Three-Dimensional Structure Inversion Through Wide Fractional Bandwidth, UAV-Based SAR Interferometry

This paper presents a novel method to retrieve the three-dimensional structure of semi-transparent media using wide fractional bandwidth interferometric synthetic aperture radar (SAR). Interferometric SAR (InSAR) is a well-established remote sensing technique capable of providing accurate topographic information of the illuminated area. According to the InSAR principle, multiple scattering within a single resolution cell cannot be resolved using a single baseline and results in a degradation of the height accuracy. Techniques such as polarimetric InSAR and SAR tomography tackle this problem using additional measurements to obtain the three-dimensional structure of the volume. However, it requires numerous observations, which are challenging to be performed in a single-pass. The method proposed in this paper utilizes instead the frequency dependency of the InSAR coherence to invert the three-dimensional structure. The dependency can be exploited for signals with wide fractional bandwidth available on unmanned aerial vehicles (UAVs). As the extinction is in general frequency-dependent, a third observation may be needed for the inversion. In this paper, simulated radar data with wide fractional bandwidth were used to demonstrate the frequency dependency of the InSAR coherence. According to the simulation results, the frequency profile can be inverted to obtain information about the three-dimensional scattering structure. This method allows a swarm of two or three UAVs to be used for frequent and accurate monitoring of semi-transparent targets, e.g., forests and vegetation.