  Airborne radar carried on-board unmanned aerial vehicles (UAV) 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
on-board 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 during low visibility conditions enables 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. Aggregating radar measurements with
the information from other sensors is broadening the applications of drones in
life-critical situations. Signal processing techniques are critical in enabling
UAV-borne radars for human vital sign detection (VSD) in multiple operation
modes. Novel radar configurations such as in a UAV swarm and tethered UAVs are
required to facilitate multi-tasking and high endurance, respectively. This
paper provides an overview of recent advances in UAV-borne VSD with a focus on
deployment modes and processing methods.
