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VENUS Ranging Study

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Technical Report

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Defence Research and Development Canada - Atlantic Research Centre Dartmouth NS

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The underwater acoustic propagation models OASES and PECan are employed to study transmission loss TL to the Victoria Experimental Network Under the Sea VENUS sensor nodes in the Strait of Georgia as a consequence of Her Majestys Canadian HMC ships operating at the Canadian Forces Maritime Experimental and Test Ranges CFMETR. Four representative frequencies are studied for a shallow acoustic source, and both hydrophones and bottom-mounted seismometers are considered as receivers at each VENUS node. Bathymetry, measured conductivity, temperature, depth CTDs, and sediment type are taken into account to study TL as affected by monthly changes in sound velocity profile. It is found that the VENUS node, Delta Dynamics Laboratory DDL-06, displays the minimum TL at 130 Hz with OASES results indicating horizontalvertical particle velocity seismic losses of 114124 dB in FebruaryDecember, and a PECan result giving pressure loss of 90 dB in January. The VENUS node, East Node EN, has similar minimal TL values, whereas the Central Node CN has higher TL due to a shallowbank off Gabriola Island interfering with line-of-sight acoustic transmissions from CFMETR. It is important to note that the OASES modelling presented in this report, which is mainly used to provide seismic TL, is derived from a range-independent environment. Therefore, the OASES results are inherently less accurate than corresponding PECan results especially in the case of modelling TL to CN where there is significant variability in the bathymetry profile from CFMETR to this node. Three dimensional acoustic propagation with PECan is used to determine the extent that out-of-plane acoustic energy arriving at each node influences TL.

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