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Im ACKNOWLED This work was Research Prog Sciences, Eng COPYRIGHT I Authors herein persons who o Cooperative R purposes. Per FMCSA, FRA, product, metho uses will give a request permis DISCLAIMER The opinions a are not necess or the program The informatio edited by TRB proving GMENT sponsored by t ram (ACRP), w ineering, and M NFORMATION are responsibl wn the copyrigh esearch Progra mission is give FTA, Office of d, or practice. ppropriate ack sion from CRP nd conclusions arily those of th sponsors. n contained in t . AEDT Christ Eric Bo United John A. Vol he Federal Avia hich is adminis edicine. e for the authen t to any previo ms (CRP) gran n with the unde the Assistant Se It is expected th nowledgment o . expressed or im e Transportatio his document w AC Web-Only Noise M opher M. Ho Wyle La Arl eker, Aaron Juliet Page States Dep pe National Cam tion Administra tered by the Tra ticity of their m usly published o ts permission to rstanding that n cretary for Res at those reprod f the source of a plied in this re n Research Bo as taken direct RP Docume odelin bbs and Yur boratories, ington, VA Hasting, Am , and Dave S artment of T Transportat bridge, MA tion (FAA). It w nsportation Re aterials and for r copyrighted m reproduce ma one of the mate earch and Tec ucing the mate ny reprinted or port are those o ard; the Nation ly from the subm nt 32: g of Gr iy A. Gurovi Inc. anda Rapo enzig ransportatio ion Systems Contrac as conducted t search Board ( obtaining writte aterial used he terial in this pub rial will be used hnology, PHMS rial in this docu reproduced ma f the researche al Academies o ission of the a ound S ch za, n Center tor’s Final Rep hrough the Airp TRB) of the Na n permissions f rein. lication for clas to imply TRB, A, or TDC endo ment for educat terial. For oth rs who perform f Sciences, Eng uthor(s). This m urfaces ort for ACRP Pr Submitted M ort Cooperative tional Academie rom publishers sroom and not AASHTO, FAA rsement of a p ional and not-fo er uses of the m ed the researc ineering, and M aterial has not oject 02-52 arch 2017 s of or -for-profit , FHWA, articular r-profit aterial, h. They edicine; been

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iv  CONTENTS LIST OF FIGURES AND TABLES ........................................................................................................ vii AUTHOR ACKNOWLEDGMENTS ..................................................................................................... xiii SUMMARY .............................................................................................................................................. xiv 1 Introduction ......................................................................................................................................... 1-1 2 Problem Statement Objectives ............................................................................................................ 2-1 3 Theory ................................................................................................................................................. 3-1 3.1. Ray Theory ......................................................................................................................................... 3-1 3.2. Diffractions ......................................................................................................................................... 3-6 3.3. Boundary Element Method ............................................................................................................... 3-10 3.4 Parabolic Equation ............................................................................................................................ 3-11 3.5 Review .............................................................................................................................................. 3-11 3.5.1 Single Impedance Discontinuity ..................................................................................................... 3-12 3.5.2 Multiple-Impedance Discontinuities ............................................................................................... 3-12 3.5.3 Practical Considerations .................................................................................................................. 3-13 3.5.4 Recommendations ........................................................................................................................... 3-13 4 Review of Ground Effects in Current Models ..................................................................................... 4-1 4.1 Federal Aviation Administration (FAA): INM/AEDT ....................................................................... 4-1 4.2 Federal Highway Administration (FHWA): TNM ............................................................................. 4-7 4.2.1. TNM Validation Site: A .................................................................................................................. 4-9 4.2.2 TNM Validation Site: B ................................................................................................................. 4-10 4.2.3 TNM Validation Site: C ................................................................................................................. 4-12 4.2.4 TNM Validation Site: D ................................................................................................................. 4-13 4.2.5 TNM Accuracy .............................................................................................................................. 4-14 4.3 Nordic Noise Group: Nord2000 ........................................................................................................ 4-15 4.4 National Park Service: Noise Model Simulation (NMSim) .............................................................. 4-17

v    4.5 Department of Defense: NOISEMAP (NMAP) ................................................................................ 4-20 4.6 Department of Defense: Advanced Acoustic Model (AAM) ........................................................... 4-22 4.7 National Aeronautics and Space Administration (NASA): Acoustic Propagation and Emulation Toolset (APET) ........................................................................................................................................ 4-22 4.8 Norwegian Aircraft Noise Calculation Model (NORTIM) ............................................................... 4-24 4.9 Hybrid Propagation Model ............................................................................................................... 4-24 4.10 Go Forward Plan Ray Models ......................................................................................................... 4-24 5 Validation Data .................................................................................................................................... 5-1 5.1 Topography and National Land Cover Database ................................................................................ 5-1 5.2 Airport Data ........................................................................................................................................ 5-3 5.2.1 Washington National Airport (DCA) ............................................................................................... 5-4 5.2.2 Boston Logan International Airport (BOS) ..................................................................................... 5-6 5.2.3 Portland International Airport (PDX) .............................................................................................. 5-9 5.2.4 Philadelphia International Airport (PHL) ........................................................................................ 5-9 5.2.5 Gatwick Airport (LGW)................................................................................................................. 5-11 5.2.6 Oakland International Airport (OAK) ............................................................................................ 5-12 5.2.7 London Heathrow Airport (LHR) .................................................................................................. 5-13 5.2.8 San Francisco International Airport (SFO) ..................................................................................... 5-15 5.3 Other Data ......................................................................................................................................... 5-17 5.3.1 NASA Lateral Attenuation Studies ................................................................................................ 5-17 5.3.2 ACOU 104 Impedance Measurements .......................................................................................... 5-17 5.4 Data Summary .................................................................................................................................. 5-17 6 Findings and Applications ................................................................................................................... 6-1 6.1 Fresnel Zone Ellipse Resistivity versus 2D Profile Cut ...................................................................... 6-2 6.2 Straight Ray Modeling ........................................................................................................................ 6-8 6.3 Ground Impedance Model .................................................................................................................. 6-9 6.4 Model Sensitivity Studies ................................................................................................................. 6-12

vi    6.5 Integrated Modeling Issues ............................................................................................................... 6-14 6.5.1 Background ..................................................................................................................................... 6-14 6.5.2 Effect of Segment Length Modeling in AEDT/INM ...................................................................... 6-14 6.5.3 AEDT Noise Fraction and Ground Effect Implementation ............................................................ 6-20 6.5.4 Application and Integrated Modeling Issues................................................................................... 6-22 6.6 Prioritized List of AEDT Improvements .......................................................................................... 6-23 6.6.1 Importing Terrain Data .................................................................................................................. 6-23 6.6.2 Method to Determine Terrain Profile ............................................................................................. 6-24 6.6.3 Flexible Segmentation of Flight Path ............................................................................................. 6-25 6.7 Data Validation ................................................................................................................................. 6-25 6.7.1 Data Validation at PDX .................................................................................................................. 6-25 6.7.2 Data Validation at SFO ................................................................................................................... 6-29 6.7.3 Data Validation at OAK .................................................................................................................. 6-36 7 Conclusions ......................................................................................................................................... 7-1 8 References ........................................................................................................................................... 8-1 9 Appendices .......................................................................................................................................... 9-1 APPENDIX A: Annotated Bibliography .................................................................................................. A-1 APPENDIX B: Logan Study Data File Formats ....................................................................................... B-1 B.1 Position Data Format ......................................................................................................................... B-1 B.2 Noise Data Format ............................................................................................................................ B-2 B.3 Meteorological Data Format ............................................................................................................. B-2 APPENDIX C: Gatwick Study Data File Formats ................................................................................... C-1 C.1 Noise and Position Data Format ........................................................................................................ C-1 C.2 Processed Engine Installation Data Format ....................................................................................... C-1 APPENDIX D: Heathrow ANOMS Data File Format ............................................................................. D-1 APPENDIX E: Washington National Airport Studies Data File Formats ................................................ E-1

vii  E.1 Part 150 Study Measurements ........................................................................................................... E-1 E.2 Navy Overwater Study at DCA Data File Formats ............................................................................ E-4 APPENDIX F: Detailed Documentation of Model Improvements ............................................................ F-1 F.1 Background .......................................................................................................................................... F-1 F.2 AEDT Input Requirements and Data ................................................................................................... F-1 F.3 Terrain and Ground Type Processing Method ..................................................................................... F-1 F.4 AEDT Segmentation Updates .............................................................................................................. F-3 F.5 Mixed Ground Impedance Modeling Method ..................................................................................... F-3 F.6 AEDT Implementation ........................................................................................................................ F-4 F.7 Additional Recommendations .............................................................................................................. F-5 APPENDIX G: AEDT User Guide Supplement ....................................................................................... G-1 G.1 AEDT Input Requirements and Data ................................................................................................. G-1 G.2 AEDT Interface .................................................................................................................................. G-3 G.3 Modeling Guidance ............................................................................................................................ G-5 LIST OF FIGURES AND TABLES LIST OF FIGURES Figure 1. Basic Ray Geometry with Reflection ........................................................................................ 3-1 Figure 2. Basic Ray Geometry with Reflection and Single Impedance Discontinuity ............................. 3-7 Figure 3. Geometry for the Geometric Theory of Diffraction. ................................................................. 3-8 Figure 4. Example Source Receiver Geometry over Strip of Different Impedance ............................... 3-10 Figure 5. Conceptual Components of Long-Range Lateral Attenuation for the Sound from Aircraft with Fuselage-Mounted Engines in SAE-AIR-5662 ......................................................................... 4-2 Figure 6. Conceptual Components of Long-Range Lateral Attenuation for the Sound from Aircraft with Wing-Mounted Engines in SAE-AIR-5662 ............................................................................... 4-2 Figure 7. Illustration of Ground-to-Ground Component of Lateral Attenuation ...................................... 4-3 Figure 8. Illustration of Air-to-Ground Component of Lateral Attenuation ............................................. 4-4

viii  Figure 9. Predicted SAE-AIR-5662 Lateral Attenuation for Lateral Distances of 450 m (Lower Solid Line) and 1500 m (Upper Solid Line) and Lateral Attenuations Measured for Airplanes with Fuselage-Mounted Engines Operating from London Gatwick Airport (LGW) ........................ 4-5 Figure 10. Predicted SAE-AIR-5662 Lateral Attenuation for Lateral Distances of 450 m (Lower Solid Line) and 1500 m (Upper Solid Line) and Lateral Attenuations Measured for Airplanes with Wing-Mounted Engines Operating from London Gatwick Airport (LGW) .............................. 4-6 Figure 11. Example setup in TNM ............................................................................................................ 4-7 Figure 12. Plan and Skew View Setup of Site A ...................................................................................... 4-9 Figure 13. Comparison of Modeled Levels versus Measured. Site A Data Shown in Red ................... 4-10 Figure 14. Plan and Skew View Setup of Site B .................................................................................... 4-11 Figure 15. Comparison of Modeled Levels versus Measured. Site B Data Shown in Red .................... 4-11 Figure 16. Plan and Skew View Setup of Site C .................................................................................... 4-12 Figure 17. Comparison of Modeled Levels versus Measured. Site C Data Shown in Red .................... 4-12 Figure 18. Plan and Skew View Setup for Site D ................................................................................... 4-13 Figure 19. Comparison of Modeled Levels versus Measured. Site D Data Shown in Red ................... 4-13 Figure 20. TNM Model Accuracy by Ground Type ............................................................................... 4-14 Figure 21. TNM Model Accuracy - All Data Plotted by Ground Type ................................................... 4-15 Figure 22. Nord2000 Calculations versus Measurements over an Impedance Discontinuity. ................ 4-16 Figure 23. Flight track at Narvik Showing Topography and Measurement Locations ........................... 4-17 Figure 24. Comparison of Measurements with the KBR and BP Methods at Site 6 .............................. 4-18 Figure 25. Contours of Ldn Calculated with the Entire Area as Soft (Dark Lines) and Hard for Water/Soft for Land (Light Gray Contours with Shading) ...................................................... 4-20 Figure 26. Comparison of EPD and EGA Models. Source and Receiver Heights of 4 ft Separated by 50 ft of Soft (flow resistivity 200 kPa s/m2 ), Flat Ground. .............................. 4-24 Figure 27. Flow Resistivity and Elevation Contours Around PDX - Profile Along Pink Line ................ 5-3 Figure 28. Noise Monitors Deployed Around DCA ................................................................................. 5-5 Figure 29. Noise Monitors 1, 2, and 3 Deployed at BOS ......................................................................... 5-7 Figure 30. Acoustic Data from 339 Departure Events at BOS ................................................................. 5-8 Figure 31. Acoustic Data from the Final 45 Departure Events at BOS .................................................... 5-8

ix    Figure 32. Noise Monitors Numbered 101-110 Around PDX .................................................................. 5-9 Figure 33. Noise Measurement Locations at PHL .................................................................................. 5-10 Figure 34. Weather File from Measurements at PHL ............................................................................. 5-11 Figure 35. Measurement Sites Similar to Those Used in the Gatwick Study. ........................................ 5-12 Figure 36. Locations of Noise Monitors Around OAK. ......................................................................... 5-13 Figure 37. Layout of Noise Monitors (numbered circles) West of LHR Airport with Overlaid Departure Tracks. ..................................................................................................................................... 5-14 Figure 38. Street View between Reservoirs Where Noise Monitors are Deployed at LHR. .................. 5-14 Figure 39. SFO and Surrounding Noise Monitoring Terminals. ............................................................ 5-16 Figure 40. Fresnel Ellipses for a 10 ft Source Height on Runway 28L with 4 ft High Receivers 10,000 ft Away - Ellipse Marking a Path Length Difference of 1/3 for 63 Hz. ........................................ 6-3 Figure 41. Extent of Coverage for all Ellipses. ......................................................................................... 6-6 Figure 42. Difference of Average Flow Resistivity Calculations for 8 kHz. ............................................ 6-7 Figure 43. Comparison of Calculation of Percent Hard (Water). ............................................................. 6-8 Figure 44. Plot of A-weighted Level Estimates Calculated by EPD vs EGA for the Range of Parameters Shown in Table 9 for all Jet Spectral Classes in AEDT. ........................................................... 6-9 Figure 45. Comparison of Model Estimates with Measurements made over Grass-covered Ground. Error Bars Represent the Standard Deviation of the Measurements. ................................................ 6-11 Figure 46. Estimates for Propagation of a Representative Spectrum of a Jet Aircraft from 1,000 ft to 3,281 ft for 1 Atmosphere Pressure, 14.5C, and 70% Relative Humidity. ............................ 6-11 Figure 47. P-value Results of EGA Sensitivity Analysis. ....................................................................... 6-13 Figure 48. Modeled Operation. ............................................................................................................... 6-15 Figure 49. Baseline Results SEL (dBA), 250 ft Overflight, Single 10,000 ft Segment, 51 x 51 Grid. ............................................................................................................................ 6-16 Figure 50. INM Grid Results (SEL, dBA) for Different Segment Lengths, 51x51 Grid, 250 ft Altitude: a) 5,000 ft b) 1,000 ft c) 500 ft d) 200 ft e) 100 ft f) 20 ft. X and Y Distances in ft. .............. 6-17 Figure 51. Baseline SEL (dBA) minus Different Segment Length Results, 51 x 51 Grid, 250 ft Altitude. 1) 5,000 ft b) 1,000 ft c) 500 ft d) 200 ft e) 100 ft f) 20 ft. X and Y Distances in nmi. .......... 6-18

x    Figure 52. Baseline SEL (dBA) minus Different Segmented Length Results, 21 x 21 Grid, 250 ft Altitude. 1) 5,000 ft b) 1,000 ft c) 500 ft d) 200 ft e) 100 ft f) 20 ft. X and Y Distances in nmi. .......................................................................................................................................... 6-19 Figure 53. Baseline SEL (dBA) Minus Different Segmented Length Results, 21x21 Grid, 1000 ft Altitude. a) 5,000 ft b) 1,000 ft c) 500 ft d) 200 ft e) 100 ft f) 20 ft. X and Y Distances in nmi. .......................................................................................................................................... 6-20 Figure 54. Noise Fraction Formulation. .................................................................................................. 6-21 Figure 55. Noise Fraction Snapshot from a Single Segment with Different Lengths. ............................ 6-21 Figure 56. INM NPD Lateral Attenuation “Adjustment.” 51 x 51 Grid, 250 ft Altitude, 1,000 ft Segment Length. ..................................................................................................................................... 6-22 Figure 57. Elevation Angles at PDX Monitors. ...................................................................................... 6-26 Figure 58. Corrected Levels at PDX Monitors. Dashed Line with Unity Slope Drawn for Comparison. ............................................................................................................................. 6-28 Figure 59. Normal Probability Plot of Difference of Corrected Levels from Monitors 101 and 107 at PDX. Dash-dotted Line Represents Gaussian Distribution. ................................................... 6-29 Figure 60. A-weighted Time Histories at GRU 35 and NMT 11 Noise Monitors. Vertical Lines Represent Arrival Times of Sound Emitted from B747-8 Departure from Runway 28R at Point of Closest Approach. ............................................................................................................... 6-30 Figure 61. Elevation Angles of Operations Satisfying Wind Speed and Signal to Noise Level Criteria at SFO. ......................................................................................................................................... 6-33 Figure 62. Comparison of Corrected Sound Levels using the Estimates of Flow Resistivities around SFO. Dashed Line with Unity Slope Drawn for Comparison. .......................................................... 6-34 Figure 63. Comparison of corrected sound levels using a flow resistivity of 150 kPa s/m2 for the SFO data set. Dashed line with unity slope drawn for comparison. ............................................... 6-35 Figure 64. Area around NMT05 at SFO. ................................................................................................ 6-36 Figure 65. Noise Monitor Placement at OAK to Capture Noise from Departures on Runway 30. ........ 6-38 Figure 66. Comparison of Corrected Levels from GRU36 and Measured Levels at NMT12. Dashed Line with Unity Slope Drawn for Comparison. ............................................................................... 6-39 Figure 67. Area Around NMT12 with Line to GRU36. ......................................................................... 6-40 Figure 68. Comparison of Levels from GRU36 Corrected only for Ground Effect on the Airfield, Air Absorption, and Spherical Spreading with Measured Levels at NMT12. Dashed Line with Unity Slope Drawn for Comparison. ....................................................................................... 6-41

xi    Figure 69. Probability Plot of Difference Between GRU36 Levels only Corrected for Airfield Ground Effect, Atmospheric Absorption and Spherical Spreading and Measured Levels at NMT12. Dash-dotted Line Represents Gaussian Distribution. .............................................................. 6-42 Figure 70. Example of DCA Departure Tracks off Runway 01............................................................... E-4 Figure 71. Example zweek File Header. .................................................................................................. E-6 Figure 72. Example A-weighted Time Histories at DCA Measurement Sites. ........................................ E-7 Figure 73. Diagram of Source – Receiver Geometry Detailing Major Axis of Fresnel Zone Ellipse as the Active Portion of the Ground Path used for Average Flow Resistivity along Profile Cut. ....... F-2 Figure 74. Recommended Updates to the AEDT Definitions Tab to Account for Ground Cover Files ................................................................................................................................ G-1 Figure 75. Recommended Updates to AEDT 2c sp1 User’s Guide Section 9.7 to Account for Ground Cover Files. ............................................................................................................................... G-2 Figure 76. Recommended Updates to the AEDT Define Metric Results – Set Processing Options Menu ......................................................................................................................................... G-4 Figure 77. Recommended Updates to AEDT 2c sp1 User’s Guide Section 5.2.4.3 to Account for Ground Cover Effects on Noise Propagation Modeling ........................................................................ G-4 Figure 78. Recommended New Section to AEDT 2c sp1 User’s Guide (Section 5.2.4.5) to Account for Ground Cover Effects Processing Options for Noise Propagation Modeling .......................... G-5 LIST OF TABLES Table 1. Parameter Values Obtained Using One-Parameter Model .......................................................... 3-5 Table 2. Parameter Values Obtained Using Two-Parameter Model ......................................................... 3-5 Table 3. Parameter Values for Hard-Backed Layer Version of One-Parameter Model............................ 3-6 Table 4. Statistical Summary of Sound Exposure Level Estimates and Measurements ......................... 4-19 Table 5. National Land Cover Database Ground Cover Classifications and Associated BASEOPS Flow Resistivity Estimates. ................................................................................................................. 5-2 Table 6. Measurement Dates and Daily Event Count ............................................................................... 5-6 Table 7. Parameter Ranges Used to Calculate the Fresnel Ellipses around PDX. .................................... 6-2 Table 8. Average Flow Resistivity Calculations with 4 ft High Receiver. ............................................... 6-5 Table 9. Ranges of Parameters used with EPD and EGA Models. ........................................................... 6-8 Table 10. Position Data Format from Logan Study for an Example Event. ............................................ B-1 Table 11. Noise Data Format from Logan Study for a Portion of an Example Event ............................. B-2 Table 12. Meteorological Data Format from Logan Study for a Portion of an Example Event .............. B-3

xii    Table 13. Noise and Position Data Format from Gatwick Study for Example Events ............................ C-1 Table 14. Processed Engine Installation Data Format from Gatwick Study for Example Events ........... C-1 Table 15. Single Operation from Database Query of ANOMS at LHR. ................................................. D-2 Table 16. Example of LD820 SLM Event Records. ................................................................................ E-1 Table 17. Keywords and Data Description of RAT File Format. ............................................................ E-3 Table 18. NLCD Land Cover Classifications and the Equivalent Estimated Flow Resistivity Value Recommendations for Use in AEDT ........................................................................................ G-3

xiii    AUTHOR ACKNOWLEDGMENTS The research team would like to express our gratitude to the project's panel members and liaison members whose efforts are an integral part of the success of this project:  Mr. Garret J. Hollarn, Panel Chair, Sr. Airport Noise Specialist/GIS Coordinator, San Diego County Regional Airport Authority  Mr. Justin W. Cook, Vice President - Airports & Acoustics, BridgeNet International  Dr. Bruce J. Ikelheimer, Acoustic Analytics  Dr. Kai Ming Li, Professor Of Mechanical Engineering, Purdue University  Mr. Dave Ong, Aircraft Noise Abatement, San Francisco International Airport  Ms. Florence Straugh, Noise Abatement Officer, Fort Lauderdale Executive Airport  FAA Liaison, Dr. Bao Tong, Office of Environment and Energy, FAA  FAA Liaison, Mr. Frank Smigelski, Office of Airport Planning & Programming  TRB Liaison, Ms. Christine Gerencher, Aviation and Environment, Technical Activities (Div.A) The PI would especially like to thank panel member Mr. Dave Ong for providing airport data from SFO and deploying a monitor at OAK to help this project. We are grateful for the patience ACRP project manager Mr. Joseph D. Navarrete showed while leading this project through some challenging phases. Particular thanks go to Dr. Keith Attenborough for agreeing to be the outside reviewer for this project and providing the ACOU 104 data for comparison with our coding of the models. His suggestions and inputs have greatly helped this project both materially and intellectually.  Dr. Keith Attenborough, Research Professor in Acoustics, The Open University The authors would like to thank Chris Blair at PDX for all the effort required to provide data to this project:  Chris Blair, Senior Noise Analyst, Port of Portland Dr. Kevin Shepherd at NASA LaRC provided measurement papers highly relevant to the objectives of this project, and the authors are grateful to be able to discuss this project with him:  Dr. Kevin Shepherd, Head, Structural Acoustics Branch, NASA Langley Research Center Dr. Darren Rhodes of the CAA in the UK also helped this project by providing data from LHR:  Dr. Darren Rhodes, Head of Environmental Research and Consultancy Department, Civil Aviation Authority (UK) Dr. Ben Sharp provided assistance with this project with his knowledge and depth of experience:  Dr. Ben Sharp, Consultant, Annandale, Virginia David Senzig provided measurement papers and experience from previous analyses that were relevant to the objectives of this project, and the authors appreciate his insight:  David Senzig, Electronics Engineer, U.S. Department of Transportation's Volpe National Transportation Systems Center Finally, the research team would like to acknowledge the original Principal Investigator, Dr. Ken Plotkin. It was his intelligence and depth of experience that started this project. With his passing went a good colleague, researcher, and friend.

xiv    SUMMARY This document provides an overview of the research performed under Airport Cooperative Research Program (ACRP) project 02-52 “Improving AEDT Noise Modeling of Hard, Soft, and Mixed Ground Surfaces”. The goal of this project is to develop a method to model the effects of single- (other than ‘soft’ ground) and mixed- impedance surfaces on the propagation of aircraft noise in a manner suitable for model implementation to improve the noise prediction accuracy of the Federal Aviation Administration’s (FAA) Aviation Environmental Design Tool (AEDT). AEDT is an integrated noise model, which currently includes a lateral attenuation adjustment to account for the effects of lateral aircraft directivity and for acoustic propagation over soft ground. This research includes an investigation of additional methods to supplement the lateral attenuation adjustment to allow for modeling noise propagation over hard and mixed ground types in AEDT. This document presents a critical review of relevant acoustic theory, a review of practical applications implementing this theory, a synthesis of available airport data that support this project, an analysis and validation of the theory with measurement data, and recommendations on improving modeling of noise propagating over hard, soft and mixed ground surfaces in AEDT. The acoustic theory review includes ray theory, diffraction, the boundary integral equation method, and the parabolic equation applied in situations with single- or multiple-impedance discontinuities. Practical considerations were also reviewed, including balancing model fidelity with computational speed. From this review, it was determined that using straight ray theory in conjunction with the one-parameter model of ground impedance and Fresnel zone average flow resistivity calculation were the best suited for calculating lateral attenuation in AEDT. The review of ground effects in current noise models included an extensive review of nine international transportation noise models that included FAA’s AEDT (and its predecessor, the Integrated Noise Model (INM)), the Federal Highway Administration’s (FHWA) Traffic Noise Model (TNM), the National Park Service’s (NPS) Noise Model Simulation (NMSim), the Department of Defense’s (DoD) NOISEMAP (NMAP) and Advanced Acoustic Model (AAM) , and the National Aeronautics and Space Administration’s (NASA) Acoustic Propagation and Emulation Toolset (APET). This review identified how ground effects are handled in the models and identified relevant implementation methods and validation analyses. Validation of the recommended ground effects modeling methods began with the identification of available ground cover data set and airport noise measurement data for use in validating the theory. Additional, supplemental databases to be used for validation were also described. Some of the data were used for the current analysis, while others may be appropriate for future analyses. The recommended methods for modeling ground effects in AEDT were evaluated using data from SFO, OAK, and PDX. The research concluded that:  Using the single-parameter model of ground impedance based upon flow resistivity estimates of categories in the National Land Cover Database along with straight ray theory as presented here accurately calculated the average lateral attenuation of aircraft operations to within 1 dB of measurements.  The methods presented here can be incorporated into AEDT’s architecture with minimal changes. In addition to decreasing segment lengths of input tracks and importing the additional terrain properties necessary for estimating ground impedance, one can make use of the existing framework of AEDT to add this capability.

xv     The AEDT user should easily be able to see the changes in AEDT noise estimates with and without the application of this method. While the presentation here relies on comparison of theory with measurements, once implemented in AEDT, the effect that applying the correction to sound propagation over non-soft ground should be evident in the change of contour levels and location. For airport operators knowledgeable about deficiencies in noise estimates when compared to measurements of noise propagating over water or mixed ground types, a comparison of noise results when applying this theory versus not applying it in AEDT may help operators explain the discrepancies. Additional recommendations on improvements in AEDT to facilitate the integration of this method into AEDT are presented in this report.

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TRB's Airport Cooperative Research Program (ACRP) Web-Only Document 32: Improving AEDT Noise Modeling of Mixed Ground Surfaces develops a method to model the effects of single- and mixed-impedance surfaces on the propagation of aircraft noise in a manner suitable for model implementation to improve the noise prediction accuracy of the Federal Aviation Administration’s (FAA) Aviation Environmental Design Tool (AEDT). AEDT is an integrated noise model, which currently includes a lateral attenuation adjustment to account for the effects of lateral aircraft directivity and for acoustic propagation over soft ground. This research includes an investigation of additional methods to supplement the lateral attenuation adjustment to allow for modeling noise propagation over hard and mixed ground types in AEDT.

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