APPLICATION OF GROUND-BASED INTERFEROMETRIC RADAR TO IMAGING SPATIAL AND TEMPORAL PATTERNS OF LANDSLIDE DISPLACEMENT

Ground-based interferometric radar (GBIR) provides a means of addressing questions about landslides that involve monitoring spatial variability of small displacements, that may also require high temporal precision (<1 hr). As an example, this study applies GBIR to measure temporal and spatial patters of movement for two landslides: A slow (~1 – 2 cm/day) landslide near Granby, Colorado, and a very slow (~1 – 2 cm/month) landslide in the Bighorn Mountains, Wyoming. Both mass movements are modest in size (less than 1 sq. km, each), yet they have significant impacts on local infrastructure. The slide near Granby, Colorado, was observed in several, long observations sessions (5 – 36 hours, each). Radar images were acquired every 15 minutes, which permitted rigorous time-series analysis with positional uncertainties of 0.3 – 0.4 mm. The resulting time series document short-term variations in slide velocity, including apparent pulsing between the head and the toe of the slide. This may reflect short-term variations in hydrogeological conditions associated with the slide. The slower landslide in the Bighorn Mountains, Wyoming, was observed using repeated observations with the GBIR. Hence, resulting radar interferograms document deformation during the intervening 1 – 2 months between observations. In this case, radar interferometry faces additional challenges from significant changes in atmospheric conditions that introduce additional signal to the interferograms. Meteorological data acquired during the surveys permits direct calculation and removal of this effect. Resulting displacements capture spatial variations of displacement that may elude benchmark surveys or other in situ measurements. Both cases also compare the application of GBIR with satellite-based radar interferometry (InSAR), as well as ground-truth provided by GPS measurements. As a tool for geodetic imaging, GBIR offers a significant improvement in temporal and spatial resolution compared with satellite and airborne radar interferometry. The sensitivity and temporal sampling of GBIR complement well the spatial resolution and 3-dimensional displacements measured with other methods, such as terrestrial laser scanners.