BELLHOP computes acoustic fields in oceanic environments via beam tracing. The environment treated consists of an acoustic medium with a sound speed that may depend on range and depth. A theoretical description may be found in:
Michael B. Porter and Homer P. Bucker, ``Gaussian beam tracing for computing ocean acoustic fields,'' J. Acoust. Soc. Amer. 82, 1349--1359 (1987).
The following programs are used with BELLHOP :
BELLHOP Main program for doing Gaussian beam tracing
PLOTRAY Produces plots of central rays of beams
ANGLES Given the source and recvr sound speeds, computes the angle of the limiting ray.
PLOTSSP Plots the sound speed profile
BELLHOP produces pressure fields in the NRL standard format. These fields can then be plotted using the following routines:
PLOTSLICE Plots a transmission loss versus range curve.
PLOTFIELD Plots a full TL field versus range and depth.
The steps in running the program are as follows:
1. Set up your environmental file and run PLOTSSP to make sure
the SSP looks reasonable.
2. Do a ray trace. That is,
A. Run BELLHOP with the ray trace option to calculate about 50
rays.
B. Run PLOTRAY to make sure you have the angular coverage you
expect. Do the rays behave irregularly? If so reduce the
step-size and try again.
3. Re-run BELLHOP using the coherent, incoherent or semicoherent
option for transmission loss. (Use the default number
of beams.)
4. Run either PLOTSLICE to plot a single transmission
loss curve or PLOTFIELD to plot a full range-depth field plot.
5. Double the number of beams and check convergence.
Files:
Name Unit Description
Input
*.ENV 1 ENVironmental data
Output
*.PRT 6 PRinT file
*.RAY 21 RAY file
*.SHD 25 SHaDe file
---------------------------------------------------------
EXAMPLE AND DESCRIPTION OF ENV FILE:
'Munk profile' ! TITLE
50.0 ! FREQ (Hz)
1 ! NMEDIA
'SVN' ! SSPOPT (Analytic or C-linear interpolation)
51 0.0 5000.0 ! DEPTH of bottom (m)
0.0 1548.52 /
200.0 1530.29 /
250.0 1526.69 /
400.0 1517.78 /
600.0 1509.49 /
800.0 1504.30 /
1000.0 1501.38 /
1200.0 1500.14 /
1400.0 1500.12 /
1600.0 1501.02 /
1800.0 1502.57 /
2000.0 1504.62 /
2200.0 1507.02 /
2400.0 1509.69 /
2600.0 1512.55 /
2800.0 1515.56 /
3000.0 1518.67 /
3200.0 1521.85 /
3400.0 1525.10 /
3600.0 1528.38 /
3800.0 1531.70 /
4000.0 1535.04 /
4200.0 1538.39 /
4400.0 1541.76 /
4600.0 1545.14 /
4800.0 1548.52 /
5000.0 1551.91 /
'V' 0.0
1 1000.0 / ! NSD SD(1:NSD) (m)
2 0.0 5000.0 / ! NRD RD(1:NRD) (m)
501 0.0 100.0 / ! NRR RR(1:NR ) (km)
'R' ! Run-type: 'R/C/I/S'
51 -11.0 11.0 / ! NBEAMS ALPHA(1:NBEAMS) (degrees)
200.0 5500.0 101.0 ! STEP (m) ZBOX (m) RBOX (km)
---------------------------------------------------------
DESCRIPTION OF INPUTS:
(1) - TITLE
Syntax: TITLE
Description:
TITLE: Title of run enclosed in sinqle quotes
(2) - FREQUENCY
Syntax: FREQ
Description:
FREQ: Frequency in Hz
(3) - NUMBER OF MEDIA
Syntax: NMEDIA (<20)
Description:
Dummy parameter for compatibility with KRAKEN.
(4) - OPTIONS
Syntax: OPTION
Description:
OPTION(1:1): Type of interpolation to be used for the SSP
'S' for cubic Spline (recommended)
'C' for C-linear
'N' for N2-linear
'A' for Analytic. The user must modify the
analytic formulas in ANALYT.FOR and re-link.
Use PLOTSSP to check that
the SSP looks the way you thought it should.
Apart from potential typos, this will also
show up fit-problems which might occur with
the spline option. Splines yield a
poor fit to certain kinds of curves, e.g.
curves with sharp bends.
OPTION(2:2): Type of top boundary condition
'V' VACUUM above top
'R' Perfectly RIGID
For open ocean problems option 'V' should be
used for the surface BC.
OPTION(3:3): Volume attenuation option
'T' Thorp attenuation formula.
'N' No volume attenuation.
OPTION(4:4): Arrival time/amplitude information
'A' to produce it ...
(5) - SOUND SPEED PROFILE
Syntax:
NMESH SIGMA Z(NSSP)
Z(1) CP(1) /
Z(2) CP(2) /
.
.
.
Z(NSSP) CP(NSSP) /
Description:
NMESH: Dummy parameter for KRAKEN compatibility
SIGMA: Dummy parameter for KRAKEN compatibility
Z(NSSP): Depth at bottom of medium (m).
This value is used to detect the last
SSP point when reading in the
profile which follows.
The following should be omitted when the 'A' option
is used (indicating that an analytic profile is
supplied by a user written subroutine).
Z(): Depth (m). Note that the surface starts at the first
depth point specified. Thus if you have say, XBT
data which starts at 50 m below the surface, then
you'll need to put in some SSP point at 0 m,
otherwise the free-surface would be placed at 50 m
giving erroneous results. Try to keep the number of
depth points to the minimum necessary to describe the
physics: a fine SSP sampling can force a fine step-size
for integrating the rays.
CP(): P-wave speed (m/s) (Must be followed by a '/'
for compatibility with the KRAKEN program.)
(6) - OPTIONS
Syntax: OPTION SIGMA
Description:
OPTION(1:1): Type of bottom boundary condition
'V' VACUUM below bottom
'R' Perfectly RIGID
SIGMA: Bottom roughness (currently ignored)
(7) - SOURCE/RECEIVER DEPTHS AND RANGES
Syntax:
NSD SD(1:NSD)
NRD RD(1:NRD)
NR R(1:NR )
Description:
NSD: The number of source depths (<51)
SD(): The source depths (m)
NRD: The number of receiver depths (<101 and NR*NRD <= 52000)
RD(): The receiver depths (m)
NR: The number of receiver ranges
(NR < 1001 and NR*NRD <= 50000)
R(): The receiver ranges (km)
This data is read in using list-directed I/O you can type it
just about any way you want, e.g. on one line or split onto
several lines. Also if the depths or ranges are equally spaced
then you can type just the first and last depths followed by a
'/' and the intermediate depths will be generated automatically.
(8) - RUN TYPE
Syntax:
OPTION
Description:
OPTION: 'R' generates a ray file
'E' generates an eigenray file
'C' for Coherent TL calculation
'I' for Incoherent TL calculation
'S' for Semicoherent TL calculation
(Lloyd mirror source pattern)
(9) - BEAM FAN
Syntax:
NBEAMS ALPHA(1:NBEAMS)
Description:
NBEAMS: Number of beams (use 0 to have the program
calculate a value automatically.
ALPHA(): Beam angles (negative angles toward surface)
For a ray trace you can type in a sequence of angles
or you can type the first and last angles followed by a
'/'. For a TL calculation, the rays must be equally spaced
otherwise the results will be incorrect.
(10) - NUMERICAL INTEGRATOR INFO
Syntax:
STEP ZBOX RBOX
Description:
STEP: The step size used for tracing the rays (m).
ZBOX: The maximum depth to trace a ray (m).
RBOX: The maximum range to trace a ray (km).
The required step size depends on many factors. This includes
frequency, size of features in the SSP (such as surface
ducts), range of rcvrs, and whether a coherent or incoherent
TL calculation is performed. If you use STEP=0.0 BELLHOP will
use a default step-size and tell you what it picked. You should
then halve the step size until the results are convergent to
your required accuracy. To obtain a smooth ray trace you should
use the spline SSP interpolation and a step-size less than the
smallest distance between SSP data points.
Rays are traced until they exit the box ( ZBOX, RBOX ). By
setting ZBOX less than the water depth you can eliminate
bottom reflections.