July 14, 2015
Dr. Catherine Edwards (University of Georgia's Skidaway Institute of Oceanography) and Dr. Renato Castelao (University of Georgia) have recently deployed an autonomous underwater vehicle (AUV), also called a “glider,” in the Gulf of Mexico to collect data on oceanographic conditions near the site of the 2010 Deepwater Horizon spill. The glider, nicknamed MODENA, is outfitted with a CTD to measure temperature, salinity, and density, an optode to measure dissolved oxygen, and a sensor that measures turbidity, chlorophyll-a, and colored dissolved organic matter (CDOM) as she profiles in the ocean. She is also equipped with a mobile acoustic receiver, which records signals emitted from tagged fish near the glider's path.
Neutral at the surface, the glider takes in a small volume of water through its nose, making it heavier than the water around it, and moves an internal battery forward on a rail by about an inch, which points it downward. Gravity pulls the glider down, and slender wings attached to the side provide lift that controls "flight". An altimeter in the nose and pressure sensors tell the glider when to reverse the process so that glider is lighter than the surrounding water and pointing up, and then glides to the surface using buoyancy. This highly efficient method of propulsion allows MODENA to sample autonomously in the ocean for 4-6 weeks at a time on alkaline batteries.
Every 4-6 hours, MODENA comes to the surface to report her position, status, and a subset of the data she collects in real time. Computers on shore note her position, process the data, and send MODENA back on her mission. These regular surfacings are also an opportunity to adjust the glider's mission based on satellite data, information from ocean models, or even the data that she's just collected. The data sent to shore in real time are also sent to the NOAA Glider Data Assembly Center (DAC) to be integrated with other real-time observations for validation and assimilation into operational ocean models. Georgia Institute of Technology PhD students Dongsik Chang and Sungjin Cho (co-advised by Dr. Edwards and Georgia Tech collaborator Fumin Zhang) have been assisting with automating piloting, data processing and visualization, and simulated experiments that helped shape the current mission.