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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

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.

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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