b'Environmental geophysics 40 x 40 m. It all sounded very promising.contoured the values by hand and madehome with a much wider horizon and- I spent the next months with pencilmy first colour graphics illustrations usingwith a word that did not exist at that and paper and programming, trying tocrayons. Below (Figure 1) you can see antime - a large network in the US. My world understand the basic physics. example scanned from the original handhad become much larger and I enjoyed With regard to computer power andcolouring from 1987. beautiful California immensely. Later, graphic visualisations, 1987 is a long timeTo me, Berkeley became a pivotal timea PhD student of mine, Esben Auken, ago, and we have almost forgotten howwhere my futureand eventually that ofwent to Berkeley for six months during it wasnot to mention the incredulousmany other people - took a new direction.his PhD and came home with the same faces of young people when you tellAfter the four months in Berkeley Iexhilaration and excitement!them about it! At that time, typically wearrived home with new excitement andBut how would we manage to get an had a non-graphical terminal connectednew insights: We had to get a transientinstrument? It cost a quarter of a million to a mainframe computer that servicedinstrument! I exhibited the hand-colouredDanish kroner and that was a huge sum a large number of people. Printing wasplots in our canteen and talked lengthilyat that point in time.on the old line printers with broad paperand with fervour about the transient rolls and no graphics options, plotters didmethod. And just as importantly, I cameTo be continued.not exist, and graphics were handmade. The small Apple computer in the corner of the office was regarded with awe and you had to sign up for a time slot to get to use it. And imagine - it was possible to write real mathematical formulas on it!! Fantastic!! So, I did what everyone else did at that time: sat down with paper and pencil. In particular I was very interested in understanding the way current diffused downwards and outwards in the ground. That was the key to understanding the assets and drawbacks of the method. I calculated analytic approximations for the current in the ground, valid at earlyFigure 1.Left: Subsurface current density at 5 s. Right: Subsurface current density at 50 s. The source and late times, and produced computeris a vertical magnetic dipole on the surface. The plot frames show only half of the image. The lateral zero is programs that could print the values onthe left vertical edge. The horizontal axis is logarithmic so that more distance could be covered in one plot; the wide paper sheets. Subsequently Itherefore, the somewhat distorted shape compared with linear plots.FEBRUARY 2022 PREVIEW 34'