portrait in the old family 1964.5 Mustang convertible
Hi, I'm Andy. With the exception of a few years during the 90s, I have been a researcher at the Applied Physics Laboratory (APL-UW) of the University of Washington for 22 years now (yikes!). However, it was only relatively recently that I returned to grad school and got my PhD in geophysics, so I am only now starting on the PI (principal investigator) track. My work mainly focuses on using sound as a remote sensing tool to study the ocean and ocean floor, but I also have worked on the propagation and scattering of both acoustic and electromagnetic waves, statistical analyses of ocean and seafloor measurements, and gravitational effects of spacecraft planetary flybys. My PhD was in theoretical and computational concerns in the geophysical inversion of physical properties of the seafloor from acoustic receptions in the ocean water column. I have been on two extended (>1mo) ocean acoustic experiment cruises.

The overarching theme of my research is solving and understanding "inverse problems" to learn about geophysical phenomena. Geophysics is Earth science, and these inverse problems are all about how to get useful information about the Earth from indirect measurements. In many scientific disciplines, we wish to learn about a quantity that we cannot measure directly. In seismology, ocean acoustics, planetary physics, we often wish to learn about the structure or composition of some interior (of the Earth, of the ocean, etc) but we can only take measurements at the surface or at some other boundary. What's a scientist to do? [more...]



PHILSEA09-10 LONG-RANGE OCEAN ACOUSTICS EXPERIMENT (with Rex Andrew, APL-UW)
In 2009 and 2010 I participated in a major ocean acoustics experiment in the Philippine Sea with APL-UW's North Pacific Acoustic Laboratory (NPAL) group. One of the key topics our research group is interested in is how oceanic sound propagation is affected by internal waves (waves down deep in the water) and by ocean "spice" (blobs of water with a different soundspeed but same density as their surroundings, so they don't behave like waves). Both these phenomena cause variations in soundspeed of the water and thus acoustic transmissions through it, and acousticians would like to understand them better. Our group is also interested in the estimation of ocean sound-speeds and temperatures from receptions of sound that we send through the water. Find out more about our use of these different methodologies in our research on my NPAL Ocean Acoustics page.


GEOPHYSICAL INVERSE THEORY MATERIALS

Over the years I've been pulling together various geophysical inversion materials onto a geophysical inverse theory resources webpage to share with others. This began with my TA'ing a graduate-level geophysical inverse theory course and then continued with my guest-teaching a number of lectures in a later year. Contents include recommended reading lists, links to web resources, a few Matlab scripts, and my lecture notes. Students, researchers, and professors alike may find something useful or interesting in here.


The NPAL/PhilSea material at left forms the majority of my funded work, but I also have a series of small side endeavors aiming to fill the gap and to explore other interests and new collaborations:




RADIO SCIENCE GRAVITY INVERSION FOR ICY MOON INTERNAL STRUCTURE (with Steve Vance, JPL-Caltech)
The nature of an icy satellite's interior relates fundamentally to its composition, thermal structure, formation and evolution history, and prospects for supporting life. Gravity measurements via radio Doppler information during spacecraft flybys are an important tool used to infer gross interior structure of these moons. Liquid water and ice layers have previously been inferred for the interiors of Jupiter's icy satellites Europa, Ganymede, and Callisto on the basis of magnetic field measurements by the Galileo probe, and on Europa and Callisto induced magnetic field signatures measured by the Galileo probe provided strong evidence for an ionic aqueous ocean. We apply geophysical inverse theory tools to assess the icy moon's interior density anomaly distribution that could be estimated from radio Doppler measurements, to support the search for mass anomalies in the ice shell (meteorites or diapiric upwellings) or near the H2O/rock interface (seamounts).


ELECTROMAGNETIC INVERSION OF ESTUARINE SALINITY STRUCTURE USING THE SIGMA PROFILER INSTRUMENT
(with Tom Sanford, APL-UW)
Screen Shot 2014-02-09 at 9.27.55 PM
The Sigma Profiler is an instrument for remotely observing estuarine salinity profiles via electromagnetic measurements. Electromagnetic (EM) waves are attenuated in seawater as a function of frequency, and conductivity structure (closely related to salinity structure) in the water can be inferred by combining measurements of EM waves at different frequencies on a distant electric field receiver. Geophysical inversion methods are applied to estimate the estuarine salinity profile from the EM measurements. Using inverse theory techniques, we take advantage of statistical rigor and let the data determine the structure of the conductivity profile and quantify the uncertainty and resolution of the salinity profile.