 Okay, I'm going to change gears a bit here and talk about the use of airborne geophysical data for mapping in the subsurface, mapping geological structures that relate to groundwater aquifers or other properties. And to do this, I'd like to make an analogy to these dot-to-dot puzzles that maybe some of you are familiar with, especially if you have young kids. It's got a bunch of numbered dots on a piece of paper, and you can reveal the magic image behind it if you follow the sequence of dots. On the right hand side, we've got our geologist's version of the dot-to-dot problem. These are 9,000 boreholes in the lower Mississippi River Valley, where I'm currently working on a project in mapping aquifer system in the alluvial plain. We're looking at an area of about 100,000 square kilometers, touching seven states, mostly in Mississippi, Arkansas, Louisiana, and Missouri. So if we grid up all of the borehole data where we have picked the elevation of the base of the surficial aquifer system, that's the map that you see on the right hand side. So the red and yellow colors are greater elevations to the base of the aquifer. The purple and black is getting deeper, so you're largely seeing an elevation gradient. And this sort of gives us the impressionist's view of the world, maybe what you would get if you looked at the dot-to-dot image on the left. And I just want to make the point that this was 10,000 roughly boreholes, like I said. You can grid up the costs and do the math if each of these holes was 100 meters deep and you spent $100 per foot, a typical drilling cost in the area. That comes out to roughly $300 million and took untold years to decades to coordinate all of these holes, obviously. That was done across many municipalities and different organizations collecting those. But what we can do with geophysics was done in just three months. So we collected this data set, it was completed just this spring, it cost just under a million dollars. And we can get a really high resolution view of that surface, the base of the aquifer elevation. And you can see my analogy to the now detailed version of the dot-to-dot image that my daughter created for me. And I just want to drive home this point. Three months, under a million dollars, years to decades, $300 million dollars. So a huge difference in transformation in what we can see in the subsurface. So in the spectrum of technologies that we have for Earth observation, we talk a lot about remote sensing and ground-based methods, but we don't talk much about airborne geophysics. And this fills a really critical scale gap in mapping subsurface geology, the things that we're talking about here today that relate to aquifers and to recharge at the watershed to basin scales. So you can see airborne geophysics really fills in the scale gap that we don't have other tools for. It's smaller in scale and more resolution than grace. It goes deeper than many of our traditional remote sensing tools that sort of end in the upper meter. That's where we start and continue in depth. And obviously larger scales than you can ever cover using ground-based geophysics or borehole data. And that's not to say that we don't need these other things. We need to do all of them, but we really need to think about more airborne geophysics to fill in that critical scale gap. This is what some of the airborne systems look like. You can see there's many different flavors, some of which are beneath helicopters, some are fixed wing. All of these fly fairly low and slow. Typical survey elevations are 30 to 100 meters above ground at something on the order of 100 kilometers per hour. The helicopter systems are better in rough terrain. They give better higher resolution. The fixed wing systems obviously better for covering large areas in more gentle terrain. Different instruments are more effective for different targets. Some are better at mapping shallow, some are better at mapping deep. So it depends a bit on the problem at hand. But they all rely on the physics of electromagnetic induction. So they map electrical resistivity in the subsurface. And so this middle image is a depth slice at about 55 meters depth in the subsurface of resistivity. And we saw an image of this in the MT talk earlier today. Here the reds generally correspond to coarser grain sediments, sands and gravels. The blues are generally finer sediments, clays and silts. And we can make slices like this at all different depths in the upper 100 meters for some instruments that could go down as deep as 500 meters. In addition to the electromagnetic sensor, we also at little additional costs can also collect two other types of data. Magnetics on the left is looking at the natural abundance of thorium, uranium and potassium in the upper 20 to 30 centimeters, which tells us something about the provenance of different soils and textures. And on the right we have magnetic data. So magnetics is looking deep down into the subsurface, kilometers or more telling us something about basement structure. So this is an example of some of the detailed work in the lower Mississippi Valley. On the left you have a shallow depth slice, 5 to 10 meters below ground. So where we see the reds, those are the coarse grain deposits and you can really see the morphology of channel systems, abandoned channels and present-day meanders. On the left hand side where it's blue, this is a backswamp deposit, so that's generally fine grain sediments, clays. On the right hand side you're looking 30 to 40 meters in depth and in the lower right of that image you see a pretty clear imprint of an abandoned channel. That's a historical channel of the ancestral Ohio Mississippi River that there's no surface expression of today, but obviously that is an important pathway for groundwater. On the bottom you're seeing a cross-section, so like I said we can interrogate these data in 3D. We're looking at about 30 kilometers in length and 100 meters in depth, so there's a lot of vertical exaggeration here. But basically the reds is the aquifer, the blue in the near surface is a confining layer, so this is a barrier to recharge in many places, and the blue at depth is where we have older tertiary units that subcrop beneath the aquifer. So from these data we've made interpreted surfaces, on the left is the base of the confining layer, on the right is the base of the aquifer, so these are the pieces of information and you can see those surfaces drawn as lines on the cross-section. So this is the information that we then pass off to hydrologists and groundwater modelers to develop groundwater model structure, and we try to do this with uncertainty, so we classify the uncertainty in the observations and how that relates to geology, and pass off to the groundwater modelers multiple plausible scenarios of subsurface geology so that they can then think about calibrating those models and quantifying uncertainty in hydrologic properties and hydrologic predictions. So this is my last slide. It's hard to see some of the background. You can see the image. This is the largest survey that we've done in the continental US by at least an order of magnitude. There's some polygons in red and blue that are hard to see. Most of those are much smaller. We've covered probably less than 2% of the continental US at this point, so there's a lot more dots still to be connected.