What InSAR can and cannot reveal about a property

For a property with good radar visibility — solid structures, hard surfaces, an unobstructed view from the satellite — multi-temporal InSAR can typically establish: whether measurable movement occurred over the observation period; its average rate along the line of sight; how movement evolved through time, including seasonal patterns, steady trends, accelerations, or step changes; and how the property's behaviour compares with its immediate surroundings.

That last comparison is often the most useful single output. A building settling at the same rate as its whole neighbourhood tells a different story than one moving differentially relative to adjacent stable ground.

InSAR cannot see structural condition — cracking, distortion, or foundation state must be assessed by engineers. It cannot directly measure below-ground processes: soil type, groundwater, voids, or foundation depth are invisible to radar. It measures along one viewing direction per geometry, so purely horizontal movement perpendicular to that direction may be underrepresented. And where a site presents no stable reflectors — dense vegetation, bare soil, frequent surface change — there may simply be no measurement points on the asset itself.

There is also a temporal boundary: radar archives constrain how far back the history reaches (systematically to 2014 with Sentinel-1, earlier only where older missions covered the site), and movement between acquisitions that exceeds what the radar wavelength can track unambiguously may be underestimated.

Treat InSAR as a historical movement record with documented uncertainty, not as a verdict on a building. In due diligence and risk review, that record answers questions nothing else answers at comparable cost — provided the answer is interpreted alongside engineering, geotechnical, and documentary evidence.