Resolving the Divide: Comparative Performance of Side Scan Sonar and Synthetic Aperture Sonar in Offshore Survey and Regulatory Compliance

Autonomous underwater vehicles (AUVs) play a central role in offshore energy surveys, enabling high-resolution seabed characterization for infrastructure planning, hazard detection, and environmental review. The world of commercial survey AUV's has undergone some incredible updates since their introduction in 2001. A newer tool to be released Synthetic Aperture Sonar (SAS)—particularly Kongsberg's HISAS—has surpassed legacy Side Scan Sonar (SSS) in clarity, depth performance, and object localization accuracy. This paper evaluates AUV based HISAS performance across varying depths, assesses terrain-aided navigation benefits, and proposes regulatory updates to current guidance that reflect these technological advances and their liabilities. Side Scan Sonar (SSS) generates plan-view seafloor imagery by emitting fan-shaped acoustic pulses perpendicular to the autonomous underwater vehicle (AUV) track and recording the intensity of the returning echoes. This method is well-suited for broad reconnaissance and environmental screening but suffers from several inherent limitations. Current AUV-based SSS systems—such as those deployed on Kongsberg's HUGIN platforms—typically operate in the 300-1200 kHz frequency range, with dual- or triple-frequency configurations available. However, earlier HUGIN systems, including the HUGIN 1000, were equipped with 100 kHz SSS modules like the EdgeTech 2200-M, offering extended range but lower resolution. Lower frequencies (e.g., 300–600 kHz) offer broader swath coverage, while higher frequencies (e.g., 900–1200 kHz) provide finer resolution for near-bottom surveys. At a typical commercial operating altitude of 40m, AUV SSS units operating at 410 kHz achieved a resolution of approximately 2-5cm across-track (range resolution) and 40-60m along-track: this gives a general resolution 0.5 m (the along-track resolution is the main limiting factor for SSS resolution with AUV acquisition due to ping rate). Post-processed SSS mosaics are typically generated at 0.5-1.0m pixel size for conventional mapping. According to the US regulatory agency, Bureau of Ocean Energy Management (BOEM) (BOEM 2022), SSS is generally capable of detecting features ≥0.5 m in size. However, its performance diminishes with increasing range due to beam divergence, leading to degraded resolution and poor feature classification. Additionally, SSS imagery is often susceptible to shadowing effects, which can obscure critical seafloor objects and compromise interpretation accuracy.