Terrain deformation mapping is one of the most important applications of satellite radar data.
It allows us to detect small movements of the Earth’s surface over large areas, without installing instruments everywhere on the ground. These movements can be linked to natural or human-induced processes such as earthquakes, volcanoes, landslides, subsidence, groundwater extraction, mining, tunnelling or infrastructure instability.
The method is based on Synthetic Aperture Radar data, or SAR. Unlike optical satellites, radar satellites can acquire images during the day or night and through clouds. This makes SAR particularly useful for regular monitoring.
From radar images to ground movement
A radar satellite sends a signal towards the Earth and records the signal that comes back. When two SAR images of the same area are acquired from similar viewing geometries at different times, their signals can be compared.
This comparison is called Interferometric SAR, or InSAR.
InSAR uses the phase of the radar signal to measure changes in distance between the satellite and the ground. When the ground moves between two acquisitions, this change appears in the interferometric signal. The result can be used to estimate displacement along the satellite’s line of sight.
This means that InSAR does not directly measure “vertical movement” or “horizontal movement” in a simple way. It measures movement towards or away from the satellite. Additional processing, assumptions, or data from different satellite viewing directions may be needed to interpret the full deformation pattern.
Why time series matter
A single interferogram can show deformation between two dates. This is useful after events such as earthquakes or volcanic unrest.
But many geohazards evolve slowly. Subsidence, landslides, infrastructure deformation or volcanic inflation may develop over months or years. For these cases, a time series is more useful.
Time-series InSAR methods process many SAR images together. They identify measurement points or distributed areas that remain coherent over time, and estimate how displacement evolves across the full observation period.
One widely used family of techniques is Persistent Scatterer Interferometry. It focuses on stable radar reflectors such as buildings, bridges, antennas, exposed rocks or other features that consistently return a strong radar signal. This makes it particularly effective in urban areas, infrastructure corridors and dry or rocky terrain. The original GEP article described this approach in detail, including the use of persistent radar targets and the derivation of multi-year motion histories.
What changed with Sentinel-1
The basic principles of InSAR have not changed, but the operational context has changed significantly.
Copernicus Sentinel-1 provides systematic radar observations designed to support applications such as land monitoring, emergency management and interferometric analysis. Sentinel-1 uses a repeat observation strategy that supports the creation of interferometric image pairs and deformation time series, and its data are made available systematically and free of charge to users.
This regular availability of SAR data has made it possible to move from occasional deformation studies to more systematic monitoring services. ESA has described how Sentinel-1 data can be automatically added to existing archives so that deformation maps can be updated regularly.
The recent Sentinel-1C commissioning results also show the continuing role of the Sentinel-1 mission for land deformation mapping, including monitoring subsidence, uplift, glacier flow, landslides and earthquakes.
What the products show
Terrain deformation products usually include:
- average displacement velocity over a period;
- displacement time series for each measurement point or area;
- quality indicators;
- reference point or reference area information;
- visualisation layers for GIS or web platforms.
These products are not a replacement for geological interpretation or field information. They are measurements that need to be interpreted in context.
For example, a point on a building may reflect the motion of that structure, not necessarily the motion of the natural ground below it. Areas with vegetation, snow, water, strong surface change or very rapid movement may have fewer reliable measurements. Atmospheric effects, orbital errors, topography and phase unwrapping also need to be handled carefully during processing.
Why platforms matter
Producing deformation maps is not only a scientific problem. It is also an operational problem.
A complete workflow may involve discovering SAR data, selecting suitable acquisitions, processing large image stacks, applying time-series algorithms, publishing results, visualising products and updating the analysis when new data become available.
This is where platforms such as GEP are useful.
GEP supports the use of EO processing services for geohazards applications and provides an environment where workflows can be packaged, deployed and made available to users. For service users, this means easier access to processing capabilities. For service providers, it creates a path to move algorithms from local or project-based implementations into operational services.
In short
Space-based deformation mapping works by comparing radar satellite images acquired over the same area at different times.
Small changes in the radar signal can reveal ground movement with high precision over large areas. With time-series methods and regular Sentinel-1 acquisitions, these measurements can support monitoring of earthquakes, volcanoes, landslides, subsidence, infrastructure and other geohazards.
The technical challenge is to process and interpret the data correctly.
The operational challenge is to make these methods accessible, repeatable and useful for real users.
That is the role GEP aims to support.
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