Interview

Abstract

Prof. Massimiliano Pieraccini from the University of Florence, Italy, talks to Electronics Letters about the applications of the work behind the paper ‘Interferometric RotoSAR’, page 1451. Prof. Massimiliano Pieraccini I have worked for about fifteen years in the field of radar technology, in particular with ground-based synthetic aperture radar (GB-SAR) and ground penetrating radar (GPR). My research group has designed, built up and tested several prototypes that have become industrial products manufactured by prominent companies. SAR is a powerful imaging technique originally developed for satellite and airborne platforms. Its main advantage in ground-based installation is that it allows the design of radar units with smaller antenna systems: half the size, when compared to conventional equipment. This is an essential feature for designing portable monitoring instrumentation. We have reported the first test of a new interferometric GB-SAR that I have named RotoSAR, as it exploits the movement of a rotating arm to synthesise an aperture size twice its diameter. It is potentially faster than any previous similar radar, and furthermore, it is able to detect the three components of the target's displacements in the field of view. This is an absolute novelty. Previous GBSAR could do that only by installing two or more sets of equipment, with the critical problem that radar image never is exactly the same from different points of view, because of interference and diffraction effects, and this has prevented evaluation of more then one component in the same physical point of the structure under test. An important limit, that until now has prevented a wider use of these radar in engineering practice, is the issue of the civil engineer needing to have not only a single displacement component of the structure under test, but at least two and possibly all three components. This radar responds to this issue. The “killer application” of GB-SAR is as safety equipment in large open quarries. Several hundred are currently operating worldwide with a consolidated market of millions of euros. The aim of these devices is to monitor the small displacements of the quarry slopes, that can be precursors of dangerous collapses. This new radar, faster then previous ones and with a mechanical design that is less stressful on the moving parts, could have a tremendous potential in this field of application. More widely, there are many landslides, that need to be monitored and GB-SAR are frequently used with this aim. Also in this field of application the RotoSAR offers important advantages: greater acquisition speed means more coherent interferometric images, therefore with better capability to detect ground deformations. Currently, we are planning an extensive measurement campaign for in-field testing of this new technology. In particular we would like to evaluate its performances in the monitoring of bridges and large buildings, such as dams. Furthermore, we are engaged in the design of a more advanced prototype able to test the highest possible acquisition speed, that seems to depend more on the mechanical performances than on electronic limits. The idea is to integrate a CWFM radar operating sweeps of 10ms with mechanical equipment designed to provide very fast rotations. It should be able to acquire a complete synthetic image in less then six seconds. A FM pulse radar could further increase the acquisition speed. Another development that we are planning to assess is the possibility of realising DEM (digital elevation model) using the data acquired by two half arcs during a single rotation. The very large baseline could cause difficult problems in data processing, but it could be worth working on it. In ten years I imagine SAR based on this principle operating at very high frequency (e.g. 77 GHz). They could have a diameter of only 20–30 cm and so they could be really portable systems.