On the Development of Ground-Based and Drone-Borne Radar System

Abstract

The interferometric SAR (InSAR) technique is an established analytical tool designed to analyze phase information provided by satellite-mounted synthetic aperture radar (SAR) to provide precise measurements of target displacement to a centimeter level of precision. The InSAR technique has already reached the practical stage in the measurement of ground subsidence in urban areas and in crustal deformation analysis associated with earthquakes and volcanic activities. The authors are currently developing radar systems for on-ground installation and mounting on drones. InSAR analysis can also be applied to the data acquired by these systems. We ultimately aim to develop technologies that will allow us to monitor the stability of opencast mine slopes, landslide slopes, and aging infrastructures. Measurements taken by ground-based radar systems can be conducted at all times automatically, without human operators. Measurement data can be accumulated at intervals of several minutes to several tens of minutes. Millimeter wave radar is internationally recognized as a collision prevention technology for automobiles. Our group has used this technology to develop a millimeter wave radar system capable of transmitting radio waves at a bandwidth (76 to 77 GHz) approved by the regulatory authorities. In field tests, this radar was verified to detect targets remotely from a distance of about 1.6 km and to measure displacement with an accuracy of about 0.2 mm. In a long-term demonstration test conducted inside an open-pit mine, the radar-collected data clearly captured the precursor phenomena of the slope failure. The radar also successfully detected anomalies corresponding to consolidation subsidence of sediment deposited by slope failure. The drone-borne radar we are developing will be used for periodical observations to be carried out several times a year. We designed the system to transmit the microwave band (12.8 to 12.95 GHz) over a longer wavelength than the millimeter wave band, as the phase information used for InSAR analysis becomes unstable with time. The frequencies of the transmitted radio waves adopted in this study, including those transmitted by the ground-based radar, were selected to comply with the Radio Law of Japan. The ground-based radar has reached a stage where it can be deployed practically in the field. Real-life use of the drone-borne radar has yet to be realized, though a prototype version of the system is now complete. We plan to develop algorithms for synthetic aperture processing and interferometric analysis in the future.