Why INS/DVL Alone Cannot Solve Long-Duration AUV Drift

The baseline GPS-denied AUV navigation architecture combines a Strapdown Inertial Navigation System (SINS) with a Doppler Velocity Log (DVL) — and both sources are well understood to produce accumulating errors. SINS errors grow through integration of accelerometer and gyroscope noise; DVL errors arise from acoustic beam geometry and seabed returns. As multiple patents in the dataset note, “inertial navigation system positioning errors accumulate continuously with time,” making long-term high-precision positioning impossible without external correction. This is the fundamental constraint that all other approaches in this analysis are designed to address.

A dual-monitoring architecture described in a 2026 patent from Beijing Zhonghang Tianyou Technology Co., Ltd. represents the current state of the art for pure INS/DVL mitigation. The system continuously monitors IMU acceleration variation and DVL wave-velocity quality fluctuation in parallel, performs independent reliability analyses of each signal, and applies a dual-determination decision logic to select the appropriate position correction scheme. Critically, it also maintains a “path position credibility score” over successive time windows — triggering path stability correction measures only when drift accumulation has exceeded a statistically significant threshold.

For deep-sea AUVs that cannot access DVL bottom-tracking returns during descent, Northwest Polytechnical University’s 2018 patent introduces a bidirectional smoothing strategy: a forward Kalman pass during the mission is supplemented by a backward re-processing pass once the AUV surfaces and acquires GPS, correcting the entire submerged trajectory retroactively. This “forward + reverse” scheme reduces mission-average positioning error without requiring any in-mission surfacing events — a significant operational advantage for deep-sea science and survey missions where surfacing mid-mission is impractical or impossible.

Acoustic Positioning as the Primary External Correction Anchor

Because INS/DVL drift is unbounded over time, the principal strategy for long-duration missions is periodic injection of absolute position fixes from acoustic systems — which are unaffected by the electromagnetic attenuation that blocks GPS. The patent dataset covers all three major acoustic positioning architectures: Long Baseline (LBL), single-beacon passive, and surface buoy-based systems, each with distinct trade-offs between infrastructure cost, positioning accuracy, and operational area.

Long Baseline (LBL): From Four Transponders to Two

Conventional LBL systems require four seabed transponders whose positions must be pre-calibrated. The key innovation from CSIC 707 Research Institute’s sparse LBL tight-coupling method (2018, updated 2020) is that it achieves positioning performance equivalent to conventional four-transponder LBL using only two transponders. As the AUV approaches the edge of one transponder pair’s coverage, it deploys a new pair and uses a local sub-filter to estimate their positions — enabling seamless, rolling coverage for large-area, long-duration missions “without restricting the AUV’s operational area to the acoustic array configuration.” Hohai University’s 2021 LBL integration patent adds a generalized cross-correlation algorithm that separates true time-delay from multipath and sound-speed-profile distortions, explicitly noting that “LBL does not accumulate errors” and can therefore bound SINS drift indefinitely within transponder coverage.

Single-Beacon Passive Acoustic: No Seabed Infrastructure Required

Southeast University’s bearing-only passive acoustic positioning method (2019) places a single acoustic source on the seabed and computes the AUV’s geodetic position from phase differences between signals received at bow and stern hydrophone arrays. By using phase difference (angle-only) rather than time-of-flight (range), the method is inherently immune to sound-speed irregularities that cause distance measurement errors. The AUV does not need to surface for position updates, preserving covertness — a decisive advantage for military and sensitive survey missions. A related Southeast University patent (2016) applies a sliding time window over multiple AUV positions to solve for location, reducing the required AUV displacement and limiting SINS error growth within each positioning window.

“Bearing-only passive acoustic positioning eliminates range-measurement sound-speed errors and removes the need to surface, making it the preferred approach for covert or military-constrained missions.”

Sound-Speed Uncertainty: The Fundamental Acoustic Bottleneck

Sound-speed variation with depth, temperature, and salinity is a fundamental accuracy bottleneck for all acoustic positioning systems, because it directly distorts time-of-flight range measurements. China University of Petroleum (East China)’s 2025 semidefinite programming method constructs a pseudo-linear positioning equation set, applies semidefinite relaxation to convert the constrained least-squares problem to a semidefinite programming problem solvable via interior-point methods, and then refines the estimate through a weighted least-squares correction step — simultaneously estimating AUV position and the unknown sound speed. This approach, which is also validated by standards from ITU on underwater acoustic propagation, removes the need to assume a known sound-speed profile, improving accuracy in thermocline-affected environments.

Surface Buoy Acoustic + MPC: Closing the Control Loop

Zhejiang University’s integrated acoustic positioning and path tracking control architecture (2021, updated 2022) uses three surface buoys emitting periodic acoustic signals; time-of-arrival differences are processed with an extended Kalman filter to estimate AUV state. During intervals between acoustic fixes, the AUV’s nominal kinematic model performs dead-reckoning. The integrated model predictive controller (MPC) handles both positioning uncertainty and ocean current disturbance simultaneously, achieving “a balance between control performance and computational efficiency.” For large-depth dives where acoustic correction is unavailable during descent, Harbin Engineering University’s 2019 patent uses a surface support ship to broadcast NED-frame position and timing information, combined with the AUV’s CTD sensor data, fused through a strong-tracking UKF algorithm to correct SINS throughout the dive — mitigating the “hundreds to thousands of meters” of error that pure-inertial descent would otherwise produce.

Machine Learning and Data-Driven Error Compensation

When sensors fail or environmental conditions degrade measurement quality, purely physics-based navigation systems lose accuracy rapidly — and hardware redundancy is expensive and space-constrained on AUVs. A distinct family of patent approaches uses machine learning to model, predict, and compensate for navigation errors without requiring additional sensors.

DVL Failure Compensation via Dynamics-Based Velocity Models

DVL failure is a critical single-point vulnerability in standard AUV navigation. Ocean University of China’s 2019 patent addresses this directly: a velocity model is trained on historical data incorporating propeller RPM, rudder angles, heading angle, and AHRS-measured accelerations and angular rates. When DVL anomalies are detected, the model-predicted velocity transparently substitutes for the DVL output, preventing the “large navigation deviations or even system paralysis” that would otherwise occur. Crucially, the training set is continuously augmented during normal operation, so the model improves as a function of each vehicle’s specific hydrodynamic characteristics over time — a self-improving system that becomes more accurate the longer the AUV operates.

FastSLAM 2.0 with Fuzzy Q-Learning for Docking Navigation

Shenyang University’s 2025 patent addresses the specific and technically demanding scenario of AUV docking — where both AUV and docking station position must be estimated simultaneously. The method extends the FastSLAM 2.0 algorithm with a fuzzy Q-learning process noise adaptation scheme, addressing the common problem that “process noise statistical characteristics are difficult to accurately measure in the underwater environment.” Without this adaptation, SLAM filter divergence produces gross positioning errors over long missions. According to research published by IEEE, adaptive noise estimation is a recognized challenge in underwater SLAM implementations, making this approach technically significant.

Seabed Coherence Mapping and Cooperative Multi-AUV Positioning

Two additional strategies extend drift correction to scenarios where neither acoustic infrastructure nor DVL is reliable: terrain-referenced navigation using seabed imagery, and cooperative positioning across AUV swarms. Both approaches eliminate dependence on any fixed external infrastructure.

Synthetic Aperture Sonar Coherence Map Navigation (Raytheon)

Raytheon Company’s coherence map navigation system — filed as a PCT application in 2017 and subsequently granted in Japan (2019, 2020) — is the most technically distinctive approach in the dataset. The system acquires complex synthetic aperture sonar returns of the seabed during an ingress pass and generates a complex seabed image. During the return egress pass, locally generated complex images are compared against the stored ingress image using a normalized cross-correlation coefficient (NCCC). A maximum NCCC indicates that the AUV’s along-track position has been found by map-matching, providing an absolute position fix with no acoustic infrastructure whatsoever. The system continuously monitors the NCCC trend to determine whether the AUV is converging to or diverging from the reference track — enabling closed-loop position correction along the entire egress path. This approach is analogous to terrain-referenced navigation used in cruise missiles, as documented by DARPA, but adapted for the underwater sonar domain.

“Seabed coherence map navigation offers the only beacon-free, infrastructure-free absolute position fix method in the dataset — uniquely suitable for denied or pristine ocean environments.”

Cooperative Multi-AUV Positioning: Distributing Accuracy Through a Swarm

Multi-AUV cooperative positioning leverages inter-vehicle acoustic ranging to provide external position corrections without any fixed infrastructure. Beijing Institute of Technology’s 2014 patent describes a fully distributed protocol in which each AUV periodically broadcasts its current position and a coordinate accuracy metric (lambda). When an AUV’s own accuracy falls below a threshold, or when at least three neighbors have higher accuracy, it updates its position using neighbor coordinates — effectively propagating high-accuracy positions through the swarm. The patent explicitly accounts for ocean current effects on positioning accuracy degradation over time. A second Beijing Institute of Technology patent from the same year uses inter-vehicle distance measurements via TDOA acoustic ranging to calibrate dead-reckoning tracking coordinates, “reducing tracking errors and extending the effective underwater working time.”

CGG Services SA’s commercial-scale cooperative positioning system for seismic survey AUV arrays (US, 2019; WO, 2015; EP, 2016) implements a formation-geometry approach: because the planned inter-vehicle spacings are known, any AUV can compute its absolute position from neighbor ranges. This approach requires no seabed infrastructure and functions as long as at least some network members have reliable position estimates. The formation geometry itself acts as a rigid positioning reference — a conceptually elegant solution that scales with fleet size. For mixed-platform scenarios, Harbin Engineering University’s 2025 patent coordinates USV-mounted acoustic positioning equipment with AUV navigation to provide continuous underwater correction without surfacing, extending the cooperative approach to heterogeneous unmanned vehicle systems, consistent with frameworks discussed by NATO for multi-domain autonomous systems interoperability.

Patent Landscape: Who Is Leading GPS-Denied AUV Navigation R&D

The patent dataset of over 50 records filed between 2011 and 2026 across Chinese, US, European, Japanese, and PCT jurisdictions reveals a highly concentrated innovation landscape dominated by Chinese academic institutions, with two significant Western commercial players holding technically distinctive positions.

Harbin Engineering University is the single most prolific assignee, with patents covering INS/DVL/LBL tight integration, SVM-based error correction, and multiple derivative institutions (Harbin Engineering University Sanya Nanhai Innovation and Development Base, Qingdao Innovation Center). Their work spans from 2011 to 2025, indicating sustained, multi-decade investment that encompasses both foundational methods and recent cooperative positioning architectures.

CSIC 707 Research Institute (China Ship Research and Development Academy) addresses the operational scalability problem through the sparse LBL tight-coupling method, enabling large-area long-duration navigation with minimal transponder infrastructure — a directly mission-relevant capability for China’s naval and oceanographic programs. Southeast University focuses specifically on passive acoustic positioning without seabed infrastructure, with the bearing-only single-source and time-window positioning methods that avoid reliance on both GPS and range measurement. Zhejiang University contributes advanced integrated positioning and control architectures, particularly the acoustic-buoy/EKF/MPC integrated framework.

Among Western assignees, CGG Services SA (France) holds a significant international patent family on cooperative multi-AUV formation positioning, with filings in the US, WO, EP, and MX jurisdictions — the only major Western commercial seismic company in the dataset with dedicated navigation IP. Raytheon Company holds the most technically distinctive approach: synthetic aperture sonar coherence map navigation, which requires no acoustic beacons of any kind. This capability is consistent with research priorities documented by ONR (US Office of Naval Research) for GPS-denied underwater navigation in contested environments. China University of Petroleum (East China) represents emerging innovation in sound-speed-robust single-beacon positioning via semidefinite programming, addressing a fundamental accuracy bottleneck that affects all acoustic navigation systems.