Brian Dushaw's Homepage

I was an oceanographer at the Applied Physics Laboratory, University of Washington from 1992-2016,.  and an an affiliate assistant/associate professor of Oceanography at the School of Oceanography, UW from 1999—2015.

My interests are in the application of long-range acoustic transmissions for ocean observation - also known as ocean acoustic tomography. An essential aspect of tomography is to understand the acoustic forward problem, so a closely related interest is understanding the nature of long-range acoustic propagation in the ocean.

Tomography is a technique that has matured; it offers excellent signal-to-noise capability for observing variability at the largest oceanic scales. Three applications I am actively pursuing are: measuring the large-scale variations of heat content in ocean basins, estimation of the radiation of low-mode internal tides from topographic features and the apparent predictability of that radiation in the ordinary tidal sense, and measuring the heat and heat transport through Fram Strait to high precision. Other interests are modeling and data assimilation (and how tomography may be used in models), and the effective use of parallel computational techniques (SMP machines, cluster of PCs, graphics cards/CUDA) in scientific analysis.

RESEARCH HIGHLIGHTS

Encyclopedia Article. An encyclopedia article on ocean acoustic tomography. The citation is:

Dushaw, B. D., 2013. ‘‘Ocean Acoustic Tomography’’ in Encyclopedia of Remote Sensing, E. G. Njoku, Ed., Springer, Springer-Verlag Berlin Heidelberg, 2013. doi: 10.1007/SpringerReference_331410

Acoustic Reverberation From an Atomic Test. I took another look at the acoustic signals generated by the 1955 atomic test "WIGWAM" in the eastern North Pacific. The sound pulse illuminated the entire North and South Pacific basins and was reflected back to California and Hawaii to be recorded as hours-long coda. A quite simple analysis produced this paper with the citation:

Dushaw, B. D., 2015. WIGWAM reverberation revisited, Bulletin Seismological Soc. Am., 105, doi: 10.1785/0120150024.

The electronic supplemenatary material for the paper can be seen on the BSSA website, or on this website HERE.

I presented these results at the UACE2017 conference. The conference paper gives a discussion on why and how I came to work on this problem:

Dushaw, B., 2017. WIGWAM Reverberation Revisited, in Proceedings Underwater Acoustics Conference and Exhibition 2017, Skiathos Island, Greece, 3-8 September 2017, 5 pp. Article

Antipodal Acoustic Thermometry. The culmination of quite a lot of numerical and historical research, we used acoustic signals from an antipodal acoustic propagation experiment in 1960 to make an estimate of the change in ocean temperature from 1960 to 2004, averaged along the sound channel axis. The signals traveled from Perth, Australia to Bermuda. The measurements in 1960 were established to have a meaningful accuracy, and equivalent signals were computed using numerical ocean state estimates for 2004. No change in travel time (hence no change in temperature from 1960 to 2004) was observed. While error bars were large, they were not particularly larger than other measurement types. The computation establishes acoustic thermometry as both a viable and important measurement type, complementary to other measurement types. The lengthy publication is open access.

Dushaw, B. D., and D. Menemenlis, 2014. Antipodal acoustic thermometry: 1960, 2004,
Deep-Sea Res. I, 86, 1−20. doi: 10.1016/j.dsr.2013.12.008

Dushaw, B. D., 2008. Another look at the 1960 Perth to Bermuda long-range acoustic propagation experiment, Geophys. Res. Lett., 35 , doi: 10.1029/2008GL033415.

Global Predictability of Mode-1 Internal Tides. This year (2015) marks the 20th anniversary of a paper published in 1995 reporting on the radiation of mode-1 internal tides from Hawaii far into the ocean's interior as measured by acoustic tomography. This radiation was confirmed a year later by observations by the TOPEX/POSEIDON satelite altimeter. I have worked on these observations, on and off, over this 20 year period. This work eventually led to the conclusion that these internal tide waves are so coherent that their amplitude and phase are in fact predictable, much like the barotropic tide. A detailed and thorough analysis of both tomography and satelite altimetry data demonstrating this predictability appeared in a publication in the journal Deep-Sea Research in 2011. While the practical value of this discovery is to be determined, the discovery is somewhat revolutionary in that it overturns firmly held views by physical oceanographers about the incoherence of ocean variability.

With support from the National Aeronautics and Space Administration, his work has been extended and refined to develop a global model that can be used to predict the tidal amplitude and phase of mode-1 internal tides anywhere in the world's oceans. The model predicts the in situ observations by acoustic tomography from the Philippine to Sargasso Seas. The animation below gives the mode-1 internal tide amplitude for the M₂ frequency; the model includes the six major tidal constituents and modes 1 and 2. The 114 pp. report describing this model can be accessed HERE (v1.1) (19 MB). The use of acoustic tomography and satelite altimetry illustrates the complementary nature of these data types – altimetry shows the spatial coherence of these internal tides, while tomography shows the temporal coherence.

(NEW - 11/10/2015) This model, together with software and documentation to enable computation of tidal predictions or plotting of maps, can be downloaded from HERE (APL site - See Supplemental Materials. A tarball of 2.4 GB in size contains the model and other aspects of the solution.) Unpacking this tarball gives the empirical model and associated software that can be used for predicting mode-1 internal tides. The tarball also disseminates the tomography and thermistor observations (time series of mode-1 amplitude derived using acoustic tomography or thermistor data), animations of mode-1 internal tides the world over, and mode-1 properties derived from climatology that allow the mode-1 solutions for SSH to be extended into the ocean's interior (mode amplitude, current, displacement, etc.).

The citations for the 2011 publication and this Technical Memorandum are:

Dushaw, B. D., P. F. Worcester, and M. A. Dzieciuch, 2011. On the predictability of mode-1 internal tides, Deep-Sea Res. I, 58, 677−698. doi: 10.1016/j.dsr.2011.04.002

Dushaw, B., 2015. An Empirical Model for Mode-1 Internal Tides Derived from Satellite Altimetry:  Computing Accurate Tidal Predictions at Arbitrary Points over the World Oceans, Technical Memorandum APL-UW TM 1-15, 114 pp.