Mitigating Geohazard Risk through Synergistic, Multi-Band InSAR Monitoring

Geohazards pose a significant and growing threat to human populations and critical infrastructure worldwide. The impact of these hazards is further exacerbated by climate change, which is intensifying the frequency and magnitude of events, making the need for effective monitoring tools more critical than ever.

Satellite radar technology, particularly Synthetic Aperture Radar (SAR) interferometry (InSAR), has emerged as a powerful tool for geohazard monitoring. By providing high-resolution, wide-area, and all-weather monitoring capabilities, InSAR enables geoscientists and engineers to detect subtle ground movements that may precede catastrophic events. However, the effectiveness of InSAR is intrinsically linked to the characteristics of the radar signal, particularly its frequency band.

Satellite radar data is typically acquired in three different frequency bands: X-band (3 cm wavelength), C-band (6 cm wavelength), and L-band (24 cm wavelength). The European Ground Motion Service (EGMS) has made InSAR data derived from the Sentinel-1 satellite constellation (operating at C-band) freely available to a wide range of users, significantly advancing the accessibility of this technology for geohazard monitoring. EGMS Sentinel-1's medium resolution data can provide a synoptic view of a wide range of phenomena, and it proved to be extremely effective in the detection of deformations on a regional scale.

Our experience with diverse geohazards highlights the value of integrating EGMS Sentinel-1 data with data from other satellite missions operating in different frequency bands, such as TerraSAR-X, PAZ, COSMO-SkyMed, COSMO Second Generation (all operating at X-band) and SAOCOM or ALOS-2 (operating at L-band). Each frequency band possesses unique characteristics that make it complementary to the others in the context of InSAR monitoring. In fact, X-band offers high spatial resolution and sensitivity to small displacements, making it ideal for monitoring localized phenomena or monitoring individual assets, while L-band, with its longer wavelength, has greater penetration capacity through vegetation compared to both X and C-band data, making it particularly useful for monitoring movements in densely vegetated areas.

The integration of data from multiple sensors enhances our ability to monitor and predict geohazards through:

• Improved Spatial Coverage and Resolution: This allows for detailed mapping of hazard-prone areas, facilitating informed land-use planning and infrastructure design decisions.
• Increased Temporal Density of Observations:  More frequent data enables the detection of incipient movements and improved prediction of geohazard evolution, which is crucial for rapidly evolving hazards.
• Improved Accuracy of Measurements: Integrating multiple data sources reduces uncertainties and yields more accurate estimates of ground deformations, which is vital for reliable hazard assessment and risk management.

This paper explores the benefits of a synergistic, multi-band InSAR monitoring approach for risk mitigation. Using a gallery of examples of how complementary data sources improve InSAR analysis, we aim to contribute to the design of more powerful decision support systems. These systems can enable timely interventions that should protect communities and infrastructure from geohazards, particularly in a changing climate.