InSAR monitoring of ground and structure movement from space
Millimetre-scale surface movement measured from radar satellites, across whole regions.
Interferometric synthetic aperture radar (InSAR) compares radar images of the same place taken on different dates to detect ground movement. It works through cloud and darkness and covers large areas at once. It is used to monitor subsidence, uplift, slope movement and infrastructure over months and years.
Along the satellite line of sight
With Sentinel-1 acquisitions
Radar penetrates cloud, works at night
Scenes span hundreds of kilometres
What is InSAR monitoring?
A radar satellite sends microwave pulses and records the returned signal, including its phase. If the ground moves between two passes, the phase changes by an amount proportional to the movement along the line of sight. Differencing the phase of two images gives an interferogram, and a stack of them gives a time series.
Multi-temporal methods such as persistent scatterer and small baseline analysis select stable reflectors, such as buildings, rocks and pipelines, and reduce atmospheric noise. The result is a map of points, each with an average velocity and a displacement history.
InSAR measures movement in one direction, the line of sight, and gives relative displacement unless tied to a reference point such as a GNSS station. It works poorly over vegetation, water and fast-changing surfaces, where the signal decorrelates.
The method is best used to find where movement is happening. Follow-up with levelling, GNSS or a drone survey then quantifies it where decisions depend on exact values.
How it works
Scope
Define the area, the period and the movement mechanisms of interest.
Acquire
Select a stack of radar scenes from a suitable satellite and orbit.
Process
Form interferograms and correct for atmosphere, orbit and topography.
Analyse
Extract velocity and time series, then interpret against geology and structures.
Report
Deliver maps, point data and a summary of findings.
What you receive
Data
a. Displacement velocity maps
b. Point time series
c. GIS-ready shapefiles or rasters
Analysis
a. Movement zone identification
b. Correlation with known causes
Reporting
a. Method statement
b. Summary report with limitations
Where it is used
SubsidenceTrack ground settling from groundwater or hydrocarbon extraction.
Reclaimed landMonitor settlement of fill at ports and coastal developments.
InfrastructureWatch pipelines, embankments, dams and roads for movement.
Slope stabilityDetect creeping slopes and landslides early.
MiningMonitor pit walls, tailings and surrounding ground.
Historic analysisUse archive data to reconstruct movement over past years.
InSAR or levelling?
| InSAR | Levelling or GNSS | |
|---|---|---|
| Coverage | Whole region from one scene | Discrete benchmarks |
| Fieldwork | None | Crews on site |
| Direction | Line of sight only | Full vertical or 3D |
| Best for | Finding where movement occurs | Exact values at control points |
Frequently asked questions
How accurate is InSAR?
Under good conditions it detects millimetre to centimetre movement along the line of sight, with accuracy depending on the target, the number of scenes and atmospheric effects. Validation against GNSS is recommended.
Can it monitor vegetated or agricultural land?
Poorly. Vegetation changes the radar signal between passes, so coherence is lost. Urban areas, rock and infrastructure give the best results.
How far back can data go?
It depends on the satellite. Sentinel-1 archives cover several years, and earlier missions allow longer histories in some regions.
Can InSAR monitor offshore structures?
Not the sea surface, as water decorrelates. It can monitor coastal land, ports, causeways and onshore facilities.
Is your site or asset moving?
Send us the area and time period and we will advise on what InSAR can detect.
