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Jim Mercer

Senior Principal Physicist

Research Professor, Earth and Space Sciences

Email

mercer@apl.washington.edu

Phone

206-543-1361

Biosketch

Dr. Mercer is a Principal Physicist at APL-UW and a Research Professor in the Department of Earth and Space Sciences at the University of Washington. He received a B.S. in Physics in 1968 and a Ph.D. in Geophysics in 1983, both from the University of Washington. Dr. Mercer is a member of several professional societies, has served on many national committees, and is currently an Associate Editor of the U.S. Navy Journal of Underwater Acoustics.

During his tenure of over 40 years at APL-UW, underwater acoustics has been the central theme of Dr. Mercer's research. His studies have covered the spectrum from basic research to advanced applications. He has authored or co-authored scores of scientific and technical publications and has served as Chief Scientist on numerous at-sea expeditions. He currently leads a team of scientists and engineers at APL-UW.

Some of the programs managed by Dr. Mercer are highlighted below.

Department Affiliation

Acoustics

Education

B.S. Physics, University of Washington, 1968

Ph.D. Physics, University of Washington, 1983

Publications

2000-present and while at APL-UW

Observations of low-frequency, long-range acoustic propagation in the Philippine Sea and comparisons with mode transport theory

Chandrayadula, T.K., S. Periyasamy, J.A. Colosi, P.F. Worcester, M.A. Dzieciuch, J.A. Mercer, and R.K. Andrew, "Observations of low-frequency, long-range acoustic propagation in the Philippine Sea and comparisons with mode transport theory," J. Acoust. Soc. Am., 147, 877-897, doi:10.1121/10.0000587, 2020.

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1 Feb 2020

The year-long Philippine Sea (2010–2011) experiment (PhilSea) was an extensive deep water acoustic propagation experiment in which there were six different sources transmitting to a water column spanning a vertical line array. The six sources were placed in an array with a radius of 330 km and transmitted at frequencies in the 200–300 Hz and 140–205 Hz bands. The PhilSea frequencies are higher than previous deep water experiments in the North Pacific for which modal analyses were performed. Further, the acoustic paths sample a two-dimensional area that is rich in internal tides, waves, and eddies. The PhilSea observations are, thus, a new opportunity to observe acoustic modal variability at higher frequencies than before and in an oceanographically dynamic region. This paper focuses on mode observations around the mid-water depths. The mode observations are used to compute narrowband statistics such as transmission loss and broadband statistics such as peak pulse intensity, travel time wander, time spreads, and scintillation indices. The observations are then compared with a new hybrid broadband transport theory. The model–data comparisons show excellent agreement for modes 1–10 and minor deviations for the rest. The discrepancies in the comparisons are related to the limitations of the hybrid model and oceanographic fluctuations other than internal waves.

Deep water acoustic range estimation based on an ocean general circulation model: Application to PhilSea10 data

Wu, M., M.P. Barmin, R.K. Andrew, P.B., Weichman, A.W. White, E.M. Lavely, M.A. Dzieciuch, J.A. Mercer, P.F. Worcester, and M.H. Ritzwoller, "Deep water acoustic range estimation based on an ocean general circulation model: Application to PhilSea10 data," J. Acoust. Soc. Am., 146, 4754-4773, doi:10.1121/1.5138606, 2019.

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1 Dec 2019

This study identifies general characteristics of methods to estimate the absolute range between an acoustic transmitter and a receiver in the deep ocean. The data are from three days of the PhilSea10 experiment with a single fixed transmitter depth (~998 m) and 150 receiver depths (~210–5388 m) of known location, and a great-circle transmitter-receiver distance of ~510 km. The proposed ranging methods compare observed acoustic records with synthetic records computed through the HYCOM (hybrid coordinate ocean model) model. More than 8900 transmissions over 3 days characterize the statistical variation of range errors. Reliable ranging methods de-emphasize the parts of the data records least likely to be reproduced by the synthetics, which include arrival amplitudes, the later parts of the acoustic records composed of nearly horizontally launched rays (i.e., the finale), and waves that sample a narrow span of ocean depths. The ranging methods proposed normalize amplitudes, measure travel times, or reject parts of the waveforms beyond a critical time. All deliver reliable range estimates based on the time and path-averaged HYCOM model, although the final method performs best. The principles behind these methods are transportable and expected to provide reliable range estimates in different deep water settings.

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.

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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