Goal 5. Provide World-Class Ground, Airborne, and Space-borne Observational Facilities and Services
NCAR Strategic Priority: Developing New Instrumentation
Advanced Weather Radar Techniques for Aviation
RAL is working under the sponsorship of the FAA's Aviation Weather Research Program to develop technologies that utilize weather radar data to support the detection and prediction of aviation hazards. Current efforts are focused on two tasks: implementing and supporting operational deployment of new radar algorithms, and conducting research and development of radar products that will utilize future capabilities of weather radars.
FY2008 Accomplishments
Four views from the Experimental NTDA Java display on 2007-09-28 22:30Z: (upper left) reflectivity plan view of a storm at 24,000 ft. altitude, with overlaid convective SIGMET polygons and a user-drawn three-segment flight track; (upper right) NTDA eddy dissipation rate plan view; (lower left) reflectivity vertical cross-section along the flight track; (lower right) NTDA EDR cross-section. Moderate and severe turbulence is evident in and above the reflectivity cores, but moderate turbulence also appears in some low-reflectivity and anvil regions.
RAL scientists have worked for more than 15 years to improve the detection of turbulence. Over the past several years they have developed the NEXRAD Turbulence Detection Algorithm (NTDA), a new approach to processing data from the national network of Next Generation Radars (NEXRADs, also called WSR-88Ds). While aviation users commonly use reflectivity from onboard radars or ground-based radar mosaics to gauge the intensity of a storm, the NTDA uses NEXRAD’s Doppler data to detect the wind variations that can shake an aircraft. By directly measuring this in-cloud turbulence intensity, the NTDA will provide airline dispatchers, air traffic managers, and pilots an important new source of information for tactical turbulence avoidance.
In FY08, NTDA was deployed on all NEXRAD’s as part of a routine software upgrade. Work began on a new version of NTDA to accommodate NEXRAD changes and to improve the NTDA’s spatial coverage and accuracy. RAL scientists and engineers also collaborated with National Severe Storms Laboratory staff to develop a prototype operational 3-D mosaic that will cover the contiguous U.S. RAL also continued development and evaluation of an improved spectrum width estimator that would substantially improve the quality of the NEXRAD measurements. The FAA has formally requested that the accuracy requirements for NEXRAD spectrum width be tightened and that the implementation of the RAL-developed technique be considered by the NEXRAD Technical Advisory Committee.
Techniques are also under development to determine whether precipitation detected with dual-polarization radars is rain, snow, mixed-phase, or freezing drizzle. The polarimetric Hydrometeor Classification Algorithm (HCA) being developed for the aviation community uses known physical properties of hydrometeors to determine habits and discriminate between liquid and frozen precipitation. The algorithm considers temperature observations as a check to prevent spurious hydrometeor designations such as rain layers above the melting layer in the atmosphere. During the past year the algorithm was improved by modifying the fuzzy logic interest fields for temperature. This was done by using National Weather Service reports in the central and eastern U.S. and computing the likelihood of snow or rain as a function of temperature. Results revealed that the transition from >50% probability of frozen precipitation to >50% liquid precipitation occurs as dry-bulb temperatures rise from 33 to 34F. There was a 95% probability of rain for temperatures > 33F and a 95% probability of snow for temperatures < 22F. Liquid precipitation is relatively rare but occurs at temperatures less than 20F. Only liquid precipitation occurred at temperatures > 38F.
FY2009 Plans:
Changes to the NEXRAD radar operational modes (particularly super-resolution, range-velocity mitigation techniques, and dual-polarization) will necessitate a maintenance upgrade, the NTDA-2. This product, which will also contain an improved data quality algorithm, will be implemented and, if all goes well, accepted for inclusion in the NEXRAD system. The NTDA 3 D mosaic will continue to undergo development and testing, and evaluation of the improved spectrum width estimator will continue.
RAL scientists and engineers, in conjunction with the In-Flight Icing team, will begin implementation of real-time versions of the freezing level and freezing drizzle algorithms. This will allow for the evaluation and ultimately inclusion of these products into icing hazard detection algorithms such as RAL’s Current Icing Potential (CIP).
The national network of WSR-88Ds is targeted to be upgraded for dual-polarimetric capabilities beginning in FY11. Specific long-term project goals are to develop remote sensing capabilities for discriminating between rain and snow, designating icing conditions in the terminal area (freezing drizzle and rain) and in-cloud, quantifying winter precipitation in support of aircraft deicing operations, and estimating precipitation-impacted visibility.