Directional Wave Spectra Sensing Module for Autonomous Underwater Vehicle Gliders

The SeaView Systems Inc. SVS-603HR sensor has been in use for around 10 years and has been at the forefront of the trend towards vehicular deployment of wave sensors. The SVS-603HR is widely used throughout the world on a variety of buoy platforms as well as surface and submersible vehicle-based deployments. This has resulted in the accumulation of both experience and data archive for these deployments. For example, a recent vehicle-based deployment of the SVS-603HR in the Gulf of Mexico produced data over a range of 38 days, targeting measurements near a reference buoy.The SVS-603HR was designed from inception to target deployment on a wide range of buoy hulls, including capabilities for RAO transfer functions that can correct for non-ideal wave following behavior. These capabilities are a key component of the adaptations that are required for deployment on vehicular platforms.Three wave sensors have been tested on Teledyne Webb Research (TWR) Slocum underwater gliders over the past decade. One of those sensors, SeaView’s SVS-603, has progressed to the point where it has now been integrated into a Slocum glider, the glider has performed multiple sea deployments, and onboard processed wave data has been transmitted to shore in near real time in a joint project by TWR and SeaView.Data from the previous deployments which exploit direct comparison of glider-based measurements obtained via fly-by collocation with existing buoy-based sensors will be used to assess the quality of directional spectra measurements that can be obtained with the Slocum Glider and inform potential improvements in the wave sensor sampling and data processing design.This experience and the data that it has produced will provide valuable insight regarding potential shortcomings of current measurements and models. In addition, much of the experience gained in recent years by deployments of the SeaView wave sensor on various surface platforms will also offer a basis for qualifying existing models and identifying areas for improvement.Previous analysis of deployment data for this system focused primarily on summary wave statistical parameters rather than directional spectra. While the basic mathematics required to create a transfer function is available, this process can be stymied by a number of issues that come up in practice such as sampling misalignment between reference platform and vehicle under test, filtering techniques that may cause misalignment between platforms and others.The overall ecosystem that SeaView has developed for testing, verification and new model design for the SVS-603HR includes a powerful emulation capability. This software system allows new models to be back-tested against data from existing deployments. For example, an improved model for wave directional spectra can be back-tested against SeaView’s extensive archive of deployment data from a wide range of platforms including buoys, surface vehicles and the TWR Slocum Glider.