Using Ground Penetrating Radar to Detect Oil in

Using Ground Penetrating Radar to Detect Oil in Ice and Snow E. Babcock 1, J. Bradford 1, H. P. Marshall 1, C. Hall 2, and D. F. Dickins 3 1 Department of Geosciences, Boise State University, Boise ID; 2 Alaska Clean Seas, Anchorage AK; 3 P. Eng. , DF Dickins Associates Ltd. , La Jolla CA

Overview • Ground Penetrating Radar (GPR) theory • Considerations for detecting oil under ice and snow • Demonstrations in controlled environment spill response • Future work

Brief History of GPR (Olhoeft, 2006) • 1926: Radar used to sound the depth of an alpine • • glacier in Austria (Stern, 1929) 1958: USAF airplane crashed on Greenland ice sheet as radar energy passes through surface to layers below 1960 s: GPR used to sound moon during Apollo 17 1970 s: Begin widespread use of GPR as a geotechnical tool 1980 s: GPR assessed as tool for oil detection under ice(Goodman et al. , 1985 and 1987)

Fundamentals of GPR • GPR uses electrical energy to interrogate the • subsurface Operates at radio frequencies – 10 MHz to 1 GHz • Transmit timed pulses of EM energy; measure reflected returns, process data, and display Annan, 2002.

Material Electrical Properties in the Arctic Marine Environment Material Relative Dielectric Permittivity Conductivity (S/m) Velocity (m/ns) Wavelength @ 500 MHz Air 1 0 0. 3 60 cm Sea Water 88 1 -5 No propagation Sea Ice 4 -8 . 01 - 0. 134 -0. 150 27 cm 1. 4 – 3. 1 0. 000001 0. 25 - 0. 168 50 cm 2 -4 0. 000010. 0005 0. 212 42 cm Snow Oil

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GPR for Oil Spill Response • • • Can we detect oil under ice and/or snow? What processing do the data require? What resolution can the system provide? What limitations do we experience? What benefits does this technology provide?

System Considerations: Data Processing • Use standard basic processing steps – Time zero shift – Bandpass filter – Spherical spreading correction • Attribute analysis – Instantaneous phase and frequency – Reflection strength – Previous work with GPR noted potential using attribute analysis to detect oil that was not possible with conventional analysis

System Considerations: Antenna Frequency • Frequency for radar survey is a trade-off – Depth of penetration – Quality of resolution – System portability • Field testing shows that GPR frequency of 500 MHz is optimal for penetration and resolution of oil under ice

System Considerations: Resolution and Detection • Using 500 MHz antennas – Detect 1 -2 cm oil layer in most scenarios – Resolve 4 -5 cm oil layer • Thin bed analysis problem – Reflection analysis alone not enough to accurately locate oil – Previous work had indicated attribute analysis as possible solution (Goodman et al. , 1985) – Consider attributes in conjunction with modeled response

System Considerations: Non-Uniqueness From Bradford et al. , 2008

System Considerations: Anisotropy Data courtesy of Alaska Clean Seas

Control Module (Digital Video Logger) - Sensors and Software PE Pro www. sensoft. ca

Prudhoe Bay, April 2007 2008 Training on North Slope

Norway, 2006 • Pulse Ekko Pro GPR • 500 and 1000 MHz • • • antennas Multi-offset acquisition to determine effective permittivity of ice Pre- and post- oil emplacement 3 D surveying over 20 x 20 m grid Large scale 2 D profiling

GPR for Oil Spill Response: Svalbard From Bradford et al. , 2008

Controlled Spill, New Hampshire, 2004, 2011 -2013 • Cold Regions Research and Engineering Lab • • (CRREL), 2011 and 2012 Indoor and outdoor testing Known ice thickness Known oil locations 500 MHz PE Pro System

GPR for Oil Spill Response: CRREL From Bradford et al. , 2010 From Bradford et al. , 2008

GPR for Oil Spill Response: CRREL 2012

GPR Limitations in the Arctic Environment • Variations in sea-ice conductivity and • • anisotropy Snow may generate spurious amplitude anomalies due to water or ice in snowpack: solution is non-unique We can ameliorate these concerns by frequent data truing and cautious interpretation

Conclusions: What Can GPR Do For Us in Arctic Spill Response? …and future research

Acknowledgements • • • My advisors John Bradford and HP Marshall CRREL and all the hardworking staff there – thanks! Alaska Clean Seas DF Dickins Associates Ltd Current funding provided by – Alaska Clean Seas – Conoco Phillips – Exxon. Mobil – Shell Oil – Statoil

References Annan, A. P. 2005. Ground-Penetrating Radar. In Near Surface Geophysics, Investigations in Geophysics No. 13. Butler, D. K. , Ed. Society of Exploration Geophysicists, Tulsa, OK. Annan, A. P. 2002. GPR – History, Trends, and Future Developments. Subsurface Sensing Technologies and Applications, 3(4): 253 -271. Bradford, J. H. and J. C. Deeds. 2006. Ground penetrating radar theory and application of thin-bed offsetdependent reflectivity. Geophysics, 71(3): K 47 -K 57. Bradford, J. H. , D. F. Dickins, and P. J. Brandvik. 2010. Detection of snow covered oil spills on sea ice using ground-penetrating radar: Geophysics, 75, G 1 -G 12, doi: 10. 1190/1. 3312184. Bradford, J. H. , D. F. Dickins, and L. Liberty. 2008. Locating oil spills under sea ice using ground-penetrating radar: The Leading Edge, 27, 1424– 1435. Martinez, A. and A. P. Byrnes. 2001. Modeling Dielectric-constant values of Geologic Materials: An Aid to Ground-Penetrating Radar Data Collection and Interpretation. Current Research in Earth Sciences, Bulletin 247. Online at http: //www. kgs. ukans. edu/Current/2001/martinez 1. hmtl Olhoeft, G. R. 2006. Applications and Frustrations in Using Ground Penetrating Radar. IEEE AESS Systems Magazine, 2: 12 -20. Questions?