Satellite observation of linear infrastructure: operational capabilities and limitations
The continuous monitoring of linear infrastructure — roads, railway lines, high-voltage electricity networks and transport pipelines — presents a structural challenge for the operators responsible for their maintenance: the geographical extent of these assets makes field inspection at the frequency required by risk management unfeasible. Earth observation from satellite platforms offers a complementary capability that allows periodic information on the condition of these corridors to be integrated into the asset management systems of operators and the competent authorities. From a technical standpoint, high-resolution optical imagery makes it possible to identify changes in the surface cover adjacent to the infrastructure — vegetation encroachment within easement strips, accumulation of materials, modifications to the immediate surroundings — provided that lighting and cloud cover conditions permit. Synthetic aperture radar interferometry (InSAR), for its part, is the most established technique for detecting subsidence and ground deformation along linear alignments, independently of atmospheric or sunlight conditions. Both modalities are complementary: optical imagery provides direct visual interpretability, whilst radar offers metric sensitivity to vertical or differential displacements of the substrate. Revisit periodicity is a determining operational parameter. Current observation constellations allow corridors of interest to be covered at frequencies ranging from several days to a few hours, depending on latitude and the available orbital architecture. For change-detection applications in critical infrastructure, the acquisition cadence must be aligned with the alert thresholds defined in the operator's preventive maintenance plans. Insufficient revisit frequency can generate detection latencies that are incompatible with operational safety requirements, whilst excessive frequency without automated processing capability produces data volumes that are difficult to manage with the available analytical resources. The limitations of the satellite-based approach must be taken into account when designing any integrated workflow. Spatial resolution conditions the detectability of small-scale anomalies, such as incipient cracks or localised defects in structural elements. Likewise, the interpretation of InSAR signals requires qualified technical personnel and adequate geodetic reference data to avoid ambiguities in displacement estimation. In this respect, satellite observation does not replace field inspection, but rather enables the prioritisation of sections requiring on-site intervention, optimising maintenance resources and reducing exposure to undetected risks across long-distance corridors. From a European regulatory perspective, critical infrastructure management frameworks impose increasing obligations regarding the monitoring and traceability of asset condition. The integration of Earth observation data into operators' information systems is a technically mature means of meeting these requirements, provided that the data chain of custody is guaranteed, interoperability with existing management systems is ensured, and derived products are validated against in situ measurements.
NASSAT - Network Satellite Systems