What is Interferometric Synthetic Aperture Radar (InSAR) Analysis?

Interferometric Synthetic Aperture Radar (InSAR) is a powerful remote sensing technique used to measure ground surface deformation with millimetre-level precision. InSAR uses earth observation radar data from satellites. It shows small changes on the Earth's surface that we cannot see.

"InSAR: Detecting ground movements invisible to the human eye."

What is InSAR?

InSAR combines radar images taken by satellites at different times to detect and measure changes in the Earth's surface. By analysing the phase differences between radar signals, scientists and engineers can identify ground movements over time.

How Does InSAR Data Analysis Work?

1. Data Collection:

   • Synthetic Aperture Radar (SAR) satellites, such as Sentinel-1, TerraSAR-X, or RADARSAT-2, capture radar images of the Earth’s surface.

   • These satellites transmit microwave signals, which bounce back after interacting with the surface.

     
     

2. Interferogram Creation:

   • Two or more SAR images of the same area, taken at different times, are combined to create an interferogram.

   • The interferogram reveals phase differences between the signals, indicating displacement or deformation.

     
     

3. Processing and Filtering:

   • Advanced techniques remove noise from atmospheric effects, vegetation, or other variables.

   • Persistent Scatterer Interferometry (PSI) and Small Baseline Subset (SBAS) are popular methods for detailed analysis.

     
     

4. Data Interpretation:

   • The system displays the processed data as deformation maps or time-series graphs. Colour gradients display the size and direction of movement.

   
   

SAR satellites emit electromagnetic pulses and the backscatter is received by onboard sensors.

Satellite System	Agency	Wavelength	Resolution	Revisit Time	Launch Year	Ideal Applications
Sentinel-1	European Space Agency (ESA)	C-band (5.6 cm)	5 - 20 m	6 - 12 days	2014	Monitoring Arctic sea ice, mapping the marine environment, assessing land surface risks, supporting forest and water management, and aiding in emergency response and humanitarian crises.
TerraSAR-X	German Aerospace Centre (DLR)	X-band (3.1 cm)	1 - 3 m	11 days	2007	DEM generation; hydrology, geology, climatology, oceanography, environmental monitoring, and disaster monitoring.
COSMO-SkyMed	Italian Space Agency (ASI)	X-band (3.1 cm)	1 - 100 m	16 days	2007	Seismic hazard analysis, environmental disaster monitoring, and agricultural mapping
RADARSAT-2	Canadian Space Agency (CSA)	C-band (5.6 cm)	3 - 100 m	24 days	2007	Monitoring the environment; Managing natural resources; Performing coastal surveillance.

Table 1: Comparison of SAR Satellite Systems

"Millimetre-precision monitoring that prevents billion-dollar disasters."

Applications of InSAR Analysis

InSAR is widely used across industries for monitoring and decision-making:

1. Infrastructure Monitoring:

   • Detecting subsidence beneath buildings, bridges, railways, and pipelines.

   • Example: InSAR helped identify subsidence in Mexico City, where groundwater extraction caused significant ground sinking.

     
     

2. Mining and Tailings Dams:

   • Monitoring ground stability around open-pit mines and tailings storage facilities.

   • Example: InSAR analysis alerted engineers to a developing instability at a tailings dam in Brazil, potentially preventing a disaster.

     
     

3. Landslide Risk Assessment:

   • Mapping and tracking slopes prone to landslides, especially after heavy rainfall or earthquakes.

     
     

4. Natural Hazards:

   • Measuring ground deformation caused by earthquakes, volcanic eruptions, and glaciers.

   • Example: Researchers used InSAR to monitor the uplift of the Yellowstone Caldera, providing critical insights into volcanic activity.

     
     

5. Environmental Monitoring:

   • Tracking coastal erosion, permafrost thaw, and groundwater depletion.

     
     

By taking multiple SAR images over a time period and stacking them on top of one another, analysts can generate interferograms that show ground subsidence.

"Non-invasive technology revolutionising infrastructure safety."

Why is InSAR Analysis Important?

• Non-Invasive and Cost-Effective: InSAR uses satellites to gather data. This means there is no need for on-site equipment or hard surveys.

  
  

• Large Scale Coverage: A single satellite pass can monitor vast regions in near real time, from cities to entire countries.

  
  

• High Precision: Detects movements as small as a few millimetres of spatial resolution, enabling early warnings for potential hazards.

  
  

• Weather Independence: InSAR uses radar, so it works day and night regardless of weather conditions. The radar waves can see through clouds, unlike optical images.

"Satellite-based monitoring: seeing through clouds when optical imagery cannot."

Aspect	Traditional Ground Surveys	GPS Networks	Optical Levelling	InSAR Analysis
Initial Setup Cost	$$$	$$$$	$$	$
Ongoing Operational Cost	$$$	$$	$$$	$
Coverage Area	Limited (point-based)	Limited (point-based)	Limited (line-based)	Extensive (area-based)
Personnel Requirements	High	Medium	High	Low
Temporal Resolution	Low (months)	Medium (days-weeks)	Low (months)	High (days-weeks)
Weather Dependency	High	Medium	High	Low
Access Requirements	Physical access needed	Physical access needed	Physical access needed	No access needed
Real-time Capability	No	Yes	No	Near real-time
Precision	1-5 mm	3-10 mm	0.5-2 mm	1-5 mm
Data Processing Time	Days	Hours	Days	Hours-days
Long-term Value	Low (one-time)	Medium	Low (one-time)	High (historical archive)
ROI for Large Areas	Poor	Poor	Poor	Excellent

Table 2: Cost-Benefit Analysis: InSAR vs Traditional Monitoring

Real-World Impact

InSAR analyses data to provide actionable insights for proactive decision-making, saving billions of dollars annually in infrastructure maintenance and disaster mitigation.

Want to learn more about what surfaces make for good or poor InSAR output? Read this article next: Good vs Poor Scatterers.