Adventures of a Geophysicist

Introduction to a new series on historical perspectives in Near Surface Geophysics, Burke Minsley, Near Surface Geophysics Section President

The field of Near Surface Geophysics has a rich history of innovation in methods, instrumentation, and software. Some of this history is preserved in the publications and textbooks from our field, but many of the interesting back-stories about the people and groups that led to important developments in our field are often lost. To preserve some of this history, the Near Surface Geophysics section will share seven short stories written by Niels Christensen, Professor Emeritus at Aarhus University, one per month posted in our newsletter and linked for posterity on our website. The stories will also be published in ASEG's Preview magazine. Niels provides a background to these stories, which documents several decades of development in electromagnetic and other geophysical methods at Aarhus University and the HydroGeophysics Group that have left an outsized impact in the field of near-surface geophysics. The links to the full versions can be found on our website below.

Background to 'Adventures of a Geophysicist - Seven Scenes from a professional life', Niels B. Christensen, Professor Emeritus, Aarhus University

During the period ~1980-2000, at the Department of Geoscience, Aarhus University, near-surface geophysics took a great leap forward with the development of several new electromagnetic methods, new instrumentation, novel field practices, and new inversion possibilities. All this happened through a unique combination of the right people at the right time, an explosive development in electronics and computer capacity, and a perceived need for mapping and monitoring groundwater resources. The development was characterised by a combination of research, teaching, practical inventiveness, and collaboration with local and regional administrative bodies who were willing to take chances by financially supporting new developments under the guarantee that, in case of failure, the work would be done in traditional ways.

Around the turn of the century, the successes brought about by the new possibilities - and, again, the right people at the national administrative and political level - inspired a political decision to start a national program of mapping all the most important water resources in Denmark, a program of unprecedented depth and scope when compared with other countries. Around this time, the HydroGeophysics Group was formed at Aarhus University to support and oversee the enormous mapping efforts to be conducted by the consulting companies who had adopted the new methods and approaches. The program went on for 15 years and is now more or less brought to its conclusion.

The legacy of the national program is a HydroGeophysics group that from its first efforts has risen to become among the best and most respected research groups in the world for electromagnetic methods, IP and SNMR, and a nation that has the best possible basis for a sustainable use of its water resources.

It was my privilege to be a part of this development in its heyday, and below are some musings from a geophysical professional career.

SCENE 1 ... in which our protagonist goes to sunny California and comes home with new ideas.

The beginning: Berkeley 1987

It's a beautiful walk from the bus stop where I get off through the campus of University of California, Berkeley: well kept green lawns and imposing university buildings each in its own style. I'm going to the Hearst Memorial Mining Building situated at the upper part of campus. It's not particularly big, but when you enter through the big heavy front doors, you arrive in an enormous entry hall that stretches from floor to ceiling through the entire building with imposing broad staircases spiraling along the outer walls; everything (I learned later) in the most beautiful Beaux-Art style. As with most of the university buildings it is a donation, in this case from Phoebe Apperson Hearst, widow of senator and mine magnate George Hearst. It is my first day at University of California in Berkeley. I have received a grant from the Danish Natural Science Research Council, and four months lie ahead of me in sunny California!

On the second floor I find the geophysics section and I'm received by professor Frank Morrison. Some months earlier, I had the audacity to write and ask if I could visit his department for some months. I did not know him beforehand, and he certainly did not know me, I just knew it was one of the hottest places to learn. So there he was, Frank Morrison, suave, with his wavy hair, a touch of gray at the temples, like a movie star from the forties with a big smile and a spark in his eye. He took me under his wing and showed me around:"

Read the rest of Scene 1 here...

SCENE 2 ... in which the transient electromagnetic method makes its entry in Denmark, and 'buried valleys' becomes a household term.

In the forest

For the umpteenth time I get up and walk to the car, a Toyota Hiace, the most recent acquisition of the Department for field use. I get into the van, start the engine, drive a bit back and forth until it is 1 m closer to the transmitter loop. I stop the engine, get out, measure the distance between the wire and the car and make a note about it. Then I walk to the receiver box of the transient instrument and for the umpteenth-plus-one time I push the button that starts a new measuring sequence. Sometimes the thought strikes me that if someone has been watching my activities for some time, it will look rather mysterious. Fortunately I never meet anyone; I have deliberately chosen a very calm and quiet place in the forest around Fløjstrup, about 10 km south of Aarhus, as far away as possible from power lines, buried cables, electric fences and other man-made installations that might disturb the measurements. Here I can experiment with what it takes to disturb the recordings: How close to the transmitter wire can I park the car? Can the car be inside the transmitter loop? How far can I move the receiver coil from the centre of the transmitter loop before it has an effect? How sloppy can I be in laying out the square 40 x 40 m transmitter loop. Etc., etc. Does the transmitter display show the correct current value, and is the meter linear? There is an endless list of issues to be tested when you get a new instrument, and by and large I spend every day for two weeks in the forest. Not bad, really. I like the place.

Read the full Scene 2 here...

SCENE 3... in which the incredible history of computing is retold

Inversion programs for electromagnetic data

In 1990, Bo Holm Jacobsen and I decided to join efforts and make a FORTRAN program that would invert all the electric and electromagnetic data types we could collect at the department, plus quite a few we did not have access to - yet. Our plan was that I would make the forward response routines while Bo would make the inversion part. At that point in time, Bo was well on the way to become the inversion guru of our department, a position that has only grown stronger over the years. The new and visionary part of the programming project was that it should include the option of joint inversion of any combination of electrical and electromagnetic (EM) methods...

Read the full Scene 3 here...

SCENE 4 ... in which our protagonist has unusual luck, goes to Australia, and finally succeeds in finding the key to fast approximate computing.

EAGE conference, Paris 1992

I'm on the roof of the conference centre where the EAGE conference is held in Paris in 1992, enjoying a beautiful sunset over the roofs of Paris with a glass of cool white wine in my hand. Life could certainly be worse. Besides making a presentation, I have another intention with being here. I'm searching for a person who might, or might not, be here...

Read the full Scene 4 here...

SCENE 5 ... in which a group of Danes (once more) make their presence felt on the North American continent, in Europe and Australia, and invite people to come to beautiful Aarhus.

An international breakthrough

In 1993, I participated in my first SAGEEP conference which was held in San Diego, California. The conference focused primarily on near-surface geophysics, which up to that point in time had been treated as a somewhat suspicious snotty-nosed upstart at most geophysics conferences, e.g. SEG and EAGE, where the main emphasis was - and still is - on the deeper parts of the Earth, in particular seismic methods used in the oil and gas industry. It was a kind of revelation for me that many other geophysicists in the world were engaged in the same subjects as I was. It made me feel part of community, where I could be one of the pioneers in a new research field. I had found a professional home....

Read the full Scene 5 here...

SCENE 6 ... in which teaching activities - and their importance in the bigger picture - are presented.

Teaching 1984 - 2011

In 1984, I became an assistant professor, and, shortly after, I started to teach a course in environmental/near-surface geophysics. At first, I used a fairly newly written compendium for post-education of geologists in geophysical methods. The compendium was initiated by The Nature Agency under the Ministry of Environment, and I had been part of group of people who wrote it. However, there was precious little material already published that addressed the curriculum of the course at the appropriate academic level, and very soon I started to write lecture notes for the course.

Read the full Scene 6 here...

SCENE 7:  So ... what came out of it all ... ?

... in which the protagonist and his good colleagues ask the questions: So - how'd it all go ? What came out of the efforts ? What is the situation today ? And what is needed in the future ?

In this seventh and last Scene, I will leave the reminiscences of my own past, turn around, and look at some of the aspects that are important for the present and the future situation regarding the precious resource of groundwater in Denmark. As always, the future is unknown and the present is more complex than anyone can grasp, but I have selected a few themes and collected the discussions under four headlines:
What is the situation for the discipline of geophysics ?
What is the status for hydrogeology ?
What is the situation with regard to politics and administration within these fields ?
And what can be expected in the future ? 

Read the full Scene 7 here...