Lowest Practicable Source Levels (LPSL)

Recent discussions have increasingly focused on designing geophysical surveys to operate using the “lowest practicable source level,” often through reductions in parameters such as total array air volume. While well intentioned, this approach can oversimplify how acoustic sources function. Total array volume is frequently used as a proxy for loudness, yet the relationship is not linear; reductions in volume do not translate proportionally into meaningful reductions in sound levels. 

In practice, overall source performance depends on a combination of design factors—including the number of elements and their configuration, which together shape the acoustic signal. These design features help optimize frequency content, suppress unwanted bubble oscillations, enhance the low-frequency energy required for high-quality imaging, and limit lateral sound propagation. Ensuring that surveys meet their geophysical objectives remains fundamental, as compromised data quality can ultimately require re-acquisition, increasing both operational activity and overall environmental exposure. 

Industry experience demonstrates that geophysical survey planning already reflects a balanced approach. Operators routinely seek to use only the source characteristics necessary to achieve imaging objectives, often within regulatory frameworks that require justification and verification of source parameters. This reflects a shared commitment to minimizing unnecessary sound while delivering reliable subsurface data. 

At the same time, there is limited evidence that broad reductions in array volume alone would deliver measurable environmental benefits. A one-size-fits-all approach is unlikely to account for the technical complexity of survey design or the variability of geological objectives. Measures that focus narrowly on source level, without considering overall survey effectiveness, risk unintended consequences for both data quality and operational efficiency. 

Geophysical survey operators continue to integrate environmental considerations into survey planning and remain committed to innovations that improve imaging performance while reducing environmental footprint. A constructive path forward is to support science-based, case-by-case approaches that balance geophysical objectives with environmental stewardship, rather than relying on simplified metrics that may not achieve their intended outcomes.