  This paper develops and compares two simple asynchronous distributed
searchlight scheduling algorithms for multiple robotic agents in nonconvex
polygonal environments. A searchlight is a ray emitted by an agent which cannot
penetrate the boundary of the environment. A point is detected by a searchlight
if and only if the point is on the ray at some instant. Targets are points
which can move continuously with unbounded speed. The objective of the proposed
algorithms is for the agents to coordinate the slewing (rotation about a point)
of their searchlights in a distributed manner, i.e., using only local sensing
and limited communication, such that any target will necessarily be detected in
finite time. The first algorithm we develop, called the DOWSS (Distributed One
Way Sweep Strategy), is a distributed version of a known algorithm described
originally in 1990 by Sugihara et al \cite{KS-IS-MY:90}, but it can be very
slow in clearing the entire environment because only one searchlight may slew
at a time. In an effort to reduce the time to clear the environment, we develop
a second algorithm, called the PTSS (Parallel Tree Sweep Strategy), in which
searchlights sweep in parallel if guards are placed according to an environment
partition belonging to a class we call PTSS partitions. Finally, we discuss how
DOWSS and PTSS could be combined with with deployment, or extended to
environments with holes.
