SEG-AGU Hydrogeophysics Workshop

8-11 July 2012
Boise, Idaho, USA

The need for sustainable management of our fresh water resources is one of the great challenges of the 21st century.

Meeting this challenge requires significant advances in both science and technology. This workshop addressed hydrogeophysical approaches for determining/predicting/studying hydrologic properties and processes in both the saturated and unsaturated zones, at scales ranging from centimeters to watersheds. Through presentations of original research in "General Sessions," and analysis and interpretation using shared hydrogeophysical datasets in "Homework Sessions," the workshop highlighted the state of the science and critical future directions. Topics were defined for the General Sessions and sessions organized around more specific topics with ~10 presentations in each session, based on the submitted abstracts. Homework Sessions allowed different investigators to independently analyze a shared dataset, with each homework designed to explore important aspects of acquiring, analyzing and interpreting hydrogeophysical data. In order to promote discussion, all accepted abstracts (for General and Homework Sessions) were presented as posters, with a 3-5 minute oral presentation as an introduction. After viewing posters, all sessions reconvened for a panel-led discussion.

General Sessions

Characterizing Near-Surface Structure and Properties

The use of geophysical methods, for imaging structure and quantifying subsurface properties, offers a degree of subsurface coverage and scale of spatial resolution that are unattainable with more traditional hydrological characterization approaches such as borehole/log analyses and pumping or tracer tests. This session discussed the advances that have been made with respect to the use of geophysical methods in this regard, with focus on (i) new forms data acquisition, analysis and inversion to improve the resolution of geophysical images and derived subsurface models; (ii) the development of improved petrophysical relationships between one or more geophysical properties and K; (iii) the exploration of promising “new” geophysical techniques, such as NMR and spectral IP, to reveal information about subsurface properties,; (iv) the use of dynamic geophysical data to monitor changes in hydrological state variables, which can then be used within a coupled inversion framework to link to the underlying property distribution; (v) work on the assimilation of multiple geophysical and hydrological data sets, and quantification of the uncertainty in the resulting property estimates. The purpose of this session was to explore the advances made in this domain, specifically with regard to their relevance to the original “big-picture” hydrological needs. This was donewithin a framework of uncertainty, such that the results could truly be of use to decision-makers for designing effective management or remediation strategies.

Advances in Monitoring and Time-Lapse Imaging of Subsurface Processes

One approach to describing a subsurface process is to develop a subsurface model and then predict the process of interest. An alternate approach is to directly monitor or image the process. Recent advances in data acquisition hardware and software, and in sensor technology, made it possible to adopt this latter approach in a wide range of settings. This session highlighted innovative uses of geophysics measurements for monitoring and time-lapse imaging for hydrogeologic applications. The session invited presentations that demonstrated new approaches to acquiring, analyzing, inverting, and/or interpreting data, and discussed the challenge of obtaining data at the required spatial and temporal resolution. Presentations included field studies, laboratory experiments, theoretical and numerical modeling. All presentations (and abstracts) were requested to include a statement of 1) the hydrogeologic application of interest; 2) the significant scientific or technological advancements; 3) the outstanding research questions, and what could be done within the community in order to address them.

Thinking About Scaling Up: Geophysical Methods at the Watershed Scale

Numerous opportunities exist to characterize hydrological processes and state variables over watershed scales, including evapotranspiration, runoff, groundwater recharge and soil moisture, among many others. Development of environmental observatories and their associated instrumentation had been accelerating within internationally funded programs, and there was a critical need to develop new sensors and informatics infrastructure for these larger-scale processes. Topics for this session included innovative environmental sensors and sensing systems, sensor networks, cyberinfrastructure to support sensors and data suppliers, and modeling approaches (such as data assimilation) that used the high-frequency and high-density data promised by environmental observatories. Suitable methods included techniques such as electrical resistivity tomography, electromagnetic induction, ground penetrating radar, near-surface seismics, air- and space-borne methods, and land-monitoring remote sensing platforms, among others. In addition, wireless sensor networks and distributed fiber optic technologies bridge the scales between ground-based measurements and remote sensing platforms. Contributions dealt with the development and application of geophysical and remote sensing techniques and/or associated modeling.

Homework Sessions

The Use of Electrical Resistivity Measurements for Monitoring Subsurface Processes: Quantifying Noise and Uncertainty

The focus of the homework in this session was the characterization of data noise and the uncertainty associated with the inversion of electrical resistivity data. The data set provided included two lines of Wenner measurements made with electrodes in the base of a recharge pond. The measurements recorded changes in the subsurface conductivity structure during and after a rainfall event prior to filling of the recharge pond; it captures periods of both increasing and decreasing water saturation. The homework: Invert the data, then characterize the measurement noise and/or the uncertainty of the inverted image.

The Ultimate Tomography Bake-Off Challenge Using Boise Hydrogeophysical Research Site Borehole Seismic and GPR Datasets

It is rare that many different investigators independently analyze a single dataset and then compare results to gain insight into uncertainty in solutions, differences in processing algorithms, or variations in petrophysical assumptions. Rarer still are instances when such an effort has been undertaken with field data. This session focused on borehole-to-borehole, and borehole-to-surface tomographic inversion and took advantage of the unique control database afforded by the Boise Hydrogeophysical Research Site. The site had acquired a coincident seismic and GPR borehole-to-borehole, and borehole-to-surface dataset with a similar geometry and source characteristics selected to produce a similar wavelength in the saturated zone. The data was made available for download from the CGISS web page on November 15, 2011. Participants in this session were invited to download all or any subset of the data and use any preferred method for inversion. The objective was to produce compressional and/or electromagnetic wave velocity tomograms and porosity distributions. "Control" data consisted of the results of previously analyzed VSP, VRP, and neutron-neutron probe surveys acquired in the two acquisition boreholes and in a coincident interior borehole. Participants' results were compared with each other and with the "control" data. The objective of the session was not to determine the "right" answer but rather to better understand differences in analysis methods.

Designing the “Perfect” Field Experiment

The focus of this homework session was to design a realistic hydrogeophysical field experiment for predicting, as accurately as possible, the transport of contaminants in a heterogeneous subsurface aquifer. Participants were provided with a 3-D, fine-scale, synthetic model of the “true” aquifer hydrogeological properties, along with boundary conditions and the nature of the source of contamination. They were then responsible for designing all aspects of the experiment to predict contaminant transport. Any geophysical and/or hydrological method, or combination of methods, could be used. The participants were responsible for both simulating and analyzing the different data sets. Care was taken to make the experiment realistic, keeping the cost and effort of the data acquisition in mind. Realistic petrophysical relationships were also employed, with noisy data. Some estimate of the relative uncertainty of the corresponding predictions was also required.

Meeting Venue

The meeting was held at Boise State University in the Lookout Room, which is on the 3rd floor of the Student Union Building.

Organizing Committee

Rosemary Knight, General Chair
James Irving
Rob Jacob
Lee Liberty
Kamini Singha
Jan van der Kruk

Sponsors

NSF
Geometrics
GeoTomo
Mount Sopris Instruments
Zonge
VistaClara Inc.
Geotomographie
Sensors & Software
Advanced Geosciences, Inc.
Geonics

External links

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