Calculations of reverberation and fathometer returns at short times using a straight-line ray-path model

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Authors
  1. Ellis, D.D.
Corporate Authors
Defence R&D Canada - Atlantic, Dartmouth NS (CAN)
Abstract
A straight-line ray-path model has been developed to calculate reverberation and fathometer returns at short times. Previous calculations of reverberation at long ranges/times have shown good agreement among various models, with very little dependence on the receiver depth. However, at times less than a few seconds the steep-angle scattering and fathometer returns begin to dominate, so normal mode and other waveguide models begin to break down, but ray models are quite efficient. At very short times the fathometer returns completely dominate, and there is a strong dependence on the receiver depth. The reverberation is calculated assuming the scattered energy in the various multipath arrivals is summed incoherently. However, the fathometer returns are specular reflections and the pressure from each arrival should be summed coherently. The equations for the model are presented, and illustrated by a number of examples from Problem XI of the Reverberation Modeling Workshop. This problem has a vertically bistatic source-receiver geometry in 100 m of isovelocity water over a flat sand-like bottom with Lambert scattering. The pulse is a Gaussian-shaded CW, with a bandwidth of 1/20 of the centre frequency. In this model the calculations show that at higher frequencies (e.g., 3500 Hz) the individual fathometer returns can be clearly seen, but at lower frequencies (e.g., 250 Hz) the pulse is longer and the returns overlap. In this case the method of fathometer summation selected, coher

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Report Number
DRDC-ATLANTIC-TM-2011-323 — Technical Memorandum
Date of publication
01 Feb 2012
Number of Pages
44
DSTKIM No
CA037352
CANDIS No
537066
Format(s):
Electronic Document(PDF)

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