Heat, Light, and Sound Research, Inc.
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Table of Contents
BELLHOP3D User Guide! "2
Heat, Light, and Sound Research, Inc.
BELLHOP3D USER GUIDE 1
I. Introduction 1
II. Under the Hood: the BELLHOP algorithm 3
A. Introduction: Beam types and overview of beam tracing" 3#
B. Theory" 8#
C. Geometric Beams" 11#
D. The Compound Matrix Method" 12#
E. Beam changes across interfaces" 14#
III. Running BELLHOP3D 17
A. Environmental Information: Basic input file" 17#
B. Environmental Information: Bathymetry" 20#
C. Environmental Information: Oceanography" 23#
D. Ray trace run: Nx2D" 27#
E. Ray trace run: Full 3D Mode" 31#
F. Transmission Loss" 31#
IV. Test Cases 34
A. Free-Space and Half-Space Propagation" 35#
B. The Perfect Wedge" 39#
C. Truncated Wedge" 43#
D. Seamount" 49#
E. The Harvard Case Eddy Scenario" 53#
F. Rotated Munk Profile" 55#
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Heat, Light, and Sound Research, Inc.
G. Korean Seas" 59#
H. Incoherent and Semi-Coherent TL options" 68#
V. Summary 71
Acknowledgments 72
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Heat, Light, and Sound Research, Inc.
BELLHOP3D USER GUIDE
I. Introduction
BELLHOP3D is a beam tracing model for predicting acoustic pressure fields in ocean
environments. It is an extension to 3D environments of the popular BELLHOP model and includes
(optionally) horizontal refraction in the lat-long plane. Of course, 3D pressure fields can be
calculated by a 2D model simply by running it on a series of radials (bearing lines) from the source.
This is the so-called Nx2D or 2.5D approach. However, that approach neglects the refraction of
sound energy out of the vertical plane associated with each bearing line. Such out-of-plane effects
can be important when there are significant horizontal gradients in the environment. These occur
with strong oceanographic features such as nonlinear internal waves, or in areas with strong
bathymetric features. This is currently an active area of research.
A very preliminary research version of BELLHOP3D was written in 1985 in FORTRAN. However, it
did not allow environmental information (sound speed and bathymetry) to be read in from input
files. Instead, the research version required a user-defined analytic function for the sound speed,
c( x, y, z ), as a function of latitude, longitude, and depth. The research version also did not allow
variable bathymetry.
Separately a Matlab conversion of the original research code was done around 2004. The Matlab
environment is much easier to develop in; however, we have chosen not to build off of that here,
since the Matlab code runs much more slowly (about 50 times slower).
The beam tracing structure leads to a particularly simple algorithm. Several types of beams are
implemented including Gaussian and hat-shaped beams, with both geometric and physics-based
spreading laws. BELLHOP3D can produce a variety of useful outputs including transmission loss,
eigenrays, arrivals, and received time-series. It allows for lat-long variation in the top and bottom
boundaries (altimetry and bathymetry), as well as full 3D variation in the sound speed profile.
Additional input files allow the specification of directional sources as well as geoacoustic properties
for the bounding media. Top and bottom reflection coefficients may also be provided. BELLHOP3D
is implemented in Fortran with Matlab wrappers to display the input and output. The code
BELLHOP3D User Guide! "1
