The NASA Icing Remote Sensing System

NASA and the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) have an on- going activity to develop remote sensing technologies for the detection and measurement of icing conditions aloft. A multiple instrument approach is the current emphasis of this activity. Utilizing radar, radiometry, and lidar, a region of supercooled liquid is identified. If the liquid water content (LWC) is sufficiently high, then the region of supercooled liquid cloud is flagged as being an aviation hazard. The instruments utilized for the current effort are an X-band vertical staring radar, a radiometer that measures twelve frequencies between 22 and 59 GHz, and a lidar ceilometer. The radar data determine cloud boundaries, the radiometer determines the sub-freezing temperature heights and total liquid water content, and the ceilome- ter refines the lower cloud boundary. Data are post- processed with a LabVIEW program with a resultant supercooled LWC profile and aircraft hazard identifica- tion. Remotely sensed measurements gathered during the 2003-2004 Alliance Icing Research Study (AIRS II) were compared to aircraft in-situ measurements. Al- though the comparison data set is quite small, the cases examined indicate that the remote sensing technique appears to be an acceptable approach.