High-Resolution Cloud Probe for the TigerShark UAV and Tethered Balloon Systems

The Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report states that clouds and aerosols continue to contribute the largest uncertainty to estimates and interpretations of the Earth’s changing energy budget. Arctic sea ice has decreased in every season, and in every successive decade since 1979. Numerical simulations predict a nearly ice-free summertime Arctic after the middle of the 21st century. Mixed-phase clouds, which contain both supercooled water drops and ice, are prevalent and persistent in the Arctic. Yet, relatively few in situ cloud measurements exist in mixed-phase clouds. How the Problem is Addressed: To date, research aircraft have accounted for the modest dataset of in situ measurements in Arctic clouds, but research aircraft are expensive to operate in Polar Regions, have limited duration, and present safety concerns. In contrast, unmanned aerial systems (UAS), which include unmanned aerial vehicles (UAV’s) and tethered balloon systems, can operate for extended periods of time in the Arctic without risk to human life. Recent technological advances in small UAV’s have been impressive, including flights into hurricanes and across the Atlantic Ocean. The DOE recently purchased a mid-size TigerShark UAV and a Skydoc tethered balloon system intended for research in mixed-phase clouds at their Oliktok Point, Alaska research station. This proposal is to develop a lightweight (<5 kg), low-power (< 100 W) combination cloud particle probe (called the TigerEye) for installation on the DOE TigerShark and tethered Balloon. The TigerEye will provide unprecedented optical resolution enabling it to distinguish small ice particles from water drops in mixed-phase clouds. What will be Accomplished in Phase I and Phase II: Phase I research will provide solid-model designs, ray- tracing and laboratory tests of all components of a prototype TigerEye. In Phase II, SPEC will fabricate a hardened version of the prototype and work directly with DOE personnel to integrate the TigerEye into TigerShark and tethered balloon systems. Flight tests will be conducted and data collected in mixed-phase clouds at the DOE facility at Oliktok Point, Alaska. The TigerEye will take advantage of SPEC’s previous experience developing microphysics probes for research aircraft, and advances in electronics that facilitate miniaturization of computers and signal conditioning. SPEC developed the cloud particle imager (CPI) in 1997, the 2D-S (stereo) optical array probe in 2004 and the Fast Cloud Droplet Probe (FCDP) in 2011. These instruments have been installed on over twenty research aircraft. Highly- miniaturized versions of these instruments will be incorporated into the TigerEye. Borrowing from it previous experience, SPEC will design and fabricate the TigerEye with 1) an FCDP that measures the size of particles from 1 to 50 microns, 2) a CPI that has a digital camera with 256 gray levels and 1- micron pixel resolution in the sample volume, and 3) an optical array probe with 5-micron pixel resolution and four gray levels. Additional features will include a serial bus and analog inputs available for capturing and recording additional measurements, such as aerosol particle size distributions, cloud condensation nuclei (CCN) concentration as a function of supersaturation, ice forming particle (IFP) activity, GPS position, heading, 3-axis acceleration, pitch, roll, yaw, wind direction and speed, temperature, humidity, pressure altitude and airspeed. The TigerEye will be fully integrated with the TigerShark data network. Commercial and Other Benefits: Improvements to climate prediction models require better measurements of the properties of Arctic mixed-phase clouds. An optical instrument designed specifically to discriminate small ice particles from water drops in Arctic mixed-phase clouds will be built and installed in a mid-size TigerShark UAV and a tethered balloon system, and deployed at Oliktok Point in Alaska. A successful demonstration project at Oliktok Point will establish the viability the Tigershark and tethered balloon to make long-term in situ measurements of the properties of aerosols and Arctic mixed-phase clouds. The TigerEye developed in Phase II and installed in the TigerShark and tethered balloon will find application in other areas, including measurements of the near-field properties of volcanic ash and measurements of aerosols on battlefields and in urban areas.