The Waterbug sub-surface sampler: Design, control and analysis

Monitoring and predicting water quality poses significant challenges. Collecting enough information to characterize bodies of water is a critical bottleneck. Collecting data and samples from the surface all the way to the bottom over a short period of time would give water scientists the best spatio-temporal picture. In this paper, we present a small, light-weight, inexpensive water sensing and sampling robot, the "Waterbug", capable of descending to depths up to 10m, collecting sensor information and a water sample, and returning to the surface. The water sampler also has limited capability to adjust buoyancy to hold depth for the purpose of measuring environmental conditions at specific locations in the water column. It is small enough that a single scientist could carry several in a backpack or it could be deployed by other robotic systems. The low cost of the node makes it feasible for blanket deployment. No tools are required for field servicing and the sample collection chamber is a common syringe that can be swapped quickly for redeployment. The main challenge was developing the system model and algorithm for achieving neutral buoyancy in the presence of system and initial condition variance. Over a range of conditions, we were able to achieve an 80% success rate for meeting the neutral buoyancy criteria and a 100% success rate in capturing a sample and returning to the surface.