Research Interests

My research uses near-surface geophysical methods to better understand processes in the shallow subsurface. Analyzing surface Ground Penetrating Radar (GPR) reflection data and cross-hole GPR tomography and vertical profiling, my research focuses on providing highly detailed images of the subsurface. Trend analysis of soil moisture is a critical aspect of this research, thus, I conduct imaging over several months. With this time lapse-imaging, I can relate the differences between images to changes in fluid movement or soil moisture. I have used electromagnetic methods (EM-31) in a similar manner to look at changes in the soil moisture content of a landfill surface barrier. To help understand a hydrothermal system, I analyzed transient electromagnetic (TEM) data. By using a variety of methods, I can provide complementary information about the Earth's physical properties resulting in more reliable interpretations of the subsurface.

I have worked in collaboration with hydrogeologists, geostatisticians, and soil scientists as well as geophysicists to study the soil moisture distribution in the vadose zone and ground water flow through porous media. I am also collaborating with a geographer to understand the response of sand dunes to climate change. Geophysical methods are an important tool to provide subsurface information on structure and physical properties to complement geological investigations. I like the interdisciplinary nature of near-surface geophysical research that allows me to interact with geologists to help solve problems of mutual interest.

My research also uses inverse methods to better understand the uncertainty and limitations of models. Many studies produce models that provide information about the subsurface. However, the estimated model parameters contain uncertainty. By analyzing the uncertainty, I can produce more reliable and meaningful subsurface models. One of my goals is to improve results by developing algorithms that better quantify the error in the resulting images. I am developing methods that incorporate data uncertainty and provide error measures that are included in my output models. I also apply different inverse methods to downhole radar data to study the advantages and limitations of each method. Understanding the uncertainty in parameter estimates will enable geoscientists and environmental managers to make better, more cost-effective decisions based on the results of geophysical investigations.

Recently, I have become a part of an exciting research team investigating Carbon Sequestration. The northwest is covered by thick sequences of basaltic lava flows. The group is studying the potential to store CO2 in the flows and in the interbeds between flows. A crucial component is monitoring, measuring, and verifying (MMV) the distribution and containment of the CO2 in the subsurface. My role is understanding the geophysical capabilities for MMV through modeling the seismic response of CO2 injected into these layered sequences. My contribution will be evaluating the capability of borehole (vertical seismic profiles) and crosshole (seismic tomography) seismic methods to determine the subsurface distribution of the injected CO2 and measure the changes in the injected fluid over time. The challenges of CO2 Sequestration and MMV are difficult, but the rewards are great.

Environmental cleanup and water usage will continue as major issues in the future. Ecological and societal decisions must be based on an accurate assessment of the relevant models. Environmental geophysics is becoming a more important and widespread technique to solve difficult, two-, three-, and four-dimensional problems, such as the geological response to climate change and the flow of contaminants. My research addresses fundamental problems, such as understanding water flow and the information content of data, that will not only benefit the geoscience community, but also society in general.

© William P. Clement 2008