Abstract
In radar remote sensing, the Terahertz (THz) spectrum is presently being investigated worldwide with focus on short-range indoor and outdoor applications. The spectrum broadens the unmanned aerial vehicle (UAV) based synthetic aperture radar (SAR) applications to indoor room profiling with sub-mm resolution and material characterization as many materials have unique fingerprints at this spectrum. SAR technique requires precise localization information of the mobile radar sensor, which in conventional SAR is achieved using an existing localization infrastructure, such as a global positioning system (GPS) and inertial measurement unit (IMU). For the indoor THz SAR, the GPS does not provide coverage in indoor complex environments, and also the state-of-art compact IMU does not provide the required sub-mm accuracy. These limitations can be overcome by utilizing an indoor localization system. Therefore, this paper presents an indoor THz simultaneous localization and mapping (SLAM) system. The system comprises of passive tags based radio frequency identification (RFID) localization system and SAR that provides the UAV localization and mapping of the in-room objects. Another challenge for the UAV based indoor THz SAR that is addressed in this paper is motion compensation (MOCO). At the THz, MOCO requires special consideration due to very small trajectory deviation is in the range of carrier wavelength. Therefore, to study the effects of the sub-mm translational errors, a testbed has been set up, and measurement results are presented in this paper along with the 3D electromagnetic simulation results for a carrier frequency of 275 GHz and bandwidth of 50 GHz. Further, to compensate these errors, the sub-mm localization system is used and the results are presented to validate the proposed solution for indoor THz SAR MOCO.
Highlights
AND RELATED WORKSynthetic Aperture Radar (SAR) is a remote sensing technique that was developed in the 1950s for military surveillance
The synthetic aperture radar (SAR) principle can be explained as the radar sensors are mounted on a mobile platform, and electromagnetic (EM) waves are transmitted towards the target at different
The high-resolution mapping further provides the shape-based object detection and classification as the images are in a good similarity to the optical domain
Summary
Synthetic Aperture Radar (SAR) is a remote sensing technique that was developed in the 1950s for military surveillance. Most of the available THz SAR testbeds are limited with the system bandwidth and follow either an ideal trajectory or equipped with high weighing IMU/INS systems that cannot be mounted on the UAV [19]–[23]. Current research with raw data trajectory estimation has been demonstrated experimentally only for Bw of sub-5 GHz. As already stated, the available commercial compact IMU/INS lacks in precision and cannot be used at THz spectrum with high Bw. This paper proposes a method for MOCO using a passive sub-mm indoor localization system and the same has been investigated. The localization is here referred to the localization of the UAV throughout the SAR trajectory and mapping is room profiling with SAR such as 2D imaging of the in-room object with the positioning accuracy close to mm based on the spatial resolution provided by the SLAM system.
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