Interferometric SAR (InSAR)
A radar technique that compares two acquisitions of the same area to measure millimetre-to-metre ground movement.
InSAR exploits the phase difference between two radar images of the same scene. Because the phase depends on distance to the ground, tiny changes in surface elevation or position show up as interference patterns called fringes.
The technique is best known for subsidence, landslide and earthquake mapping, but it has growing relevance to carbon work: peatland surface motion tracks water-table depth, and drained peat subsides as it oxidises. InSAR therefore offers an indirect, spatially continuous proxy for peat condition that would otherwise require dense field instrumentation.
Its practical constraints are coherence and geometry. Vegetation change, ploughing or steep terrain decorrelate the signal between passes, and the method measures displacement along the line of sight rather than true vertical motion.
Frequently asked questions
What is coherence in InSAR?
Coherence measures how similar the radar response is between two passes. Low coherence means the surface changed or scattered differently, making the phase unusable.
Can InSAR measure biomass directly?
No. It measures geometric change. Biomass must be inferred indirectly, for example through peat subsidence or canopy structure models.