Remote Monitoring of LRRS Radar Towers Using Guided Wave / Acoustic Emission Technology

Advanced radar notification offered by the network of AN/FPS-117 LRRS radar towers is a critical item for warfighter capabilities. Many of these sites are over 50 years old and have had very little NDI inspection. The Tactical Shelters, Radomes, and Towers Program Office and the NDI team in the 809th MXSS at Hill AFB have managed the inspection of these towers, but they are complex structures with many difficult-to-access welds; this makes inspection time-consuming and challenging. The location of many LRRS towers in remote Alaska makes regular inspection expensive and difficult. Structural failure of an AN/FPS-117 LRRS tower would lead to high repair costs, risk of injury to operators who work/live in the radome tower, and reduced radar awareness in critical regions. Monitoring this critical, ageing system is essential for ensuring “Global Persistent Awareness”. Guidedwave has developed an Acoustic Emission (AE) procedure for inspecting the LRRS towers, including the use of novel, patented shear AE sensors. This technology fills the AFLCMC/HBZIB need for an efficient, accurate, and non-intrusive NDI technology. During a recent Phase II SBIR project, this technique has been refined and successfully demonstrated on 5 LRRS towers in Alaska and Hawaii and the EFAC tower at Hill AFB, including the detection of several large (and otherwise undetected) crack defects and areas of concern that should be monitored in many of the towers. In addition to the SBIR project, Guidedwave and a private company have invested >$500k to develop a remote monitoring AE technology for civil infrastructure. Guidedwave has successfully developed and installed a remote-monitoring system that includes AE technology and automatically initiates data collection on a predefined schedule, transmits the data to a remote server, and processes the data to display simplified trending information accessible to the customer via website. Guidedwave proposes to leverage this technology and experience to develop an automated AE remote monitoring technology for the LRRS towers. Prototype systems will be installed at the Kokee and EFAC towers with cell/satellite modems that transmit test data to a web server. Bespoke software will interpret the data IAW Guidedwave’s test protocol for the AB199 and AB259 tower designs and display simplified inspection data for the end users in the 809th NDI group. The use of multiplexing technology and clever sensor grouping will reduce system cost, and automated data analysis software will reduce the need for expert data interpretation. The technology developed under this project will be directly applicable to other radar towers, including similar designs adopted by the Canadian Air Force’s AN/TPS-70 towers and FAA and NOAA civilian towers. Additional applications could include wind turbines, which have similar cyclic loading conditions and a significant need for enhanced, affordable structural health monitoring capabilities.