upper atmosphere), especially during magnetic storms and other disturbances. Scientists continue to seek ways around these hurdles so that geodetic RS satellites can continue to evolve.

GRACE and other satellite programs implemented during the first decade of the twenty-first century have provided a great deal of geodetic data in a relatively short time, inspiring scientists to build even more state-of-the-art RS satellite systems to examine more of the earth's unexplored areas, such as its lithosphere and other parts of the planet's interior. Indeed, the evolution of RS satellite systems and their application to the exploration of the earth is expected to continue into the long term.

NASA–ISRO Synthetic Aperture Radar (NISAR), a high-precision Earth observation satellite jointly developed by the National Aeronautics and Space Administration (NASA) and the Indian Space Research Organisation (ISRO), was launched on July 30, 2025. NISAR uses dual-frequency radar (L-band and S-band) to observe Earth with very high precision. It can detect small changes in Earth’s surface, such as ground movement, earthquakes, landslides, and glacier shifts. The mission is important for climate monitoring, disaster prediction, and environmental change studies through frequent global mapping. It also stands out as one of the most advanced Earth observation collaborations with open scientific data access worldwide.

The first satellite in the Meteorological Operational Second Generation (MetOp-SG) series, MetOp-SG-A1, was also launched in 2025 by the European Space Agency (ESA) and the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) to enhance global monitoring of the atmosphere, oceans, and Earth’s surface with more advanced observational instruments.

Principal Terms

geodesy: the study of the earth's shape, topography, and physical features and forces

global positioning system (GPS): the network established by satellites to navigate and map the earth

lithosphere: Earth’s rigid outer layer, consisting of the crust and the uppermost mantle

mantle: the thick layer of mostly solid rock located between Earth’s crust and core. Although extremely hot, most mantle material remains solid and slowly flows over geologic time

plate tectonics: the scientific theory that Earth’s lithosphere is divided into moving tectonic plates whose interactions produce earthquakes, volcanoes, mountain building, and seafloor spreading

post-glacial rebound: the process by which the earth's crust slowly returns to its original position after a glacier dissipates or moves away from the subduction zone

subduction: a tectonic process in which one lithospheric plate sinks beneath another plate and descends into the mantle at a convergent plate boundary

Bibliography

Argus, Donald F., and W. Richard Peltier. “Constraining Models of Postglacial Rebound Using Space Geodesy: A Detailed Assessment of Model ICE-5G (VM2) and Its Relatives.” Geophysical Journal International, vol. 181, no. 2, 2010, pp. 697–723, doi:10.1111/j.1365-246X.2010.04562.x. Accessed 28 May 2026.

Bensen, G. D., et al. “Processing Seismic Ambient Noise Data to Obtain Reliable Broad-Band Surface Wave Dispersion Measurements.” Geophysical Journal International, vol. 169, no. 3, 1 June 2007, pp. 1239–60, doi:10.1111/j.1365-246X.2007.03374.x. Accessed 28 May 2026.

“Deformation.” U.S. Geological Survey, Earthquake Hazards Program, 15 Nov. 2022, www.usgs.gov/programs/earthquake-hazards/science/deformation. Accessed 28 May 2026.

“Earth Facts.” NASA Science, science.nasa.gov/earth/facts/. Accessed 28 May 2026.

“Entering the Space Age: The Evolution of Satellite Geodesy at the Coast and Geodetic Survey.” NOAA, 19 Mar. 2024, web.archive.org/web/20240529132635/celebrating200years.noaa.gov/foundations/satellite_geodesy/welcome.html#intro. Accessed 28 May 2026.

“GRACE Fact Sheet.” NASA Science, NASA Earth Observatory, science.nasa.gov/earth/earth-observatory/grace-fact-sheet/. Accessed 28 May 2026.

“History of the Academy.” Académie des sciences, Institut de France, academie-sciences.fr/en/history-academy. Accessed 28 May 2026.

“Landsat 7.” U.S. Geological Survey, www.usgs.gov/landsat-missions/landsat-7. Accessed 28 May 2026.

Leick, Alfred. GPS Satellite Surveying. 3rd ed., Wiley, 2004.

Lillesand, Thomas, et al. Remote Sensing and Image Interpretation. 6th ed., Wiley, 2008.

“Lithosphere and Asthenosphere.” Geology In, 2025, www.geologyin.com/2025/02/lithosphere-and-asthenosphere.html. Accessed 28 May 2026.

Martin, Angel, et al. “Compact Integration of a GSM-19 Sensor with High-Precision Positioning Using VRS GNSS Technology.” Sensors, vol. 9, no. 4, 2009, pp. 2944–50.

Maus, S., et al. “Earth's Lithospheric Magnetic Field Determined by Spherical Harmonic Degree 90 from CHAMP Satellite Measurements.” Geophysical Journal International, vol. 164, no. 2, 2006, pp. 319–30.

“MODIS Data.” NASA Moderate Resolution Imaging Spectroradiometer, NASA Goddard Space Flight Center, modis.gsfc.nasa.gov/data/. Accessed 28 May 2026.

“NASA-ISRO’s NISAR Mission Set to Capture Earth’s Land, Ice in Detail.” NASA Science, 30 July 2025, science.nasa.gov/blogs/nisar/2025/07/30/nasa-isros-nisar-mission-set-to-capture-earths-land-ice-in-detail/. Accessed 28 May 2026.

“National Oceanic and Atmospheric Administration.” NOAA, www.noaa.gov/. Accessed 28 May 2026.

“NASA–ISRO Synthetic Aperture Radar (NISAR).” NASA Science, NASA, 14 Apr. 2026, science.nasa.gov/mission/nisar/. Accessed 28 May 2026.

“New MetOp Second Generation Weather Satellite Returns First Data.” European Space Agency, 2 Sept. 2025, www.esa.int/Applications/Observing_the_Earth/Meteorological_missions/MetOp_Second_Generation/New_MetOp_Second_Generation_weather_satellite_returns_first_data. Accessed 28 May 2026.

Peltier, W. R. “Global Glacial Isostatic Adjustment: Paleogeodetic and Space-Geodetic Tests of the ICE-4G.” Journal of Quaternary Science, vol. 17, nos. 5–6, 2002, pp. 491–510.

“Pierre-Louis Moreau de Maupertuis.” Encyclopedia Britannica, www.britannica.com/biography/Pierre-Louis-Moreau-de-Maupertuis. Accessed 28 May 2026.

“Plate Tectonics.” Fundamentals of Geology (Schulte), Lumen Learning via LibreTexts, geo.libretexts.org/Bookshelves/Geology/Fundamentals_of_Geology_(Schulte)/05%3A_Plate_Tectonics/5.08%3A_Plate_Tectonics. Accessed 28 May 2026.

“Remote Sensing.” NASA Science, NASA Earth Observatory, science.nasa.gov/earth/earth-observatory/remote-sensing/. Accessed 28 May 2026.

Seeber, Günter. Satellite Geodesy. Rev. ed., Walter de Gruyter, 2008.

Segall, Paul, and James L. Davis. “GPS Applications for Geodynamics and Earthquake Studies.” Annual Review of Earth and Planetary Sciences, vol. 25, 1997, pp. 301–36, doi:10.1146/annurev.earth.25.1.301. Accessed 28 May 2026.

“Tectonics.” Nature, www.nature.com/subjects/tectonics/nature. Accessed 28 May 2026.

"What Is Geodesy?" National Ocean Service, 6 June 2024, oceanservice.noaa.gov/facts/geodesy.html. Accessed 28 May 2026.