David Y. Lai

Assessment of Pulsed Lidar Measurements of Aircraft Wake Vortex Positions Using a Lidar Simulator

A lidar simulator tool was developed to simulate realistic raw signal data generated from a wake vortex velocity field as measured by the existing Lockheed Martin Coherent Technologies (LMCT) pulsed lidar currently being used to in field measurements of aircraft wake vortices. The raw lidar data is processed and the resulting product files are input into the existing LMCTs Wake Vortex Processing Algorithm for determining position and circulation strength versus wake age. Outputs from the Wake Vortex Processing Algorithm are then compared to the truth data used to generate the raw lidar signal data. Accuracy of the lidar measurements of lateral and vertical vortex positions is evaluated by exercising the lidar simulator, using input wake vortex fields based on analytical vortex models and 3-D Large Eddy Simulation numerical model outputs for different aircraft vortex, lidar and environment conditions. This study shows that the mean biases for the lidar measurements for vortex positions are small, about 4-7m for the lateral position and 13m for the vertical positions.

Progress on an ICAO Wake Turbulence Re-Categorization Effort

This paper describes progress on an ICAO tasking to the FAA and Eurocontrol to lead an effort to harmonize wake turbulence separation standards for existing and new aircraft and to safely increase capacity. The first phase of the re-categorization effort looked at placing the existing traffic mix of both the U.S. and Europe into 6 categories. The second phase of the effort will determine static pair-wise spacing that will work for all atmospheric conditions. The final phase of re-categorization will provide dynamic pair-wise spacing that will vary with atmospheric conditions and aircraft performance. This paper provides the methodology of the first phase of re-categorization and gives examples of new aircraft categories that show capacity increases over today’s U.S. and ICAO categories.

Development of an Improved Pulsed Lidar Circulation Estimation Algorithm and Performance Results for Denver OGE Data

A new algorithm for estimating circulation strength of aircraft wake vortices from pulsed coherent lidar measurements is described and results from processing Out of Ground Effect (OGE) field data from NASA measurements made at the Denver International Airport in 2003 are compared to results obtained using the Lockheed Martin Spectral Space Processing (Legacy) algorithm. The key improvements of the new algorithm over the Legacy algorithm concern the (a) vortex system matched filters, (b) maximum likelihood ratio algorithm, and (c) ambient wind correction. An overview of the algorithm is presented highlighting the differences between this new algorithm and the Legacy algorithm. The performance of both algorithms will be shown for FAA Large weight-category aircraft and compared to historical circulation decay estimates for similar conditions from other field campaigns.

Assessment of Lockheed Martin's Aircraft Wake Vortex Circulation Estimation Algorithms Using Simulated Lidar Data

A new algorithm for estimating circulation strength of aircraft wake vortices is under development by Lockheed Martin and is being evaluated by NorthWest Research Associates, Inc. (NWRA) under the National Aeronautics and Space Administration Research Announcement (NASA-NRA) NextGen Airportal Program. The algorithm is being developed with the aid of Lockheed Martin’s Coherent Wind Lidar Simulator, developed under the same NASA-NRA program. A brief description of the simulator tool is presented. An overview of both the legacy estimation algorithm and the new algorithm under development is presented which highlights the differences between the two algorithms. The performance of both algorithms is assessed using simulated lidar data generated from analytic wake models and Large Eddy Simulation (LES) vortex wind fields with ambient turbulence eddy dissipation rates (EDR) of 4 x 10 -5 , 5 x 10 -4 and 1.45 x 10 -2 m 2 s -3 . Algorithm performance is quantified in terms of standard deviation and bias of estimates as a function of SNR.

First Results from the NASA Wake Vortex Measurements at the Memphis International Airport

New measurements of aircraft wake vortices and concurrent meteorological measurements are being made at the Memphis International Airport by NorthWest Research Associates, Inc. (NWRA), with the support of Coherent Research Group, LLC (CRG), under the National Aeronautics and Space Administration (NASA) Airspace Systems Program. The meteorological measurements began in March 2013 and are continuing today. These measurements consist of vertical temperature profiles, point wind and temperature measurements, and supporting meteorological measurements (rain, pressure, etc.). In addition, a Halo Photonics StreamLine® lidar has been used since April, 2013 to provide vertical profiles of wind speed and direction. Finally, a Lockheed Martin Coherent Technology (LMCT) WindTracer® lidar, owned and operated by Arizona State University, has been used since June, 2013. Both the LMCT lidar and the Halo Photonics lidar have been used to measure aircraft wake vortices and to provide additional wind information. These measurements are being used to characterize the evolution of aircraft wake vortices generated In Ground Effect (IGE) and to correlate those measurements with atmospheric conditions. The first results from these measurements that show the dependence of wake evolution on atmospheric conditions are presented.

COMPARISON OF NUMERICAL MODEL SIMULATIONS AND SFO WAKE VORTEX WINDLINE MEASUREMENTS

In order to provide quantitative support for the Simultaneous Offset Instrument Approach (SOIA) procedure, an extensive data collection effort was undertaken at San Francisco International Airport by the Federal Aviation Administration (FAA). During the time period from March 2000 to October 2002, wake vortex data was measured for over 260,000 landing aircraft. The data set includes wake vortex measurements from small, large, and heavy category aircraft. The measurements consist of cross-runway wind speed recorded every two seconds from three windlines, comprised of a series of propeller anemometers on three-foot poles near the threshold of runways 28L and 28R. The resulting data set is being used to demonstrate the feasibility of SOIA and to guide the improvement of the wake vortex model in the FAA airspace simulation tool Airspace Simulation and Analysis for TERPS (ASAT). The authors show that a slightly modified version of the Aircraft VOrtex Spacing System (AVOSS) Prediction Algorithm (APA) produces lateral position predictions that agree well with the windline data. The authors also show that the data and the APA results agree with results produced by Terminal Area Simulation System (TASS ), a numerical code developed by the National Aeronautic Space Administration (NASA). These comparisons between code and data provide an independent validation of the lateral transport estimates using windline sensors and give increased confidence in both the data obtained from the windline sensors and the ability to predict vortex evolution using numerical simulations.

Fast-time Wake Vortex Model Predictions Compared with Observations Behind Landing Aircraft Near the Ground (Invited)

NASA has recently collected a large dataset of wake vortex and weather observations at Memphis International Airport. The wake data consists primarily of vortices generated between one and two wingspans above the ground. Most of the landings in the dataset include field observations of all the required environmental and aircraft data needed for input into fast-time wake vortex prediction models; including vertical profiles of wind speed, air temperature and eddy dissipation rate, as well as the aircraft weights. Prior to the collection of this data set there was only a small amount of data that could be used in the evaluation of the skill of fast-time wake vortex prediction models when the vortices were generated within a couple wingspans of the ground surface. This new data set significantly increases the amount of data available for the assessment of the models in this important region. Comparison of three fast-time model predictions with the new Memphis data indicates there are several areas where the models can be improved in the in ground effect region; specifically better parameterization of the effect of turbulence, and inclusion of the effect of headwind.

Assessment of Pulsed Lidar Measurements of Aircraft Wakes Using a Lidar Simulator: Vortex Position Estimates for IGE, Linking, and Oblique Viewing, and Dependence of Vortex Lifetime on SNR

4NorthWest Research Associates, Inc., Redmond, WA, 98052 A lidar simulator tool was developed to simulate realistic raw lidar signal data generated from a wake vortex velocity field as measured by the existing Lockheed Martin Coherent Technologies (LMCT) WindTracer � pulsed lidar, currently used in the field to measure aircraft wake vortices. The raw lidar data is processed and the resulting product files are input into the existing LMCT Wake Vortex Processing Algorithm to estimate position and circulation strength versus wake age. The estimates from the Wake Vortex Processing Algorithm are then compared to truth data used to generate the raw lidar signal data. Accuracy of the Wake Vortex Processing Algorithm estimates of lateral and vertical position is evaluated by exercising the lidar simulator using input wake vortex fields based on analytical vortex models and 3-D Large Eddy Simulation computations for two aircraft types under IGE, OGE linking, and oblique viewing conditions. This study shows that the mean biases of the vortex position estimates for IGE and OGE linking vortices are small and similar to those for non-linking vortices in the OGE region reported in an earlier study 1 . The use of the lidar at oblique angles relative to the trailing line vortices does not introduce significant differences in the position biases. An analysis of the vortex lifetime estimates with SNR variations suggests avoiding lidar measurements for SNRs below 0 dB.

Spatial distribution of surface wave field in coastal regions using spaceborne synthetic aperture radar images

An algorithm to retrieve swell wavelength and significant wave height from spaceborne synthetic aperture radar (SAR) images is used to study the spatial distribution of the surface wave field in the coastal region west of the mouth of the Columbia River. This algorithm utilizes the SAR image itself to obtain wind speed and direction needed in the retrieval process. Collocated in situ wind or scatterometer wind measurements are not needed in this retrieval. The wave parameters derived from 142 archived Standard Beam Mode Radarsat SAR images were validated with concurrent moored buoy measurements. Spatial variability of the surface wave field in the region is investigated using wave parameters derived from over 140 SAR images at three sites, and two SAR images. This study shows that the variation of swell wavelengths is consistent with linear wave dynamics as the swell propagates from deep to shallow water depths. Examination of the evolution of the significant wave heights suggests that significant differences in energy dissipation are found in the region.

An Intercomparison Study Using Electromagnetic Three-Component Turbulent Velocity Probes

An intercomparison study was performed with four Russian-made, electromagnetic probes capable of measuring three components of oceanic turbulent velocities and two single-axis velocity sensors familiar to western scientists, namely, a hot-film anemometer and an airfoil shear probe. The intercomparison measurements were conducted in a water flume tank in the Marine Scientific Production Corporation on Fishery Technology facility in Kaliningrad, Russia. Measurements were obtained in the turbulent region generated behind a grid at three different mean flow speeds (0.7, 1.1, and 1.7 m s 21). In all the intercomparison runs, data from the electromagnetic velocity probes behave in a manner expected from the sensor and filtering characteristics. On the average, turbulent velocity variances from the electromagnetic probes are about 620% of those from both the hot-film and airfoil probes.