  We propose a novel scheme for surveillance of a dynamic ground convoy moving
along a non-linear trajectory, by aerial agents that maintain a uniformly
spaced formation on a time-varying elliptical orbit encompassing the convoy.
Elliptical orbits are used as they are more economical than circular orbits for
circumnavigating the group of targets in the moving convoy. The proposed scheme
includes an algorithm for computing feasible elliptical orbits, a vector
guidance law for agent motion along the desired orbit, and a cooperative
strategy to control the speeds of the aerial agents in order to quickly achieve
and maintain the desired formation. It achieves mission objectives while
accounting for linear and angular speed constraints on the aerial agents. The
scheme is validated through simulations and actual experiments with a convoy of
ground robots and a team of quadrotors as the aerial agents, in a motion
capture environment.
