Simulations and Data Analysis for Air Force Optical Turbulence Forecasting Applications


Book Description

We completed a series of Direct-Numerical and Large-Eddy Simulations (DNS and LES) of wind-shear instability and gravity wave breaking and associated analysis to characterize atmospheric turbulence and its optical impacts. We also analyzed hundreds of rawinsonde profiles to determine the parameters associated with turbulence layers observed in the troposphere and stratosphere. Finally, we developed a Bayesian Hierarchical Modeling (BHM) framework for combining the simulation and observational results so that atmospheric turbulence and optical turbulence atmospheric decision aids can be developed and improved. These results can also be used to develop subgrid-scale turbulence and optical turbulence parameterizations for operational mesoscale Numerical Weather Prediction models, e.g., the Weather Research and Forecasting Model (WRF).




Optical Turbulence Forecasting


Book Description

This report is a tutorial on the effects of atmospheric turbulence upon systems which rely upon the propagation of LASER beams. In addition to providing a simplified presentation of turbulence theory and optical effects, it describes the state of the art of the new technique of radiosonde estimation of index of refraction fluctuations. Suggestions are given for future research which will help to answer current Air Force needs. The feasibility of some laser systems will depend upon the value of r0, the coherence length (which is related to “C2n” which in turn is related to the degree of turbulence). At present, the statistics of “r0” are inadequate.




Modeling, Simulation, and Estimation of Optical Turbulence


Book Description

This dissertation documents three new contributions to simulation and modeling of optical turbulence. The first contribution is the formalization, optimization, and validation of a modeling technique called successively conditioned rendering (SCR). The SCR technique is empirically validated by comparing the statistical error of random phase screens generated with the technique. The second contribution is the derivation of the covariance delineation theorem, which provides theoretical bounds on the error associated with SCR. It is shown empirically that the theoretical bound may be used to predict relative algorithm performance. Therefore, the covariance delineation theorem is a powerful tool for optimizing SCR algorithms. For the third contribution, we introduce a new method for passively estimating optical turbulence parameters, and demonstrate the method using experimental data. The technique was demonstrated experimentally, using a 100 m horizontal path at 1.25 m above sun-heated tarmac on a clear afternoon. For this experiment, we estimated C2n ≈ 6.01 · 10-9 m-23 , l0 ≈ 17.9 mm, and L0 ≈ 15.5 m.




Low Altitude Atmospheric Turbulence LO-LOCAT Phase III Interim Report


Book Description

The contents of this report describe accomplishments during the first half of the Low-Level Critical Air Turbulence (LO-LOCAT) Phase III program. Data that were obtained during flight over routes near McConnell Air Force Base, Kansas, and Edwards Air Force Base, California, are presented. Also included are time histories of some of the larger magnitude gust velocities recorded over the Peterson Field, Colorado route. Approximately 72 hours of low-level (0-1000 feet) turbulence and associated meteorological data recorded from August 16, 1968, through January 8, 1969, are presented. The turbulence environment is analyzed in terms of gust velocity primary peaks, amplitude samples, rms values, maximum values and derived equivalent gusts. Mathematical expressions for turbulence spectra and scale length statistics, and correlations between atmospheric gust velocities and meteorological and geophysical phenomena are shown. The most predominant characteristics of these data are the increases in rms values, scale lengths, Taylor micro scales and maximum gust values as compared to the LO-LOCAT Phases I and II data. These differences are attributed to the increased speed of the Phase III airplane which is providing a better definition of the longer wavelengths of atmospheric turbulence. This report consists of two volumes. Volume I contains a discussion of data acquisition and quality, along with a preliminary analysis of turbulence and meteorological data.










Atmospheric Turbulence Simulation Techniques with Application to Flight Analysis


Book Description

Statistical modeling of atmospheric turbulence is discussed. The statistical properties of atmospheric turbulence, in particular the probability distribution, the spectra, and the coherence are reviewed. Different atmospheric turbulence simulation models are investigated, and appropriate statistical analyses are carried out to verify their validity. The models for simulation are incorporated into a computer model of aircraft flight dynamics. Statistical results of computer simulated landings for an aircraft having characteristics of a DC-8 are reported for the different turbulence simulation techniques. The significance of various degrees of sophistication in the turbulence simulation techniques on the landing performance of the aircraft is discussed.







Medium Altitude Critical Atmospheric Turbulence (MEDCAT) Data Processing and Analysis


Book Description

The report describes the processing and analysis phases of the Medium Altitude Critical Atmospheric Turbulence (MEDCAT) Project. The primary objective of this project was to collect true gust velocity in the 20,000 to 40,000 foot altitude regime to be used to establish, validate, and/or modify future aerospace vehicle design criteria. The data, collected by the Air Force from seven bases in the Continental United States consists of 278 flights performed in the regions of the MEDCAT altitude band predicted by a meteorologist as being most likely to contain clear air turbulence. Two trubulence-instrumented aircraft - an F-106A, and an F-100F - were used to collect the data. Of the 40 hours judged as being in turbulence 81 percent was characterized as being of less intensity than 1.5 ft/sec rms true gust velocity. (Author).