CASIUS 6 USBL calibration tool (Calibration of Attitude Sensors In USBL Systems) is Sonardyne’s new and improved USBL calibration and verification tool integrated with V6.00 of Ranger 2 and Marksman, which optimises the performance and accuracy of Ultra-Short BaseLine (USBL) acoustic positioning systems by accurately calibrating the biases between the USBL transceiver(s) and the vessel’s attitude and heading sensors. The tool uses the location and time of that the data is collected at to automatically model, and correct for changes in tide and refraction.

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 6 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 6 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.