Bolette Badberg Jensen defends her thesis,<\/p>\n
Developing crosshole ground penetrating radar towards efficient contaminated site investigations<\/strong><\/p>\n Supervisors:<\/strong> Assessment Committee:<\/strong> Summary:<\/strong> A digital version of the PhD thesis can be obtained from the PhD secretary Mikala Heckscher at<\/em>\u00a0mikala@ign.ku.dk<\/p>\n","protected":false},"excerpt":{"rendered":" Bolette Badberg Jensen defends her thesis, Developing crosshole ground penetrating radar towards efficient contaminated site investigations Supervisors: Associate Professor Majken C. L. Zibar, IGN Nina Tuxen, Capital Region of DK Aikaterini Tsitonaki, WSP Denmark Thomas Mejer Hansen, AU Professor Lars Nielsen, IGN Assessment Committee: Senior Lecturer James Irving, University of Lausanne \u2013 Switzerland Chief Consultant […]<\/p>\n","protected":false},"author":0,"featured_media":145752,"template":"","class_list":["post-145751","event","type-event","status-publish","has-post-thumbnail","hentry","event_category-phd-thesis-defense"],"acf":[],"aioseo_notices":[],"yoast_head":"\n
\nAssociate Professor Majken C. L. Zibar, IGN
\nNina Tuxen, Capital Region of DK
\nAikaterini Tsitonaki, WSP Denmark
\nThomas Mejer Hansen, AU
\nProfessor Lars Nielsen, IGN<\/p>\n
\nSenior Lecturer James Irving, University of Lausanne \u2013 Switzerland
\nChief Consultant Flemming J\u00f8rgensen, Central Denmark Region
\nProfessor Karsten H\u00f8gh Jensen (chair), IGN<\/p>\n
\nHeterogeneous glacial deposits dominate large parts of the Northern Hemisphere. In these landscapes, high resolution characterization of the geology is crucial for understanding contaminant transport at polluted sites. Geological characterization based on borehole logs often proves insufficient in describing heterogeneity between boreholes. This PhD project was initiated with the objective of developing a methodology to use ground penetrating radar (GPR) as part of contaminated site investigations as a minimally invasive method for mapping geological heterogeneity between boreholes.
\nFirst, a simple linear approach for geophysical inversion of recorded radar amplitude data was developed. A linear model can introduce errors in the estimated subsurface models. This modeling error was quantified and accounted for by including a Gaussian description of the error in the inversion. Accounting for the modeling error was fundamental to successfully obtain 2D subsurface models from inversion of amplitude data.
\nThen, since water in the boreholes seemed to affect the GPR data to a surprisingly large degree, datasets obtained in boreholes with and without water were compared to quantify the influence from water-filled boreholes in clay till environments. The results show that the water-filled boreholes cause a three-fold increase of radar amplitudes, and that the mean frequency of the waveform data is reduced by approximately one third. In order to obtain high-quality subsurface estimates from crosshole GPR recorded in clay till, removing the water from the boreholes is recommended to ensure accuracy of the data hence increase the reliability of subsequent inversion results.
\nFinally, crosshole GPR was used at an industrial contaminated site in a clay till setting and the developed inversion approach was applied to obtain subsurface model estimates of the radar wave velocity and attenuation, independently. The GPR results were compared to borehole logs, grain size analyses and relative permeability data from the site. The GPR data analysis provided valuable information about the geology between boreholes and the original conceptual geological model could be refined. A silt layer with a thickness of a few decimeters, likely important for flow and transport processes, was resolved by GPR data.<\/p>\n