How Trying to Measure Seismic Waves with GPS Led to the Development of a New Kind of Tide Gauge
About the Event:
About fifteen years ago I began working on developing methods so that GPS could be used to measure ground displacements during large earthquakes. At the time, almost all geodesists estimated station positions once per day, as this is entirely adequate for tectonic applications. Standard geodetic analysis tools (then and now) ignore the error caused by signals that reflect off the land surface. My group quickly realized that surface reflections were the largest error source in GPS seismology and developed tools to mitigate their impact. That early work in GPS seismology ultimately inspired my current work in hydrogeodesy - where reflected GPS signals are used to turn a GPS antenna into a bi-static radar. The reflected GPS signals can be used to measure many natural surfaces, including soil moisture, snow depth, water levels, and vegetation water content. We have been able to take advantage of GPS data from the EarthScope Plate Boundary Observatory (PBO) to apply these reflection methods on a large scale; we call this initiative PBO H2O (http://xenon.colorado.edu/portal). In this talk, I will provide some background on GPS for tectonic and seismic applications, explain how GPS reflections work, and then show water cycle products derived from GPS data. I will also share some newer work I’ve done using GPS data to measure ash in volcanic plumes.
About the Speaker:
Kristine M. Larson is a geodesist. After graduating from Harvard University in 1985, she studied geophysics at the Scripps Institution of Oceanography. Her PhD used the nascent GPS system to measure crustal deformation in southern California. In 1990 she took a faculty position in the Department of Aerospace Engineering Sciences at the University of Colorado. For many years her group applied GPS to traditional geophysical problems, including measuring plate boundary deformation, global plate motions, and volcanic deformation. In the early 2000s she moved to geodetic signals with larger speeds, including ice sheet motions and seismic displacements. For the last decade her research group has focused on developing environmental applications for reflected GPS signals, including soil moisture, snow depth, vegetation water content, sea level, firn density, and permafrost melt.
Larson was elected an AGU Fellow in 2011, EGU Medalist in 2015, and in 2017 was awarded an honorary doctorate from Chalmers University of Technology.