Types of offshore survey work
Prior to construction, offshore surveys using a variety of small nearshore and larger offshore vessels are conducted to acquire information for state and federal permits applications and shape project design. Benthic habitats important to marine life and archaeological resources important to indigenous people are mapped to minimize project impacts.
Two of the most common types of pre-construction survey activities are geophysical and geotechnical surveys. Both surveys require a permit and approval from federal and/or state agencies based on location.
High-Resolution Geophysical (HRG) surveys are conducted to map the seafloor, the geology beneath the seafloor, and to identify archaeological resources and debris left by other ocean users. Equipment used during these surveys includes both acoustic equipment using varying frequencies of sound and passive sensors that do not emit sound. The sensors are either hull-mounted or towed above the seafloor behind the vessel. During HRG survey operations, vessels typically move at a low speed, between 2-4 knots (3-5 mph) transiting along straight survey lines.
Only a few HRG sources used in offshore wind surveys operate at frequencies detectable to marine mammals. Federal agencies have determined that no injury to marine mammals or protected species is expected from these HRG sources as the sound has been shown to diminish rapidly with distance (BOEM 2018
). The sources used in offshore wind that are detectable produce much lower energy and travel far shorter distances from the vessel than those used by oil & gas for exploration miles below the seafloor. The terms “seismic testing” and “seismic blasting” refer to powerful sound sources such as air guns used in oil & gas exploration and are not used in HRG offshore wind surveys.