  Autonomous tracking of suspicious unmanned aerial vehicles (UAVs) by
legitimate monitoring UAVs (or monitors) can be crucial to public safety and
security. It is non-trivial to optimize the trajectory of a monitor while
conceiving its monitoring intention, due to typically non-convex propulsion and
thrust power functions. This paper presents a novel framework to jointly
optimize the propulsion and thrust powers, as well as the 3D trajectory of a
solar-powered monitor which conducts covert, video-based, UAV-on-UAV tracking
and surveillance. A multi-objective problem is formulated to minimize the
energy consumption of the monitor and maximize a weighted sum of distance
keeping and altitude changing, which measures the disguising of the monitor.
Based on the practical power models of the UAV propulsion, thrust and hovering,
and the model of the harvested solar power, the problem is non-convex and
intangible for existing solvers. We convexify the propulsion power by variable
substitution, and linearize the solar power. With successive convex
approximation, the resultant problem is then transformed with tightened
constraints and efficiently solved by the proximal difference-of-convex
algorithm with extrapolation in polynomial time. The proposed scheme can be
also applied online. Extensive simulations corroborate the merits of the
scheme, as compared to baseline schemes with partial or no disguising.
