Software-defined Ground-Based Synthetic Aperture Radar Interferometry

This paper presents an experimental implementation of ground-based interferometric synthetic aperture radar based on the low cost USRP platform and a computer. The purpose of the proposed system is to measure small displacements of the monitored targets over a long time period. These types of measurements are particularly useful in the field of civil engineering and ecology. Common applications are landslide monitoring or bridge and building deformation analysis, as well as glacier movement monitoring. The system implements stepped-frequency radar operation with a maximum bandwidth of 1500 MHz (500 – 2000 MHz). As expected with all interferometric measurements, due to the cyclic nature of the phase shift, the displacement must be smaller than a certain fraction of the wavelength of operation; otherwise the result will be ambiguous. In our case the displacement must be smaller (in absolute value) than a quarter of the transmitted wavelength. Due to the fact that in a software-defined radio the frequency is user selectable in a very wide range, the system can be configured to adapt to the magnitude of the expected displacement.