Distributed Atmospheric Sensing using Small UAS and Doppler Radar Jack Elston * , Brian Argrow † University of Colorado, Boulder, CO, 80309, USA Adam Houston ‡ , Jamie Lahowetz § University of Nebraska, Lincoln, NE, 68588, USA A distributed sensing system has been developed to probe an atmospheric airmass boundary with simultaneous dual-Doppler sensing and in-situ sampling using an Unmanned Vehicle System (UAS). In support of this effort, a suite of software was developed to allow for real time visualization of radar and UA information. Through this interface, controllers were able to effectively control a UA to an area of interest based upon meteorological infor- mation. An existing ad-hoc network was augmented to allow for the effective dissemination of telemetry, sensor data, and control throughout the multi-user network. Furthermore, a UA was developed that could carry the various sensors and conduct the required mis- sion. These efforts were verified by flight operations conducted at the Pawnee National Grasslands under CoA 2008-WSA-51. I. Introduction A ccording to the National Weather Service, in 2004 (most recent data posted) severe weather caused 369 fatalities, over 2400 injuries, and $26.8 billion in the United States. 1 These losses could be dramatically reduced with effective advanced prediction and warning systems. Tornadoes are especially violent products of severe storms and thus the study of tornado formation and evolution is a public safety necessity. The inability to determine the volumetric thermodynamic state of the atmosphere between the ground and the base of the mesocyclone remains a major barrier towards a deeper understanding of tornado genesis. The limitations of remote sensing are evident; one cannot remotely sense the thermodynamic field, these data can only be obtained with in situ sensing. Research into tornadogenesis will not progress significantly until there are measurements of the thermo- dynamic and microphysical properties aloft in the vitally important rear-flank region of supercell storms. A consensus of research in the last 25 years makes it clear that a small downdraft of a few kilometers width, known as the ”rear-flank downdraft” plays a causative role in tornado formation. 1, 2 But recent studies have produced a quandary: surface observations from instrumented vehicles beneath this downdraft indicate that it typically arrives at the ground relatively warm and potentially buoyant compared to typical thunderstorm downdrafts, while studies of the flow in and around this downdraft suggest that it is negatively buoyant aloft. It is surmised that this negative buoyancy, if present in sufficient quantities upstream of the location of potential tornado formation, causes the rotation that is eventually reoriented and concentrated into a tornado. Unfortunately, barriers toward the study of the rear-flank downdraft have not been easily overcome. While weather radar can return detailed precipitation and wind-field data, it cannot return directly-measured thermodynamic data. Balloons cannot ascend through strong downdrafts and these flows are much too dangerous for penetration using manned aircraft, as evidenced by the inadvertent penetration of a rear-flank downdraft. 2 * Graduate Research Assistant, Department of Aerospace Engineering Sciences. Student Member † Associate Professor, Director Research and Engineering Center for Unmanned Vehicles. Senior Member. ‡ Assistant Professor, Department of Geosciences. § Research Assistant, Department of Geosciences 1 of 6 American Institute of Aeronautics and Astronautics