Doppler Velocity Log (DVL) navigation for observation-class ROVs

Abstract

Doppler Velocity Logs (DVLs) have become increasingly popular as navigation tools on remotely-operated vehicles, autonomous underwater vehicles, and human-occupied vehicles for over a decade. Using acoustic measurements to capture bottom tracking velocity measurements, DVLs can provide updated velocities which can in turn be used to calculate distance traveled. Thus, DVLs can perform as fundamental components of dead-reckoning (DR) underwater navigation systems and aided-inertial navigation systems (INS). Historically, the use of DVLs has been restricted to larger vehicles and vessels that possess the payload capacity and the data bandwidth to carry the subsea transducer arrays. Recently, several manufacturers have developed a new class of smaller DVLs that mark a dramatic reduction in size while maintaining comparable performance characteristics to their larger brothers and sisters. Many of these can be found as components that are integrated into the navigation systems on commercially available autonomous underwater vehicles. An exciting development in this class of DVL has been a fully self-contained system that measures approximately 4.5 inches in diameter and 10 inches in length and approximately 1 pound when submerged. Assembled with an internal compass, pitch, and roll sensor, the Explorer DVL provides a plug-and-play capability for a dead-reckoning navigation solution that can be integrated into a variety of underwater platforms. These smaller, self-contained DVLs, coupled with the payload capacity and data throughput of some observation-class ROVs, present an exciting opportunity for self-contained, dead-reckoning navigation. A dead-reckoning navigation solution on a small, man-portable observation-class ROV can be integrated into existing navigation software and control systems to provide improved survey capabilities and spatial awareness for a class of ROV that is finding increasing demand as a survey tool. Improvements and miniaturization in the technology for both the navigation system and the vehicles now grant the ability to utilize technology on platforms that are much smaller than their work-class ROV and manned submersible counterparts. Applications of this capability range from offshore bottom inspections that require self-contained positioning to support or bolster traditional acoustic positioning methods, to inshore pipeline and tunnel inspections that require geographic, real-time positioning where traditional acoustic positioning or smart tether technologies are not available. Confined access navigation, under wharfs, piers, ship hulls, or within enclosed structures is now possible with the class of vehicles that are very often called upon to perform inspection tasks in these environments. The author has been working with Teledyne-RDI and VideoRay to integrate and test a self-contained, phased-array DVL on the VideoRay Pro4 mini-ROV. The Pro4 has the demonstrated ability to carry the payload of the DVL, combined with the data bandwidth and the power supply to effectively host the navigation system and provide the necessary topside user interface. This paper will review the author's testing of the DVL navigation system in controlled environments, and compare system performance against positioning from Real-Time Kinematic GPS as well as against known benchmarks on a closed course. The author will also demonstrate how he has integrated the DVL with the VideoRay Pro4, an observation-class ROV that possesses the heading, pitch, roll, and depth data necessary to process the DVL data for real-world, geographic positions in three-dimensions. The paper will review the results of the integrated system performance in open water on a controlled course, the results of testing this integrated solution in a confined water tunnel, and demonstrate the application of this solution on a ship hull inspection.