# InSAR ground motion monitoring with satellite radar InSAR compares radar images of the same area, acquired from the same viewing geometry at different times. The phase change of the echo shows how far the ground or a structure has moved towards or away from the satellite. Using many images, the European Ground Motion Service specifies a mean velocity resolution better than 1 mm per year. ## What InSAR is InSAR stands for interferometric synthetic aperture radar. A radar is an active system: it sends pulses of microwave energy and records the echo, so it provides its own illumination and works without sunlight. Unlike an optical sensor, a radar can see through clouds, fog and dust [1]. Copernicus Sentinel-1 is such a radar satellite and gathers data day and night [6]. A synthetic aperture radar records both the amplitude and the phase of the echo. The phase carries information about changes in the distance between the sensor and the target [1]. Interferometry compares the phase of two images of the same area, acquired from the same geometry, to make these changes visible. Sentinel-1 works at a wavelength of about 5.55 cm [1]. Modern processing combines many images instead of two. These multi-interferogram techniques overcome limits of the basic method such as atmospheric noise [1]. Persistent scatterer interferometry, one of these techniques, relies on measurement points whose radar echo stays stable over time [1]. With such techniques, Sentinel-1 tracks how surface features such as houses, bridges and rocky outcrops move vertically and sideways over time [6]. ## The European Ground Motion Service The European Ground Motion Service (EGMS) is part of the Copernicus Land Monitoring Service. It uses Sentinel-1 radar data to measure ground motion across Europe, and the data are free for anyone to use [5]. It is updated once a year [4]. EGMS comes in three product levels [2]: - **Basic:** displacement along the satellite's line of sight, relative to a reference point within each processed area. - **Calibrated:** the same data referenced to a model derived from GNSS measurements, so that values are absolute and comparable across areas. This is the main product for most users. - **Ortho:** vertical and east-west movement, derived from the calibrated product and resampled to a 100 m grid. * **Satellite:** Copernicus Sentinel-1 (radar) * **Mean velocity resolution:** better than 1 mm per year * **Point resolution:** 5 by 20 m for persistent scatterers * **Ortho grid:** 100 m * **Release window:** five years; latest release (April 2026) covers 2020 to 2024 * **Cost:** free of charge Specifications from the EGMS product description, version 3.0, August 2025 [2], and ESA [5]. **Figure:** Graz from above with thousands of coloured EGMS points on a regular grid over a satellite image. Almost all points are green or yellow-green. A small group of red points lies in the south-east of the city. Graz in the EGMS ortho product, vertical movement, release 2020 to 2024: each point is a cell of the 100 m grid, coloured by its mean velocity. Almost all points are close to stable; a small group in the south-east moves down, and the EGMS Explorer gives the marked point a mean velocity of minus 8.7 mm per year. Generated using European Union's Copernicus Land Monitoring Service information (EGMS, release 2020 to 2024). Background: contains modified Copernicus Sentinel data 2025 (Sentinel-2, 1 September 2025). Points taken from the EGMS Explorer and laid over the background by LETO SPACE. [8] ## Where it helps Radar interferometry is increasingly used to assess ground deformation risk for large infrastructure, the European Ground Motion Service provides millimetre-accuracy maps at European scale, and satellite imagery supports every stage of the infrastructure life cycle, from site selection to post-construction monitoring [7]: - **Planning:** ground deformation risk maps help characterise potential sites. - **Construction:** large-scale monitoring of the surroundings detects deformation caused by the works, for example by tunnelling. - **Operation:** the wide coverage suits linear infrastructure such as railways, roads, electric lines and pipelines, whose size makes monitoring on site costly. EGMS maps subsidence and landslides; even modest subsidence can weaken buildings, bridges, railway lines, sewer pipes, dams and sea defences [5]. ## What you get For each measurement point, the EGMS calibrated product provides the mean velocity, the acceleration, the amplitude of seasonal movement and the full displacement time series [2]. In practice this becomes: - a map of measurement points coloured by velocity in millimetres per year - time series for single buildings, bridge sections or route segments - a list of zones where movement exceeds a threshold that you define - a basis for targeting on-site equipment at the zones at risk [7] ## Limits **Limits** - **Only along the line of sight:** The radar measures movement along its line of sight. It is less sensitive to movement in the north-south direction, which EGMS does not measure with InSAR \[2]. - **Vegetation and change:** Changing vegetation, ploughed fields and demolition or construction disturb the signal \[1]. The specified minimum point density is 5,000 per km² in continuous urban areas and 100 per km² in open land with little vegetation \[2]. - **Steep terrain:** In areas of high relief, radar geometry effects (layover, foreshortening and shadow) leave gaps, and the ortho product has no values there \[2]. - **Not real time:** EGMS is updated once a year \[4]. Where a risk develops quickly, ground instruments are needed for real-time monitoring. In mining, satellite data complement in-situ sensors such as ground-based radar and piezometers in monitoring the stability of open pits and tailings dams \[7]. ## How we help Because EGMS data are free, they are a good first step: they show whether ground motion matters for your sites or routes before you specify anything. If you need more, for example recent data during construction works or monitoring linked to your asset management, we write the [requirements](https://leto.space/consulting/procurement/) and compare the providers. [More on strategy and use cases](https://leto.space/consulting/strategy/) The marketplace on [Spacegraph](https://leto.space/spacegraph/), our discovery platform, has a use-case category for infrastructure integrity. ## Related use cases - [Monitoring pipelines and grid corridors](https://leto.space/use-cases/pipeline-corridor-monitoring/): Ground motion, vegetation and activity along energy routes. - [Monitoring rail infrastructure](https://leto.space/use-cases/rail-infrastructure-monitoring/): Track condition and trackside vegetation from satellite data. - [Construction and real estate](https://leto.space/industries/construction-and-real-estate/): All use cases for construction, infrastructure and real estate. - [Mobility and logistics](https://leto.space/industries/mobility-and-logistics/): Use cases for road, rail, aviation and maritime transport. ## Frequently asked questions ### What is InSAR? InSAR stands for interferometric synthetic aperture radar. A radar satellite sends microwave pulses and records the strength and the phase of the echo. Interferometry compares the phase of two images of the same area taken from the same geometry, which reveals changes in the distance between the satellite and the ground [1]. Combining many images over time turns these changes into a history of movement for each measurement point. ### How accurate is InSAR? For the European Ground Motion Service, the specified mean velocity resolution is better than 1 mm per year. The standard deviation of a single displacement value is 4 mm in the basic product and 8 mm in the calibrated and ortho products [2]. The mean velocity has a specified standard deviation of 0.7 mm per year; in the basic and calibrated products this applies to points with a coherence above 0.7, which means a stable radar echo [2]. ### Is the EGMS data free, and how current is it? Yes, the data are free and accessible to anyone [5]. The service is updated once a year, and the EGMS Explorer shows the latest two releases [4]. Each release covers a five-year window [2]; the latest, published in April 2026, covers 2020 to 2024 [3]. If you need data on current works, that becomes a requirement for a dedicated service. ### How do we start a pilot? Look at the free EGMS data for your sites or routes first. They can show whether ground motion is an issue and where. Then decide whether you need more: newer data, a denser network of points or a combination with sensors on site. Our [consulting overview](https://leto.space/consulting/) shows the path from the problem to operation. ## Sources 1. [European Ground Motion Service (EGMS): Algorithm Theoretical Basis Document, version 4, Copernicus Land Monitoring Service, European Environment Agency (EEA), 2025-08-07](https://library.land.copernicus.eu/products/European_Ground_Motion_Service_Algorithm_Theoretical_Basis_Document_v4.html) 2. [European Ground Motion Service (EGMS): Product Description and Format Specification, version 3.0, Copernicus Land Monitoring Service, European Environment Agency (EEA), 2025-08-07](https://library.land.copernicus.eu/products/European_Ground_Motion_Service_Product_Description_v3.html) 3. [Product update: European Ground Motion Service 2024, Copernicus Land Monitoring Service, 2026-04-29](https://land.copernicus.eu/en/news/egms-annual-update-brings-new-data-improvements-to-egms-explorer) 4. [European Ground Motion Service (product page), Copernicus Land Monitoring Service, accessed 2026-10-06](https://land.copernicus.eu/en/products/european-ground-motion-service) 5. [Tap into Europe in motion (European Ground Motion Service), European Space Agency (ESA), 2022-07-26](https://www.esa.int/Applications/Observing_the_Earth/Copernicus/Sentinel-1/Tap_into_Europe_in_motion) 6. [Sentinel-1 mission… did you know?, European Space Agency (ESA), 2025-11-03](https://www.esa.int/Applications/Observing_the_Earth/Copernicus/Sentinel-1/Sentinel-1_mission_did_you_know) 7. [EU Space Market Report 2026, Issue 1, EU Agency for the Space Programme (EUSPA), 2026-05-26](https://www.euspa.europa.eu/sites/default/files/documents/EU_Space_Market_Report_2026.pdf) 8. [EGMS Explorer: Ortho vertical product (EGMS-ORTHO-U-2024-patch1), release 2020 to 2024, Copernicus Land Monitoring Service, European Environment Agency (EEA), accessed 2026-10-08](https://egms.land.copernicus.eu/) Page: