The effects of spatial field shifts in sensitivity measures

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Authors
  1. Dosso, S.E.
  2. Morley, M.
  3. Giles, P.M.
  4. McCammon, D.F.
  5. Brooke, G.H.
Corporate Authors
Defence R&D Canada - Atlantic, Dartmouth NS (CAN);Victoria Univ, Victoria BC (CAN) Centre for Earth and Ocean Research;McCammon Acoustical Consulting, Waterville NS (CAN);General Dynamics Canada Ltd, Le Gardeur QC (CAN)
Abstract
This report considers the effect of spatial shifts of acoustic-field structure on measures of acoustic sensitivity to variability and/or uncertainty in environmental parameters, particularly bathymetry. In general, acoustic-field perturbations due to an environmental perturbation can be considered to consist of two components: a spatial shift of the field structure, and a change to the field in addition to this shift. Quantifying the sensitivity at a fixed point without accounting for the field shift can result in high sensitivities that seem counter-intuitive. A robust numerical approach to determining field shifts is developed that maximizes the correlation between reference and perturbed acoustic fields defined over suitable range-depth windows. Fixed-point and field-shifted values can be computed for deterministic sensitivities (based on a specific environmental perturbation) or for stochastic sensitivities (based on Monte Carlo sampling of environmental uncertainty). Sensitivity studies are carried out for an environmental model based on the Malta Plateau. The study indicates that for low frequencies and/or small perturbations to bathymetry, the field-shift component of sensitivity dominates, and field-shift correction substantially reduces the sensitivity. The effectiveness of field-shift corrections decreases with frequency, perturbation size, and overall complexity of the bathymetry. There appears to be little or no advantage to field-shift correction for sensitivitie

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Report Number
DRDC-ATLANTIC-CR-2007-102 — Contractor Report
Date of publication
01 Jun 2008
Number of Pages
58
DSTKIM No
CA031512
CANDIS No
530446
Format(s):
CD ROM

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