Page 31 - Winter 2009

Standards
ASA STANDARD GOES UNDERWATER
Michael A. Bahtiarian
Noise Control Engineering, Inc. 799 Middlesex Turnpike Billerica, Massachusetts 01821
This fall the Acoustical Society of
America (ASA) published a new
standard for the measurement of
underwater sound from ships.
ANSI/ASA S12.64-2009/Part 1,
“American National Standard, Quantities
and Procedures for Description and
Measurement of Underwater Sound from
Ships-Part 1: General Requirements” as it is now known, has a couple of firsts. It is the first ASA noise standard concerned with underwater sound. More importantly it is the first known civilian standard in the world for quantifying the underwater sound of ships. The need for this standard grows out of envi- ronmental concerns and efforts to reduce all types of vessel emissions. Initially, the focus was on the reducing ballast water and engine emissions, but concern about ship noise has been growing over the past decade or more.
The standard was developed by S12/Working Group 47, a subgroup of ANSI Accredited Standards Committee S12, Noise, which is administered by the ASA. Members of the working group included professionals from government, aca- demia, and industry. Government members included per- sonnel from Naval Sea Systems Command (NAVSEA), Naval Surface Warfare Center (NSWC), and National Oceanic and Atmospheric Administration (NOAA). Academia included members from the University of Delaware, Lamont-Doherty Earth Observatory, Florida Atlantic University, University of Rhode Island, and University of New Hampshire. Industry included private consultants to Fortune500 companies. International participation came from Canada, United Kingdom, the Netherlands, and Australia.
Since World War II, the field of underwater acoustics has been the sole concern of the navies of the world, which have used this special knowledge to hide their submarines while in the hunt for enemy submarines and surface combatants. The non-military interest in underwater sound is attributable mostly to reducing anthropogenic noise or man’s impact on marine animals. “Excessive underwater noise has the poten- tial to interfere with a marine animal’s ability to perform a variety of critical life functions such as navigate, communi- cate, find food, etc.”1
A further necessity of this new standard for measuring ship noise came from the author’s involvement in design, construc- tion and testing of quiet research vessels starting around 2001. The U.S. Department of the Interior, National Oceanic and Atmospheric Administration has procured a fleet of ships that perform fish stock assessment (fish counting) using sonar. To
conduct such activity, NOAA needed a new Class of quiet fisheries research ves- sels. The first of the Class is the OSCAR DYSON which was put into service around 2004. Since that time, three simi- lar vessels (HENRY BIGELOW, PIECES and BELL SHAMADA) have been deliv- ered to NOAA. Other quiet vessels
include a coastal research vessel for the University of Delaware (R/V SHARP), two Regional Class Research Vessels (RCRV), and one Arctic Area Research Vessel (AARV). Both the RCRV and AARV are expected to be funded by the National Science Foundation (NSF). However, RCRV has not yet been funded and AARV is, at time of writing, undergoing shipyard selection.
The contracts for all of these quiet research vessels have underwater noise requirements that either already have been verified or will need to be verified in the future. All existing vessels have had their underwater sound measured at one of four different U.S. Navy facilities (one on the U.S. East Coast, two on the U.S. West Coast and one in Alaska).
It is hoped that the new standard will promote consis- tency among those reporting sound measurements including non-military government agencies, non-government organi- zations (NGOs) and the private sector. The standard describes requirements for instrumentation, measurement procedure and post processing. The standard has three dif- ferent grades denoted A, B, and C. Grade A is the precision method intended for contract requirement conformance testing. Grade B is an engineering method which could be used for less critical contract requirements and/or periodic assessments. Grade C is a survey method which would be used for periodic assessments and “quick-look” tests.
The section on “Instrumentation” covers types of hydrophones, data acquisition systems, distance ranging and calibration. Hydrophones need to be omni-directional and be capable of measuring over the frequency response speci- fied for each grade. Grades A and B require three hydrophones and Grade C requires just one hydrophone. Data acquisition systems need to be able to perform over the specified frequency range, take one-third octave band meas- urements and, in some cases, narrowband measurements. The standard is primarily based on one-third octave band fil- tering with frequency ranges that depend on the Grade. Grade A is from the 10 to 50,000 Hz one-third octave bands. Grade B is from the 20 to 25,000 Hz one-third octave bands and Grade C is from the 50 to 10,000 Hz one-third octave bands.
30 Acoustics Today, October 2009
“...it is the first known civilian standard in the world for quantifying the underwater sound of ships.”