b'Environmental geophysics Environmental geophysicsWelcome readers to this issuesUniversity and the state of electrical column on geophysics applied to thegeophysics from the 1970s to the 1990s. environment. I am continuing the seriesAnd yet another geophysical war story, that was started a few Preview issuesthis time on overcoming programming ago: Seven Scenes - reminiscences byissues that most of us would find hard to Niels Christensen on his career at Aarhusimagine. Over to NielsMike Hatch Associate Editorfor Environmental geophysics michael.hatch@adelaide.edu.auPivotal moments: Seven scenes from a geophysics adventureinversion guru of our department, awas given the acronym SELMA: position that has only grown strongerSimultaneous Electromagnetic Modelling over the years. The new and visionaryand Analysis. Shortly after we started, I part of the programming project wasfound a portrait of the Swedish writer that it should include the option ofSelma Lagerlf, framed it and put it joint inversion of any combination ofon a shelf in my office (Figure 1). Quite electrical and electromagnetic (EM)often I have been asked if that was my methods. grandmother, to which I replied: No, its not, it is Selma Lagerlf. However, there All EM methods have a limitedmight be some truth in it; you could say resolution capability of the subsurfacethat she became the guardian angel of resistivity due to unavoidable dataour programming efforts, peering down Niels B. Christensen noise, the incompleteness of the dataat us from the shelf.Professor Emeritus sets, and inconsistencies between Department of Earth Sciencesthe - necessarily simplified - models Aarhus Universityused in the inversion and the infinite nbc@geo.au.dk complexity of nature. Some of the more spectacular cases of poor resolving Scene 3 power have a name of their own: high resistivity equivalence, low resistivityin which the incredible history ofequivalence, inability to discern poor computing is retold with a geophysicalconductors, layer suppression, etc. twist. Different EM methods and data types see the subsurface differently, and consequently their most prominent Inversion programs forequivalences, that are characteristic electromagnetic data of the methods, are also different. This is why a combination of data from In 1990, Bo Holm Jacobsen and Idifferent methods, e.g. galvanic and decided to join efforts and write ainductive methods, has the potential to FORTRAN program that would invertresolve some of the equivalences found all the electric and electromagneticin the individual methods, and improve data types we could collect at thethe resolution of the subsurface department, plus quite a few we didresistivity distribution.not have access to - yet. Our plan was that I would make the forward responseOur ambition was to make a program routines while Bo would make thethat would jointly invert data from inversion part. At that point in time,any combination of electrical andFigure 1.Selma Lagerlf, 1908. (Public domain Bo was well on the way to become theelectromagnetic methods. The programhttp://www.marbacka.com/press/SLF_042.jpg)33 PREVIEW JUNE 2022'