Understanding High Resolution Geophysical (HRG) Surveys

This fact sheet, produced by the Bureau of Ocean Energy Management (BOEM), covers questions and answers to high resolution geophysical (HRG) surveys and their potential effect on marine life.

What are HRG Surveys?

Before offshore wind construction begins, companies gather information to characterize the seafloor with high-resolution geophysical (HRG) surveys. HRG surveys use a suite of active sound sources to produce sounds that are reflected off features within the water column, on the seafloor, and below the seabed. 

Survey equipment can be mounted on the ship or towed behind a survey vessel. HRG surveys often combine tools, such as multibeam echosounder, side-scan sonar, and sub bottom profiler into one subsurface package: an Autonomous Underwater Vehicle (AUV), which is operated approximately 50 feet above the seafloor. 

The sound sources used in HRG surveys are much lower in energy than deep penetration seismic airgun surveys, which use high-energy sound pulses to penetrate deeper (thousands of meters) into the seafloor to map certain geological features, such as oil and gas deposits. Offshore wind energy projects do not use deep penetration seismic airgun surveys.