Sea Technology

DEC 2014

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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www.sea-technology.com December 2014 / st 47 that will identify the theoretical mitigation zones. In order to ensure model accuracy and comparison with survey results, a dense set of offcial bathymetry data parameters for the location, source position, and performance parameters for the sources and hydrophones deployed has to be used along with environmental data. Modeling Seiche Measurements Ltd. (Holsworthy, England) utilizes a range-dependent, parabolic equation modeling solution based on the RAMGeo code created by the Naval Research Laboratory in Washington, D.C. Using this technique, many complex attributes can be applied to the model, including a large bathymetry data set to provide an authentic seabed profle, specifc seabed sedi- ment layers to defne absorption, refection and refraction characteristics, and water column density and salinity for accurate speed of sound defnition. Techniques Historically, a number of seabed recorders are used in order to collect the measured data from the source. These W orldwide, government agencies and regulators are showing an increasing interest in sound source verif- cation (SSV) techniques, analysis and results in order to as- sess the impact of sound on marine mammals and the envi- ronment. The purpose of the SSV is to monitor, measure and record sound levels generated during man-made operations within the seas and oceans. By example, agencies require an SSV to be undertaken for seismic survey source arrays, prior to full operations commencing. Broadband decibel (dB) levels are calculated for 190 dB, 180 dB, 160 dB and, increasingly, 120 dB, and empirical distances are identifed from the source location. This information is then utilized in order to defne marine mammal mitigation zones to be applied to a particular survey and location. Many different factors will affect the propaga- tion of the sound from the source, including bathym- etry, salinity, water depth and temperature. Initially, a model is produced based on the actual site location Sound Source Verifcation to Assess Marine Mammal Impact Drift Buoy, Towed Array Solutions By Brian Heath • Roy Wyatt (Top) The drift buoy. (Bottom) Drift buoy tracks covering a 20-kilometer range. (Seismic source in the center.)

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