Improved monitoring of wave frequency motions discussed at OTC

Tracy Dulle
Technology Editor, Surface Systems & Vessels

HOUSTON -- Differential global positioning system (DGPS) technology is improving at a fast pace, according to a study released at the 2008 Offshore Technology Conference. The study showed that modern DGPS is much better at measuring frequency motion than previously thought.

"Floating offshore installations are usually equipped with both GPS and INS [inertial navigation systems]," said Pierre Liagre with BP America Production Co. "The study shows modern GPS have the same ability as INS to measure wave frequency motions."

Using marine data collected on the BPHolstein truss spar during hurricane Katrina and BP Atlantis semisubmersible during a 2006 winter storm, the wave frequency motions extracted from the DGPS signals after correcting for pitch and roll motions show very good agreement with the INS signals in the time domain, Liagre said.

The combined technology can be beneficial, Liagre said. The independent DGPS measurements can be used to verify the accuracy, orientation, and sign conventions of the INS. INS can be calibrated by the GPS signals and the INS can provide position and angle updates between the one second GPS updates. Additionally, GPS may lose its signal and the INS can continue to compute the positions and angle during the period of lost GPS signal.

05/07/2008