TWO-WAY TIME SPREADING AND PATH LOSS IN SHALLOW WATER AT 20-40 kHz

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Authors
  1. Hines, P.C.
  2. Collier, J.
  3. Theriault, J.A.
Corporate Authors
Defence Research Establishment Atlantic, Dartmouth NS (CAN)
Abstract
Two-way time spreading and path-loss measurements were collected in water 100 m deep, off the coast of Nova Scotia. Data were collected at frequencies of 10-22 kHz, 27-20 kHz, and 35-37 kHz using linear FM pulses 0.160 s in duration. THe source-receiver was an anchored, high-frequency active sonar, and the target was a free-drifting echo repeater. Sonar and target positions were recorded using a portable tracking range. In the paper, two-way time spreading and path loss measurements are compared with modeled estimates obtained using an enhanced version of the generic sonar model (GSM). THe GSM estimates of time spreading due to multipath propagation compare favorably with the experimental data. The model indicates that the path loss for individual eigenrays was extremely sensitive to fluctuations in the sound-speed profile. THis led to substantial variation in the model output dpending on the choice of profile. In place of the model, an empirical estimate of path loss was computed from the data. We obtained a two-way spreading loss of 2(18.4 log 10 (R)) where R is the range from sonar to target. The data were also used to compute the standard deviation of the received echo intensity at each frequency. The standard deviation was computed two different ways. First it was computed using the peak echo level from each of the pulses at a given frequency. Then, it was computed from the total energy received from each of the pings. TRUNCATED
Keywords
Time spreading;Sound speed profiles
Date of publication
30 Apr 1997
Number of Pages
10
Reprinted from
IEEE J. of Oceanic Engineering, vol 22, no 2, 1997, p 199-309
DSTKIM No
97-03497
CANDIS No
503685
Format(s):
Hardcopy;Document Image stored on Optical Disk

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