1. The GPS Reflections Group led by Dr. Kristine M. Larson (University of Colorado at Boulder), and including Professor Eric E. Small (University of Colorado), Dr. Valery U. Zavorotny (NOAA) and Dr. John J. Braun (UCAR).
The prize is awarded to this team of researchers for their discovery that standard geodetic GPS instruments are sensitive to hydrological influences and the subsequent development of a new, unexpected, and cost-effective technique, GPS Interferometric Reflectometry (GPS-IR), to measure soil moisture, snow depth, and vegetation water content.
GPS-IR is based on the discovery that the “noise” (interference pattern) observed with ordinary GPS instruments correlates with the water content of the reflecting surface in the vicinity of the receiving antenna.
This method of measuring soil moisture complements the cosmic ray technique (COSMOS) of Dr. Marek Zreda and Dr. Darin Desilets, a work previously honored by PSIPW back in 2010. Whereas COSMOS provides soil moisture averages over a circular area of radius 300 m to a depth of several decimeters, continuously-operating GPS receivers can be used to estimate soil moisture variations over areas of radius 50 m to a maximum depth of 6 cm, with greatest sensitivity to the upper 1 cm of soil depth at near saturation.
Furthermore, GPS-IR has the advantage of relying on an existing GPS infrastructure installed by surveyors and geoscientists that covers an increasingly large portion of the global surface (including more than 12,000 continuously-operating GPS systems on and near a wide range of soil and vegetation types around the world).
Its ability to reliably measure and track snow depth is extremely important because on-site snow distribution data are sparse and remotely sensed data are coarse-scale and imprecise. The ability of GPS-IR to sense and track vegetation growth complements conventional remote sensing data that have limited temporal coverage and do not work well in the presence of clouds.
Dr. Kristine M. Larson
Dr. Kristine M. Larson is Professor in the Department of Aerospace Engineering Sciences and the Environmental Engineering Program, University of Colorado at Boulder.
• Ph.D. 1990; Institute of Geophysics and Planetary Sciences, Scripps Institution of Oceanography, University of California at San Diego, Geophysics.
• B.A. 1985; Harvard University, Engineering Mechanics.
2013: University of Colorado Boulder Faculty Assembly Award for Excellence in Research
2006: Japan Society for the Promotion of Science (JSPS) Award.
2005: AGU Geodesy Section Award, recognizing major advances in geodesy.
1997-1998: National Science Foundation POWRE Award.
1994: NASA Group Achievement Award, Jet Propulsion Laboratory, in recognition of significant advances developing new techniques that permit the determination of an absolute global reference frame accurate to one centimeter with measurements from the Global Positioning System.
1993: National Science Foundation Career Advancement Program Award.
1992: NASA Group Achievement Award, Jet Propulsion Laboratory, in recognition of the pioneering OASIS/GIPSY software package that has set the world standard for global positioning system-based orbit determination and global geodetic measurement accuracy.
Dr. Eric E. Small
Dr. Eric E. Small is Professor in the Department of Geological Sciences, University of Colorado at Boulder.
• Postdoctoral Research Associate, 1998; Department of Civil and Environmental Engineering, MIT.
• Ph.D. 1998; Earth Sciences Department, University of California Santa Cruz.
• B.A. 1993; Williams College, Williamstown, Massachusetts, Geology.
Dr. Valery U. Zavorotny
Dr. Valery U. Zavorotny is a Physicist at the Physical Science Division of the Earth System Research Laboratory, National Atmospheric and Oceanic Administration (NAOA).
• Ph.D. 1979; Institute of Atmospheric Physics, USSR Academy of Science, Moscow, Physics and Mathematics.
• M.Sc.; Warsaw Technical University, Poland, Solid State Technology.
2014: Distinguished Lecturer, IEEE/Geoscience and Remote Sensing Society.
2010: Recognition for Best Reviewers for the IEEE Transactions on Geoscience and Remote Sensing (TGRS).
Dr. John J. Braun
Dr. John J. Braun is a Project Scientist for the Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC) Program at the University Corporation for Atmospheric Research (UCAR).
• Ph.D. 2004; University of Colorado at Boulder, Aerospace Engineering Sciences.
• MS. 1997; University of Colorado at Boulder, Aerospace Engineering Sciences.
• B.A. 1991; University of Colorado at Boulder, Physics and Mathematics.
First, I wish to thank the Prince Sultan Bin Abdulaziz Prize Council for recognizing our group’s work to develop cost-efficient instrumentation to measure soil moisture, snow depth, and vegetation water content. It is a great honor to be in Riyadh and to receive this prize. It is a pleasure to share this with my colleagues Eric Small, John Braun, and Valery Zavorotny.
I am a GPS geodesist. Generally this means that my job is to measure how the ground moves. How does a GPS geodesist win a prize given for measuring water? It turns out it started when I was trying to measure how the ground moves during an earthquake. To improve how well GPS could do this, I began to work on eliminating the effect of ground reflections on the GPS signals because they produce inaccurate positions. Eventually we were successful at deriving empirical corrections for ground reflections; it was this initial work that ultimately led me to try to measure ground reflections on purpose - specifically for hydrological applications.
While in principle ground reflections measured by a GPS instrument will be sensitive to changes in water content, there was a small problem to overcome: GPS instruments are designed to reject ground reflections. But if these technical difficulties could be overcome, we would be able take advantage of existing instrumentation operated by geophysicists and surveyors - installed to measure non-hydrologic parameters such as fault motions and land boundaries. Given that installing and maintaining any kind of scientific network is expensive, this is an incredible cost-savings. An added benefit of using GPS instruments to measure hydrologic parameters is that it increases the stakeholders for those networks. Going forward, I envision these stakeholders working together to build new GPS (and GNSS) networks for both traditional positioning and hydrological users. This could be particularly useful in regions that are not currently operating soil moisture networks.
I would like to end this short speech with both some professional and personal acknowledgements. First, none of this water cycle research could have been done without the Global Positioning System, which is truly a technological achievement in and of itself. What started out as just an idea became a reality via generous funding from both NSF and NASA. Having shown our ideas worked at a few sites, we were able to demonstrate it on a broader scale by taking advantage of the EarthScope Plate Boundary Observatory. I am very grateful to the people that designed, installed and maintained that GPS network. For myself, I want to thank my family, but especially my father, for always encouraging me to pursue a career in engineering and my husband for supporting me during these past twenty-five years.
Kristine M. Larson
1. Larson, K.M., E. Gutmann, V. Zavorotny, J. Braun, M. Williams, and F. Nievinski. "Can We Measure Snow Depth with GPS Receivers?" Geophys. Res. Lett., 36, L17502, doi:10.1029/2009GL039430, 2009.
2. Larson, K.M., J. Braun, E. E. Small, V. Zavorotny, E. Gutmann, and A. Bilich. "GPS multipath and its relation to near-surface soil moisture", IEEE-JSTARS, Vol 3(1), pp. 91-99, 10.1109/JSTARS.2009.2033612, 2010.
3. Zavorotny, V., K. M. Larson, J.J. Braun, E. E. Small, E. Gutmann and A. Bilich. "A physical model for GPS multipath caused by ground reflections: toward bare soil moisture retrievals", IEEE-JSTARS, Vol. 3(1), pp. 100-110, 10.1109/JSTARS.2009.2033608, 2010.
4. Small, E.E., K.M. Larson, and J. J. Braun. "Sensing Vegetation Growth with GPS Reflections", Geophys. Res. Lett., 37, L12401, doi:10.1029/2010GL042951, 2010.
5. Chew, C.C., E.E. Small, K.M. Larson, and V. Zavorotny. "Effects of Near-Surface Soil Moisture on GPS SNR Data: Development of a Retrieval Algorithm for Volumetric Soil Moisture", IEEE Trans. Geo. Rem. Sens., doi:10.1109/TGRS.2013.2242332, 2013.
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