Geo-mystics
Mar. 5th, 2008 07:30 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
hertinknessThere was a brown bag lunch at work today, where the presenter discussed a new technology for imaging aquifers using a magnetic survey. Now, magnetic surveys are nothing new- you take a magnetometer and go around a grid, measuring the field at each point. They've put such instruments on satellites, as in the mourned, unreplaced MAGSAT. These surveys are limited in that they detect everything contributing to the magnetic field at the surface, from the earth's core to the underground electric cable. But these guys have gotten around it in an ingenious little way to image at the very depth they want: they create an electrical circuit in the aquifer.
As was explained at lunch today, they accomplish this by putting electrodes connected with a wire down two wells anywhere from 500 ft to five miles apart, hooking the assembly up to a small generator, and firing it up. The water in the aquifer conducts the electricity (with varying degrees of efficiency, depending on the concentration of electrolytes within) and creates its own magnetic field, which crews can measure at the surface with a magnetometer; if the aquifer has preferential flow paths, the current will follow them as well. They take the field data back to the lab, and more or less run Monte Carlo simulations varying the resistivity, local magnetic field, etc. until they get something that most closely matches the field data.
This, like most new technologies, is almost prohibitively expensive for the type of work that I do. But the ability to see flow paths is key, whether you're tracing contaminants, looking for the source of a dam seep, or trying to find new groundwater resources. I kind of hope that as it becomes more popular, the cost to do this kind of work will go down.
I also found it hillarious when the MBA that was giving the presentation mispronounced "fast Fourier transform."
As was explained at lunch today, they accomplish this by putting electrodes connected with a wire down two wells anywhere from 500 ft to five miles apart, hooking the assembly up to a small generator, and firing it up. The water in the aquifer conducts the electricity (with varying degrees of efficiency, depending on the concentration of electrolytes within) and creates its own magnetic field, which crews can measure at the surface with a magnetometer; if the aquifer has preferential flow paths, the current will follow them as well. They take the field data back to the lab, and more or less run Monte Carlo simulations varying the resistivity, local magnetic field, etc. until they get something that most closely matches the field data.
This, like most new technologies, is almost prohibitively expensive for the type of work that I do. But the ability to see flow paths is key, whether you're tracing contaminants, looking for the source of a dam seep, or trying to find new groundwater resources. I kind of hope that as it becomes more popular, the cost to do this kind of work will go down.
I also found it hillarious when the MBA that was giving the presentation mispronounced "fast Fourier transform."
