For all of my family and friends that don't know I will be traveling to Australia for three weeks in May of 2014. The purpose of the trip is to us noninvasive geophysical methods to identify possible fresh water aquifers for the aboriginal people of Australia. The site location is on the Anangu Pitjantjatjara Yankunytjatjara (APY) lands. In case your wondering, I have no idea how to pronounce that either! I have attached a screen shot from Google Earth so that you can see where we are going to be. We will be in the heart of the outback where the nearest populated area is the small aboriginal town of Fregon. This town will show up if typed into google maps if your interested to find it's location.
We all know from experience that water is necessity for human survival and as you can imagine it is extremely rare in the outback. From the satellite image you can see that surface water is going to be rare in this part of the world. So the small communities on the APY lands depend on ground water. Unfortunately, we do not know a lot known about the aquifers in this area, due to the shear desolation. Wells in this region are drilled to a mean depth of 50 m (~1440 ft) and the water out of these wells is usually poor quality because of the high amount of salt in the water. In order to determine where the water is we will be using a geophysical method called nuclear magnetic resonance (NMR). To estimate the quality of the water we will be using a method called time domain electromagnetics (TEM). We are doing these surveys because we will be traveling for ~2 days by car with a large portion of this being off road. Although our geophysical equipment weights 1000's of pounds it is still a lot easier to transport than a large rotary drill rig. In this case the non-invasive geophysical methods will help characterize the aquifer before using the necessary resources to mobilize and drill a water well.
Nuclear Magnetic Resonance
Nuclear magnetic resonance is our method of choice for detecting water is a lot more accurate than witching a well. Since we are going to be in the heart of the outback it is going to be important that we know exactly where the water is. I can tell you there is no scientific basis in "witching" a well, typically there is water everywhere and no matter where you drill your hole you will hit water. It would be really nice to only cary two rods into the desert because the modern "witching" equipment is shown below and weighs a ton!
Although nuclear magnetic resonance has been around since the 70's and uses the same principles as a medical MRI. If you've ever had an MRI you know that you are placed into a very confining space, that looks like a donut. This donut produces a constant background magnetic field which greatly increases the ability to make the measurement. As you can image in the middle of the outback we don't have the ability generate our own background magnetic field. The ability to make this measurement without controlling that background field is brand new! It is the only geophysical measurement that directly measures the amount of liquid water in the subsurface.
The method itself capitalizes on hydrogen atoms rotating in a magnetic field, in our case it this field is the Earth's background field. When we apply a large magnetic field, the hydrogen in the water rotate and produce a detectable magnetic field. The strength of this field is directly proportional to the amount of water in the subsurface. This allows us to quantify the amount of water underneath the loop. This is much better than holding out two metal wires and then hoping for water!
Time Domain Electromagnetics
The time domain electromagnetic method works by producing a large magnetic field that produces currents in the ground underneath the loop. The induced currents produce a secondary magnetic field that we can measure. The amount of current induced in the ground is dependent on the geophysical parameter conductivity. This method will tell us about the quality of the water, if it exists. If the water is very salty we will get a very strong signal back because the magnetic field will induce a very large current. So after analysis we will not only have the location and amount of water but we will have an idea of the quality of water.
Figure from (http://www.ncwater.org/education_and_technical_assistance/ground_water/TDEM/)
Since I couldn't get the link working on the cover photo I give credit Andrew C. Wallis Via Flickr. This is a beautiful image and will be just a couple hundred kilometers north of our location. I hope we have time to get by and see it.
( https://www.flickr.com/photos/awphoto/2767050907/in/photolist-7dyFif-crfMVw-yGi4u-21wuGE-e52HWX-7ynu5A-9HAK2C-bsAjSA-2gzZwr-bsNvT9-b9XXnc-6RHa5P-73RRhQ-e5ChQa-e5ukVC-aL5RqX-e4YSCs-jEXdBh-5dvRQg-9A8tv1-biiR58-ecdcZi-bafkm4-dL36ms-6WLwkZ-au5gwJ-bnSxsH-jPhEtj-egj1pH-aCavCh-adCn9U-7gtHcG-aJ4CtH-9aV4rW-e8dqrh-62qsQW-9A5uVn-e58nHh-aD9iSX-d354fG-ebXp4-9xPg6o-fZcXdd-nakaoK-BzZQ6-7bwKRi-9vXLme-duWrbi-a8CjYt-5fVzeC/ )
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