Complementary control allocation for a Lagrangian seafloor imaging platform

The depth controller for a Lagrangian imaging float is detailed, and performance results from simulation and field experiments are used to demonstrate the utility of a model based controller with a complementary control allocation approach. The float is an over actuated system in depth/altitude, which is the only degree of freedom controlled. Vertical control is accomplished using a combination of active buoyancy modulation and a conventional propeller thruster. The proposed depth control algorithm is designed to take advantage of the high authority, high bandwidth inputs available from the thruster, and the low bandwidth trim input available from the buoyancy controller. The float vertical dynamics are modeled as a double integrator in the input force, and empirically derived parameters are used to simulate actuator inputs and system response over pre-recorded bathymetry profiles. Simulation and preliminary experimental results indicate that significant reductions in actuator power can be achieved in field conditions, and that the combination of thruster and buoyancy control provide the altitude tracking performance required for benthic imaging.