Noncontact Vital Sign Detection with UAV-Borne Radars: An Overview of Recent Advances

Airborne radar carried on board unmanned aerial vehicles (UAVs) is serving as the harbinger of new remote sensing applications for security and rescue in inclement environments. The mobility and agility of UAVs, along with intelligent onboard sensors (cameras, acoustics, and radar), are more effective during the early stages of disaster response. The ability of radars to penetrate through objects and operate in low-visibility conditions enables the detection of occluded human subjects on and under debris when other sensing modalities fail. Recently, radars have been deployed on UAVs to measure minute human physiological parameters, such as respiratory and heart rates while sensing through clothing and building materials. Signal processing techniques are critical in enabling UAV-borne radars for human vital sign detection (VSD) in multiple operation modes. UAV radar interferometry provides valuable VSD in both hovering and flying motions. In the synthetic aperture radar (SAR) configuration, UAV-based VSD is available at a high spatial resolution. Novel radar configurations, such as in through-material sensing, UAV swarm, and tethered UAVs, are required to penetrate obstacles, facilitate multitasking, and allow for high endurance, respectively. This article provides an overview of the recent advances in UAV-borne VSD, with a focus on the deployment modes and processing methods.