A GBSAR Operating in Monostatic and Bistatic Modalities for Retrieving the Displacement Vector

Abstract

GBSAR (Ground-Based Synthetic Aperture Radar) systems are popular remote sensing instruments for detecting ground changes of slopes, and small displacements of large structures as bridges, dams, construction works. These radars are able to provide maps of displacement along range direction only. In this letter the authors propose to use a transponder for operating a conventional linear GBSAR as a bistatic radar with the aim to acquire two different components of the displacement of the targets in the field of view.

Cross-Pol Transponder with Frequency Shifter for Bistatic Ground-Based Synthetic Aperture Radar

“…For obtaining good displacement measurements in both directions with the bistatic configuration, L should be in the order of magnitude of the distance between radar and target [6].…”

“…As described in Reference [6], the simplest transponder consists of only two antennas and an amplifier. However, a major problem of any transponder is its possible oscillation.…”

“…In the specific case of the transponder described above, the cross-polarization of the antenna pointing at the radar does not affect the bistatic operation if the second receiving antenna of the radar head is cross-polarized with respect to the transmitting antenna (see Figure 2). A further advantage of the cross-polarization is that monostatic and bistatic signals have different polarizations, so possible artifacts (described in Reference [6]) due to the mixing of bistatic and monostatic signals are greatly mitigated. Another effective way to avoid the oscillation of a high gain transponder is to shift the output frequency using a suitable frequency shifter.…”

“…These radars are able to provide displacement maps but have a major limitation: They only detect the displacement component along the range direction. Recently, in a piece published in the IEEE Geoscience and Remote Sensing Letters [6], the authors of this paper proposed a novel mono/bistatic GBSAR configuration for retrieving two components of the displacement vector using a transponder. The transponder proposed in that paper consisted of two co-polarized horn antennas and an amplifier.…”

“…However, this solution had two possible problems: (1) The gain is limited by the poor isolation between the two co-pol antennas operating at the same frequency. (2) As monostatic and bistatic signals are in the same polarization and in the same frequency, large targets behind the transponder can give monostatic signals mixed to bistatic signals that produce artifacts in the bistatic image [6].…”