CASIUS USBL calibration tool (Calibration of Attitude Sensors In USBL Systems) is a Microsoft Windows based software application that optimises the performance and accuracy of Ultra-Short BaseLine (USBL) acoustic positioning systems by accurately calibrating a vessel’s attitude sensors such as Gyros and Vertical Reference Units (VRUs).

The process starts by deploying a reference acoustic transponder on the seabed. Next, the vessel sails in a pre-determined calibration pattern over and around the transponder whilst simultaneously collecting DGPS, USBL, VRU and Gyro Compass data. During this process, the data is logged by the USBL system and CASIUS application for post-processing.

Once the vessel has performed its calibration pattern over the seabed transponder, the DGPS and USBL acoustic range data is processed by CASIUS to compute an unbiased estimate of the reference beacon position, the grid sound velocity and the antenna offsets.

USBL data is then compared with predicted data from the DGPS/ reference transponder to estimate the pitch, roll and heading errors. This process is repeated until the result is optimised.