UAS-based low-altitude freezing precipitation observation system: development updates and initial field deployment results.

Freezing rain and freezing drizzle can produce nearly undetectable hazards with potentially catastrophic consequences for aircraft within the terminal area. For this reason, in 2015, the Federal Aviation Administration (FAA) introduced a new icing certification rule restricting flights into and out of commercial airports during freezing precipitation to prevent icing-related accidents. Compliance with appendices "C" and "O" of the 2015 ruling (§25.1419 and §25.1420) required the precise forecast and observation of precipitation type in the lower atmosphere. However, the lack of direct observations of the low-altitude freezing precipitation environment creates a challenge for forecasters, flight crews, dispatchers, and air traffic controllers.

This research demonstrates how Unmanned Aerial Vehicles (UAVs) can be designed and instrumented to create Unmanned Aerial Weather Measurement Systems (WxUAS) capable of sampling the low-altitude freezing precipitation environment. The proposed WxUAS provides in-situ samples of pressure, temperature, relative humidity, liquid water content, particle size count, and remote samples of reflectivity and Doppler velocity from an onboard, vertically pointing millimeter wave (mmWave) radar. Leveraging the mobility of UAVs, the proposed WxUAS creates a spatial distribution of the measured atmospheric parameters. Via repetition of the flight pattern at regular intervals, the proposed WxUAS captures the temporal evolution of the measured parameters' spatial distribution. Together, the spatiotemporal aspects of the WxUAS measurements can be used for local studies of the low-altitude freezing precipitation environment and provide local validation for new models and classification algorithms. Once scaled, the system can bridge the measurements from current observation systems, increasing flight operations safety.

This presentation will inform on the initial results from field tests, developmental updates on new sensors, and operational lessons learned.