Hi, I'm Andy. I have been a research engineer at the Applied Physics Laboratory (APL-UW) of the University of Washington for the past 10 years, but my actual research focus is geophysics. My work mainly studies the physics of sound wave propagation and scattering in the ocean and ocean floor, but I also have worked on the scattering of radar waves and gravitational effects of spacecraft planetary flybys. In addition to my project work, I have also been finishing my PhD in the Department of Earth & Space Sciences (ESS), supported by the APL Graduate Fellowship, our lab's grow-your-own-PI program. I expect to finally defend in February 2010, and immediately afterward face the very exciting change in title from Engineer to Physicist.

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. What's a scientist to do? [more...]



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 TAing a graduate-level geophysical inverse theory course and then continued with my substitute teaching several weeks of it 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.




NONLINEAR FILTERS & SMOOTHERS TUTORIAL
Part of my inverse theory research relies on concepts from recursive filters, so I had to take some time to come up to speed on those. In section 6.1 of the classic textbook Applied Optimal Estimation (Gelb ed., 1974) are two simple radar tracking examples used to demonstrate several nonlinear filters. I've programmed up a Matlab script to recompute those examples, and have added other filters to compare and contrast them in both linear and nonlinear cases. Maybe you'll find them useful yourself in comparing properties of various standard recursive filters and smoothers. Check it out!

NPAL TCTD CHAIN AND PHILSEA'09 CRUISE
This past spring I was in the Philippine Sea with APL-UW's North Pacific Acoustic Laboratory (NPAL) group, on a test-cruise in preparation for a full experiment in the same location in 2010. A major focus of this research group is the estimation of ocean sound-speeds and temperatures from receptions of sound sent through the water. A new instrument in our experiments is hoped to contribute to a better understanding of ocean processes, in turn improving understanding of "where the sound goes". The instrument is a new, 800m long version of a "towed CTD chain" (TCTD). It's an oceanographic cable that contains with 88 sensors of conductivity, temperature, and pressure spread along its length. This is exciting because traditional, individual CTD casts give geographic point measurements, whereas this newest version of the towed instrument would give ~5m x ~5m resolution in a 500m-deep, 2D slice of the ocean for as far as it is towed. Unfortunately there were a number of technical troubles with this new system during this cruise; we hope for better things to come from it in the future. Members and colleagues of the APL-UW ocean acoustic community can use your passwords to access the part of this site containing TCTD notes, data, cruise report, test results, and documentation photos. And anyone can access the other section of the site with the TCTD deployment/recovery pictures, miscellaneous other technical pictures (including acoustic sources and TCTD) and fun "personal interest" pictures from the cruise.