ADVANCEMENTS IN SUBSEA POSITIONING ACCURACY FOR OFFSHORE PIPELINE INSTALLATIONS IN DEEPWATER ENVIRONMENTS: AN INS–USBL SENSOR FUSION APPROACH

Accurate subsea positioning is an indispensable element of offshore pipeline installation operations, particularly within deepwater environments where even minor misalignments can precipitate severe safety hazards, environmental degradation, and substantial economic liabilities. Conventional acoustic-based positioning systems, including Ultra-Short Baseline (USBL) configurations, have historically served as the workhorse for subsea positioning. However, these systems face pronounced challenges in deepwater scenarios, such as signal multipath propagation, acoustic noise interference, dynamic vessel motions, and water column stratification, which collectively compromise their positioning precision. This study proposes an advanced integration of an Inertial Navigation System (INS) with USBL technology, employing a tightly coupled Extended Kalman Filter (EKF) framework to synergistically fuse complementary sensor streams. The proposed approach is designed to mitigate drift inherent to inertial solutions while stabilizing absolute positioning fixes under challenging acoustic conditions. A comprehensive empirical field campaign conducted in a representative deepwater environment, at a nominal depth of 1500 meters, demonstrates that the integrated INS–USBL architecture reduced lateral positioning errors by approximately 38% relative to USBL alone, with improvements in vertical accuracy of 26%. These advances translate directly into significant operational and economic advantages, including the reduction of corrective re-lay operations and enhanced compliance with increasingly stringent subsea environmental regulatory frameworks. The results provide compelling evidence for the adoption of multi-sensor fusion techniques in offshore engineering, highlighting a promising direction for future research in the integration of Doppler Velocity Logs (DVL) and seabed-referenced aiding sensors to achieve centimeter-level positioning tolerances. The findings of this work support safer, more sustainable, and more cost-efficient subsea pipeline installations, thereby contributing to the broader objective of resilient offshore energy infrastructure.