Deformation Measurements of Earth Dams Using a Ground Based Interferometric Radar (GBIR)

The ability to measure and monitor deformations of earth dams is an important component of dam safety inspection programs. Monitoring dam movements helps to verify acceptable in-situ performance and detect unexpected or unsafe conditions. Conventional techniques for monitoring surface deformations of dams typically involve survey methods that only measure specific points and require extensive survey campaigns to map large areas. There is a need for measurement techniques that provide a more complete picture of deformation. Repeat-pass radar interferometry is a measurement technique to detect and quantify very small movements by combining radar imagery of the same scene collected at different times. The technique is based on small changes in the phase of the reflected radar signal, which can be related to line-of-sight movements. Radar interferometry has been successfully used for years from satellite-based platforms to monitor large spatial-scale movements associated with phenomena such as permanent ground movements from earthquakes and ground subsidence from oil and water extraction. Ground-based interferometric radar (GBIR) is an emerging technology that offers several advantages over satellite-based measurements for measuring civil engineering structures, including earth dams. The University of Missouri has a unique GBIR system that is being used in an on-going study at several earth dams located in Kansas and Missouri. This paper presents an overview of deformation measurements using interferometric radar, as well as a description of the GBIR system at the University of Missouri. Results from GBIR measurements performed over several months at an earth dam embankment are presented and discussed. The results demonstrate the ability to maintain signal coherence in the radar returns over multiple months. As expected, no measurable movements were observed over time spans when the reservoir level remained constant. Complications from atmospheric effects are discussed along with results that may show small movements due to changing reservoir levels.