ADCP data collected from a Liquid Robotics Wave Glider®

Liquid Robotics, Inc. (LRI) has developed an autonomous vehicle, the Wave Glider®, which utilizes wave energy for propulsion, Iridium® Satellite for command, control and data exfiltration and GPS satellite transmissions for positioning. The vehicle consists of a low-profile surface float outfitted with solar panels, energy storage and shore communication infrastructure and a subsurface wing located at approximately seven meters depth connected to each other by a sophisticated tether. The wing is designed to respond to the wave energy at its depth in such a way that it provides propulsion for the vehicle toward any location chosen by the operator. The wave energy thus harnessed by the vehicle can be used for locomotion to any point of interest as well as for station keeping (by driving in a tight circle) once that position is reached. Real time communication with the shore-based operator allows monitoring of platform's location and data gathered, commanding movement to a new position, or even complete repurposing of the mission. The capability of the Wave Glider® to accomplish its mission in a variety of environments with a variety of mission profiles is now well proven. In addition, the Wave Glider® is of course capable of carrying a variety of sensor payloads. LRI and Teledyne RD Instruments (TRDI) have now partnered to provide current profile measurements from the vehicle. An initial encouraging field test in 2009 showed the feasibility sufficiently to merit further work, though there was some indication that asymmetric motion of the surface float (it tends to skate on wave faces in some sea states) combined with low resolution GPS sampling could be biasing the velocity measurements. This led to additional testing of a Wave Glider® equipped with an ADCP, higher resolution GPS and an Inertial Motion Unit in 2010. Once the extensive integration project was completed sufficiently, a new field campaign was launched for comparison of the new, more integrated Wave Glider® ADCP measurements with those of a bottom mounted Workhorse ADCP that was deployed as an independent reference. The mission profile for this field campaign included programming the Wave Glider® to circle between the shallow water in which the reference ADCP was deployed to the deeper water of a submerged canyon. In this way measurements could be taken in shallow water, where bottom tracking capability could be effectively relied upon to remove platform motion, and in deeper water where the bottom was out of range and the relative motion of the platform removed by other means. Given the change in depth, there is no reason to assume the reference ADCP measurements are valid in the deeper water. However, comparison of the reference instrument in the shallow water with the relative velocity removed by bottom track and by the other methods can prove the utility of the other methods, and continuity of measurement between the shallow, referenced and deep, unreferenced regimes would indicate that the measurement in both instances is correct. We report on the initial results of the field testing, and on the current status of the integration.