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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

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.

Seasonal occurrence and diel calling behavior of Antarctic blue whales and fin whales in relation to environmental conditions off the west coast of South Africa

Shabangu, F.W., K.P. Findlay, D. Yemane, K.M. Stafford, M. van den Berg, B. Blows, and R.K. Andrew, "Seasonal occurrence and diel calling behavior of Antarctic blue whales and fin whales in relation to environmental conditions off the west coast of South Africa," J. Mar. Syst., 190, 25-39, doi:10.1016/j.jmarsys.2018.11.002, 2018.

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1 Feb 2019

Passive acoustic monitoring was used to detect the sounds of rarely sighted Antarctic blue and fin whales to investigate their seasonal occurrence (as presence or absence of whale calls) and behaviour (as determined from call rates) in the Benguela ecosystem. Data were collected using autonomous acoustic recorders deployed on oceanographic moorings for 16.26 months off the west coast of South Africa in 2014 and 2015. Satellite derived environmental variables were used as predictors of whale acoustic occurrence and behaviour. Migratory Antarctic blue and fin whales were acoustically present in South African waters between May and August with call occurrence peaks in July whereas some fin whales extended their presence to November. No whale calls were recorded in summer for either species, suggesting whales use the Benguela ecosystem as an overwintering ground and migration route. Antarctic blue whales produced both their characteristic Z-call and their feeding associated D-call. Fin whales produced calls characteristic of animals from the eastern Antarctic fin whale acoustic population. Random forest models identified environmental variables such as sea surface temperature anomaly, sea surface height, wind speed, months of the year, Ekman upwelling index and log-transformed chlorophyll-a as the most important predictors of call occurrence and call rates of blue and fin whales. Here we present the first acoustic recordings of Antarctic blue and fin whales in the Benguela ecosystem, and provide preliminary information to investigate seasonal abundance and distribution of these large baleen whale populations. This work demonstrates the feasibility of cost-effectively monitoring Antarctic top-consumer baleen whales in the Benguela ecosystem.

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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