Using Ground Penetrating Radar to Detect Oil in Ice and Snow

E. Babcock1, J. Bradford1, H.P. Marshall1, C. Hall2, and D.F. Dickins3

1Department of Geosciences, Boise State University, Boise ID; 2Alaska Clean Seas, Anchorage AK; 3P.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

• 1960s: GPR used to sound moon during Apollo 17

• 1970s: Begin widespread use of GPR as a geotechnical tool

• 1980s: 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

No propagation

Sea Ice 4-8 .01 - 0.1 0.134-0.150 27 cm

Snow 1.4 – 3.1 0.000001 0.25 - 0.168 50 cm

Oil 2-4 0.00001-0.0005

0.212 42 cm

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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 Prowww.sensoft.ca

2008 Training on North SlopePrudhoe Bay, April 2007

• Pulse Ekko Pro GPR• 500 and 1000 MHz

antennas• Multi-offset

acquisition to determine effective permittivity of ice

• Pre- and post- oil emplacement 3D surveying over 20 x 20 m grid

• Large scale 2D profiling

Norway, 2006

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

From Bradford et al., 2010

GPR for Oil Spill Response: CRREL

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 GPRDo 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– ExxonMobil– Shell Oil– Statoil

ReferencesAnnan, 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 offset-dependent reflectivity. Geophysics, 71(3): K47-K57.

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, G1-G12, 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/martinez1.hmtl

Olhoeft, G.R. 2006. Applications and Frustrations in Using Ground Penetrating Radar. IEEE AESS Systems Magazine, 2: 12-20.

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