A three-antenna synthetic aperture radar interferometer (InSAR) with a statistically optimal data processor for three-dimensional (3-D) terrain mapping has been proposed recently to reduce the phase ambiguity and data-noise drawbacks of the conventional two-antenna SAR interferometry technique. In this paper, a numerical simulator is developed to assess the achievable performance and various design tradeoffs of the three-antenna InSAR. The most critical conditions for the new reduced-ambiguity system operating on realistic scenes are taken into account. The phase-unwrapping procedure is included in the simulator to compare the new and the conventional technique in terms of both phase and height-estimation accuracy. The performance achievable by a three-antenna airborne InSAR system on a given site are analyzed, and the parameter optimization of the new system is investigated. The results of several case studies show that the new technique can outperform the conventional one significantly for a typical airborne configuration, especially for high-terrain steepness. It provides reduced-phase aliasing and better estimation accuracy. So, the phase unwrapping is simplified and high-quality maps of terrain height can be obtained. As a limit, absolute phase retrieval can be achieved with good accuracy and the unwrapping procedure can be avoided.

This study explores the potential of Synthetic Aperture Radar (SAR) to aid Unmanned Aerial Vehicle (UAV) navigation when Inertial Navigation System (INS) measurements are not accurate enough to eliminate drifts from a planned trajectory. This problem can affect medium-altitude long-endurance (MALE) UAV class, which permits heavy and wide payloads (as required by SAR) and flights for thousands of kilometres accumulating large drifts. The basic idea is to infer position and attitude of an aerial platform by inspecting both amplitude and phase of SAR images acquired onboard. For the amplitude-based approach, the system navigation corrections are obtained by matching the actual coordinates of ground landmarks with those automatically extracted from the SAR image. When the use of SAR amplitude is unfeasible, the phase content can be exploited through SAR interferometry by using a reference Digital Terrain Model (DTM). A feasibility analysis was carried out to derive system requirements by exploring both radiometric and geometric parameters of the acquisition setting. We showed that MALE UAV, specific commercial navigation sensors and SAR systems, typical landmark position accuracy and classes, and available DTMs lead to estimate UAV coordinates with errors bounded within ±12 m, thus making feasible the proposed SAR-based backup system.

The authors propose the use of a high-speed interferometric radar for remotely measuring both transient displacements and steady-state vibrations of architectural heritage structures in order to test their stability conditions. Demonstrative results of application of the technique to a prominent cultural heritage artwork, the tower of Giotto in Florence, Italy, are reported.

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