Two-view sonar geometry improves undersea mapping accuracy
Beyond the Flat Seafloor: A Closed-Form Two-View Constraint to Aid Sidescan Sonar Reconstruction
RoboticsComputer Vision and Pattern Recognition
Summary
Sidescan sonar is a tool used to map the seafloor, but it typically assumes the seafloor is flat which can cause errors. This paper presents a new way to use the geometry from two viewpoints to better pinpoint features underwater without assuming a flat surface. The authors found that the uncertainty in locating features depends strongly on how the sonar devices are angled and positioned during measurements. This work also offers advice on planning sonar surveys to reduce ambiguity based on the vehicle’s path and sensor setup.
What this means in practice
- •For marine survey teams: Plan sonar survey paths to minimize location uncertainty by adjusting vehicle trajectories based on the identified geometric constraints.
- •For underwater vehicle operators: Improve feature reconstruction accuracy by accounting for elevation misalignment and optimal crossing angles during sidescan sonar data collection.
Authors
Kalin Norman, Joshua G. Mangelson
Abstract
Sidescan sonar is a common sensor for both manned and autonomous marine exploration and mapping, yet very few methods build upon or exploit the geometric projection model of the sensor. As sidescan sonar is limited to a 1D range measurement, many approximations are frequently used, including the long-standing assumption of a flat seafloor. Rather than make similar approximations, this paper focuses on a multi-view geometry based approach and formalizes a two-view geometric constraint and proves that a shared feature is constrained to a locus within the intersection of a sphere and a plane. In addition, we characterize what governs the size of the ambiguity locus through Monte Carlo simulation that is grounded in real aperture and mounting geometry for both a surface vessel and an underwater vehicle. We translate additional simulations of relative trajectories for both vehicle platforms into concrete survey-planning guidance. Our results show that locus length is strongly governed by elevation misalignment, and peaks at a moderate oblique crossing angle of approximately 20 degrees, with minimal locus lengths obtained at near parallel and anti-parallel passes.