In-flight icing hazards: comparison of ground, model and pilot in-situ based severity products

As an aircraft flies through supercooled liquid water, the liquid freezes instantaneously to the leading edges of the airframe thus altering its lift, drag, and weight characteristics. In-flight icing is a contributing factor to many aviation accidents, and the reliable detection of this hazard is a fundamental concern to aviation safety. Recently, products have been developed by the scientific community to provide in-flight icing warnings. NASA's Icing Remote Sensing System (NIRSS) deploys a vertically–pointing Ka–band radar, a laser ceilometer, and a profiling multi-channel microwave radiometer for the diagnosis of terminal area in-flight icing hazards with high spatial and temporal resolution. NCAR's Current Icing Product (CIP) combines model output with satellite, radar, lightning, and ground observations to produce a gridded, three-dimensional depiction of icing severity and other fields on an hourly basis. Pilot reports are the best and only source of information on in-situ icing conditions encountered by an aircraft. The goal of this analysis was to ascertain how the testbed NIRSS icing severity product and the operational CIP severity product compare to pilot reports of icing severity, and how NIRSS and CIP compare to each other. Several thousand pilot reports over NASA's system location in Cleveland, Ohio were matched with the CIP during the period of 2006 to 2010. Preliminary results show that NIRSS's probability of detecting positive pilot reports was 85%, and the probability for negative icing was 72%. CIP's probability for positive icing was 80% and the probability for negative icing was 36%. NIRSS's severity categorizations explain 34% of pilot reported severity category variance, while CIP severity explains 20% of pilot report category variance. The icing severity product from the ground-based NASA testbed system compared very favorably with the operational model-based product and pilot reported in-situ icing.