Autonomous Sampling of Water Columns Using Gliding Robotic Fish: Algorithms and Harmful-Algae-Sampling Experiments

Gliding robotic fish, which is a hybrid of underwater gliders and robotic fish, is energy efficient and highly maneuverable and holds strong promise for long-duration monitoring of underwater environments. In this paper, a novel scheme is proposed for autonomously sampling multiple water columns using gliding robotic fish. The scheme exploits energy-efficient spiral-down motion to sample each water column, followed by sagittal-plane glide-up toward the direction of the next water column. Once surfacing, the robot uses Global Positioning System guidance to reach the next column location through swimming. To enhance the path-tracking performance, a two-degree-of-freedom controller involving H-infinity control is used in the spiral motion, and a sliding-mode controller is employed to regulate the yaw angle during glide-up. The sampling scheme has been implemented on a gliding robotic fish prototype, Grace, and verified first in pool experiments and then in field experiments involving the sampling of harmful algae concentration in the Wintergreen Lake, Michigan.