Sonar Vessel Noise Survey 

Reports of recent whale and dolphin deaths on and near the New York and New Jersey shores, and public concerns of marine noise impacts from offshore wind development activities, prompted an investigation into the sonar noise levels produced by exploratory survey vessels working in ocean areas leased by the Bureau of Ocean Energy Management (BOEM). This technical report presents the methodology, analysis and results of a brief independent investigation of underwater noise levels from a sonar survey vessel, conducted offshore New Jersey on May 8, 2023. Underwater acoustic recordings were acquired between 8:09 and 9:40 am, approximately 43 nautical miles (NM) east of Barnegat Light, Long Beach Island, NJ, near a mobile geophysical survey vessel, the Miss Emma McCall (vessel). A “sparker” sub-bottom profiler (SBP) and several mid-frequency (MF) positioning system sonars (USBL) were measured including two impulsive, intermittent USBLs at 19.5 and 20 KHz, and two FM swept-sine USBLs at 21 to 32 KHz. An SBP listed for the vessel operating above 85 KHz was not measured as it was above instrumentation range. Transmission loss (TL) was larger at higher frequencies generally above 3000 Hz due to excess attenuation which is expected for the distances measured and shallow-water acoustic conditions.

Peak sound levels were controlled by the sparker and measured 151.6 dB,peak re 1uPA at 0.5 NM. The sparker source level (SL) was estimated at 224 dB,peak re 1uPa@1m, consistent with the sparker manufacturer’s published SL of 2 Bars/m (226 dB,peak re 1uPa). Using NOAA National Marine Fisheries Service (NOAA Fisheries or NMFS) 2020 guidelines based on Crocker and Fratantonio (2016), the sparker RMS level is estimated at 219 dB,rms re 1uPA@1m.

Vessel continuous noise included propulsion and dynamic positioning (DP) thruster noise emissions. Vessel noise was tonal, containing multiple cyclical/rotational tonal noise components from 9.5 Hz to several kilohertz, and was highly audible at 0.5, 1 and 2 NM. Vessel tonal noise was audible and measurable at 4 NM. Vessel continuous noise measured 126.5 dB,rms re 1uPA at 0.5 NM. Total vessel continuous noise with sparker was 128.5 dB,rms re 1uPA at 0.5 NM.

The vessel’s Incidental Harassment Application (IHA) was reviewed. The USBLs are impulsive yet were not listed or analyzed in the vessel IHA application. Vessel propulsion and DP thruster noise were also not listed or analyzed in the IHA application. The sparker proxy SL,rms used in the IHA application was cited as 16 dB quieter than expected based on manufacturer published levels harmonized with NMFS guidance for RMS noise levels. The IHA listed a 160 dB,rms Level B Behavioral Harassment threshold of 141 meters for the sparker impulsive noise, whereas the threshold using the NMFS Level B spreadsheet tool for calculating the distance to the Level B threshold with manufacturer data returned a distance of 890 meters.

To meet the NMFS 120 dB,rms behavioral harassment limit for continuous noise, the distance required is approximately 1 nautical mile (1852 meters). However, the vessel was operating with a vessel separation distance of 500 meters for the North American right whale (NARW) and other ESA-listed mammals and 50 or 100 meters for all other marine mammals. The IHA is silent regarding the 120 dB,rms Level B behavioral harassment threshold.

The data acquired during the survey and subsequent review of the IHA application raise concerns of sufficient NOAA review and mitigation distances to protect the critically endangered NARW and other marine species from behavioral harassment and temporary threshold shift (TTS) impacts.

Robert Rand, Rand Acoustics, Brunswick, Maine
September 22, 2023

Download original document: “Sonar Vessel Noise Survey”