A high frequency GPR application to the cultural heritage survey: the search of the "Battle of Anghiari" by Leonardo da Vinci

In this paper the application of a high-frequency large-bandwidth synthetic-aperture penetrating radar for inspecting masonry structures is described. The system, operating in a non-contact manner, has been expressly developed and tested for detecting embedded discontinuities in historic painted walls, where contact must be avoided in order to avert damaging the painting. The radar signal was a Continuous Wave Step Frequency (CW-SF) waveform, scanning a 4 GHz bandwidth at 10 GHz center frequency, thus providing high resolution images of the investigated structures. By mechanically moving the transmitting and receiving antennas, the radar system synthesizes a linear aperture of up to 2 m. An extensive measurement campaign was carried out on an ancient (sixteenth century) hall: The Hall of 500, in Palazzo Vecchio, Florence (Italy). This investigation was aimed at finding evidence of discontinuities in the masonry where fragments of the famous fresco "Battle of Anghiari" by Leonardo da Vinci could be hidden.