This project aims to further develop and refine a method to extract near-surface soil moisture estimates from Global Positioning System (GPS) receivers as a continental-scale soil moisture network and to evaluate errors to establish the underlying uncertainty in the estimates. Specifically, the investigators will (a) quantify how various aspects of the physical environment influence soil moisture estimates, including (i) vertical profiles of soil moisture and texture; (ii) vegetation amount and structure; and (iii) topography and surface roughness, and evaluate the physical environment around each of the Earthscope Plate Boundary Observatory (PBO) sites for suitability for the GPS soil moisture technique; (b) evaluate how antenna and receiver design/performance and satellite signals influence the soil moisture content time series derived from GPS signal-to-noise ratio (SNR) data, and evaluate the equipment used by PBO because its network is large, homogeneous, and well-maintained.
This project is a collaboration between hydrologists, climate scientists, electrical engineers, and GPS geodesists. A broad range of data will be collected from seven field sites, including GPS, in situ soil moisture, meteorological, and vegetation information. The different data types will be combined using an integrated modeling system designed to understand how the physical environment and antenna/receiver design influence GPS SNR data. This will yield a retrieval algorithm for soil moisture from GPS SNR data that is guided by physical principles.
This research will benefit society by providing important new soil moisture data for hydrological and climate studies and weather forecasting. Two graduate students will be supported and trained in a interdisciplinary educational program including hydrology, remote sensing, and GPS geodesy.
Measurements of soil moisture are necessary for weather forecasting, climate studies, and drought prediction. Consistent and accurate measurements of snowpack and melt rate are essential for management of water supply and flood control systems. Measurements of vegetation growth are needed both for improving agricultural yield and drought monitoring. Existing soil moisture, snowpack, and vegetation networks either sample infrequently, utilize inconsistent sensing technologies, or measure an area that is too small to be useful for many hydrologic applications and research. We have developed methods to use GPS receivers to measure each of these quantities: soil moisture, snow depth, and vegetation water content. This method can be applied to existing GPS sites, including the NSF-funded EarthScope Plate Boundary Observatory. The attached figures show examples of water cycle products developed from this research. Over 300 sites are evaluated daily; most of the sites are in the western United States. All our products are updated daily and are made available to the public. We have developed a website to distribute these data and have documented our methods both on this website and in journal publications. We are working with various research laboratories to help them assimilate these new water cycle data into their analyses. All data products are available at http://xenon.colorado.edu/portal. Educational material on GPS, tectonics, and water cycle products are also linked to this website.
