iXSea ROVINS provides marine survey specialist with enhanced heave compensation - and the promise of more besides
Calesurvey works with sister companies Calegeo and Calefleet to provide world-class marine survey and contracting services to the offshore energy and telecommunications industries. The companies are constantly on the lookout for new technologies that could enhance the quality of the geophysical and hydrographic site investigations that form their core business.
On this occasion, Calesurvey was in the market for a superior motion sensor to use in conjunction with a variety of instruments, most notably an R2Sonic multibeam echosounder (MBES), onboard the Kommandor Stuart, the company's dedicated DP-2 geophysical survey vessel. Based on upcoming survey work in the seas around Greenland, where challenging, long-period swells are common, Calesurvey was particularly interested in the heave compensation performance of the motion sensor.
iXBlue proposed Calesurvey use one of its ROVINS units to provide the necessary input required by the MBES. ROVINS is based on iXBlue's innovative fiber-optic gyroscope technology and is an underwater product intended for use by the offshore industry in water depths of up to 3000 metres. The unit provides accurate position, heading and attitude data and combines a survey-grade, fully-featured, inertial navigation system (INS). Crucially, ROVINS displays the best heave accuracy in the market: 2.5 cm or 2.5% of amplitude, whichever is lower. This outstanding performance comes from using the SMART HEAVE algorithm, which intelligently filters the vertical acceleration data prior to integration and applies a 100-second delay on the datastream, during which short-term motion history is taken into account, ultimately to provide the best possible heave output.
iXBlue engineers were on hand to install the ROVINS unit on the Kommandor Stuart and to help iron out one or two minor integration issues in preparation for a trial in the North Sea. One of the key advantages of the unit was the ability to easily mount it on the same pole as the MBES. Having the motion of the two instruments so intimately coupled avoided any problems arising from twisting and shaking of the pole during the survey operations.
Most importantly, the survey results from the MBES contained half of the heave artefacts that Calesurvey was accustomed to, with twice the overall heave accuracy. Using SMART HEAVE, the MBES survey was within Calesurvey's target specification and achieved Special Order standard as defined by the International Hydrographic Organisation (IHO), and this before any post-processing of the data.
The trial was also successful in demonstrating to Calesurvey's clients ROVINS ability to provide the vessel's position in the absence of a GPS input. ROVINS in-built INS will be of considerable benefit when the vessel is operating, as is planned, in higher latitudes with high sun-spot activity, when the likelihood of GPS drop-outs rises appreciably.
iXBlue's collaboration with Calesurvey has highlighted the value of using an inertial grade motion sensor to provide heave compensation for MBES survey work. In future, it is likely that the ROVINS unit will be of value in more ways than this, as Calesurvey strives to provide its clients with the best possible survey results in the most demanding environments.