Freezing Rain Detection and Reporting by Novel Ceilometer and Forward Scatter Sensor

Ceilometers are known to be robust, stand-alone, and cost-effective lidar-based remote sensing instruments. Typically, ceilometers are used in aviation to detect cloud base heights. Ceilometers are also used, however, for atmospheric profiling and the applications of profile information are increasing. Ceilometer attenuated backscatter profile data can be used to obtain much more information than simple cloud base heights. The use of depolarization measurement will enable differentiation of liquid cloud droplets and ice crystals and the differentiation of rain/drizzle and snowfall. In addition, the detection of the melting layer and potential icing conditions are easier to identify.

Novel visibility and present weather sensor Vaisala Forward Scatter Sensor FD70 at simplest can be configured only as visibility sensor for Runway Visual Range application or with present weather option to report prevailing conditions. Top-end performance configuration makes the FD70 identify precipitation particle by particle and report present weather, precipitation type, intensity, accumulation, droplet size distribution, radar reflectivity, droplet fall speed distribution and kinetic energy.

The most challenging and, at times, the most important precipitation types for operational decision making are freezing rain and freezing drizzle. In this presentation we demonstrate the power of combining novel Ceilometer CL61 with depolarization ratio profile measurements and forward scatter sensor FD70 capabilities to improve freezing rain detection and reporting. We use case example to show how the combination of CL61 and FD70 will improve situational awareness of current conditions for meteorologist in duty to enable them to make critical decisions and more accurate forecasts of the conditions to improve the safety of airfield operations both on the ground and aloft.