GeoLog

GPR

Imaggeo on Mondays: The Final Effort

We’ve all been there: long hours in the field, a task that seems never ending but which has to be finished today. This week’s Imaggeo on Mondays image is brought to you by Patrick Klenk who highlights the importance of how ‘getting the job done’ relies on good team work!

Two years ago I posted this picture to imaggeo as a tribute to everyone who ever experienced the perils and pitfalls of outdoor field experiments and especially to the colleagues who help you to pull through in the end. It is their scientific spirit which allows to add that indispensable calibration measurement making the difference between a heap of nice-to-look-at data and a quantifiable dataset — even if this means staying on for that extra hour in quickly fading daylight while the cold of a late autumn night encroaches already relentlessly upon your exposed field site.

Final Effort (Credit: Patrick Klenk via imaggeo.egu.eu)

Final Effort (Credit: Patrick Klenk via imaggeo.egu.eu)

In this particular case, we started out on a bright late autumn day, planning to quickly complete a week-long series of Ground-Penetrating Radar  (GPR) experiments on our ASSESS test site in the vicinity of Heidelberg, Germany.  Most certainly, we intended to be finished long before this picture was taken — but alas, as most environmental scientists who are concerned with experimental field studies can probably relate to, outdoor experiments often do not work out exactly as planned and especially timetables get overturned more often than not. In the end, this field day turned out to be the last usable field day for that season and only through the final team effort pictured here we were able to successfully complete a quite involved series of GPR experiments.

The aim of these GPR experiments is to quantify near-surface soil hydraulic properties through the observation of soil water dynamics with non-invasive measurement methods directly at the field scale.  To date, the quantification of soil hydraulic properties remain the holy grail of soil sciences, since they are difficult to determine but widely required for a range of applications such as precision agriculture or the prediction of contaminant flow through the subsurface. Traditional approaches, which determine soil hydraulic properties e.g. from soil samples in the laboratory, suffer from their high cost, their destructive nature and from issues of transferability of the results back to the field. We specifically designed our test-site with a complicated but known subsurface structure to allow for the development of quantitative, high-resolution observations of soil water dynamics with GPR.  In brief, our approach compares GPR observations of soil water dynamics related processes such as: water sprinkling from above the surface (infiltration) or a varying water table depth (achieved by pumping water in and out of the structure from below: imbibition and drainage) to numerical simulations of both subsurface water flow and the expected GPR response. Our research then focuses (i) on observation based estimation methods of the parameters which are needed by the models we use to calculate physical property distributions (inversion) and (ii) on data assimilation methods (i.e. a form of continuously integrating modelled states of a physical system with available observational data) to optimally combine all available information for quantifying the soil properties in question.

 

Patrick is a physicist, currently working as a postdoc with the soil physics group at the Institute of Environmental Physics, Heidelberg University, Germany, on novel approaches for developing Ground-Penetrating radar for quantitative soil hydrology.

 

By Patrick Klenk, postdoctoral researcher at the Institute of Environmental Physics, Heidelberg University, Germany

 

References

Buchner, J.S., Wollschläger U., Roth K. (2012), Inverting surface GPR data using FDTD simulation and automatic detection of reflections to estimate subsurface water content and geometry, Geophysics, 77, H45-H55, doi:10.1190/geo2011-0467.1.

Dagenbach, A., J. S. Buchner, P. Klenk, and K. Roth (2013), Identifying a soil hydraulic parameterisation from on-ground GPR time lapse measurements of a pumping experiment, Hydrol. Earth Syst. Sci., 17(2), 611–618,doi:10.5194/hess-17-611-2013.

Klenk, P., Jaumann, S., and Roth, K. (2014): Current limits for high precision GPR measurements, in ‘Proc. 15th International Conference on Ground Penetrating Radar (GPR2014), 30 June-04 July 2014, Brussels, Belgium, available online shortly.

Klenk, Patrick,  Developing Ground-Penetrating Radar for Quantitative Soil Hydrology, PhD-Thesis, Heidelberg University, 2012, http://www.ub.uni-heidelberg.de/archiv/14329.

 

Imaggeo is the EGU’s open access geosciences image repository. Photos uploaded to Imaggeo can be used by scientists, the press and the public provided the original author is credited. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. You can submit your photos here.

 

 

Real life Minesweeper

Reading GeoLog when you should be working? We are all guilty of a little procrastination, but, sometimes, the parallels between science and the games we play to postpone the next write-up are closer than you’d think. Victor Archambault, a scientist from US Radar, reveals how playing Minesweeper mimics the way geoscientists analyse data in the field…

We have all played the infamous Minesweeper that comes with our computer, but few realise the principles of the game are used in a variety of fields and by scientific communities worldwide. In the game, the player is given numbers to make educated guesses as to where the mines will be in order to both avoid the dangers and uncover all the other tiles. This principle is no different from real life, where trained industry workers and scientists use electromagnetic waves to get clues about what might be under the surface. This could mean finding pipelines running through the foundations of a building, excavating an archaeological site, or even trying to identify and disarm a minefield.

The game. (Credit: Victor Archambault)

In the game. (Credit: Victor Archambault)

The Minesweeper game places nice neat little numbers everywhere that are both clear and easy to read but this isn’t the case with Ground Penetrating Radar (GPR), the technique used by scientists and other professionals to find out what’s underground. Depending on what you’re looking for, and what materials you’re penetrating, the images can be anything from a strange-looking pattern of waves, similar to a heart rate monitor at the hospital, to a rough 3D rendering straight from a cartoon.  This picture shows the variation in what you may see as you look into the internal structure of a cement supporting wall. As you can see, there are multiple ways to view it, which helps us make our most accurate guess.  This can be very useful in construction or city planning, allowing people to know what is currently there to use and what should be avoided.

In real life. (Credit: Victor Archambault/USRadar)

…And in real life. (Credit: Victor Archambault/US Radar)

The diagram below shows a GPR device as it is pushed along a surface. The waves spread downward in a fan-like shape and you can see an object before you are directly above it and after you have walked over it. Careful attention is needed to be sure not to miss any small artifacts you may be searching for.  The more constant and consistent the material is, the more complete and efficient the data will be for the user to read. Just as Superman cannot see through lead, the “radar mower” will struggle to see through certain types of materials – such as moist and clay-filled soils that have higher soil electricity conductivity.

'Mowing' the lawn to get a look at what lies under the surface. (Credit: Victor Archambault/USRadar)

“Mowing” the lawn to get a look at what lies under the surface. (Credit: Victor Archambault/US Radar)

Another way professionals use this technology is in oceanic plane crashes where large bodies of water are needed to be scanned for wreckage to help locate survivors. This involves a large, highly equipped plane to fly over the water – just like the ground scanning counterparts – and scan the ocean surface and below for clues as to the whereabouts of suspicious dots or shadows. It is more complex than most ground GPR designs because all elements of the radar need to be locked in place and it requires precise measurements for position correction.

Using electromagnetic waves in our daily lives continues to be more and more productive.  From catching a car that’s speeding to seeing a prenatal baby in the womb, we can see its implications to help us and better humanity. Minesweeper is a popular way to procrastinate, I hope next time you kick back and relax with a game, you look at it with more of a scientific eye! 

By Victor Archambault, US Radar