The use of x-band radar to support the detection of in-flight icing hazards by the NASA Icing Remote Sensing System

In-flight icing hazards from supercooled small drops, drizzle and freezing rain pose a threat to all aircraft. Several products have been developed to provide hazard warning of in-flight icing to the aviation community. NCAR's Current Icing Product1 (CIP) was developed to provide a near-realtime assessment of the hazard presented by supercooled liquid water (SLW) aloft in an algorithm that combines data from satellites, the Rapid Update Cycle (RUC) model, the national 2-D composite of S-band NEXRAD radar reflectivity, surface observations and pilot reports (PIREPs). NIRSS2 (Fig. 1) was developed by NASA to provide a ground-based, qualitative in-flight icing hazard assessment in the airport environment with commercially available instrumentation. The system utilizes a multichannel radiometer3, built by Radiometrics Corporation, to derive the temperature profile and integrated liquid water (ILW). NIRSS's radar is a modified airborne X-band model WU-870 made by Honeywell. The ceilometer used is a standard Vaisala CT25K Laser Ceilometer. The data from the vertically pointing ceilometer and X-band radar are only used to define the cloud bases and tops. The liquid water content (LWC) is then distributed within the cloud layers by the system software. A qualitative icing hazard profile is produced where the vertical temperature is between 0 and -20°C and there is measurable LWC.