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 even gravitational effects of spacecraft planetary flybys. My PhD was in theoretical and computational concerns in the 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...]



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 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.




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!




PHILSEA09-10 LONG-RANGE OCEAN ACOUSTICS EXPERIMENT

In 2009 and 2010 I participated in an ocean acoustics experiment in the Philippine Sea with APL-UW's North Pacific Acoustic Laboratory (NPAL) group. Some of the key things our research group is interested in are how oceanic sound propagation is affected by internal waves (waves down deep in the water) and ocean "spice" (which is a tongue-in-cheek nickname for "warm and salty" water). Both these phenomena cause variations in soundspeed of the water, but in different ways, 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.

In addition to our acoustic equipment on these cruises, we also took a new towed cabled instrument that we bought, which was to directly measure temperatures and conductivities and pressures at high resolution in the top half-kilometer of the ocean. These measurements would then give us unprecedented information about those internal wave and "spice" processes which affect the acoustics. Unfortunately, the instrument didn't perform too well and we didn't get near the amount or quality of data we were looking for. But we did get something, and one project of mine has been eking out what I can from it under the original idea of analyzing internal wave and ocean spice content in the region of the experiment (in collaboration with APL-UW's Frank Henyey). Still in progress -- more on that in the near future...