Satellite Remote Sensing for Hazard Monitoring

Satellite remote sensing observes mountain surfaces repeatedly from space to detect changes that may signal slope failure. It identifies instability by combining visible surface features, terrain geometry and measured ground deformation across a time series of images. It indicates where movement may be developing, but does not by itself prove that collapse is imminent.

How instability is detected

Different sensors reveal complementary signs of unstable terrain.

• Repeated optical images can reveal new cracks, scarps, displaced blocks, vegetation loss, altered drainage and expansion of an existing landslide.
• Stereo imagery and elevation data produce a digital elevation model, from which slope, relief, aspect and drainage can be mapped to identify terrain susceptible to failure.
• Synthetic Aperture Radar sends microwave pulses and can observe through clouds and darkness, which is valuable in frequently cloud-covered mountains.
• Interferometric SAR compares radar phase across repeat passes to measure small changes in satellite line-of-sight distance, revealing slow slope deformation before visible failure in suitable conditions.

From observations to hazard assessment

Analysts distinguish persistent movement from seasonal or sensor-related change by examining several dates rather than a single image.

• Deformation maps are combined with geology, slope, drainage, land cover, rainfall and seismic information to locate unstable sectors and possible triggers.
• Historical landslide inventories help identify recurring spatial patterns and support susceptibility zonation.
• High-change locations can be prioritised for field inspection, ground instruments and evacuation planning, reducing the search area in inaccessible terrain.

Limitations and safeguards

Remote sensing is strongest as a screening and monitoring tool, not as a stand-alone prediction system.

• Optical imagery is obstructed by cloud, shadow and snow, while radar may suffer from layover, shadow and loss of coherence over vegetation or rapidly changing snow.
• Radar primarily measures motion along its line of sight, so some movement directions may be poorly detected.
• Revisit interval, spatial resolution and atmospheric effects can obscure rapid or very local failures; field surveys, GNSS and ground-based instruments remain necessary for validation.