Date of Award

2018

Degree Type

Thesis

Degree Name

Master of Science in Ocean Engineering

Department

Ocean Engineering

First Advisor

Chris Roman

Abstract

A modified SCOUT autonomous kayak, owned by the Roman Lab, performs geo-referenced depth profiles at pre-defined spatial locations. The vehicle uses a single azimuth thruster to approach a goal location, and holds station while a depth profile occurs. Using an autonomous surface vehicle (ASV) to deploy a vertical profiler enables precise but adaptive sampling in typically under-sampled environments. The profiler lowers tubing into the water column with a winch, and discrete fluid samples are taken using a peristaltic pump. A conductivity, temperature, and depth (CTD) probe relates the sample depth to sensor measurements by matching their timestamps. Water quality optical sensors, housed in the vehicle hull, are plumbed in-line with the pump for continuous measurement of pumped water properties. The profiler is designed, constructed, and tested to identify relevant system characteristics, such as flush time.

The system flush time is predicted based on the total profiler volume, and maximum pump flow rate. During flushing, a step response is induced in sensor measurements due to the transition between two discrete samples. Step response testing validates the predicted flush time such that a complete system flush occurs during pump operation. Closed loop tests indicate that the optical sensors are robust to large changes in the fluid sample temperature. The completed profiler is integrated with the SCOUT ASV, and field tested at Upper Pettaquamscutt Basin, North Kingston, Rhode Island.

An initial field trial occurred with concurrent manual vertical profiling done by Dr. Veronica Berounsky. Automated dissolved oxygen measurements are found to correlate with the manual vertical profile. The vehicle's stationkeeping performance is found to be satisfactory by staying within 10 meters of the target point. Subsequent field trials confirmed that automated profiling is consistent, and repeatable.

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