Aging public infrastructure is both a growing financial burden and a serious safety risk. Road collapses caused by deteriorating underground structures are a recurring danger, yet agencies responsible for maintenance often lack the budgets and personnel required to survey the extensive networks of assets thoroughly.
Traditional inspection techniques are slow, costly, and geographically limited. On-site visual inspections and vehicle-mounted ground-penetrating radar (GPR) require substantial labor and can only examine small sections at a time, making comprehensive coverage impractical. Because cavity formation and subsurface degradation develop below the surface before a sudden collapse occurs, surface-focused observation methods have struggled to provide early, actionable warnings.
Using SAR satellites to find hidden public infrastructure risks
NTT has reported what it calls the world’s first successful demonstration of a satellite-based method to identify early warning signs of underground cavity formation using Synthetic Aperture Radar (SAR). SAR uses radio waves that can penetrate asphalt and other surfaces; by analysing how those waves scatter, the method detects three principal precursors to collapse: underground cavity formation, disturbance within the ground, and resulting surface unevenness.
The approach examines scattering patterns produced by radio waves transmitted with multiple polarisations. Distinct scattering behaviours reveal different physical conditions: NTT’s research links “double-bounce reflection” with the presence of an underground cavity, “volume scattering” with internal ground disturbance, and “surface scattering” with unevenness on the roadway. By comparing satellite measurements taken at different times, analysts can track how these conditions evolve and identify areas where risk is increasing.
Because the system relies on satellite-only data, it can pinpoint high-risk locations without the need to deploy inspection crews to every site. NTT estimates this approach could reduce the cost of identifying underground cavities by roughly 85 percent compared with vehicle-mounted GPR, and says the method has been validated against actual road cavity inspection data.
From data to real-world impact
Unlike predictive models that infer risk by combining utility maps, environmental records, and other datasets, this SAR-based method directly measures physical conditions using radio-wave scattering. NTT contends that this direct measurement enables high-confidence detection using only satellite observations.
A major operational benefit of satellite monitoring is the ability to observe infrastructure on a recurring schedule. Because SAR satellites revisit areas regularly, they can detect rapidly developing deterioration that periodic, multi-year on-site inspections might miss. This increased monitoring cadence aims to reduce the chance that accelerating cavity formation goes unnoticed.
The technique is primarily designed to detect cavities forming nearer the surface. NTT positions it as complementary to an optical fibre-based ground monitoring system it also develops, which targets deeper subsurface progression. Combining both technologies could provide a more complete view of cave-in risk across different depths.
NTT plans to advance the technology beyond demonstration by conducting further experiments with local governments to refine reliability and support operational deployment. The company aims to collaborate with municipalities and commercial partners to streamline inspection workflows and make monitoring more data-driven and cost-effective.
This work falls under NTT’s C89 brand, which focuses on applying satellite data to a range of public infrastructure risks. For asset managers and public-sector technology leaders, the research suggests a shift from expensive, labor-intensive inspections toward frequent, wide-area data analysis that can target field resources more effectively.
See also: SK Telecom: Why the AI infrastructure bottleneck matters
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