No abstract

Accurate wind information is required to support some of the key applications envisioned for future air traffic concepts. A Wind Information Analysis Framework is described to assess wind information needs for different applications. The framework is applied in a Four-Dimensional Trajectory Based Operations (4D-TBO) application using simplified versions of the framework's elements to demonstrate its utility. Realistic ranges of wind information accuracy limitations in terms of wind forecast and Flight Management System wind representation errors are studied. Their impacts on 4D-TBO performance in terms of Required Time of Arrival compliance and fuel burn are presented. Interpretations of the findings to determine wind information requirements are provided.

Two independent methods of measuring the transmittance of cirrus clouds are compared. Both used a CO(2) pulsed Doppler lidar at a wavelength of 10.59 microm. The first method used backscatter from the calibration target El Chichon stratospheric cloud that was present over Boulder in 1982 and 1983. The second method used conical lidar scans at different zenith angles when uniform cirrus decks were present. Extinction coefficients measured from both methods average 0.1 km(-1) for tenuous cirrus 1.0 km thick to 0.78 km(-1) for cirrus several kilometers thick. There is a wide standard deviation in extinction values. Extinction-tobackscatter ratios S vary from <1000 sr for tenuous clouds to 2600 sr for dense clouds. Mie scattering and extinction calculations for spherical ice particles of 10-50 microm in radius lead to ratios S > 2000 sr, so long as the ice absorption is entered into the calculations. The backscattering ratio for ice cylinders is 1 order of magnitude lower than for spheres. Backscatter in the IR may, therefore, be reasonably well modeled by some combination of spheres and cylinders. Cloud thickness statistics from lidar returns show that cirrus decks average ~500 m thick. Clouds thinner than 300 m were often overlooked by the unaided surface-based observer. These preliminary results are in rather close agreement with the LOWTRAN 6 cirrus cloud model predictions.

The ability to successfully achieve NextGen navigation procedures such as 4D-Trajectory Based Operations (4D-TBO) and Interval Management (IM) is dependent on the characteristics of the wind environments in which they are conducted as well as the quality of wind forecasts utilized by ground-based and airborne systems. In order to quantify the feasibility of such procedures, sensitivity analyses are commonly conducted using real or fast-time flight simulations with input from wind scenarios constructed from actual or simulated winds and wind forecasts. It is important to provide wind scenario inputs that are realistic and representative with regard to the key characteristics and metrics for the procedure being evaluated. Furthermore, it is important to translate the wind error tolerances determined from the sensitivity analyses to current or expected operational wind forecast model capabilities. This paper describes methods for utilizing data from current numerical weather prediction models to construct wind scenarios for NextGen wind impact studies and presents results of a wind forecast model performance study that can be used to translate error tolerances to achievable forecast model capabilities.