Earth’s atmosphere as a global sensor
The AtmoSense program is based on the fact that energy propagates from the Earth’s surface to the ionosphere, but in a way that is not yet understood enough to be able to use the atmosphere as a sensor. The new program, says the agency, is a fundamental science program that seeks to understand the propagation of mechanical and electromagnetic energy from the surface of the Earth through the Earth’s ionosphere due to transient events such as meteorological sources, geophysical sources, prompt hazards, and others.
“No physical sensor or aggregation of electronic sensors, can continuously and globally detect disturbances that take place on or above the earth’s surface,” says the agency. “But the physical atmosphere itself may offer such a sensing capability, if it can be understood and tapped into.”
Events like thunderstorms, tornadoes, volcanos, and tsunamis make big “three-dimensional wakes” that propagate to the upper reaches of the ionosphere and leave a mark there. Since that energy traverses several other layers of atmosphere – the troposphere, stratosphere, and mesosphere – on its way up to the ionosphere, says the agency, the idea is to try and identify the disturbances the “wake” is making along its way to see if researchers can capture information to indicate what type of event caused it.
“Maybe I don’t have to directly observe events like an earthquake or tsunami,” says Air Force Major C. David Lewis, AtmoSense program manager in DARPA’s Defense Sciences Office. “Perhaps I can learn what occurred from information in the atmosphere. I want to find out how much information is available, and if I can disaggregate the signal I’m interested in from other natural phenomena creating noise in the background.”
The AtmoSense program is seeking proposers from the atmospheric science community, who have extensive experience in atmospheric modeling and simulation. Also of interest are experts offering very unique ways to measure atmospheric properties, such as the basic gas law variables – i.e., pressure, volume, density, temperature – or derivatives of such. Beyond these basic atmospheric variables, says the agency, the mesosphere and lower ionosphere provide electromagnetic opportunities for measurement due to their charged nature.
“We typically model, simulate, and measure properties in the troposphere, which is where terrestrial weather happens,” says Lewis. “But we don’t really make those measurements in the stratosphere or the mesosphere, or the bottom part of the ionosphere, because no one has really been keenly interested in it and it’s hard to get up there. Sometimes the mesosphere is even called the ‘ignorosphere,’ but we know that information traverses it, so we’re really looking for scientists and engineers with unique ways of potentially measuring different aspects of the atmosphere.”
Another key area is measuring and understanding background noise – created by jet streams, compression of the fluid, shear forces, Coriolis forces, etc. – that trigger some sort of turbulence that weakens or destroys signals of interest.
“When it comes to geophysical and meteorological sources of atmospheric disturbance,” says Lewis, “there’s a frequency spectrum emitted from infrasound all the way up to the ultrasound. Some of those frequencies are more immune to atmospheric entropy than others, and those are what we’d like to capture.”
The AtmoSense program calls for two phases: The first phase is concept development (27 months), and the second phase is proof of principle field testing (12 months). If successful, says the agency, AtmoSense could enable new ways in the future to identify and give insight into events such as earthquakes, tsunamis, storms, tornados, and asteroid activity.
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