This document summarizes a study comparing three atmospheric sound propagation models: ISO 9613-2, a parabolic equation model, and a modal model. The study found that ISO 9613-2 performed better than expected when accounting for atmospheric attenuation. The modal model had difficulty finding complex ducted modes as expected. Further areas of study are suggested, including comparing ISO 9613-2 to the parabolic equation model and adding continuum modes to the modal model.

1. Motivation
Our Results
Summary
A Comparison of 3 Atmospheric Sound
Propagation Models
C.Latimer
Supervised by Dr.Nick Ovenden
Department of Mathematics
University of London
Masters Project Presentation, 2015
Charlie Latimer Comparison of Sound Models

2. Motivation
Our Results
Summary
Outline
1 Motivation
The Task
Previous Work
2 Our Results
Main Results
Comparison
Charlie Latimer Comparison of Sound Models

3. Motivation
Our Results
Summary
The Task
Previous Work
Outline
1 Motivation
The Task
Previous Work
2 Our Results
Main Results
Comparison
Charlie Latimer Comparison of Sound Models

4. Motivation
Our Results
Summary
The Task
Previous Work
The Models Studied.
ISO 9613-2, an International Standard
Parabolic equation modal
Modal model
Charlie Latimer Comparison of Sound Models

5. Motivation
Our Results
Summary
The Task
Previous Work
Factors that Affect Sound Pressure Levels
Meteorology
Temperature & wind
inversions
Downwind or upwind
Attenuation
Geometric spreading
Atmospheric attenuation
Ground attenuation
Figure: Waxler’s profile
Charlie Latimer Comparison of Sound Models

6. Motivation
Our Results
Summary
The Task
Previous Work
Outline
1 Motivation
The Task
Previous Work
2 Our Results
Main Results
Comparison
Charlie Latimer Comparison of Sound Models

7. Motivation
Our Results
Summary
The Task
Previous Work
Previous Work
ISO-8297 Industrial plants, ISO-1996
Community events, ISO-3740 Machinery
N. Ovenden, S. Shaffer & H. Fernando
modelled free-way noised under various
meteorological profiles
R. Waxler studied modal solutions without
ray theory model
Charlie Latimer Comparison of Sound Models

8. Motivation
Our Results
Summary
Main Results
Comparison
Outline
1 Motivation
The Task
Previous Work
2 Our Results
Main Results
Comparison
Charlie Latimer Comparison of Sound Models

9. Motivation
Our Results
Summary
Main Results
Comparison
ISO 9613-2
ISO 9613-2 accounts for
atmospheric attenuation
Choice of G is important, yet
subjective
Figure: G=0
Figure: G=0.5
Figure: G=1
Charlie Latimer Comparison of Sound Models

10. Motivation
Our Results
Summary
Main Results
Comparison
Starting Field - Ray Theory Model
Used as a starting field for the
parabolic equation and modal
models
Models a quiescent
atmosphere
Figure: 630Hz, 1.5m source
Figure: 63Hz, 2m source
Charlie Latimer Comparison of Sound Models

11. Motivation
Our Results
Summary
Main Results
Comparison
The Parabolic Equation Model
Finite differencing of a
Helmholtz equation, coupled
with ray theory
The wide angle approximation
is accurate up to angles of
about 35o
Figure: Case b meteorology, 63-2500Hz
Figure: No meteorology, 250Hz
Figure: Case b meteorology, 250Hz
Charlie Latimer Comparison of Sound Models

12. Motivation
Our Results
Summary
Main Results
Comparison
The Modal Model
Sound field split into ducted
and continuum modes
The ducted modes are
located using a shooting
algorithm and a NSEW
algorithm
Figure: 63 Hz modal solution
Charlie Latimer Comparison of Sound Models

13. Motivation
Our Results
Summary
Main Results
Comparison
Outline
1 Motivation
The Task
Previous Work
2 Our Results
Main Results
Comparison
Charlie Latimer Comparison of Sound Models

14. Motivation
Our Results
Summary
Main Results
Comparison
Broadband Signals - ISO vs PE
Figure: ISO 9613-2, G=0.5
Figure: PEM, under Waxler’s sound profile
Figure: Above: Comparison at 2m.
Below: Comparison at 70m.
Charlie Latimer Comparison of Sound Models

15. Motivation
Our Results
Summary
Main Results
Comparison
Mono Frequency Signals - PE vs Modal
Figure: Above: Modal 63Hz. Below: PE 63Hz
Figure: Difference in SPL. Positive value
corresponds to PEM being louder.
Charlie Latimer Comparison of Sound Models

16. Motivation
Our Results
Summary
Summary
ISO 9613-2 is better than expected.
Finding the complex ducted modes is harder than expected.
Further study
Comparing methods the superseded ISO 9613-2 with the parabolic
equation model.
Adding in the continuum modes to the modal model to see if they
reconcile results.
Charlie Latimer Comparison of Sound Models