USBL positioning system estimates ROV’s coordinates with 0.07 per cent slant range accuracy

Vessel & ROV News - January 17, 2012

EvoLogics' S2C USBL (Ultra-Short BaseLine) underwater positioning system demonstrated a highly accurate performance in a recent series of pool tests, estimating the position of a ROV for baffle bolt inspection in nuclear power plants.

The Submarine System for Inspection (SUSI) ROV, which was developed by AREVA, is a device used for ultrasonic inspection of nuclear reactor vessel baffle bolts. The ROV’s positioning system is required to document time and exact location of each measurement taken as the ROV examines numerous bolts that hold the baffle plates together. Such positioning system must deliver an accurate performance without obstructing or slowing down the inspection procedure.

In December 2011 EvoLogics USBL system was tested in a tracking scenario that emulates the baffle bolts testing procedure. These trials were conducted in a test pool, as such a positioning system must deliver accurate results in a confined space, where noise and multipath challenge the performance of underwater acoustic devices.

An S2C USBL is a combined underwater communication and positioning device that provides both tracking of remote targets and data transmissions. The system implements the S2C (Sweep Spread Carrier) technology, ensuring reliable performance even in noisy environments.

An S2C USBL device with a conical transducer beam pattern served as a transceiver and was mounted at the side of the test pool. An S2C underwater acoustic modem, mounted on the ROV with the transducer pointing vertically upwards, was used as a transponder. The ROV was located at the bottom of the pool within the transceiver’s transducer beam.

The S2C USBL system estimated the distance to the ROV with a highly accurate result: the RMS deviation comprised 0.04° at 2.1m distance. This result corresponds to a 0.07 per cent 1 drms slant range accuracy.

To verify the results, the ROV was moved across a vertical 85 x 100 mm testing grid with reference points that represented the actual baffle bolts. The system demonstrated consistent results and the 0.07% slant range accuracy was confirmed.

EvoLogics experts were satisfied with the system’s performance and found it suitable for tracking the ROV for baffle bolt inspections.

EvoLogics GmbH is a Berlin-based manufacturer of underwater acoustic communication systems, acoustic positioning systems and other solutions for the maritime industry.