Remote Rock-Fall Monitoring with an Interferometric Radar System

A ground based interferometric radar system was employed for a two-day trial period to monitor potential rock-fall of an at risk slope in Glenwood Canyon, CO. The slope of concern is directly above Interstate 70 and has previously released damaging rock-fall. A monitoring system could provide improved safety for motorists and the opportunity to mitigate potential rock-fall or slope movement prior to highway damage. Displacement measurements were made from near the rim of the south side of the canyon, approximately 1000 feet above the highway and 3000 feet across the canyon from the slope of interest on the north side. The compact interferometric radar system was installed in the remote canyon location via helicopter access. The system was operated continuously during the trial period with no disturbance to the highway below or other nearby facilities. The interferometric radar system utilizes the stepped-frequency-continuous-wave (SFCW) technique along with a synthetic aperture (SAR). The analyzed radar data are overlain on a digital terrain model (DTM) to illustrate the locations of the measured pixels. Approximately 40,000 pixel locations were simultaneously monitored to accurately measure movements of 0.01 inches or greater. Measurements were performed at approximately 6 minute intervals. The maximum line-of-sight displacements measured within the 22 hour testing period were approximately 0.30 - 0.50 inches. The measured displacements appear to be influenced by daily temperature cycles. The time domain data were then differentiated in order to calculate the velocity of each measured pixel; an increasing velocity has been shown to be an indicator of imminent slope failure. Although it was not possible, due to the time limited data set, to determine if any of the monitored movement indicates potential of a rock fall hazard, the interferometric radar system has been shown to be a viable monitoring option.