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Rex Andrew

Principal Engineer

Email

rex@apl.washington.edu

Phone

206-543-1250

Biosketch

Rex Andrew's research interests involve the use of acoustic signals to infer the properties of the source mechanism itself or the medium through which the signals propagate. In the ocean, this field is commonly known as acoustical oceanography. This discipline requires the combination of statistical signal and array processing theory with the physics of wave propagation for proper interpretation.

Department Affiliation

Acoustics

Education

B.S. Physics, University of Washington, 1981

M.S. Electrical Engineering, University of Washington, 1987

Ph.D. Electrical and Computer Engineering, University of Victoria, 1999

Publications

2000-present and while at APL-UW

Decadal trends in low-frequency ambient ocean noise for seven sites in the North Pacific Ocean

Andrew, R.K., B.M. Howe, and J.A. Mercer, "Decadal trends in low-frequency ambient ocean noise for seven sites in the North Pacific Ocean," U.S. Navy J. Underwater Acoust., 66, 2016.

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1 Oct 2016

Nearly two decades of ambient noise measurements at seven open-ocean sites in the North Pacific Ocean basin have revealed a complex pattern of long-term trends. The trends in the Northeastern Pacific Ocean show a significant decrease of almost 2 dB/decade. Along the Aleutian archipelago, the levels are either slightly increasing or remaining flat. Levels in two north central Pacific Ocean sites are essentially flat. The mechanisms driving these trends appear to be more subtle than simply the number of merchant ships or the local wind speed. Climatically-influenced basin-scale acoustic propagation conditions may have an important role.

Low-frequency pulse propagation over 510 km in the Philippine Sea: A comparison of observed and theoretical pulse spreading

Andrew, R.K., A. Ganse, R.W. White, J.A. Mercer, M.A. Dzieciuch, P.F. Worcester, and J.A. Colosi, "Low-frequency pulse propagation over 510 km in the Philippine Sea: A comparison of observed and theoretical pulse spreading," J. Acoust. Soc. Am., 140, 216-228, doi:10.1121/1.4954259, 2016.

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1 Jul 2016

Observations of the spread of wander-corrected averaged pulses propagated over 510 km for 54 h in the Philippine Sea are compared to Monte Carlo predictions using a parabolic equation and path-integral predictions. Two simultaneous m-sequence signals are used, one centered at 200 Hz, the other at 300 Hz; both have a bandwidth of 50 Hz. The internal wave field is estimated at slightly less than unity Garrett-Munk strength. The observed spreads in all the early ray-like arrivals are very small, <1 ms (for pulse widths of 17 and 14 ms), which are on the order of the sampling period. Monte Carlo predictions show similar very small spreads. Pulse spread is one consequence of scattering, which is assumed to occur primarily at upper ocean depths where scattering processes are strongest and upward propagating rays refract downward. If scattering effects in early ray-like arrivals accumulate with increasing upper turning points, spread might show a similar dependence. Real and simulation results show no such dependence. Path-integral theory prediction of spread is accurate for the earliest ray-like arrivals, but appears to be increasingly biased high for later ray-like arrivals, which have more upper turning points.

A test of deep water Rytov theory at 284-Hz and 107-km in the Philippine Sea

Andrew, R.K., A.W. White, J.A. Mercer, M.A. Dzieciuch, P.F. Worcester, and J.A. Colosi, "A test of deep water Rytov theory at 284-Hz and 107-km in the Philippine Sea," J. Acoust. Soc. Am., 138, 2015-2023, doi:, 2015.

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1 Oct 2015

Predictions of log-amplitude variance are compared against sample log-amplitude variances reported by White, Andrew, Mercer, Worcester, Dzieciuch, and Colosi [J. Acoust. Soc. Am. 134, 3347–3358 (2013)] for measurements acquired during the 2009 Philippine Sea experiment and associated Monte Carlo computations. The predictions here utilize the theory of Munk and Zachariasen [J. Acoust. Soc. Am. 59, 818–838 (1976)]. The scattering mechanism is the Garrett%u2013Munk internal wave spectrum scaled by metrics based on measured environmental profiles. The transmitter was at 1000 m depth and the receivers at nominal range 107 km and depths 600–1600 m. The signal was a broadband m-sequence centered at 284 Hz. Four classes of propagation paths are examined: the first class has a single upper turning point at about 60 m depth; the second and third classes each have two upper turning points at roughly 250 m; the fourth class has three upper turning points at about 450 m. Log-amplitude variance for all paths is predicted to be 0.04–0.09, well within the regime of validity of either Born or Rytov scattering. The predictions are roughly consistent with the measured and Monte Carlo log-amplitude variances, although biased slightly low. Paths turning in the extreme upper ocean (near the mixed layer) seem to incorporate additional scattering mechanisms not included in the original theory.

More Publications

Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center
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